Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/rzhang/linux

[cascardo/linux.git] / net / core / skbuff.c

/*
 *      Routines having to do with the 'struct sk_buff' memory handlers.
 *
 *      Authors:        Alan Cox <alan@lxorguk.ukuu.org.uk>
 *                      Florian La Roche <rzsfl@rz.uni-sb.de>
 *
 *      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
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/kmemcheck.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/in.h>
#include <linux/inet.h>
#include <linux/slab.h>
#include <linux/tcp.h>
#include <linux/udp.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 <linux/errqueue.h>
#include <linux/prefetch.h>
#include <linux/if_vlan.h>

#include <net/protocol.h>
#include <net/dst.h>
#include <net/sock.h>
#include <net/checksum.h>
#include <net/ip6_checksum.h>
#include <net/xfrm.h>

#include <asm/uaccess.h>
#include <trace/events/skb.h>
#include <linux/highmem.h>
#include <linux/capability.h>
#include <linux/user_namespace.h>

struct kmem_cache *skbuff_head_cache __read_mostly;
static struct kmem_cache *skbuff_fclone_cache __read_mostly;
int sysctl_max_skb_frags __read_mostly = MAX_SKB_FRAGS;
EXPORT_SYMBOL(sysctl_max_skb_frags);

/**
 *      skb_panic - private function for out-of-line support
 *      @skb:   buffer
 *      @sz:    size
 *      @addr:  address
 *      @msg:   skb_over_panic or skb_under_panic
 *
 *      Out-of-line support for skb_put() and skb_push().
 *      Called via the wrapper skb_over_panic() or skb_under_panic().
 *      Keep out of line to prevent kernel bloat.
 *      __builtin_return_address is not used because it is not always reliable.
 */
static void skb_panic(struct sk_buff *skb, unsigned int sz, void *addr,
                      const char msg[])
{
        pr_emerg("%s: text:%p len:%d put:%d head:%p data:%p tail:%#lx end:%#lx dev:%s\n",
                 msg, addr, skb->len, sz, skb->head, skb->data,
                 (unsigned long)skb->tail, (unsigned long)skb->end,
                 skb->dev ? skb->dev->name : "<NULL>");
        BUG();
}

static void skb_over_panic(struct sk_buff *skb, unsigned int sz, void *addr)
{
        skb_panic(skb, sz, addr, __func__);
}

static void skb_under_panic(struct sk_buff *skb, unsigned int sz, void *addr)
{
        skb_panic(skb, sz, addr, __func__);
}

/*
 * kmalloc_reserve is a wrapper around kmalloc_node_track_caller that tells
 * the caller if emergency pfmemalloc reserves are being used. If it is and
 * the socket is later found to be SOCK_MEMALLOC then PFMEMALLOC reserves
 * may be used. Otherwise, the packet data may be discarded until enough
 * memory is free
 */
#define kmalloc_reserve(size, gfp, node, pfmemalloc) \
         __kmalloc_reserve(size, gfp, node, _RET_IP_, pfmemalloc)

static void *__kmalloc_reserve(size_t size, gfp_t flags, int node,
                               unsigned long ip, bool *pfmemalloc)
{
        void *obj;
        bool ret_pfmemalloc = false;

        /*
         * Try a regular allocation, when that fails and we're not entitled
         * to the reserves, fail.
         */
        obj = kmalloc_node_track_caller(size,
                                        flags | __GFP_NOMEMALLOC | __GFP_NOWARN,
                                        node);
        if (obj || !(gfp_pfmemalloc_allowed(flags)))
                goto out;

        /* Try again but now we are using pfmemalloc reserves */
        ret_pfmemalloc = true;
        obj = kmalloc_node_track_caller(size, flags, node);

out:
        if (pfmemalloc)
                *pfmemalloc = ret_pfmemalloc;

        return obj;
}

/*      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.
 *
 */

struct sk_buff *__alloc_skb_head(gfp_t gfp_mask, int node)
{
        struct sk_buff *skb;

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

        /*
         * Only clear those fields we need to clear, not those that we will
         * actually initialise below. Hence, don't put any more fields after
         * the tail pointer in struct sk_buff!
         */
        memset(skb, 0, offsetof(struct sk_buff, tail));
        skb->head = NULL;
        skb->truesize = sizeof(struct sk_buff);
        atomic_set(&skb->users, 1);

        skb->mac_header = (typeof(skb->mac_header))~0U;
out:
        return skb;
}

/**
 *      __alloc_skb     -       allocate a network buffer
 *      @size: size to allocate
 *      @gfp_mask: allocation mask
 *      @flags: If SKB_ALLOC_FCLONE is set, allocate from fclone cache
 *              instead of head cache and allocate a cloned (child) skb.
 *              If SKB_ALLOC_RX is set, __GFP_MEMALLOC will be used for
 *              allocations in case the data is required for writeback
 *      @node: numa node to allocate memory on
 *
 *      Allocate a new &sk_buff. The returned buffer has no headroom and a
 *      tail room of at least 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 flags, int node)
{
        struct kmem_cache *cache;
        struct skb_shared_info *shinfo;
        struct sk_buff *skb;
        u8 *data;
        bool pfmemalloc;

        cache = (flags & SKB_ALLOC_FCLONE)
                ? skbuff_fclone_cache : skbuff_head_cache;

        if (sk_memalloc_socks() && (flags & SKB_ALLOC_RX))
                gfp_mask |= __GFP_MEMALLOC;

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

        /* We do our best to align skb_shared_info on a separate cache
         * line. It usually works because kmalloc(X > SMP_CACHE_BYTES) gives
         * aligned memory blocks, unless SLUB/SLAB debug is enabled.
         * Both skb->head and skb_shared_info are cache line aligned.
         */
        size = SKB_DATA_ALIGN(size);
        size += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
        data = kmalloc_reserve(size, gfp_mask, node, &pfmemalloc);
        if (!data)
                goto nodata;
        /* kmalloc(size) might give us more room than requested.
         * Put skb_shared_info exactly at the end of allocated zone,
         * to allow max possible filling before reallocation.
         */
        size = SKB_WITH_OVERHEAD(ksize(data));
        prefetchw(data + size);

        /*
         * Only clear those fields we need to clear, not those that we will
         * actually initialise below. Hence, don't put any more fields after
         * the tail pointer in struct sk_buff!
         */
        memset(skb, 0, offsetof(struct sk_buff, tail));
        /* Account for allocated memory : skb + skb->head */
        skb->truesize = SKB_TRUESIZE(size);
        skb->pfmemalloc = pfmemalloc;
        atomic_set(&skb->users, 1);
        skb->head = data;
        skb->data = data;
        skb_reset_tail_pointer(skb);
        skb->end = skb->tail + size;
        skb->mac_header = (typeof(skb->mac_header))~0U;
        skb->transport_header = (typeof(skb->transport_header))~0U;

        /* make sure we initialize shinfo sequentially */
        shinfo = skb_shinfo(skb);
        memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
        atomic_set(&shinfo->dataref, 1);
        kmemcheck_annotate_variable(shinfo->destructor_arg);

        if (flags & SKB_ALLOC_FCLONE) {
                struct sk_buff_fclones *fclones;

                fclones = container_of(skb, struct sk_buff_fclones, skb1);

                kmemcheck_annotate_bitfield(&fclones->skb2, flags1);
                skb->fclone = SKB_FCLONE_ORIG;
                atomic_set(&fclones->fclone_ref, 1);

                fclones->skb2.fclone = SKB_FCLONE_CLONE;
                fclones->skb2.pfmemalloc = pfmemalloc;
        }
out:
        return skb;
nodata:
        kmem_cache_free(cache, skb);
        skb = NULL;
        goto out;
}
EXPORT_SYMBOL(__alloc_skb);

/**
 * __build_skb - build a network buffer
 * @data: data buffer provided by caller
 * @frag_size: size of data, or 0 if head was kmalloced
 *
 * Allocate a new &sk_buff. Caller provides space holding head and
 * skb_shared_info. @data must have been allocated by kmalloc() only if
 * @frag_size is 0, otherwise data should come from the page allocator
 *  or vmalloc()
 * The return is the new skb buffer.
 * On a failure the return is %NULL, and @data is not freed.
 * Notes :
 *  Before IO, driver allocates only data buffer where NIC put incoming frame
 *  Driver should add room at head (NET_SKB_PAD) and
 *  MUST add room at tail (SKB_DATA_ALIGN(skb_shared_info))
 *  After IO, driver calls build_skb(), to allocate sk_buff and populate it
 *  before giving packet to stack.
 *  RX rings only contains data buffers, not full skbs.
 */
struct sk_buff *__build_skb(void *data, unsigned int frag_size)
{
        struct skb_shared_info *shinfo;
        struct sk_buff *skb;
        unsigned int size = frag_size ? : ksize(data);

        skb = kmem_cache_alloc(skbuff_head_cache, GFP_ATOMIC);
        if (!skb)
                return NULL;

        size -= SKB_DATA_ALIGN(sizeof(struct skb_shared_info));

        memset(skb, 0, offsetof(struct sk_buff, tail));
        skb->truesize = SKB_TRUESIZE(size);
        atomic_set(&skb->users, 1);
        skb->head = data;
        skb->data = data;
        skb_reset_tail_pointer(skb);
        skb->end = skb->tail + size;
        skb->mac_header = (typeof(skb->mac_header))~0U;
        skb->transport_header = (typeof(skb->transport_header))~0U;

        /* make sure we initialize shinfo sequentially */
        shinfo = skb_shinfo(skb);
        memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
        atomic_set(&shinfo->dataref, 1);
        kmemcheck_annotate_variable(shinfo->destructor_arg);

        return skb;
}

/* build_skb() is wrapper over __build_skb(), that specifically
 * takes care of skb->head and skb->pfmemalloc
 * This means that if @frag_size is not zero, then @data must be backed
 * by a page fragment, not kmalloc() or vmalloc()
 */
struct sk_buff *build_skb(void *data, unsigned int frag_size)
{
        struct sk_buff *skb = __build_skb(data, frag_size);

        if (skb && frag_size) {
                skb->head_frag = 1;
                if (page_is_pfmemalloc(virt_to_head_page(data)))
                        skb->pfmemalloc = 1;
        }
        return skb;
}
EXPORT_SYMBOL(build_skb);

#define NAPI_SKB_CACHE_SIZE     64

struct napi_alloc_cache {
        struct page_frag_cache page;
        size_t skb_count;
        void *skb_cache[NAPI_SKB_CACHE_SIZE];
};

static DEFINE_PER_CPU(struct page_frag_cache, netdev_alloc_cache);
static DEFINE_PER_CPU(struct napi_alloc_cache, napi_alloc_cache);

static void *__netdev_alloc_frag(unsigned int fragsz, gfp_t gfp_mask)
{
        struct page_frag_cache *nc;
        unsigned long flags;
        void *data;

        local_irq_save(flags);
        nc = this_cpu_ptr(&netdev_alloc_cache);
        data = __alloc_page_frag(nc, fragsz, gfp_mask);
        local_irq_restore(flags);
        return data;
}

/**
 * netdev_alloc_frag - allocate a page fragment
 * @fragsz: fragment size
 *
 * Allocates a frag from a page for receive buffer.
 * Uses GFP_ATOMIC allocations.
 */
void *netdev_alloc_frag(unsigned int fragsz)
{
        return __netdev_alloc_frag(fragsz, GFP_ATOMIC | __GFP_COLD);
}
EXPORT_SYMBOL(netdev_alloc_frag);

static void *__napi_alloc_frag(unsigned int fragsz, gfp_t gfp_mask)
{
        struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);

        return __alloc_page_frag(&nc->page, fragsz, gfp_mask);
}

void *napi_alloc_frag(unsigned int fragsz)
{
        return __napi_alloc_frag(fragsz, GFP_ATOMIC | __GFP_COLD);
}
EXPORT_SYMBOL(napi_alloc_frag);

/**
 *      __netdev_alloc_skb - allocate an skbuff for rx on a specific device
 *      @dev: network device to receive on
 *      @len: 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 NET_SKB_PAD 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 len,
                                   gfp_t gfp_mask)
{
        struct page_frag_cache *nc;
        unsigned long flags;
        struct sk_buff *skb;
        bool pfmemalloc;
        void *data;

        len += NET_SKB_PAD;

        if ((len > SKB_WITH_OVERHEAD(PAGE_SIZE)) ||
            (gfp_mask & (__GFP_DIRECT_RECLAIM | GFP_DMA))) {
                skb = __alloc_skb(len, gfp_mask, SKB_ALLOC_RX, NUMA_NO_NODE);
                if (!skb)
                        goto skb_fail;
                goto skb_success;
        }

        len += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
        len = SKB_DATA_ALIGN(len);

        if (sk_memalloc_socks())
                gfp_mask |= __GFP_MEMALLOC;

        local_irq_save(flags);

        nc = this_cpu_ptr(&netdev_alloc_cache);
        data = __alloc_page_frag(nc, len, gfp_mask);
        pfmemalloc = nc->pfmemalloc;

        local_irq_restore(flags);

        if (unlikely(!data))
                return NULL;

        skb = __build_skb(data, len);
        if (unlikely(!skb)) {
                skb_free_frag(data);
                return NULL;
        }

        /* use OR instead of assignment to avoid clearing of bits in mask */
        if (pfmemalloc)
                skb->pfmemalloc = 1;
        skb->head_frag = 1;

skb_success:
        skb_reserve(skb, NET_SKB_PAD);
        skb->dev = dev;

skb_fail:
        return skb;
}
EXPORT_SYMBOL(__netdev_alloc_skb);

/**
 *      __napi_alloc_skb - allocate skbuff for rx in a specific NAPI instance
 *      @napi: napi instance this buffer was allocated for
 *      @len: length to allocate
 *      @gfp_mask: get_free_pages mask, passed to alloc_skb and alloc_pages
 *
 *      Allocate a new sk_buff for use in NAPI receive.  This buffer will
 *      attempt to allocate the head from a special reserved region used
 *      only for NAPI Rx allocation.  By doing this we can save several
 *      CPU cycles by avoiding having to disable and re-enable IRQs.
 *
 *      %NULL is returned if there is no free memory.
 */
struct sk_buff *__napi_alloc_skb(struct napi_struct *napi, unsigned int len,
                                 gfp_t gfp_mask)
{
        struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
        struct sk_buff *skb;
        void *data;

        len += NET_SKB_PAD + NET_IP_ALIGN;

        if ((len > SKB_WITH_OVERHEAD(PAGE_SIZE)) ||
            (gfp_mask & (__GFP_DIRECT_RECLAIM | GFP_DMA))) {
                skb = __alloc_skb(len, gfp_mask, SKB_ALLOC_RX, NUMA_NO_NODE);
                if (!skb)
                        goto skb_fail;
                goto skb_success;
        }

        len += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
        len = SKB_DATA_ALIGN(len);

        if (sk_memalloc_socks())
                gfp_mask |= __GFP_MEMALLOC;

        data = __alloc_page_frag(&nc->page, len, gfp_mask);
        if (unlikely(!data))
                return NULL;

        skb = __build_skb(data, len);
        if (unlikely(!skb)) {
                skb_free_frag(data);
                return NULL;
        }

        /* use OR instead of assignment to avoid clearing of bits in mask */
        if (nc->page.pfmemalloc)
                skb->pfmemalloc = 1;
        skb->head_frag = 1;

skb_success:
        skb_reserve(skb, NET_SKB_PAD + NET_IP_ALIGN);
        skb->dev = napi->dev;

skb_fail:
        return skb;
}
EXPORT_SYMBOL(__napi_alloc_skb);

void skb_add_rx_frag(struct sk_buff *skb, int i, struct page *page, int off,
                     int size, unsigned int truesize)
{
        skb_fill_page_desc(skb, i, page, off, size);
        skb->len += size;
        skb->data_len += size;
        skb->truesize += truesize;
}
EXPORT_SYMBOL(skb_add_rx_frag);

void skb_coalesce_rx_frag(struct sk_buff *skb, int i, int size,
                          unsigned int truesize)
{
        skb_frag_t *frag = &skb_shinfo(skb)->frags[i];

        skb_frag_size_add(frag, size);
        skb->len += size;
        skb->data_len += size;
        skb->truesize += truesize;
}
EXPORT_SYMBOL(skb_coalesce_rx_frag);

static void skb_drop_list(struct sk_buff **listp)
{
        kfree_skb_list(*listp);
        *listp = NULL;
}

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;

        skb_walk_frags(skb, list)
                skb_get(list);
}

static void skb_free_head(struct sk_buff *skb)
{
        unsigned char *head = skb->head;

        if (skb->head_frag)
                skb_free_frag(head);
        else
                kfree(head);
}

static void skb_release_data(struct sk_buff *skb)
{
        struct skb_shared_info *shinfo = skb_shinfo(skb);
        int i;

        if (skb->cloned &&
            atomic_sub_return(skb->nohdr ? (1 << SKB_DATAREF_SHIFT) + 1 : 1,
                              &shinfo->dataref))
                return;

        for (i = 0; i < shinfo->nr_frags; i++)
                __skb_frag_unref(&shinfo->frags[i]);

        /*
         * If skb buf is from userspace, we need to notify the caller
         * the lower device DMA has done;
         */
        if (shinfo->tx_flags & SKBTX_DEV_ZEROCOPY) {
                struct ubuf_info *uarg;

                uarg = shinfo->destructor_arg;
                if (uarg->callback)
                        uarg->callback(uarg, true);
        }

        if (shinfo->frag_list)
                kfree_skb_list(shinfo->frag_list);

        skb_free_head(skb);
}

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

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

        case SKB_FCLONE_ORIG:
                fclones = container_of(skb, struct sk_buff_fclones, skb1);

                /* We usually free the clone (TX completion) before original skb
                 * This test would have no chance to be true for the clone,
                 * while here, branch prediction will be good.
                 */
                if (atomic_read(&fclones->fclone_ref) == 1)
                        goto fastpath;
                break;

        default: /* SKB_FCLONE_CLONE */
                fclones = container_of(skb, struct sk_buff_fclones, skb2);
                break;
        }
        if (!atomic_dec_and_test(&fclones->fclone_ref))
                return;
fastpath:
        kmem_cache_free(skbuff_fclone_cache, fclones);
}

static void skb_release_head_state(struct sk_buff *skb)
{
        skb_dst_drop(skb);
#ifdef CONFIG_XFRM
        secpath_put(skb->sp);
#endif
        if (skb->destructor) {
                WARN_ON(in_irq());
                skb->destructor(skb);
        }
#if IS_ENABLED(CONFIG_NF_CONNTRACK)
        nf_conntrack_put(skb->nfct);
#endif
#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
        nf_bridge_put(skb->nf_bridge);
#endif
}

/* Free everything but the sk_buff shell. */
static void skb_release_all(struct sk_buff *skb)
{
        skb_release_head_state(skb);
        if (likely(skb->head))
                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);
}
EXPORT_SYMBOL(__kfree_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;
        trace_kfree_skb(skb, __builtin_return_address(0));
        __kfree_skb(skb);
}
EXPORT_SYMBOL(kfree_skb);

void kfree_skb_list(struct sk_buff *segs)
{
        while (segs) {
                struct sk_buff *next = segs->next;

                kfree_skb(segs);
                segs = next;
        }
}
EXPORT_SYMBOL(kfree_skb_list);

/**
 *      skb_tx_error - report an sk_buff xmit error
 *      @skb: buffer that triggered an error
 *
 *      Report xmit error if a device callback is tracking this skb.
 *      skb must be freed afterwards.
 */
void skb_tx_error(struct sk_buff *skb)
{
        if (skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY) {
                struct ubuf_info *uarg;

                uarg = skb_shinfo(skb)->destructor_arg;
                if (uarg->callback)
                        uarg->callback(uarg, false);
                skb_shinfo(skb)->tx_flags &= ~SKBTX_DEV_ZEROCOPY;
        }
}
EXPORT_SYMBOL(skb_tx_error);

/**
 *      consume_skb - free an skbuff
 *      @skb: buffer to free
 *
 *      Drop a ref to the buffer and free it if the usage count has hit zero
 *      Functions identically to kfree_skb, but kfree_skb assumes that the frame
 *      is being dropped after a failure and notes that
 */
void consume_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;
        trace_consume_skb(skb);
        __kfree_skb(skb);
}
EXPORT_SYMBOL(consume_skb);

void __kfree_skb_flush(void)
{
        struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);

        /* flush skb_cache if containing objects */
        if (nc->skb_count) {
                kmem_cache_free_bulk(skbuff_head_cache, nc->skb_count,
                                     nc->skb_cache);
                nc->skb_count = 0;
        }
}

static inline void _kfree_skb_defer(struct sk_buff *skb)
{
        struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);

        /* drop skb->head and call any destructors for packet */
        skb_release_all(skb);

        /* record skb to CPU local list */
        nc->skb_cache[nc->skb_count++] = skb;

#ifdef CONFIG_SLUB
        /* SLUB writes into objects when freeing */
        prefetchw(skb);
#endif

        /* flush skb_cache if it is filled */
        if (unlikely(nc->skb_count == NAPI_SKB_CACHE_SIZE)) {
                kmem_cache_free_bulk(skbuff_head_cache, NAPI_SKB_CACHE_SIZE,
                                     nc->skb_cache);
                nc->skb_count = 0;
        }
}
void __kfree_skb_defer(struct sk_buff *skb)
{
        _kfree_skb_defer(skb);
}

void napi_consume_skb(struct sk_buff *skb, int budget)
{
        if (unlikely(!skb))
                return;

        /* Zero budget indicate non-NAPI context called us, like netpoll */
        if (unlikely(!budget)) {
                dev_consume_skb_any(skb);
                return;
        }

        if (likely(atomic_read(&skb->users) == 1))
                smp_rmb();
        else if (likely(!atomic_dec_and_test(&skb->users)))
                return;
        /* if reaching here SKB is ready to free */
        trace_consume_skb(skb);

        /* if SKB is a clone, don't handle this case */
        if (skb->fclone != SKB_FCLONE_UNAVAILABLE) {
                __kfree_skb(skb);
                return;
        }

        _kfree_skb_defer(skb);
}
EXPORT_SYMBOL(napi_consume_skb);

/* Make sure a field is enclosed inside headers_start/headers_end section */
#define CHECK_SKB_FIELD(field) \
        BUILD_BUG_ON(offsetof(struct sk_buff, field) <          \
                     offsetof(struct sk_buff, headers_start));  \
        BUILD_BUG_ON(offsetof(struct sk_buff, field) >          \
                     offsetof(struct sk_buff, headers_end));    \

static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
{
        new->tstamp             = old->tstamp;
        /* We do not copy old->sk */
        new->dev                = old->dev;
        memcpy(new->cb, old->cb, sizeof(old->cb));
        skb_dst_copy(new, old);
#ifdef CONFIG_XFRM
        new->sp                 = secpath_get(old->sp);
#endif
        __nf_copy(new, old, false);

        /* Note : this field could be in headers_start/headers_end section
         * It is not yet because we do not want to have a 16 bit hole
         */
        new->queue_mapping = old->queue_mapping;

        memcpy(&new->headers_start, &old->headers_start,
               offsetof(struct sk_buff, headers_end) -
               offsetof(struct sk_buff, headers_start));
        CHECK_SKB_FIELD(protocol);
        CHECK_SKB_FIELD(csum);
        CHECK_SKB_FIELD(hash);
        CHECK_SKB_FIELD(priority);
        CHECK_SKB_FIELD(skb_iif);
        CHECK_SKB_FIELD(vlan_proto);
        CHECK_SKB_FIELD(vlan_tci);
        CHECK_SKB_FIELD(transport_header);
        CHECK_SKB_FIELD(network_header);
        CHECK_SKB_FIELD(mac_header);
        CHECK_SKB_FIELD(inner_protocol);
        CHECK_SKB_FIELD(inner_transport_header);
        CHECK_SKB_FIELD(inner_network_header);
        CHECK_SKB_FIELD(inner_mac_header);
        CHECK_SKB_FIELD(mark);
#ifdef CONFIG_NETWORK_SECMARK
        CHECK_SKB_FIELD(secmark);
#endif
#ifdef CONFIG_NET_RX_BUSY_POLL
        CHECK_SKB_FIELD(napi_id);
#endif
#ifdef CONFIG_XPS
        CHECK_SKB_FIELD(sender_cpu);
#endif
#ifdef CONFIG_NET_SCHED
        CHECK_SKB_FIELD(tc_index);
#ifdef CONFIG_NET_CLS_ACT
        CHECK_SKB_FIELD(tc_verd);
#endif
#endif

}

/*
 * You should not add any new code to this function.  Add it to
 * __copy_skb_header above instead.
 */
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(tail);
        C(end);
        C(head);
        C(head_frag);
        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_copy_ubufs  -       copy userspace skb frags buffers to kernel
 *      @skb: the skb to modify
 *      @gfp_mask: allocation priority
 *
 *      This must be called on SKBTX_DEV_ZEROCOPY skb.
 *      It will copy all frags into kernel and drop the reference
 *      to userspace pages.
 *
 *      If this function is called from an interrupt gfp_mask() must be
 *      %GFP_ATOMIC.
 *
 *      Returns 0 on success or a negative error code on failure
 *      to allocate kernel memory to copy to.
 */
int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask)
{
        int i;
        int num_frags = skb_shinfo(skb)->nr_frags;
        struct page *page, *head = NULL;
        struct ubuf_info *uarg = skb_shinfo(skb)->destructor_arg;

        for (i = 0; i < num_frags; i++) {
                u8 *vaddr;
                skb_frag_t *f = &skb_shinfo(skb)->frags[i];

                page = alloc_page(gfp_mask);
                if (!page) {
                        while (head) {
                                struct page *next = (struct page *)page_private(head);
                                put_page(head);
                                head = next;
                        }
                        return -ENOMEM;
                }
                vaddr = kmap_atomic(skb_frag_page(f));
                memcpy(page_address(page),
                       vaddr + f->page_offset, skb_frag_size(f));
                kunmap_atomic(vaddr);
                set_page_private(page, (unsigned long)head);
                head = page;
        }

        /* skb frags release userspace buffers */
        for (i = 0; i < num_frags; i++)
                skb_frag_unref(skb, i);

        uarg->callback(uarg, false);

        /* skb frags point to kernel buffers */
        for (i = num_frags - 1; i >= 0; i--) {
                __skb_fill_page_desc(skb, i, head, 0,
                                     skb_shinfo(skb)->frags[i].size);
                head = (struct page *)page_private(head);
        }

        skb_shinfo(skb)->tx_flags &= ~SKBTX_DEV_ZEROCOPY;
        return 0;
}
EXPORT_SYMBOL_GPL(skb_copy_ubufs);

/**
 *      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_fclones *fclones = container_of(skb,
                                                       struct sk_buff_fclones,
                                                       skb1);
        struct sk_buff *n;

        if (skb_orphan_frags(skb, gfp_mask))
                return NULL;

        if (skb->fclone == SKB_FCLONE_ORIG &&
            atomic_read(&fclones->fclone_ref) == 1) {
                n = &fclones->skb2;
                atomic_set(&fclones->fclone_ref, 2);
        } else {
                if (skb_pfmemalloc(skb))
                        gfp_mask |= __GFP_MEMALLOC;

                n = kmem_cache_alloc(skbuff_head_cache, gfp_mask);
                if (!n)
                        return NULL;

                kmemcheck_annotate_bitfield(n, flags1);
                n->fclone = SKB_FCLONE_UNAVAILABLE;
        }

        return __skb_clone(n, skb);
}
EXPORT_SYMBOL(skb_clone);

static void skb_headers_offset_update(struct sk_buff *skb, int off)
{
        /* Only adjust this if it actually is csum_start rather than csum */
        if (skb->ip_summed == CHECKSUM_PARTIAL)
                skb->csum_start += off;
        /* {transport,network,mac}_header and tail are relative to skb->head */
        skb->transport_header += off;
        skb->network_header   += off;
        if (skb_mac_header_was_set(skb))
                skb->mac_header += off;
        skb->inner_transport_header += off;
        skb->inner_network_header += off;
        skb->inner_mac_header += off;
}

static void copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
{
        __copy_skb_header(new, old);

        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;
}

static inline int skb_alloc_rx_flag(const struct sk_buff *skb)
{
        if (skb_pfmemalloc(skb))
                return SKB_ALLOC_RX;
        return 0;
}

/**
 *      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_headroom(skb);
        unsigned int size = skb_end_offset(skb) + skb->data_len;
        struct sk_buff *n = __alloc_skb(size, gfp_mask,
                                        skb_alloc_rx_flag(skb), NUMA_NO_NODE);

        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;
}
EXPORT_SYMBOL(skb_copy);

/**
 *      __pskb_copy_fclone      -  create copy of an sk_buff with private head.
 *      @skb: buffer to copy
 *      @headroom: headroom of new skb
 *      @gfp_mask: allocation priority
 *      @fclone: if true allocate the copy of the skb from the fclone
 *      cache instead of the head cache; it is recommended to set this
 *      to true for the cases where the copy will likely be cloned
 *
 *      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_fclone(struct sk_buff *skb, int headroom,
                                   gfp_t gfp_mask, bool fclone)
{
        unsigned int size = skb_headlen(skb) + headroom;
        int flags = skb_alloc_rx_flag(skb) | (fclone ? SKB_ALLOC_FCLONE : 0);
        struct sk_buff *n = __alloc_skb(size, gfp_mask, flags, NUMA_NO_NODE);

        if (!n)
                goto out;

        /* Set the data pointer */
        skb_reserve(n, headroom);
        /* 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;

                if (skb_orphan_frags(skb, gfp_mask)) {
                        kfree_skb(n);
                        n = NULL;
                        goto out;
                }
                for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
                        skb_shinfo(n)->frags[i] = skb_shinfo(skb)->frags[i];
                        skb_frag_ref(skb, i);
                }
                skb_shinfo(n)->nr_frags = i;
        }

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

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

/**
 *      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;
        int size = nhead + skb_end_offset(skb) + ntail;
        long off;

        BUG_ON(nhead < 0);

        if (skb_shared(skb))
                BUG();

        size = SKB_DATA_ALIGN(size);

        if (skb_pfmemalloc(skb))
                gfp_mask |= __GFP_MEMALLOC;
        data = kmalloc_reserve(size + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)),
                               gfp_mask, NUMA_NO_NODE, NULL);
        if (!data)
                goto nodata;
        size = SKB_WITH_OVERHEAD(ksize(data));

        /* Copy only real data... and, alas, header. This should be
         * optimized for the cases when header is void.
         */
        memcpy(data + nhead, skb->head, skb_tail_pointer(skb) - skb->head);

        memcpy((struct skb_shared_info *)(data + size),
               skb_shinfo(skb),
               offsetof(struct skb_shared_info, frags[skb_shinfo(skb)->nr_frags]));

        /*
         * if shinfo is shared we must drop the old head gracefully, but if it
         * is not we can just drop the old head and let the existing refcount
         * be since all we did is relocate the values
         */
        if (skb_cloned(skb)) {
                /* copy this zero copy skb frags */
                if (skb_orphan_frags(skb, gfp_mask))
                        goto nofrags;
                for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
                        skb_frag_ref(skb, i);

                if (skb_has_frag_list(skb))
                        skb_clone_fraglist(skb);

                skb_release_data(skb);
        } else {
                skb_free_head(skb);
        }
        off = (data + nhead) - skb->head;

        skb->head     = data;
        skb->head_frag = 0;
        skb->data    += off;
#ifdef NET_SKBUFF_DATA_USES_OFFSET
        skb->end      = size;
        off           = nhead;
#else
        skb->end      = skb->head + size;
#endif
        skb->tail             += off;
        skb_headers_offset_update(skb, nhead);
        skb->cloned   = 0;
        skb->hdr_len  = 0;
        skb->nohdr    = 0;
        atomic_set(&skb_shinfo(skb)->dataref, 1);
        return 0;

nofrags:
        kfree(data);
nodata:
        return -ENOMEM;
}
EXPORT_SYMBOL(pskb_expand_head);

/* 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;
}
EXPORT_SYMBOL(skb_realloc_headroom);

/**
 *      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, skb_alloc_rx_flag(skb),
                                        NUMA_NO_NODE);
        int oldheadroom = skb_headroom(skb);
        int head_copy_len, head_copy_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);

        skb_headers_offset_update(n, newheadroom - oldheadroom);

        return n;
}
EXPORT_SYMBOL(skb_copy_expand);

/**
 *      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;
}
EXPORT_SYMBOL(skb_pad);

/**
 *      pskb_put - add data to the tail of a potentially fragmented buffer
 *      @skb: start of the buffer to use
 *      @tail: tail fragment of the buffer to use
 *      @len: amount of data to add
 *
 *      This function extends the used data area of the potentially
 *      fragmented buffer. @tail must be the last fragment of @skb -- or
 *      @skb itself. 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 *pskb_put(struct sk_buff *skb, struct sk_buff *tail, int len)
{
        if (tail != skb) {
                skb->data_len += len;
                skb->len += len;
        }
        return skb_put(tail, len);
}
EXPORT_SYMBOL_GPL(pskb_put);

/**
 *      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 skb_pull_inline(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_frag_size(&skb_shinfo(skb)->frags[i]);

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

                skb_frag_size_set(&skb_shinfo(skb)->frags[i++], len - offset);

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

                for (; i < nfrags; i++)
                        skb_frag_unref(skb, i);

                if (skb_has_frag_list(skb))
                        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;
                        consume_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;
}
EXPORT_SYMBOL(___pskb_trim);

/**
 *      __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_has_frag_list(skb))
                goto pull_pages;

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

                if (size >= eat)
                        goto pull_pages;
                eat -= 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)) {
                                        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++) {
                int size = skb_frag_size(&skb_shinfo(skb)->frags[i]);

                if (size <= eat) {
                        skb_frag_unref(skb, i);
                        eat -= size;
                } else {
                        skb_shinfo(skb)->frags[k] = skb_shinfo(skb)->frags[i];
                        if (eat) {
                                skb_shinfo(skb)->frags[k].page_offset += eat;
                                skb_frag_size_sub(&skb_shinfo(skb)->frags[k], eat);
                                eat = 0;
                        }
                        k++;
                }
        }
        skb_shinfo(skb)->nr_frags = k;

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

        return skb_tail_pointer(skb);
}
EXPORT_SYMBOL(__pskb_pull_tail);

/**
 *      skb_copy_bits - copy bits from skb to kernel buffer
 *      @skb: source skb
 *      @offset: offset in source
 *      @to: destination buffer
 *      @len: number of bytes to copy
 *
 *      Copy the specified number of bytes from the source skb to the
 *      destination buffer.
 *
 *      CAUTION ! :
 *              If its prototype is ever changed,
 *              check arch/{*}/net/{*}.S files,
 *              since it is called from BPF assembly code.
 */
int skb_copy_bits(const struct sk_buff *skb, int offset, void *to, int len)
{
        int start = skb_headlen(skb);
        struct sk_buff *frag_iter;
        int i, copy;

        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;
                skb_frag_t *f = &skb_shinfo(skb)->frags[i];

                WARN_ON(start > offset + len);

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

                        if (copy > len)
                                copy = len;

                        vaddr = kmap_atomic(skb_frag_page(f));
                        memcpy(to,
                               vaddr + f->page_offset + offset - start,
                               copy);
                        kunmap_atomic(vaddr);

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

        skb_walk_frags(skb, frag_iter) {
                int end;

                WARN_ON(start > offset + len);

                end = start + frag_iter->len;
                if ((copy = end - offset) > 0) {
                        if (copy > len)
                                copy = len;
                        if (skb_copy_bits(frag_iter, 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;
}
EXPORT_SYMBOL(skb_copy_bits);

/*
 * 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)
{
        put_page(spd->pages[i]);
}

static struct page *linear_to_page(struct page *page, unsigned int *len,
                                   unsigned int *offset,
                                   struct sock *sk)
{
        struct page_frag *pfrag = sk_page_frag(sk);

        if (!sk_page_frag_refill(sk, pfrag))
                return NULL;

        *len = min_t(unsigned int, *len, pfrag->size - pfrag->offset);

        memcpy(page_address(pfrag->page) + pfrag->offset,
               page_address(page) + *offset, *len);
        *offset = pfrag->offset;
        pfrag->offset += *len;

        return pfrag->page;
}

static bool spd_can_coalesce(const struct splice_pipe_desc *spd,
                             struct page *page,
                             unsigned int offset)
{
        return  spd->nr_pages &&
                spd->pages[spd->nr_pages - 1] == page &&
                (spd->partial[spd->nr_pages - 1].offset +
                 spd->partial[spd->nr_pages - 1].len == offset);
}

/*
 * Fill page/offset/length into spd, if it can hold more pages.
 */
static bool spd_fill_page(struct splice_pipe_desc *spd,
                          struct pipe_inode_info *pipe, struct page *page,
                          unsigned int *len, unsigned int offset,
                          bool linear,
                          struct sock *sk)
{
        if (unlikely(spd->nr_pages == MAX_SKB_FRAGS))
                return true;

        if (linear) {
                page = linear_to_page(page, len, &offset, sk);
                if (!page)
                        return true;
        }
        if (spd_can_coalesce(spd, page, offset)) {
                spd->partial[spd->nr_pages - 1].len += *len;
                return false;
        }
        get_page(page);
        spd->pages[spd->nr_pages] = page;
        spd->partial[spd->nr_pages].len = *len;
        spd->partial[spd->nr_pages].offset = offset;
        spd->nr_pages++;

        return false;
}

static bool __splice_segment(struct page *page, unsigned int poff,
                             unsigned int plen, unsigned int *off,
                             unsigned int *len,
                             struct splice_pipe_desc *spd, bool linear,
                             struct sock *sk,
                             struct pipe_inode_info *pipe)
{
        if (!*len)
                return true;

        /* skip this segment if already processed */
        if (*off >= plen) {
                *off -= plen;
                return false;
        }

        /* ignore any bits we already processed */
        poff += *off;
        plen -= *off;
        *off = 0;

        do {
                unsigned int flen = min(*len, plen);

                if (spd_fill_page(spd, pipe, page, &flen, poff,
                                  linear, sk))
                        return true;
                poff += flen;
                plen -= flen;
                *len -= flen;
        } while (*len && plen);

        return false;
}

/*
 * Map linear and fragment data from the skb to spd. It reports true if the
 * pipe is full or if we already spliced the requested length.
 */
static bool __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
                              unsigned int *offset, unsigned int *len,
                              struct splice_pipe_desc *spd, struct sock *sk)
{
        int seg;
        struct sk_buff *iter;

        /* map the linear part :
         * If skb->head_frag is set, this 'linear' part is backed by a
         * fragment, and if the head is not shared with any clones then
         * we can avoid a copy since we own the head portion of this page.
         */
        if (__splice_segment(virt_to_page(skb->data),
                             (unsigned long) skb->data & (PAGE_SIZE - 1),
                             skb_headlen(skb),
                             offset, len, spd,
                             skb_head_is_locked(skb),
                             sk, pipe))
                return true;

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

                if (__splice_segment(skb_frag_page(f),
                                     f->page_offset, skb_frag_size(f),
                                     offset, len, spd, false, sk, pipe))
                        return true;
        }

        skb_walk_frags(skb, iter) {
                if (*offset >= iter->len) {
                        *offset -= iter->len;
                        continue;
                }
                /* __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(iter, pipe, offset, len, spd, sk))
                        return true;
        }

        return false;
}

ssize_t skb_socket_splice(struct sock *sk,
                          struct pipe_inode_info *pipe,
                          struct splice_pipe_desc *spd)
{
        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(sk);
        ret = splice_to_pipe(pipe, spd);
        lock_sock(sk);

        return ret;
}

/*
 * Map data from the skb to a pipe. Should handle both the linear part,
 * the fragments, and the frag list.
 */
int skb_splice_bits(struct sk_buff *skb, struct sock *sk, unsigned int offset,
                    struct pipe_inode_info *pipe, unsigned int tlen,
                    unsigned int flags,
                    ssize_t (*splice_cb)(struct sock *,
                                         struct pipe_inode_info *,
                                         struct splice_pipe_desc *))
{
        struct partial_page partial[MAX_SKB_FRAGS];
        struct page *pages[MAX_SKB_FRAGS];
        struct splice_pipe_desc spd = {
                .pages = pages,
                .partial = partial,
                .nr_pages_max = MAX_SKB_FRAGS,
                .flags = flags,
                .ops = &nosteal_pipe_buf_ops,
                .spd_release = sock_spd_release,
        };
        int ret = 0;

        __skb_splice_bits(skb, pipe, &offset, &tlen, &spd, sk);

        if (spd.nr_pages)
                ret = splice_cb(sk, pipe, &spd);

        return ret;
}
EXPORT_SYMBOL_GPL(skb_splice_bits);

/**
 *      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 start = skb_headlen(skb);
        struct sk_buff *frag_iter;
        int i, copy;

        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;

                WARN_ON(start > offset + len);

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

                        if (copy > len)
                                copy = len;

                        vaddr = kmap_atomic(skb_frag_page(frag));
                        memcpy(vaddr + frag->page_offset + offset - start,
                               from, copy);
                        kunmap_atomic(vaddr);

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

        skb_walk_frags(skb, frag_iter) {
                int end;

                WARN_ON(start > offset + len);

                end = start + frag_iter->len;
                if ((copy = end - offset) > 0) {
                        if (copy > len)
                                copy = len;
                        if (skb_store_bits(frag_iter, 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, const struct skb_checksum_ops *ops)
{
        int start = skb_headlen(skb);
        int i, copy = start - offset;
        struct sk_buff *frag_iter;
        int pos = 0;

        /* Checksum header. */
        if (copy > 0) {
                if (copy > len)
                        copy = len;
                csum = ops->update(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;
                skb_frag_t *frag = &skb_shinfo(skb)->frags[i];

                WARN_ON(start > offset + len);

                end = start + skb_frag_size(frag);
                if ((copy = end - offset) > 0) {
                        __wsum csum2;
                        u8 *vaddr;

                        if (copy > len)
                                copy = len;
                        vaddr = kmap_atomic(skb_frag_page(frag));
                        csum2 = ops->update(vaddr + frag->page_offset +
                                            offset - start, copy, 0);
                        kunmap_atomic(vaddr);
                        csum = ops->combine(csum, csum2, pos, copy);
                        if (!(len -= copy))
                                return csum;
                        offset += copy;
                        pos    += copy;
                }
                start = end;
        }

        skb_walk_frags(skb, frag_iter) {
                int end;

                WARN_ON(start > offset + len);

                end = start + frag_iter->len;
                if ((copy = end - offset) > 0) {
                        __wsum csum2;
                        if (copy > len)
                                copy = len;
                        csum2 = __skb_checksum(frag_iter, offset - start,
                                               copy, 0, ops);
                        csum = ops->combine(csum, csum2, pos, copy);
                        if ((len -= copy) == 0)
                                return csum;
                        offset += copy;
                        pos    += copy;
                }
                start = end;
        }
        BUG_ON(len);

        return csum;
}
EXPORT_SYMBOL(__skb_checksum);

__wsum skb_checksum(const struct sk_buff *skb, int offset,
                    int len, __wsum csum)
{
        const struct skb_checksum_ops ops = {
                .update  = csum_partial_ext,
                .combine = csum_block_add_ext,
        };

        return __skb_checksum(skb, offset, len, csum, &ops);
}
EXPORT_SYMBOL(skb_checksum);

/* 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;
        struct sk_buff *frag_iter;
        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;

                WARN_ON(start > offset + len);

                end = start + skb_frag_size(&skb_shinfo(skb)->frags[i]);
                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_atomic(skb_frag_page(frag));
                        csum2 = csum_partial_copy_nocheck(vaddr +
                                                          frag->page_offset +
                                                          offset - start, to,
                                                          copy, 0);
                        kunmap_atomic(vaddr);
                        csum = csum_block_add(csum, csum2, pos);
                        if (!(len -= copy))
                                return csum;
                        offset += copy;
                        to     += copy;
                        pos    += copy;
                }
                start = end;
        }

        skb_walk_frags(skb, frag_iter) {
                __wsum csum2;
                int end;

                WARN_ON(start > offset + len);

                end = start + frag_iter->len;
                if ((copy = end - offset) > 0) {
                        if (copy > len)
                                copy = len;
                        csum2 = skb_copy_and_csum_bits(frag_iter,
                                                       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;
}
EXPORT_SYMBOL(skb_copy_and_csum_bits);

 /**
 *      skb_zerocopy_headlen - Calculate headroom needed for skb_zerocopy()
 *      @from: source buffer
 *
 *      Calculates the amount of linear headroom needed in the 'to' skb passed
 *      into skb_zerocopy().
 */
unsigned int
skb_zerocopy_headlen(const struct sk_buff *from)
{
        unsigned int hlen = 0;

        if (!from->head_frag ||
            skb_headlen(from) < L1_CACHE_BYTES ||
            skb_shinfo(from)->nr_frags >= MAX_SKB_FRAGS)
                hlen = skb_headlen(from);

        if (skb_has_frag_list(from))
                hlen = from->len;

        return hlen;
}
EXPORT_SYMBOL_GPL(skb_zerocopy_headlen);

/**
 *      skb_zerocopy - Zero copy skb to skb
 *      @to: destination buffer
 *      @from: source buffer
 *      @len: number of bytes to copy from source buffer
 *      @hlen: size of linear headroom in destination buffer
 *
 *      Copies up to `len` bytes from `from` to `to` by creating references
 *      to the frags in the source buffer.
 *
 *      The `hlen` as calculated by skb_zerocopy_headlen() specifies the
 *      headroom in the `to` buffer.
 *
 *      Return value:
 *      0: everything is OK
 *      -ENOMEM: couldn't orphan frags of @from due to lack of memory
 *      -EFAULT: skb_copy_bits() found some problem with skb geometry
 */
int
skb_zerocopy(struct sk_buff *to, struct sk_buff *from, int len, int hlen)
{
        int i, j = 0;
        int plen = 0; /* length of skb->head fragment */
        int ret;
        struct page *page;
        unsigned int offset;

        BUG_ON(!from->head_frag && !hlen);

        /* dont bother with small payloads */
        if (len <= skb_tailroom(to))
                return skb_copy_bits(from, 0, skb_put(to, len), len);

        if (hlen) {
                ret = skb_copy_bits(from, 0, skb_put(to, hlen), hlen);
                if (unlikely(ret))
                        return ret;
                len -= hlen;
        } else {
                plen = min_t(int, skb_headlen(from), len);
                if (plen) {
                        page = virt_to_head_page(from->head);
                        offset = from->data - (unsigned char *)page_address(page);
                        __skb_fill_page_desc(to, 0, page, offset, plen);
                        get_page(page);
                        j = 1;
                        len -= plen;
                }
        }

        to->truesize += len + plen;
        to->len += len + plen;
        to->data_len += len + plen;

        if (unlikely(skb_orphan_frags(from, GFP_ATOMIC))) {
                skb_tx_error(from);
                return -ENOMEM;
        }

        for (i = 0; i < skb_shinfo(from)->nr_frags; i++) {
                if (!len)
                        break;
                skb_shinfo(to)->frags[j] = skb_shinfo(from)->frags[i];
                skb_shinfo(to)->frags[j].size = min_t(int, skb_shinfo(to)->frags[j].size, len);
                len -= skb_shinfo(to)->frags[j].size;
                skb_frag_ref(to, j);
                j++;
        }
        skb_shinfo(to)->nr_frags = j;

        return 0;
}
EXPORT_SYMBOL_GPL(skb_zerocopy);

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_checksum_start_offset(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);
        }
}
EXPORT_SYMBOL(skb_copy_and_csum_dev);

/**
 *      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;
}
EXPORT_SYMBOL(skb_dequeue);

/**
 *      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;
}
EXPORT_SYMBOL(skb_dequeue_tail);

/**
 *      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);
}
EXPORT_SYMBOL(skb_queue_purge);

/**
 *      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);
}
EXPORT_SYMBOL(skb_queue_head);

/**
 *      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);
}
EXPORT_SYMBOL(skb_queue_tail);

/**
 *      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);
}
EXPORT_SYMBOL(skb_unlink);

/**
 *      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_queue_after(list, old, newsk);
        spin_unlock_irqrestore(&list->lock, flags);
}
EXPORT_SYMBOL(skb_append);

/**
 *      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);
}
EXPORT_SYMBOL(skb_insert);

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_frag_size(&skb_shinfo(skb)->frags[i]);

                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.
                                 */
                                skb_frag_ref(skb, i);
                                skb_shinfo(skb1)->frags[0].page_offset += len - pos;
                                skb_frag_size_sub(&skb_shinfo(skb1)->frags[0], len - pos);
                                skb_frag_size_set(&skb_shinfo(skb)->frags[i], 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);

        skb_shinfo(skb1)->tx_flags = skb_shinfo(skb)->tx_flags & SKBTX_SHARED_FRAG;
        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);
}
EXPORT_SYMBOL(skb_split);

/* Shifting from/to a cloned skb is a no-go.
 *
 * Caller cannot keep skb_shinfo related pointers past calling here!
 */
static int skb_prepare_for_shift(struct sk_buff *skb)
{
        return skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC);
}

/**
 * skb_shift - Shifts paged data partially from skb to another
 * @tgt: buffer into which tail data gets added
 * @skb: buffer from which the paged data comes from
 * @shiftlen: shift up to this many bytes
 *
 * Attempts to shift up to shiftlen worth of bytes, which may be less than
 * the length of the skb, from skb to tgt. Returns number bytes shifted.
 * It's up to caller to free skb if everything was shifted.
 *
 * If @tgt runs out of frags, the whole operation is aborted.
 *
 * Skb cannot include anything else but paged data while tgt is allowed
 * to have non-paged data as well.
 *
 * TODO: full sized shift could be optimized but that would need
 * specialized skb free'er to handle frags without up-to-date nr_frags.
 */
int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen)
{
        int from, to, merge, todo;
        struct skb_frag_struct *fragfrom, *fragto;

        BUG_ON(shiftlen > skb->len);
        BUG_ON(skb_headlen(skb));       /* Would corrupt stream */

        todo = shiftlen;
        from = 0;
        to = skb_shinfo(tgt)->nr_frags;
        fragfrom = &skb_shinfo(skb)->frags[from];

        /* Actual merge is delayed until the point when we know we can
         * commit all, so that we don't have to undo partial changes
         */
        if (!to ||
            !skb_can_coalesce(tgt, to, skb_frag_page(fragfrom),
                              fragfrom->page_offset)) {
                merge = -1;
        } else {
                merge = to - 1;

                todo -= skb_frag_size(fragfrom);
                if (todo < 0) {
                        if (skb_prepare_for_shift(skb) ||
                            skb_prepare_for_shift(tgt))
                                return 0;

                        /* All previous frag pointers might be stale! */
                        fragfrom = &skb_shinfo(skb)->frags[from];
                        fragto = &skb_shinfo(tgt)->frags[merge];

                        skb_frag_size_add(fragto, shiftlen);
                        skb_frag_size_sub(fragfrom, shiftlen);
                        fragfrom->page_offset += shiftlen;

                        goto onlymerged;
                }

                from++;
        }

        /* Skip full, not-fitting skb to avoid expensive operations */
        if ((shiftlen == skb->len) &&
            (skb_shinfo(skb)->nr_frags - from) > (MAX_SKB_FRAGS - to))
                return 0;

        if (skb_prepare_for_shift(skb) || skb_prepare_for_shift(tgt))
                return 0;

        while ((todo > 0) && (from < skb_shinfo(skb)->nr_frags)) {
                if (to == MAX_SKB_FRAGS)
                        return 0;

                fragfrom = &skb_shinfo(skb)->frags[from];
                fragto = &skb_shinfo(tgt)->frags[to];

                if (todo >= skb_frag_size(fragfrom)) {
                        *fragto = *fragfrom;
                        todo -= skb_frag_size(fragfrom);
                        from++;
                        to++;

                } else {
                        __skb_frag_ref(fragfrom);
                        fragto->page = fragfrom->page;
                        fragto->page_offset = fragfrom->page_offset;
                        skb_frag_size_set(fragto, todo);

                        fragfrom->page_offset += todo;
                        skb_frag_size_sub(fragfrom, todo);
                        todo = 0;

                        to++;
                        break;
                }
        }

        /* Ready to "commit" this state change to tgt */
        skb_shinfo(tgt)->nr_frags = to;

        if (merge >= 0) {
                fragfrom = &skb_shinfo(skb)->frags[0];
                fragto = &skb_shinfo(tgt)->frags[merge];

                skb_frag_size_add(fragto, skb_frag_size(fragfrom));
                __skb_frag_unref(fragfrom);
        }

        /* Reposition in the original skb */
        to = 0;
        while (from < skb_shinfo(skb)->nr_frags)
                skb_shinfo(skb)->frags[to++] = skb_shinfo(skb)->frags[from++];
        skb_shinfo(skb)->nr_frags = to;

        BUG_ON(todo > 0 && !skb_shinfo(skb)->nr_frags);

onlymerged:
        /* Most likely the tgt won't ever need its checksum anymore, skb on
         * the other hand might need it if it needs to be resent
         */
        tgt->ip_summed = CHECKSUM_PARTIAL;
        skb->ip_summed = CHECKSUM_PARTIAL;

        /* Yak, is it really working this way? Some helper please? */
        skb->len -= shiftlen;
        skb->data_len -= shiftlen;
        skb->truesize -= shiftlen;
        tgt->len += shiftlen;
        tgt->data_len += shiftlen;
        tgt->truesize += shiftlen;

        return shiftlen;
}

/**
 * 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;
}
EXPORT_SYMBOL(skb_prepare_seq_read);

/**
 * 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 arbitrary,
 *       this limitation is the cost for zerocopy sequential
 *       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)) {
                if (st->frag_data) {
                        kunmap_atomic(st->frag_data);
                        st->frag_data = NULL;
                }
                return 0;
        }

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

        if (abs_offset < block_limit && !st->frag_data) {
                *data = st->cur_skb->data + (abs_offset - st->stepped_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 = skb_frag_size(frag) + st->stepped_offset;

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

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

                        return block_limit - abs_offset;
                }

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

                st->frag_idx++;
                st->stepped_offset += skb_frag_size(frag);
        }

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

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

        return 0;
}
EXPORT_SYMBOL(skb_seq_read);

/**
 * 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_atomic(st->frag_data);
}
EXPORT_SYMBOL(skb_abort_seq_read);

#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
 *
 * 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);
}
EXPORT_SYMBOL(skb_find_text);

/**
 * skb_append_datato_frags - append the user data to a skb
 * @sk: sock  structure
 * @skb: skb structure to be appended 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 = skb_shinfo(skb)->nr_frags;
        int copy;
        int offset = 0;
        int ret;
        struct page_frag *pfrag = &current->task_frag;

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

                if (!sk_page_frag_refill(sk, pfrag))
                        return -ENOMEM;

                /* copy the user data to page */
                copy = min_t(int, length, pfrag->size - pfrag->offset);

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

                /* copy was successful so update the size parameters */
                skb_fill_page_desc(skb, frg_cnt, pfrag->page, pfrag->offset,
                                   copy);
                frg_cnt++;
                pfrag->offset += copy;
                get_page(pfrag->page);

                skb->truesize += copy;
                atomic_add(copy, &sk->sk_wmem_alloc);
                skb->len += copy;
                skb->data_len += copy;
                offset += copy;
                length -= copy;

        } while (length > 0);

        return 0;
}
EXPORT_SYMBOL(skb_append_datato_frags);

int skb_append_pagefrags(struct sk_buff *skb, struct page *page,
                         int offset, size_t size)
{
        int i = skb_shinfo(skb)->nr_frags;

        if (skb_can_coalesce(skb, i, page, offset)) {
                skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], size);
        } else if (i < MAX_SKB_FRAGS) {
                get_page(page);
                skb_fill_page_desc(skb, i, page, offset, size);
        } else {
                return -EMSGSIZE;
        }

        return 0;
}
EXPORT_SYMBOL_GPL(skb_append_pagefrags);

/**
 *      skb_push_rcsum - push skb and update receive checksum
 *      @skb: buffer to update
 *      @len: length of data pulled
 *
 *      This function performs an skb_push on the packet and updates
 *      the CHECKSUM_COMPLETE checksum.  It should be used on
 *      receive path processing instead of skb_push unless you know
 *      that the checksum difference is zero (e.g., a valid IP header)
 *      or you are setting ip_summed to CHECKSUM_NONE.
 */
static unsigned char *skb_push_rcsum(struct sk_buff *skb, unsigned len)
{
        skb_push(skb, len);
        skb_postpush_rcsum(skb, skb->data, len);
        return skb->data;
}

/**
 *      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)
{
        unsigned char *data = skb->data;

        BUG_ON(len > skb->len);
        __skb_pull(skb, len);
        skb_postpull_rcsum(skb, data, len);
        return skb->data;
}
EXPORT_SYMBOL_GPL(skb_pull_rcsum);

/**
 *      skb_segment - Perform protocol segmentation on skb.
 *      @head_skb: buffer to segment
 *      @features: features for the output path (see dev->features)
 *
 *      This function performs segmentation on the given skb.  It returns
 *      a pointer to the first in a list of new skbs for the segments.
 *      In case of error it returns ERR_PTR(err).
 */
struct sk_buff *skb_segment(struct sk_buff *head_skb,
                            netdev_features_t features)
{
        struct sk_buff *segs = NULL;
        struct sk_buff *tail = NULL;
        struct sk_buff *list_skb = skb_shinfo(head_skb)->frag_list;
        skb_frag_t *frag = skb_shinfo(head_skb)->frags;
        unsigned int mss = skb_shinfo(head_skb)->gso_size;
        unsigned int doffset = head_skb->data - skb_mac_header(head_skb);
        struct sk_buff *frag_skb = head_skb;
        unsigned int offset = doffset;
        unsigned int tnl_hlen = skb_tnl_header_len(head_skb);
        unsigned int partial_segs = 0;
        unsigned int headroom;
        unsigned int len = head_skb->len;
        __be16 proto;
        bool csum, sg;
        int nfrags = skb_shinfo(head_skb)->nr_frags;
        int err = -ENOMEM;
        int i = 0;
        int pos;
        int dummy;

        __skb_push(head_skb, doffset);
        proto = skb_network_protocol(head_skb, &dummy);
        if (unlikely(!proto))
                return ERR_PTR(-EINVAL);

        sg = !!(features & NETIF_F_SG);
        csum = !!can_checksum_protocol(features, proto);

        /* GSO partial only requires that we trim off any excess that
         * doesn't fit into an MSS sized block, so take care of that
         * now.
         */
        if (sg && csum && (features & NETIF_F_GSO_PARTIAL)) {
                partial_segs = len / mss;
                if (partial_segs > 1)
                        mss *= partial_segs;
                else
                        partial_segs = 0;
        }

        headroom = skb_headroom(head_skb);
        pos = skb_headlen(head_skb);

        do {
                struct sk_buff *nskb;
                skb_frag_t *nskb_frag;
                int hsize;
                int size;

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

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

                if (!hsize && i >= nfrags && skb_headlen(list_skb) &&
                    (skb_headlen(list_skb) == len || sg)) {
                        BUG_ON(skb_headlen(list_skb) > len);

                        i = 0;
                        nfrags = skb_shinfo(list_skb)->nr_frags;
                        frag = skb_shinfo(list_skb)->frags;
                        frag_skb = list_skb;
                        pos += skb_headlen(list_skb);

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

                                size = skb_frag_size(frag);
                                if (pos + size > offset + len)
                                        break;

                                i++;
                                pos += size;
                                frag++;
                        }

                        nskb = skb_clone(list_skb, GFP_ATOMIC);
                        list_skb = list_skb->next;

                        if (unlikely(!nskb))
                                goto err;

                        if (unlikely(pskb_trim(nskb, len))) {
                                kfree_skb(nskb);
                                goto err;
                        }

                        hsize = skb_end_offset(nskb);
                        if (skb_cow_head(nskb, doffset + headroom)) {
                                kfree_skb(nskb);
                                goto err;
                        }

                        nskb->truesize += skb_end_offset(nskb) - hsize;
                        skb_release_head_state(nskb);
                        __skb_push(nskb, doffset);
                } else {
                        nskb = __alloc_skb(hsize + doffset + headroom,
                                           GFP_ATOMIC, skb_alloc_rx_flag(head_skb),
                                           NUMA_NO_NODE);

                        if (unlikely(!nskb))
                                goto err;

                        skb_reserve(nskb, headroom);
                        __skb_put(nskb, doffset);
                }

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

                __copy_skb_header(nskb, head_skb);

                skb_headers_offset_update(nskb, skb_headroom(nskb) - headroom);
                skb_reset_mac_len(nskb);

                skb_copy_from_linear_data_offset(head_skb, -tnl_hlen,
                                                 nskb->data - tnl_hlen,
                                                 doffset + tnl_hlen);

                if (nskb->len == len + doffset)
                        goto perform_csum_check;

                if (!sg) {
                        if (!nskb->remcsum_offload)
                                nskb->ip_summed = CHECKSUM_NONE;
                        SKB_GSO_CB(nskb)->csum =
                                skb_copy_and_csum_bits(head_skb, offset,
                                                       skb_put(nskb, len),
                                                       len, 0);
                        SKB_GSO_CB(nskb)->csum_start =
                                skb_headroom(nskb) + doffset;
                        continue;
                }

                nskb_frag = skb_shinfo(nskb)->frags;

                skb_copy_from_linear_data_offset(head_skb, offset,
                                                 skb_put(nskb, hsize), hsize);

                skb_shinfo(nskb)->tx_flags = skb_shinfo(head_skb)->tx_flags &
                        SKBTX_SHARED_FRAG;

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

                                i = 0;
                                nfrags = skb_shinfo(list_skb)->nr_frags;
                                frag = skb_shinfo(list_skb)->frags;
                                frag_skb = list_skb;

                                BUG_ON(!nfrags);

                                list_skb = list_skb->next;
                        }

                        if (unlikely(skb_shinfo(nskb)->nr_frags >=
                                     MAX_SKB_FRAGS)) {
                                net_warn_ratelimited(
                                        "skb_segment: too many frags: %u %u\n",
                                        pos, mss);
                                goto err;
                        }

                        if (unlikely(skb_orphan_frags(frag_skb, GFP_ATOMIC)))
                                goto err;

                        *nskb_frag = *frag;
                        __skb_frag_ref(nskb_frag);
                        size = skb_frag_size(nskb_frag);

                        if (pos < offset) {
                                nskb_frag->page_offset += offset - pos;
                                skb_frag_size_sub(nskb_frag, offset - pos);
                        }

                        skb_shinfo(nskb)->nr_frags++;

                        if (pos + size <= offset + len) {
                                i++;
                                frag++;
                                pos += size;
                        } else {
                                skb_frag_size_sub(nskb_frag, pos + size - (offset + len));
                                goto skip_fraglist;
                        }

                        nskb_frag++;
                }

skip_fraglist:
                nskb->data_len = len - hsize;
                nskb->len += nskb->data_len;
                nskb->truesize += nskb->data_len;

perform_csum_check:
                if (!csum) {
                        if (skb_has_shared_frag(nskb)) {
                                err = __skb_linearize(nskb);
                                if (err)
                                        goto err;
                        }
                        if (!nskb->remcsum_offload)
                                nskb->ip_summed = CHECKSUM_NONE;
                        SKB_GSO_CB(nskb)->csum =
                                skb_checksum(nskb, doffset,
                                             nskb->len - doffset, 0);
                        SKB_GSO_CB(nskb)->csum_start =
                                skb_headroom(nskb) + doffset;
                }
        } while ((offset += len) < head_skb->len);

        /* Some callers want to get the end of the list.
         * Put it in segs->prev to avoid walking the list.
         * (see validate_xmit_skb_list() for example)
         */
        segs->prev = tail;

        /* Update GSO info on first skb in partial sequence. */
        if (partial_segs) {
                int type = skb_shinfo(head_skb)->gso_type;

                /* Update type to add partial and then remove dodgy if set */
                type |= SKB_GSO_PARTIAL;
                type &= ~SKB_GSO_DODGY;

                /* Update GSO info and prepare to start updating headers on
                 * our way back down the stack of protocols.
                 */
                skb_shinfo(segs)->gso_size = skb_shinfo(head_skb)->gso_size;
                skb_shinfo(segs)->gso_segs = partial_segs;
                skb_shinfo(segs)->gso_type = type;
                SKB_GSO_CB(segs)->data_offset = skb_headroom(segs) + doffset;
        }

        /* Following permits correct backpressure, for protocols
         * using skb_set_owner_w().
         * Idea is to tranfert ownership from head_skb to last segment.
         */
        if (head_skb->destructor == sock_wfree) {
                swap(tail->truesize, head_skb->truesize);
                swap(tail->destructor, head_skb->destructor);
                swap(tail->sk, head_skb->sk);
        }
        return segs;

err:
        kfree_skb_list(segs);
        return ERR_PTR(err);
}
EXPORT_SYMBOL_GPL(skb_segment);

int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
{
        struct skb_shared_info *pinfo, *skbinfo = skb_shinfo(skb);
        unsigned int offset = skb_gro_offset(skb);
        unsigned int headlen = skb_headlen(skb);
        unsigned int len = skb_gro_len(skb);
        struct sk_buff *lp, *p = *head;
        unsigned int delta_truesize;

        if (unlikely(p->len + len >= 65536))
                return -E2BIG;

        lp = NAPI_GRO_CB(p)->last;
        pinfo = skb_shinfo(lp);

        if (headlen <= offset) {
                skb_frag_t *frag;
                skb_frag_t *frag2;
                int i = skbinfo->nr_frags;
                int nr_frags = pinfo->nr_frags + i;

                if (nr_frags > MAX_SKB_FRAGS)
                        goto merge;

                offset -= headlen;
                pinfo->nr_frags = nr_frags;
                skbinfo->nr_frags = 0;

                frag = pinfo->frags + nr_frags;
                frag2 = skbinfo->frags + i;
                do {
                        *--frag = *--frag2;
                } while (--i);

                frag->page_offset += offset;
                skb_frag_size_sub(frag, offset);

                /* all fragments truesize : remove (head size + sk_buff) */
                delta_truesize = skb->truesize -
                                 SKB_TRUESIZE(skb_end_offset(skb));

                skb->truesize -= skb->data_len;
                skb->len -= skb->data_len;
                skb->data_len = 0;

                NAPI_GRO_CB(skb)->free = NAPI_GRO_FREE;
                goto done;
        } else if (skb->head_frag) {
                int nr_frags = pinfo->nr_frags;
                skb_frag_t *frag = pinfo->frags + nr_frags;
                struct page *page = virt_to_head_page(skb->head);
                unsigned int first_size = headlen - offset;
                unsigned int first_offset;

                if (nr_frags + 1 + skbinfo->nr_frags > MAX_SKB_FRAGS)
                        goto merge;

                first_offset = skb->data -
                               (unsigned char *)page_address(page) +
                               offset;

                pinfo->nr_frags = nr_frags + 1 + skbinfo->nr_frags;

                frag->page.p      = page;
                frag->page_offset = first_offset;
                skb_frag_size_set(frag, first_size);

                memcpy(frag + 1, skbinfo->frags, sizeof(*frag) * skbinfo->nr_frags);
                /* We dont need to clear skbinfo->nr_frags here */

                delta_truesize = skb->truesize - SKB_DATA_ALIGN(sizeof(struct sk_buff));
                NAPI_GRO_CB(skb)->free = NAPI_GRO_FREE_STOLEN_HEAD;
                goto done;
        }

merge:
        delta_truesize = skb->truesize;
        if (offset > headlen) {
                unsigned int eat = offset - headlen;

                skbinfo->frags[0].page_offset += eat;
                skb_frag_size_sub(&skbinfo->frags[0], eat);
                skb->data_len -= eat;
                skb->len -= eat;
                offset = headlen;
        }

        __skb_pull(skb, offset);

        if (NAPI_GRO_CB(p)->last == p)
                skb_shinfo(p)->frag_list = skb;
        else
                NAPI_GRO_CB(p)->last->next = skb;
        NAPI_GRO_CB(p)->last = skb;
        __skb_header_release(skb);
        lp = p;

done:
        NAPI_GRO_CB(p)->count++;
        p->data_len += len;
        p->truesize += delta_truesize;
        p->len += len;
        if (lp != p) {
                lp->data_len += len;
                lp->truesize += delta_truesize;
                lp->len += len;
        }
        NAPI_GRO_CB(skb)->same_flow = 1;
        return 0;
}

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",
                                                sizeof(struct sk_buff_fclones),
                                                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;
        struct sk_buff *frag_iter;
        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;

                WARN_ON(start > offset + len);

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

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

        skb_walk_frags(skb, frag_iter) {
                int end;

                WARN_ON(start > offset + len);

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

/* As compared with skb_to_sgvec, skb_to_sgvec_nomark only map skb to given
 * sglist without mark the sg which contain last skb data as the end.
 * So the caller can mannipulate sg list as will when padding new data after
 * the first call without calling sg_unmark_end to expend sg list.
 *
 * Scenario to use skb_to_sgvec_nomark:
 * 1. sg_init_table
 * 2. skb_to_sgvec_nomark(payload1)
 * 3. skb_to_sgvec_nomark(payload2)
 *
 * This is equivalent to:
 * 1. sg_init_table
 * 2. skb_to_sgvec(payload1)
 * 3. sg_unmark_end
 * 4. skb_to_sgvec(payload2)
 *
 * When mapping mutilple payload conditionally, skb_to_sgvec_nomark
 * is more preferable.
 */
int skb_to_sgvec_nomark(struct sk_buff *skb, struct scatterlist *sg,
                        int offset, int len)
{
        return __skb_to_sgvec(skb, sg, offset, len);
}
EXPORT_SYMBOL_GPL(skb_to_sgvec_nomark);

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;
}
EXPORT_SYMBOL_GPL(skb_to_sgvec);

/**
 *      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_has_frag_list(skb)) {
                /* 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_has_frag_list(skb1) ||
                            skb_tailroom(skb1) < tailbits)
                                ntail = tailbits + 128;
                }

                if (copyflag ||
                    skb_cloned(skb1) ||
                    ntail ||
                    skb_shinfo(skb1)->nr_frags ||
                    skb_has_frag_list(skb1)) {
                        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_GPL(skb_cow_data);

static void sock_rmem_free(struct sk_buff *skb)
{
        struct sock *sk = skb->sk;

        atomic_sub(skb->truesize, &sk->sk_rmem_alloc);
}

/*
 * Note: We dont mem charge error packets (no sk_forward_alloc changes)
 */
int sock_queue_err_skb(struct sock *sk, struct sk_buff *skb)
{
        if (atomic_read(&sk->sk_rmem_alloc) + skb->truesize >=
            (unsigned int)sk->sk_rcvbuf)
                return -ENOMEM;

        skb_orphan(skb);
        skb->sk = sk;
        skb->destructor = sock_rmem_free;
        atomic_add(skb->truesize, &sk->sk_rmem_alloc);

        /* before exiting rcu section, make sure dst is refcounted */
        skb_dst_force(skb);

        skb_queue_tail(&sk->sk_error_queue, skb);
        if (!sock_flag(sk, SOCK_DEAD))
                sk->sk_data_ready(sk);
        return 0;
}
EXPORT_SYMBOL(sock_queue_err_skb);

struct sk_buff *sock_dequeue_err_skb(struct sock *sk)
{
        struct sk_buff_head *q = &sk->sk_error_queue;
        struct sk_buff *skb, *skb_next;
        unsigned long flags;
        int err = 0;

        spin_lock_irqsave(&q->lock, flags);
        skb = __skb_dequeue(q);
        if (skb && (skb_next = skb_peek(q)))
                err = SKB_EXT_ERR(skb_next)->ee.ee_errno;
        spin_unlock_irqrestore(&q->lock, flags);

        sk->sk_err = err;
        if (err)
                sk->sk_error_report(sk);

        return skb;
}
EXPORT_SYMBOL(sock_dequeue_err_skb);

/**
 * skb_clone_sk - create clone of skb, and take reference to socket
 * @skb: the skb to clone
 *
 * This function creates a clone of a buffer that holds a reference on
 * sk_refcnt.  Buffers created via this function are meant to be
 * returned using sock_queue_err_skb, or free via kfree_skb.
 *
 * When passing buffers allocated with this function to sock_queue_err_skb
 * it is necessary to wrap the call with sock_hold/sock_put in order to
 * prevent the socket from being released prior to being enqueued on
 * the sk_error_queue.
 */
struct sk_buff *skb_clone_sk(struct sk_buff *skb)
{
        struct sock *sk = skb->sk;
        struct sk_buff *clone;

        if (!sk || !atomic_inc_not_zero(&sk->sk_refcnt))
                return NULL;

        clone = skb_clone(skb, GFP_ATOMIC);
        if (!clone) {
                sock_put(sk);
                return NULL;
        }

        clone->sk = sk;
        clone->destructor = sock_efree;

        return clone;
}
EXPORT_SYMBOL(skb_clone_sk);

static void __skb_complete_tx_timestamp(struct sk_buff *skb,
                                        struct sock *sk,
                                        int tstype)
{
        struct sock_exterr_skb *serr;
        int err;

        serr = SKB_EXT_ERR(skb);
        memset(serr, 0, sizeof(*serr));
        serr->ee.ee_errno = ENOMSG;
        serr->ee.ee_origin = SO_EE_ORIGIN_TIMESTAMPING;
        serr->ee.ee_info = tstype;
        if (sk->sk_tsflags & SOF_TIMESTAMPING_OPT_ID) {
                serr->ee.ee_data = skb_shinfo(skb)->tskey;
                if (sk->sk_protocol == IPPROTO_TCP &&
                    sk->sk_type == SOCK_STREAM)
                        serr->ee.ee_data -= sk->sk_tskey;
        }

        err = sock_queue_err_skb(sk, skb);

        if (err)
                kfree_skb(skb);
}

static bool skb_may_tx_timestamp(struct sock *sk, bool tsonly)
{
        bool ret;

        if (likely(sysctl_tstamp_allow_data || tsonly))
                return true;

        read_lock_bh(&sk->sk_callback_lock);
        ret = sk->sk_socket && sk->sk_socket->file &&
              file_ns_capable(sk->sk_socket->file, &init_user_ns, CAP_NET_RAW);
        read_unlock_bh(&sk->sk_callback_lock);
        return ret;
}

void skb_complete_tx_timestamp(struct sk_buff *skb,
                               struct skb_shared_hwtstamps *hwtstamps)
{
        struct sock *sk = skb->sk;

        if (!skb_may_tx_timestamp(sk, false))
                return;

        /* take a reference to prevent skb_orphan() from freeing the socket */
        sock_hold(sk);

        *skb_hwtstamps(skb) = *hwtstamps;
        __skb_complete_tx_timestamp(skb, sk, SCM_TSTAMP_SND);

        sock_put(sk);
}
EXPORT_SYMBOL_GPL(skb_complete_tx_timestamp);

void __skb_tstamp_tx(struct sk_buff *orig_skb,
                     struct skb_shared_hwtstamps *hwtstamps,
                     struct sock *sk, int tstype)
{
        struct sk_buff *skb;
        bool tsonly;

        if (!sk)
                return;

        tsonly = sk->sk_tsflags & SOF_TIMESTAMPING_OPT_TSONLY;
        if (!skb_may_tx_timestamp(sk, tsonly))
                return;

        if (tsonly)
                skb = alloc_skb(0, GFP_ATOMIC);
        else
                skb = skb_clone(orig_skb, GFP_ATOMIC);
        if (!skb)
                return;

        if (tsonly) {
                skb_shinfo(skb)->tx_flags = skb_shinfo(orig_skb)->tx_flags;
                skb_shinfo(skb)->tskey = skb_shinfo(orig_skb)->tskey;
        }

        if (hwtstamps)
                *skb_hwtstamps(skb) = *hwtstamps;
        else
                skb->tstamp = ktime_get_real();

        __skb_complete_tx_timestamp(skb, sk, tstype);
}
EXPORT_SYMBOL_GPL(__skb_tstamp_tx);

void skb_tstamp_tx(struct sk_buff *orig_skb,
                   struct skb_shared_hwtstamps *hwtstamps)
{
        return __skb_tstamp_tx(orig_skb, hwtstamps, orig_skb->sk,
                               SCM_TSTAMP_SND);
}
EXPORT_SYMBOL_GPL(skb_tstamp_tx);

void skb_complete_wifi_ack(struct sk_buff *skb, bool acked)
{
        struct sock *sk = skb->sk;
        struct sock_exterr_skb *serr;
        int err;

        skb->wifi_acked_valid = 1;
        skb->wifi_acked = acked;

        serr = SKB_EXT_ERR(skb);
        memset(serr, 0, sizeof(*serr));
        serr->ee.ee_errno = ENOMSG;
        serr->ee.ee_origin = SO_EE_ORIGIN_TXSTATUS;

        /* take a reference to prevent skb_orphan() from freeing the socket */
        sock_hold(sk);

        err = sock_queue_err_skb(sk, skb);
        if (err)
                kfree_skb(skb);

        sock_put(sk);
}
EXPORT_SYMBOL_GPL(skb_complete_wifi_ack);

/**
 * 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_headlen(skb)) ||
            unlikely((int)start + off > skb_headlen(skb) - 2)) {
                net_warn_ratelimited("bad partial csum: csum=%u/%u len=%u\n",
                                     start, off, skb_headlen(skb));
                return false;
        }
        skb->ip_summed = CHECKSUM_PARTIAL;
        skb->csum_start = skb_headroom(skb) + start;
        skb->csum_offset = off;
        skb_set_transport_header(skb, start);
        return true;
}
EXPORT_SYMBOL_GPL(skb_partial_csum_set);

static int skb_maybe_pull_tail(struct sk_buff *skb, unsigned int len,
                               unsigned int max)
{
        if (skb_headlen(skb) >= len)
                return 0;

        /* If we need to pullup then pullup to the max, so we
         * won't need to do it again.
         */
        if (max > skb->len)
                max = skb->len;

        if (__pskb_pull_tail(skb, max - skb_headlen(skb)) == NULL)
                return -ENOMEM;

        if (skb_headlen(skb) < len)
                return -EPROTO;

        return 0;
}

#define MAX_TCP_HDR_LEN (15 * 4)

static __sum16 *skb_checksum_setup_ip(struct sk_buff *skb,
                                      typeof(IPPROTO_IP) proto,
                                      unsigned int off)
{
        switch (proto) {
                int err;

        case IPPROTO_TCP:
                err = skb_maybe_pull_tail(skb, off + sizeof(struct tcphdr),
                                          off + MAX_TCP_HDR_LEN);
                if (!err && !skb_partial_csum_set(skb, off,
                                                  offsetof(struct tcphdr,
                                                           check)))
                        err = -EPROTO;
                return err ? ERR_PTR(err) : &tcp_hdr(skb)->check;

        case IPPROTO_UDP:
                err = skb_maybe_pull_tail(skb, off + sizeof(struct udphdr),
                                          off + sizeof(struct udphdr));
                if (!err && !skb_partial_csum_set(skb, off,
                                                  offsetof(struct udphdr,
                                                           check)))
                        err = -EPROTO;
                return err ? ERR_PTR(err) : &udp_hdr(skb)->check;
        }

        return ERR_PTR(-EPROTO);
}

/* This value should be large enough to cover a tagged ethernet header plus
 * maximally sized IP and TCP or UDP headers.
 */
#define MAX_IP_HDR_LEN 128

static int skb_checksum_setup_ipv4(struct sk_buff *skb, bool recalculate)
{
        unsigned int off;
        bool fragment;
        __sum16 *csum;
        int err;

        fragment = false;

        err = skb_maybe_pull_tail(skb,
                                  sizeof(struct iphdr),
                                  MAX_IP_HDR_LEN);
        if (err < 0)
                goto out;

        if (ip_hdr(skb)->frag_off & htons(IP_OFFSET | IP_MF))
                fragment = true;

        off = ip_hdrlen(skb);

        err = -EPROTO;

        if (fragment)
                goto out;

        csum = skb_checksum_setup_ip(skb, ip_hdr(skb)->protocol, off);
        if (IS_ERR(csum))
                return PTR_ERR(csum);

        if (recalculate)
                *csum = ~csum_tcpudp_magic(ip_hdr(skb)->saddr,
                                           ip_hdr(skb)->daddr,
                                           skb->len - off,
                                           ip_hdr(skb)->protocol, 0);
        err = 0;

out:
        return err;
}

/* This value should be large enough to cover a tagged ethernet header plus
 * an IPv6 header, all options, and a maximal TCP or UDP header.
 */
#define MAX_IPV6_HDR_LEN 256

#define OPT_HDR(type, skb, off) \
        (type *)(skb_network_header(skb) + (off))

static int skb_checksum_setup_ipv6(struct sk_buff *skb, bool recalculate)
{
        int err;
        u8 nexthdr;
        unsigned int off;
        unsigned int len;
        bool fragment;
        bool done;
        __sum16 *csum;

        fragment = false;
        done = false;

        off = sizeof(struct ipv6hdr);

        err = skb_maybe_pull_tail(skb, off, MAX_IPV6_HDR_LEN);
        if (err < 0)
                goto out;

        nexthdr = ipv6_hdr(skb)->nexthdr;

        len = sizeof(struct ipv6hdr) + ntohs(ipv6_hdr(skb)->payload_len);
        while (off <= len && !done) {
                switch (nexthdr) {
                case IPPROTO_DSTOPTS:
                case IPPROTO_HOPOPTS:
                case IPPROTO_ROUTING: {
                        struct ipv6_opt_hdr *hp;

                        err = skb_maybe_pull_tail(skb,
                                                  off +
                                                  sizeof(struct ipv6_opt_hdr),
                                                  MAX_IPV6_HDR_LEN);
                        if (err < 0)
                                goto out;

                        hp = OPT_HDR(struct ipv6_opt_hdr, skb, off);
                        nexthdr = hp->nexthdr;
                        off += ipv6_optlen(hp);
                        break;
                }
                case IPPROTO_AH: {
                        struct ip_auth_hdr *hp;

                        err = skb_maybe_pull_tail(skb,
                                                  off +
                                                  sizeof(struct ip_auth_hdr),
                                                  MAX_IPV6_HDR_LEN);
                        if (err < 0)
                                goto out;

                        hp = OPT_HDR(struct ip_auth_hdr, skb, off);
                        nexthdr = hp->nexthdr;
                        off += ipv6_authlen(hp);
                        break;
                }
                case IPPROTO_FRAGMENT: {
                        struct frag_hdr *hp;

                        err = skb_maybe_pull_tail(skb,
                                                  off +
                                                  sizeof(struct frag_hdr),
                                                  MAX_IPV6_HDR_LEN);
                        if (err < 0)
                                goto out;

                        hp = OPT_HDR(struct frag_hdr, skb, off);

                        if (hp->frag_off & htons(IP6_OFFSET | IP6_MF))
                                fragment = true;

                        nexthdr = hp->nexthdr;
                        off += sizeof(struct frag_hdr);
                        break;
                }
                default:
                        done = true;
                        break;
                }
        }

        err = -EPROTO;

        if (!done || fragment)
                goto out;

        csum = skb_checksum_setup_ip(skb, nexthdr, off);
        if (IS_ERR(csum))
                return PTR_ERR(csum);

        if (recalculate)
                *csum = ~csum_ipv6_magic(&ipv6_hdr(skb)->saddr,
                                         &ipv6_hdr(skb)->daddr,
                                         skb->len - off, nexthdr, 0);
        err = 0;

out:
        return err;
}

/**
 * skb_checksum_setup - set up partial checksum offset
 * @skb: the skb to set up
 * @recalculate: if true the pseudo-header checksum will be recalculated
 */
int skb_checksum_setup(struct sk_buff *skb, bool recalculate)
{
        int err;

        switch (skb->protocol) {
        case htons(ETH_P_IP):
                err = skb_checksum_setup_ipv4(skb, recalculate);
                break;

        case htons(ETH_P_IPV6):
                err = skb_checksum_setup_ipv6(skb, recalculate);
                break;

        default:
                err = -EPROTO;
                break;
        }

        return err;
}
EXPORT_SYMBOL(skb_checksum_setup);

/**
 * skb_checksum_maybe_trim - maybe trims the given skb
 * @skb: the skb to check
 * @transport_len: the data length beyond the network header
 *
 * Checks whether the given skb has data beyond the given transport length.
 * If so, returns a cloned skb trimmed to this transport length.
 * Otherwise returns the provided skb. Returns NULL in error cases
 * (e.g. transport_len exceeds skb length or out-of-memory).
 *
 * Caller needs to set the skb transport header and free any returned skb if it
 * differs from the provided skb.
 */
static struct sk_buff *skb_checksum_maybe_trim(struct sk_buff *skb,
                                               unsigned int transport_len)
{
        struct sk_buff *skb_chk;
        unsigned int len = skb_transport_offset(skb) + transport_len;
        int ret;

        if (skb->len < len)
                return NULL;
        else if (skb->len == len)
                return skb;

        skb_chk = skb_clone(skb, GFP_ATOMIC);
        if (!skb_chk)
                return NULL;

        ret = pskb_trim_rcsum(skb_chk, len);
        if (ret) {
                kfree_skb(skb_chk);
                return NULL;
        }

        return skb_chk;
}

/**
 * skb_checksum_trimmed - validate checksum of an skb
 * @skb: the skb to check
 * @transport_len: the data length beyond the network header
 * @skb_chkf: checksum function to use
 *
 * Applies the given checksum function skb_chkf to the provided skb.
 * Returns a checked and maybe trimmed skb. Returns NULL on error.
 *
 * If the skb has data beyond the given transport length, then a
 * trimmed & cloned skb is checked and returned.
 *
 * Caller needs to set the skb transport header and free any returned skb if it
 * differs from the provided skb.
 */
struct sk_buff *skb_checksum_trimmed(struct sk_buff *skb,
                                     unsigned int transport_len,
                                     __sum16(*skb_chkf)(struct sk_buff *skb))
{
        struct sk_buff *skb_chk;
        unsigned int offset = skb_transport_offset(skb);
        __sum16 ret;

        skb_chk = skb_checksum_maybe_trim(skb, transport_len);
        if (!skb_chk)
                goto err;

        if (!pskb_may_pull(skb_chk, offset))
                goto err;

        skb_pull_rcsum(skb_chk, offset);
        ret = skb_chkf(skb_chk);
        skb_push_rcsum(skb_chk, offset);

        if (ret)
                goto err;

        return skb_chk;

err:
        if (skb_chk && skb_chk != skb)
                kfree_skb(skb_chk);

        return NULL;

}
EXPORT_SYMBOL(skb_checksum_trimmed);

void __skb_warn_lro_forwarding(const struct sk_buff *skb)
{
        net_warn_ratelimited("%s: received packets cannot be forwarded while LRO is enabled\n",
                             skb->dev->name);
}
EXPORT_SYMBOL(__skb_warn_lro_forwarding);

void kfree_skb_partial(struct sk_buff *skb, bool head_stolen)
{
        if (head_stolen) {
                skb_release_head_state(skb);
                kmem_cache_free(skbuff_head_cache, skb);
        } else {
                __kfree_skb(skb);
        }
}
EXPORT_SYMBOL(kfree_skb_partial);

/**
 * skb_try_coalesce - try to merge skb to prior one
 * @to: prior buffer
 * @from: buffer to add
 * @fragstolen: pointer to boolean
 * @delta_truesize: how much more was allocated than was requested
 */
bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from,
                      bool *fragstolen, int *delta_truesize)
{
        int i, delta, len = from->len;

        *fragstolen = false;

        if (skb_cloned(to))
                return false;

        if (len <= skb_tailroom(to)) {
                if (len)
                        BUG_ON(skb_copy_bits(from, 0, skb_put(to, len), len));
                *delta_truesize = 0;
                return true;
        }

        if (skb_has_frag_list(to) || skb_has_frag_list(from))
                return false;

        if (skb_headlen(from) != 0) {
                struct page *page;
                unsigned int offset;

                if (skb_shinfo(to)->nr_frags +
                    skb_shinfo(from)->nr_frags >= MAX_SKB_FRAGS)
                        return false;

                if (skb_head_is_locked(from))
                        return false;

                delta = from->truesize - SKB_DATA_ALIGN(sizeof(struct sk_buff));

                page = virt_to_head_page(from->head);
                offset = from->data - (unsigned char *)page_address(page);

                skb_fill_page_desc(to, skb_shinfo(to)->nr_frags,
                                   page, offset, skb_headlen(from));
                *fragstolen = true;
        } else {
                if (skb_shinfo(to)->nr_frags +
                    skb_shinfo(from)->nr_frags > MAX_SKB_FRAGS)
                        return false;

                delta = from->truesize - SKB_TRUESIZE(skb_end_offset(from));
        }

        WARN_ON_ONCE(delta < len);

        memcpy(skb_shinfo(to)->frags + skb_shinfo(to)->nr_frags,
               skb_shinfo(from)->frags,
               skb_shinfo(from)->nr_frags * sizeof(skb_frag_t));
        skb_shinfo(to)->nr_frags += skb_shinfo(from)->nr_frags;

        if (!skb_cloned(from))
                skb_shinfo(from)->nr_frags = 0;

        /* if the skb is not cloned this does nothing
         * since we set nr_frags to 0.
         */
        for (i = 0; i < skb_shinfo(from)->nr_frags; i++)
                skb_frag_ref(from, i);

        to->truesize += delta;
        to->len += len;
        to->data_len += len;

        *delta_truesize = delta;
        return true;
}
EXPORT_SYMBOL(skb_try_coalesce);

/**
 * skb_scrub_packet - scrub an skb
 *
 * @skb: buffer to clean
 * @xnet: packet is crossing netns
 *
 * skb_scrub_packet can be used after encapsulating or decapsulting a packet
 * into/from a tunnel. Some information have to be cleared during these
 * operations.
 * skb_scrub_packet can also be used to clean a skb before injecting it in
 * another namespace (@xnet == true). We have to clear all information in the
 * skb that could impact namespace isolation.
 */
void skb_scrub_packet(struct sk_buff *skb, bool xnet)
{
        skb->tstamp.tv64 = 0;
        skb->pkt_type = PACKET_HOST;
        skb->skb_iif = 0;
        skb->ignore_df = 0;
        skb_dst_drop(skb);
        secpath_reset(skb);
        nf_reset(skb);
        nf_reset_trace(skb);

        if (!xnet)
                return;

        skb_orphan(skb);
        skb->mark = 0;
}
EXPORT_SYMBOL_GPL(skb_scrub_packet);

/**
 * skb_gso_transport_seglen - Return length of individual segments of a gso packet
 *
 * @skb: GSO skb
 *
 * skb_gso_transport_seglen is used to determine the real size of the
 * individual segments, including Layer4 headers (TCP/UDP).
 *
 * The MAC/L2 or network (IP, IPv6) headers are not accounted for.
 */
unsigned int skb_gso_transport_seglen(const struct sk_buff *skb)
{
        const struct skb_shared_info *shinfo = skb_shinfo(skb);
        unsigned int thlen = 0;

        if (skb->encapsulation) {
                thlen = skb_inner_transport_header(skb) -
                        skb_transport_header(skb);

                if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6)))
                        thlen += inner_tcp_hdrlen(skb);
        } else if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6))) {
                thlen = tcp_hdrlen(skb);
        }
        /* UFO sets gso_size to the size of the fragmentation
         * payload, i.e. the size of the L4 (UDP) header is already
         * accounted for.
         */
        return thlen + shinfo->gso_size;
}
EXPORT_SYMBOL_GPL(skb_gso_transport_seglen);

static struct sk_buff *skb_reorder_vlan_header(struct sk_buff *skb)
{
        if (skb_cow(skb, skb_headroom(skb)) < 0) {
                kfree_skb(skb);
                return NULL;
        }

        memmove(skb->data - ETH_HLEN, skb->data - skb->mac_len - VLAN_HLEN,
                2 * ETH_ALEN);
        skb->mac_header += VLAN_HLEN;
        return skb;
}

struct sk_buff *skb_vlan_untag(struct sk_buff *skb)
{
        struct vlan_hdr *vhdr;
        u16 vlan_tci;

        if (unlikely(skb_vlan_tag_present(skb))) {
                /* vlan_tci is already set-up so leave this for another time */
                return skb;
        }

        skb = skb_share_check(skb, GFP_ATOMIC);
        if (unlikely(!skb))
                goto err_free;

        if (unlikely(!pskb_may_pull(skb, VLAN_HLEN)))
                goto err_free;

        vhdr = (struct vlan_hdr *)skb->data;
        vlan_tci = ntohs(vhdr->h_vlan_TCI);
        __vlan_hwaccel_put_tag(skb, skb->protocol, vlan_tci);

        skb_pull_rcsum(skb, VLAN_HLEN);
        vlan_set_encap_proto(skb, vhdr);

        skb = skb_reorder_vlan_header(skb);
        if (unlikely(!skb))
                goto err_free;

        skb_reset_network_header(skb);
        skb_reset_transport_header(skb);
        skb_reset_mac_len(skb);

        return skb;

err_free:
        kfree_skb(skb);
        return NULL;
}
EXPORT_SYMBOL(skb_vlan_untag);

int skb_ensure_writable(struct sk_buff *skb, int write_len)
{
        if (!pskb_may_pull(skb, write_len))
                return -ENOMEM;

        if (!skb_cloned(skb) || skb_clone_writable(skb, write_len))
                return 0;

        return pskb_expand_head(skb, 0, 0, GFP_ATOMIC);
}
EXPORT_SYMBOL(skb_ensure_writable);

/* remove VLAN header from packet and update csum accordingly. */
static int __skb_vlan_pop(struct sk_buff *skb, u16 *vlan_tci)
{
        struct vlan_hdr *vhdr;
        unsigned int offset = skb->data - skb_mac_header(skb);
        int err;

        __skb_push(skb, offset);
        err = skb_ensure_writable(skb, VLAN_ETH_HLEN);
        if (unlikely(err))
                goto pull;

        skb_postpull_rcsum(skb, skb->data + (2 * ETH_ALEN), VLAN_HLEN);

        vhdr = (struct vlan_hdr *)(skb->data + ETH_HLEN);
        *vlan_tci = ntohs(vhdr->h_vlan_TCI);

        memmove(skb->data + VLAN_HLEN, skb->data, 2 * ETH_ALEN);
        __skb_pull(skb, VLAN_HLEN);

        vlan_set_encap_proto(skb, vhdr);
        skb->mac_header += VLAN_HLEN;

        if (skb_network_offset(skb) < ETH_HLEN)
                skb_set_network_header(skb, ETH_HLEN);

        skb_reset_mac_len(skb);
pull:
        __skb_pull(skb, offset);

        return err;
}

int skb_vlan_pop(struct sk_buff *skb)
{
        u16 vlan_tci;
        __be16 vlan_proto;
        int err;

        if (likely(skb_vlan_tag_present(skb))) {
                skb->vlan_tci = 0;
        } else {
                if (unlikely((skb->protocol != htons(ETH_P_8021Q) &&
                              skb->protocol != htons(ETH_P_8021AD)) ||
                             skb->len < VLAN_ETH_HLEN))
                        return 0;

                err = __skb_vlan_pop(skb, &vlan_tci);
                if (err)
                        return err;
        }
        /* move next vlan tag to hw accel tag */
        if (likely((skb->protocol != htons(ETH_P_8021Q) &&
                    skb->protocol != htons(ETH_P_8021AD)) ||
                   skb->len < VLAN_ETH_HLEN))
                return 0;

        vlan_proto = skb->protocol;
        err = __skb_vlan_pop(skb, &vlan_tci);
        if (unlikely(err))
                return err;

        __vlan_hwaccel_put_tag(skb, vlan_proto, vlan_tci);
        return 0;
}
EXPORT_SYMBOL(skb_vlan_pop);

int skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16 vlan_tci)
{
        if (skb_vlan_tag_present(skb)) {
                unsigned int offset = skb->data - skb_mac_header(skb);
                int err;

                /* __vlan_insert_tag expect skb->data pointing to mac header.
                 * So change skb->data before calling it and change back to
                 * original position later
                 */
                __skb_push(skb, offset);
                err = __vlan_insert_tag(skb, skb->vlan_proto,
                                        skb_vlan_tag_get(skb));
                if (err) {
                        __skb_pull(skb, offset);
                        return err;
                }

                skb->protocol = skb->vlan_proto;
                skb->mac_len += VLAN_HLEN;

                skb_postpush_rcsum(skb, skb->data + (2 * ETH_ALEN), VLAN_HLEN);
                __skb_pull(skb, offset);
        }
        __vlan_hwaccel_put_tag(skb, vlan_proto, vlan_tci);
        return 0;
}
EXPORT_SYMBOL(skb_vlan_push);

/**
 * alloc_skb_with_frags - allocate skb with page frags
 *
 * @header_len: size of linear part
 * @data_len: needed length in frags
 * @max_page_order: max page order desired.
 * @errcode: pointer to error code if any
 * @gfp_mask: allocation mask
 *
 * This can be used to allocate a paged skb, given a maximal order for frags.
 */
struct sk_buff *alloc_skb_with_frags(unsigned long header_len,
                                     unsigned long data_len,
                                     int max_page_order,
                                     int *errcode,
                                     gfp_t gfp_mask)
{
        int npages = (data_len + (PAGE_SIZE - 1)) >> PAGE_SHIFT;
        unsigned long chunk;
        struct sk_buff *skb;
        struct page *page;
        gfp_t gfp_head;
        int i;

        *errcode = -EMSGSIZE;
        /* Note this test could be relaxed, if we succeed to allocate
         * high order pages...
         */
        if (npages > MAX_SKB_FRAGS)
                return NULL;

        gfp_head = gfp_mask;
        if (gfp_head & __GFP_DIRECT_RECLAIM)
                gfp_head |= __GFP_REPEAT;

        *errcode = -ENOBUFS;
        skb = alloc_skb(header_len, gfp_head);
        if (!skb)
                return NULL;

        skb->truesize += npages << PAGE_SHIFT;

        for (i = 0; npages > 0; i++) {
                int order = max_page_order;

                while (order) {
                        if (npages >= 1 << order) {
                                page = alloc_pages((gfp_mask & ~__GFP_DIRECT_RECLAIM) |
                                                   __GFP_COMP |
                                                   __GFP_NOWARN |
                                                   __GFP_NORETRY,
                                                   order);
                                if (page)
                                        goto fill_page;
                                /* Do not retry other high order allocations */
                                order = 1;
                                max_page_order = 0;
                        }
                        order--;
                }
                page = alloc_page(gfp_mask);
                if (!page)
                        goto failure;
fill_page:
                chunk = min_t(unsigned long, data_len,
                              PAGE_SIZE << order);
                skb_fill_page_desc(skb, i, page, 0, chunk);
                data_len -= chunk;
                npages -= 1 << order;
        }
        return skb;

failure:
        kfree_skb(skb);
        return NULL;
}
EXPORT_SYMBOL(alloc_skb_with_frags);

/* carve out the first off bytes from skb when off < headlen */
static int pskb_carve_inside_header(struct sk_buff *skb, const u32 off,
                                    const int headlen, gfp_t gfp_mask)
{
        int i;
        int size = skb_end_offset(skb);
        int new_hlen = headlen - off;
        u8 *data;

        size = SKB_DATA_ALIGN(size);

        if (skb_pfmemalloc(skb))
                gfp_mask |= __GFP_MEMALLOC;
        data = kmalloc_reserve(size +
                               SKB_DATA_ALIGN(sizeof(struct skb_shared_info)),
                               gfp_mask, NUMA_NO_NODE, NULL);
        if (!data)
                return -ENOMEM;

        size = SKB_WITH_OVERHEAD(ksize(data));

        /* Copy real data, and all frags */
        skb_copy_from_linear_data_offset(skb, off, data, new_hlen);
        skb->len -= off;

        memcpy((struct skb_shared_info *)(data + size),
               skb_shinfo(skb),
               offsetof(struct skb_shared_info,
                        frags[skb_shinfo(skb)->nr_frags]));
        if (skb_cloned(skb)) {
                /* drop the old head gracefully */
                if (skb_orphan_frags(skb, gfp_mask)) {
                        kfree(data);
                        return -ENOMEM;
                }
                for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
                        skb_frag_ref(skb, i);
                if (skb_has_frag_list(skb))
                        skb_clone_fraglist(skb);
                skb_release_data(skb);
        } else {
                /* we can reuse existing recount- all we did was
                 * relocate values
                 */
                skb_free_head(skb);
        }

        skb->head = data;
        skb->data = data;
        skb->head_frag = 0;
#ifdef NET_SKBUFF_DATA_USES_OFFSET
        skb->end = size;
#else
        skb->end = skb->head + size;
#endif
        skb_set_tail_pointer(skb, skb_headlen(skb));
        skb_headers_offset_update(skb, 0);
        skb->cloned = 0;
        skb->hdr_len = 0;
        skb->nohdr = 0;
        atomic_set(&skb_shinfo(skb)->dataref, 1);

        return 0;
}

static int pskb_carve(struct sk_buff *skb, const u32 off, gfp_t gfp);

/* carve out the first eat bytes from skb's frag_list. May recurse into
 * pskb_carve()
 */
static int pskb_carve_frag_list(struct sk_buff *skb,
                                struct skb_shared_info *shinfo, int eat,
                                gfp_t gfp_mask)
{
        struct sk_buff *list = shinfo->frag_list;
        struct sk_buff *clone = NULL;
        struct sk_buff *insp = NULL;

        do {
                if (!list) {
                        pr_err("Not enough bytes to eat. Want %d\n", eat);
                        return -EFAULT;
                }
                if (list->len <= eat) {
                        /* Eaten as whole. */
                        eat -= list->len;
                        list = list->next;
                        insp = list;
                } else {
                        /* Eaten partially. */
                        if (skb_shared(list)) {
                                clone = skb_clone(list, gfp_mask);
                                if (!clone)
                                        return -ENOMEM;
                                insp = list->next;
                                list = clone;
                        } else {
                                /* This may be pulled without problems. */
                                insp = list;
                        }
                        if (pskb_carve(list, eat, gfp_mask) < 0) {
                                kfree_skb(clone);
                                return -ENOMEM;
                        }
                        break;
                }
        } while (eat);

        /* Free pulled out fragments. */
        while ((list = shinfo->frag_list) != insp) {
                shinfo->frag_list = list->next;
                kfree_skb(list);
        }
        /* And insert new clone at head. */
        if (clone) {
                clone->next = list;
                shinfo->frag_list = clone;
        }
        return 0;
}

/* carve off first len bytes from skb. Split line (off) is in the
 * non-linear part of skb
 */
static int pskb_carve_inside_nonlinear(struct sk_buff *skb, const u32 off,
                                       int pos, gfp_t gfp_mask)
{
        int i, k = 0;
        int size = skb_end_offset(skb);
        u8 *data;
        const int nfrags = skb_shinfo(skb)->nr_frags;
        struct skb_shared_info *shinfo;

        size = SKB_DATA_ALIGN(size);

        if (skb_pfmemalloc(skb))
                gfp_mask |= __GFP_MEMALLOC;
        data = kmalloc_reserve(size +
                               SKB_DATA_ALIGN(sizeof(struct skb_shared_info)),
                               gfp_mask, NUMA_NO_NODE, NULL);
        if (!data)
                return -ENOMEM;

        size = SKB_WITH_OVERHEAD(ksize(data));

        memcpy((struct skb_shared_info *)(data + size),
               skb_shinfo(skb), offsetof(struct skb_shared_info,
                                         frags[skb_shinfo(skb)->nr_frags]));
        if (skb_orphan_frags(skb, gfp_mask)) {
                kfree(data);
                return -ENOMEM;
        }
        shinfo = (struct skb_shared_info *)(data + size);
        for (i = 0; i < nfrags; i++) {
                int fsize = skb_frag_size(&skb_shinfo(skb)->frags[i]);

                if (pos + fsize > off) {
                        shinfo->frags[k] = skb_shinfo(skb)->frags[i];

                        if (pos < off) {
                                /* 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.
                                 */
                                shinfo->frags[0].page_offset += off - pos;
                                skb_frag_size_sub(&shinfo->frags[0], off - pos);
                        }
                        skb_frag_ref(skb, i);
                        k++;
                }
                pos += fsize;
        }
        shinfo->nr_frags = k;
        if (skb_has_frag_list(skb))
                skb_clone_fraglist(skb);

        if (k == 0) {
                /* split line is in frag list */
                pskb_carve_frag_list(skb, shinfo, off - pos, gfp_mask);
        }
        skb_release_data(skb);

        skb->head = data;
        skb->head_frag = 0;
        skb->data = data;
#ifdef NET_SKBUFF_DATA_USES_OFFSET
        skb->end = size;
#else
        skb->end = skb->head + size;
#endif
        skb_reset_tail_pointer(skb);
        skb_headers_offset_update(skb, 0);
        skb->cloned   = 0;
        skb->hdr_len  = 0;
        skb->nohdr    = 0;
        skb->len -= off;
        skb->data_len = skb->len;
        atomic_set(&skb_shinfo(skb)->dataref, 1);
        return 0;
}

/* remove len bytes from the beginning of the skb */
static int pskb_carve(struct sk_buff *skb, const u32 len, gfp_t gfp)
{
        int headlen = skb_headlen(skb);

        if (len < headlen)
                return pskb_carve_inside_header(skb, len, headlen, gfp);
        else
                return pskb_carve_inside_nonlinear(skb, len, headlen, gfp);
}

/* Extract to_copy bytes starting at off from skb, and return this in
 * a new skb
 */
struct sk_buff *pskb_extract(struct sk_buff *skb, int off,
                             int to_copy, gfp_t gfp)
{
        struct sk_buff  *clone = skb_clone(skb, gfp);

        if (!clone)
                return NULL;

        if (pskb_carve(clone, off, gfp) < 0 ||
            pskb_trim(clone, to_copy)) {
                kfree_skb(clone);
                return NULL;
        }
        return clone;
}
EXPORT_SYMBOL(pskb_extract);