FreeBSD/Linux Kernel Cross Reference
sys/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/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 <net/protocol.h>
    #include <net/dst.h>
    #include <net/sock.h>
    #include <net/checksum.h>
    #include <net/xfrm.h>
    
    #include <asm/uaccess.h>
    #include <trace/events/skb.h>
    #include <linux/highmem.h>
    
    struct kmem_cache *skbuff_head_cache __read_mostly;
    static struct kmem_cache *skbuff_fclone_cache __read_mostly;
    
    static void sock_pipe_buf_release(struct pipe_inode_info *pipe,
                                      struct pipe_buffer *buf)
    {
            put_page(buf->page);
    }
    
    static void sock_pipe_buf_get(struct pipe_inode_info *pipe,
                                    struct pipe_buffer *buf)
    {
            get_page(buf->page);
    }
    
    static int sock_pipe_buf_steal(struct pipe_inode_info *pipe,
                                   struct pipe_buffer *buf)
    {
            return 1;
    }
    
    
    /* Pipe buffer operations for a socket. */
    static const struct pipe_buf_operations sock_pipe_buf_ops = {
            .can_merge = 0,
            .map = generic_pipe_buf_map,
           .unmap = generic_pipe_buf_unmap,
           .confirm = generic_pipe_buf_confirm,
           .release = sock_pipe_buf_release,
           .steal = sock_pipe_buf_steal,
           .get = sock_pipe_buf_get,
   };
   
   /*
    *      Keep out-of-line to prevent kernel bloat.
    *      __builtin_return_address is not used because it is not always
    *      reliable.
    */
   
   /**
    *      skb_over_panic  -       private function
    *      @skb: buffer
    *      @sz: size
    *      @here: address
    *
    *      Out of line support code for skb_put(). Not user callable.
    */
   static void skb_over_panic(struct sk_buff *skb, int sz, void *here)
   {
           pr_emerg("%s: text:%p len:%d put:%d head:%p data:%p tail:%#lx end:%#lx dev:%s\n",
                    __func__, here, skb->len, sz, skb->head, skb->data,
                    (unsigned long)skb->tail, (unsigned long)skb->end,
                    skb->dev ? skb->dev->name : "<NULL>");
           BUG();
   }
   
   /**
    *      skb_under_panic -       private function
    *      @skb: buffer
    *      @sz: size
    *      @here: address
    *
    *      Out of line support code for skb_push(). Not user callable.
    */
   
   static void skb_under_panic(struct sk_buff *skb, int sz, void *here)
   {
           pr_emerg("%s: text:%p len:%d put:%d head:%p data:%p tail:%#lx end:%#lx dev:%s\n",
                    __func__, here, skb->len, sz, skb->head, skb->data,
                    (unsigned long)skb->tail, (unsigned long)skb->end,
                    skb->dev ? skb->dev->name : "<NULL>");
           BUG();
   }
   
   
   /*
    * 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)
   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.
    *
    */
   
   /**
    *      __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;
   #ifdef NET_SKBUFF_DATA_USES_OFFSET
           skb->mac_header = ~0U;
   #endif
   
           /* 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 *child = skb + 1;
                   atomic_t *fclone_ref = (atomic_t *) (child + 1);
   
                   kmemcheck_annotate_bitfield(child, flags1);
                   kmemcheck_annotate_bitfield(child, flags2);
                   skb->fclone = SKB_FCLONE_ORIG;
                   atomic_set(fclone_ref, 1);
   
                   child->fclone = SKB_FCLONE_UNAVAILABLE;
                   child->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 fragment, 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()
    * 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);
           skb->head_frag = frag_size != 0;
           atomic_set(&skb->users, 1);
           skb->head = data;
           skb->data = data;
           skb_reset_tail_pointer(skb);
           skb->end = skb->tail + size;
   #ifdef NET_SKBUFF_DATA_USES_OFFSET
           skb->mac_header = ~0U;
   #endif
   
           /* 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;
   }
   EXPORT_SYMBOL(build_skb);
   
   struct netdev_alloc_cache {
           struct page_frag        frag;
           /* we maintain a pagecount bias, so that we dont dirty cache line
            * containing page->_count every time we allocate a fragment.
            */
           unsigned int            pagecnt_bias;
   };
   static DEFINE_PER_CPU(struct netdev_alloc_cache, netdev_alloc_cache);
   
   #define NETDEV_FRAG_PAGE_MAX_ORDER get_order(32768)
   #define NETDEV_FRAG_PAGE_MAX_SIZE  (PAGE_SIZE << NETDEV_FRAG_PAGE_MAX_ORDER)
   #define NETDEV_PAGECNT_MAX_BIAS    NETDEV_FRAG_PAGE_MAX_SIZE
   
   static void *__netdev_alloc_frag(unsigned int fragsz, gfp_t gfp_mask)
   {
           struct netdev_alloc_cache *nc;
           void *data = NULL;
           int order;
           unsigned long flags;
   
           local_irq_save(flags);
           nc = &__get_cpu_var(netdev_alloc_cache);
           if (unlikely(!nc->frag.page)) {
   refill:
                   for (order = NETDEV_FRAG_PAGE_MAX_ORDER; ;) {
                           gfp_t gfp = gfp_mask;
   
                           if (order)
                                   gfp |= __GFP_COMP | __GFP_NOWARN;
                           nc->frag.page = alloc_pages(gfp, order);
                           if (likely(nc->frag.page))
                                   break;
                           if (--order < 0)
                                   goto end;
                   }
                   nc->frag.size = PAGE_SIZE << order;
   recycle:
                   atomic_set(&nc->frag.page->_count, NETDEV_PAGECNT_MAX_BIAS);
                   nc->pagecnt_bias = NETDEV_PAGECNT_MAX_BIAS;
                   nc->frag.offset = 0;
           }
   
           if (nc->frag.offset + fragsz > nc->frag.size) {
                   /* avoid unnecessary locked operations if possible */
                   if ((atomic_read(&nc->frag.page->_count) == nc->pagecnt_bias) ||
                       atomic_sub_and_test(nc->pagecnt_bias, &nc->frag.page->_count))
                           goto recycle;
                   goto refill;
           }
   
           data = page_address(nc->frag.page) + nc->frag.offset;
           nc->frag.offset += fragsz;
           nc->pagecnt_bias--;
   end:
           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);
   
   /**
    *      __netdev_alloc_skb - allocate an skbuff for rx on a specific device
    *      @dev: network device to receive on
    *      @length: length to allocate
    *      @gfp_mask: get_free_pages mask, passed to alloc_skb
    *
    *      Allocate a new &sk_buff and assign it a usage count of one. The
    *      buffer has unspecified headroom built in. Users should allocate
    *      the headroom they think they need without accounting for the
    *      built in space. The built in space is used for optimisations.
    *
    *      %NULL is returned if there is no free memory.
    */
   struct sk_buff *__netdev_alloc_skb(struct net_device *dev,
                                      unsigned int length, gfp_t gfp_mask)
   {
           struct sk_buff *skb = NULL;
           unsigned int fragsz = SKB_DATA_ALIGN(length + NET_SKB_PAD) +
                                 SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
   
           if (fragsz <= PAGE_SIZE && !(gfp_mask & (__GFP_WAIT | GFP_DMA))) {
                   void *data;
   
                   if (sk_memalloc_socks())
                           gfp_mask |= __GFP_MEMALLOC;
   
                   data = __netdev_alloc_frag(fragsz, gfp_mask);
   
                   if (likely(data)) {
                           skb = build_skb(data, fragsz);
                           if (unlikely(!skb))
                                   put_page(virt_to_head_page(data));
                   }
           } else {
                   skb = __alloc_skb(length + NET_SKB_PAD, gfp_mask,
                                     SKB_ALLOC_RX, NUMA_NO_NODE);
           }
           if (likely(skb)) {
                   skb_reserve(skb, NET_SKB_PAD);
                   skb->dev = dev;
           }
           return skb;
   }
   EXPORT_SYMBOL(__netdev_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);
   
   static void skb_drop_list(struct sk_buff **listp)
   {
           struct sk_buff *list = *listp;
   
           *listp = NULL;
   
           do {
                   struct sk_buff *this = list;
                   list = list->next;
                   kfree_skb(this);
           } while (list);
   }
   
   static inline void skb_drop_fraglist(struct sk_buff *skb)
   {
           skb_drop_list(&skb_shinfo(skb)->frag_list);
   }
   
   static void skb_clone_fraglist(struct sk_buff *skb)
   {
           struct sk_buff *list;
   
           skb_walk_frags(skb, list)
                   skb_get(list);
   }
   
   static void skb_free_head(struct sk_buff *skb)
   {
           if (skb->head_frag)
                   put_page(virt_to_head_page(skb->head));
           else
                   kfree(skb->head);
   }
   
   static void skb_release_data(struct sk_buff *skb)
   {
           if (!skb->cloned ||
               !atomic_sub_return(skb->nohdr ? (1 << SKB_DATAREF_SHIFT) + 1 : 1,
                                  &skb_shinfo(skb)->dataref)) {
                   if (skb_shinfo(skb)->nr_frags) {
                           int i;
                           for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
                                   skb_frag_unref(skb, i);
                   }
   
                   /*
                    * If skb buf is from userspace, we need to notify the caller
                    * the lower device DMA has done;
                    */
                   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, true);
                   }
   
                   if (skb_has_frag_list(skb))
                           skb_drop_fraglist(skb);
   
                   skb_free_head(skb);
           }
   }
   
   /*
    *      Free an skbuff by memory without cleaning the state.
    */
   static void kfree_skbmem(struct sk_buff *skb)
   {
           struct sk_buff *other;
           atomic_t *fclone_ref;
   
           switch (skb->fclone) {
           case SKB_FCLONE_UNAVAILABLE:
                   kmem_cache_free(skbuff_head_cache, skb);
                   break;
   
           case SKB_FCLONE_ORIG:
                   fclone_ref = (atomic_t *) (skb + 2);
                   if (atomic_dec_and_test(fclone_ref))
                           kmem_cache_free(skbuff_fclone_cache, skb);
                   break;
   
           case SKB_FCLONE_CLONE:
                   fclone_ref = (atomic_t *) (skb + 1);
                   other = skb - 1;
   
                   /* The clone portion is available for
                    * fast-cloning again.
                    */
                   skb->fclone = SKB_FCLONE_UNAVAILABLE;
   
                   if (atomic_dec_and_test(fclone_ref))
                           kmem_cache_free(skbuff_fclone_cache, other);
                   break;
           }
   }
   
   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
   #ifdef NET_SKBUFF_NF_DEFRAG_NEEDED
           nf_conntrack_put_reasm(skb->nfct_reasm);
   #endif
   #ifdef CONFIG_BRIDGE_NETFILTER
           nf_bridge_put(skb->nf_bridge);
   #endif
   /* XXX: IS this still necessary? - JHS */
   #ifdef CONFIG_NET_SCHED
           skb->tc_index = 0;
   #ifdef CONFIG_NET_CLS_ACT
           skb->tc_verd = 0;
   #endif
   #endif
   }
   
   /* Free everything but the sk_buff shell. */
   static void skb_release_all(struct sk_buff *skb)
   {
           skb_release_head_state(skb);
           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);
   
   /**
    *      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);
   
   static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
   {
           new->tstamp             = old->tstamp;
           new->dev                = old->dev;
           new->transport_header   = old->transport_header;
           new->network_header     = old->network_header;
           new->mac_header         = old->mac_header;
           new->inner_transport_header = old->inner_transport_header;
           new->inner_network_header = old->inner_transport_header;
           skb_dst_copy(new, old);
           new->rxhash             = old->rxhash;
           new->ooo_okay           = old->ooo_okay;
           new->l4_rxhash          = old->l4_rxhash;
           new->no_fcs             = old->no_fcs;
           new->encapsulation      = old->encapsulation;
   #ifdef CONFIG_XFRM
           new->sp                 = secpath_get(old->sp);
   #endif
           memcpy(new->cb, old->cb, sizeof(old->cb));
           new->csum               = old->csum;
           new->local_df           = old->local_df;
           new->pkt_type           = old->pkt_type;
           new->ip_summed          = old->ip_summed;
           skb_copy_queue_mapping(new, old);
           new->priority           = old->priority;
   #if IS_ENABLED(CONFIG_IP_VS)
           new->ipvs_property      = old->ipvs_property;
   #endif
           new->pfmemalloc         = old->pfmemalloc;
           new->protocol           = old->protocol;
           new->mark               = old->mark;
           new->skb_iif            = old->skb_iif;
           __nf_copy(new, old);
   #if IS_ENABLED(CONFIG_NETFILTER_XT_TARGET_TRACE)
           new->nf_trace           = old->nf_trace;
   #endif
   #ifdef CONFIG_NET_SCHED
           new->tc_index           = old->tc_index;
   #ifdef CONFIG_NET_CLS_ACT
           new->tc_verd            = old->tc_verd;
   #endif
   #endif
           new->vlan_tci           = old->vlan_tci;
   
           skb_copy_secmark(new, old);
   }
   
   /*
    * 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 *)head->private;
                                   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);
                   page->private = (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 *)head->private;
           }
   
           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 *n;
   
           if (skb_orphan_frags(skb, gfp_mask))
                   return NULL;
   
           n = skb + 1;
           if (skb->fclone == SKB_FCLONE_ORIG &&
               n->fclone == SKB_FCLONE_UNAVAILABLE) {
                   atomic_t *fclone_ref = (atomic_t *) (n + 1);
                   n->fclone = SKB_FCLONE_CLONE;
                   atomic_inc(fclone_ref);
           } else {
                   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);
                   kmemcheck_annotate_bitfield(n, flags2);
                   n->fclone = SKB_FCLONE_UNAVAILABLE;
           }
   
           return __skb_clone(n, skb);
   }
   EXPORT_SYMBOL(skb_clone);
   
   static void copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
   {
   #ifndef NET_SKBUFF_DATA_USES_OFFSET
           /*
            *      Shift between the two data areas in bytes
            */
           unsigned long offset = new->data - old->data;
   #endif
   
           __copy_skb_header(new, old);
   
   #ifndef NET_SKBUFF_DATA_USES_OFFSET
           /* {transport,network,mac}_header are relative to skb->head */
           new->transport_header += offset;
           new->network_header   += offset;
           if (skb_mac_header_was_set(new))
                   new->mac_header       += offset;
           new->inner_transport_header += offset;
           new->inner_network_header   += offset;
   #endif
           skb_shinfo(new)->gso_size = skb_shinfo(old)->gso_size;
           skb_shinfo(new)->gso_segs = skb_shinfo(old)->gso_segs;
           skb_shinfo(new)->gso_type = skb_shinfo(old)->gso_type;
   }
   
   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     -       create copy of an sk_buff with private head.
    *      @skb: buffer to copy
    *      @headroom: headroom of new skb
    *      @gfp_mask: allocation priority
    *
    *      Make a copy of both an &sk_buff and part of its data, located
    *      in header. Fragmented data remain shared. This is used when
    *      the caller wishes to modify only header of &sk_buff and needs
    *      private copy of the header to alter. Returns %NULL on failure
    *      or the pointer to the buffer on success.
    *      The returned buffer has a reference count of 1.
    */
   
   struct sk_buff *__pskb_copy(struct sk_buff *skb, int headroom, gfp_t gfp_mask)
   {
           unsigned int size = skb_headlen(skb) + headroom;
           struct sk_buff *n = __alloc_skb(size, gfp_mask,
                                           skb_alloc_rx_flag(skb), 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);
  
  /**
   *      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
          /* {transport,network,mac}_header and tail are relative to skb->head */
          skb->tail             += off;
          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;
          /* Only adjust this if it actually is csum_start rather than csum */
          if (skb->ip_summed == CHECKSUM_PARTIAL)
                  skb->csum_start += 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;
          int off;
  
          if (!n)
                  return NULL;
  
          skb_reserve(n, newheadroom);
  
          /* Set the tail pointer and length */
          skb_put(n, skb->len);
  
          head_copy_len = oldheadroom;
          head_copy_off = 0;
          if (newheadroom <= head_copy_len)
                  head_copy_len = newheadroom;
          else
                  head_copy_off = newheadroom - head_copy_len;
  
          /* Copy the linear header and data. */
          if (skb_copy_bits(skb, -head_copy_len, n->head + head_copy_off,
                            skb->len + head_copy_len))
                  BUG();
  
          copy_skb_header(n, skb);
  
          off                  = newheadroom - oldheadroom;
          if (n->ip_summed == CHECKSUM_PARTIAL)
                  n->csum_start += off;
  #ifdef NET_SKBUFF_DATA_USES_OFFSET
          n->transport_header += off;
          n->network_header   += off;
          if (skb_mac_header_was_set(skb))
                  n->mac_header += off;
          n->inner_transport_header += off;
          n->inner_network_header    += off;
  #endif
  
          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);
  
  /**
   *      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;
  
          /* 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;
          }
  
          return false;
  }
  
  /*
   * Map data from the skb to a pipe. Should handle both the linear part,
   * the fragments, and the frag list. It does NOT handle frag lists within
   * the frag list, if such a thing exists. We'd probably need to recurse to
   * handle that cleanly.
   */
  int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
                      struct pipe_inode_info *pipe, unsigned int tlen,
                      unsigned int flags)
  {
          struct partial_page partial[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 = &sock_pipe_buf_ops,
                  .spd_release = sock_spd_release,
          };
          struct sk_buff *frag_iter;
          struct sock *sk = skb->sk;
          int ret = 0;
  
          /*
           * __skb_splice_bits() only fails if the output has no room left,
           * so no point in going over the frag_list for the error case.
           */
          if (__skb_splice_bits(skb, pipe, &offset, &tlen, &spd, sk))
                  goto done;
          else if (!tlen)
                  goto done;
  
          /*
           * now see if we have a frag_list to map
           */
          skb_walk_frags(skb, frag_iter) {
                  if (!tlen)
                          break;
                  if (__skb_splice_bits(frag_iter, pipe, &offset, &tlen, &spd, sk))
                          break;
          }
  
  done:
          if (spd.nr_pages) {
                  /*
                   * 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;
  }
  
  /**
   *      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)
  {
          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 = csum_partial(skb->data + offset, copy, csum);
                  if ((len -= copy) == 0)
                          return csum;
                  offset += copy;
                  pos     = copy;
          }
  
          for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
                  int end;
                  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 = csum_partial(vaddr + frag->page_offset +
                                               offset - start, copy, 0);
                          kunmap_atomic(vaddr);
                          csum = csum_block_add(csum, csum2, pos);
                          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);
                          csum = csum_block_add(csum, csum2, pos);
                          if ((len -= copy) == 0)
                                  return csum;
                          offset += copy;
                          pos    += copy;
                  }
                  start = end;
          }
          BUG_ON(len);
  
          return csum;
  }
  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);
  
  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);
  
          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 seqeuental
   *       reads of potentially non linear data.
   *
   * Note 2: Fragment lists within fragments are not implemented
   *       at the moment, state->root_skb could be replaced with
   *       a stack for this purpose.
   */
  unsigned int skb_seq_read(unsigned int consumed, const u8 **data,
                            struct skb_seq_state *st)
  {
          unsigned int block_limit, abs_offset = consumed + st->lower_offset;
          skb_frag_t *frag;
  
          if (unlikely(abs_offset >= st->upper_offset))
                  return 0;
  
  next_skb:
          block_limit = skb_headlen(st->cur_skb) + 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
   * @state: uninitialized textsearch state variable
   *
   * Finds a pattern in the skb data according to the specified
   * textsearch configuration. Use textsearch_next() to retrieve
   * subsequent occurrences of the pattern. Returns the offset
   * to the first occurrence or UINT_MAX if no match was found.
   */
  unsigned int skb_find_text(struct sk_buff *skb, unsigned int from,
                             unsigned int to, struct ts_config *config,
                             struct ts_state *state)
  {
          unsigned int ret;
  
          config->get_next_block = skb_ts_get_next_block;
          config->finish = skb_ts_finish;
  
          skb_prepare_seq_read(skb, from, to, TS_SKB_CB(state));
  
          ret = textsearch_find(config, state);
          return (ret <= to - from ? ret : UINT_MAX);
  }
  EXPORT_SYMBOL(skb_find_text);
  
  /**
   * skb_append_datato_frags - append the user data to a skb
   * @sk: sock  structure
   * @skb: skb structure to be appened with user data.
   * @getfrag: call back function to be used for getting the user data
   * @from: pointer to user message iov
   * @length: length of the iov message
   *
   * Description: This procedure append the user data in the fragment part
   * of the skb if any page alloc fails user this procedure returns  -ENOMEM
   */
  int skb_append_datato_frags(struct sock *sk, struct sk_buff *skb,
                          int (*getfrag)(void *from, char *to, int offset,
                                          int len, int odd, struct sk_buff *skb),
                          void *from, int length)
  {
          int frg_cnt = 0;
          skb_frag_t *frag = NULL;
          struct page *page = NULL;
          int copy, left;
          int offset = 0;
          int ret;
  
          do {
                  /* Return error if we don't have space for new frag */
                  frg_cnt = skb_shinfo(skb)->nr_frags;
                  if (frg_cnt >= MAX_SKB_FRAGS)
                          return -EFAULT;
  
                  /* allocate a new page for next frag */
                  page = alloc_pages(sk->sk_allocation, 0);
  
                  /* If alloc_page fails just return failure and caller will
                   * free previous allocated pages by doing kfree_skb()
                   */
                  if (page == NULL)
                          return -ENOMEM;
  
                  /* initialize the next frag */
                  skb_fill_page_desc(skb, frg_cnt, page, 0, 0);
                  skb->truesize += PAGE_SIZE;
                  atomic_add(PAGE_SIZE, &sk->sk_wmem_alloc);
  
                  /* get the new initialized frag */
                  frg_cnt = skb_shinfo(skb)->nr_frags;
                  frag = &skb_shinfo(skb)->frags[frg_cnt - 1];
  
                  /* copy the user data to page */
                  left = PAGE_SIZE - frag->page_offset;
                  copy = (length > left)? left : length;
  
                  ret = getfrag(from, skb_frag_address(frag) + skb_frag_size(frag),
                              offset, copy, 0, skb);
                  if (ret < 0)
                          return -EFAULT;
  
                  /* copy was successful so update the size parameters */
                  skb_frag_size_add(frag, copy);
                  skb->len += copy;
                  skb->data_len += copy;
                  offset += copy;
                  length -= copy;
  
          } while (length > 0);
  
          return 0;
  }
  EXPORT_SYMBOL(skb_append_datato_frags);
  
  /**
   *      skb_pull_rcsum - pull skb and update receive checksum
   *      @skb: buffer to update
   *      @len: length of data pulled
   *
   *      This function performs an skb_pull on the packet and updates
   *      the CHECKSUM_COMPLETE checksum.  It should be used on
   *      receive path processing instead of skb_pull unless you know
   *      that the checksum difference is zero (e.g., a valid IP header)
   *      or you are setting ip_summed to CHECKSUM_NONE.
   */
  unsigned char *skb_pull_rcsum(struct sk_buff *skb, unsigned int len)
  {
          BUG_ON(len > skb->len);
          skb->len -= len;
          BUG_ON(skb->len < skb->data_len);
          skb_postpull_rcsum(skb, skb->data, len);
          return skb->data += len;
  }
  EXPORT_SYMBOL_GPL(skb_pull_rcsum);
  
  /**
   *      skb_segment - Perform protocol segmentation on skb.
   *      @skb: buffer to segment
   *      @features: features for the output path (see dev->features)
   *
   *      This function performs segmentation on the given skb.  It returns
   *      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 *skb, netdev_features_t features)
  {
          struct sk_buff *segs = NULL;
          struct sk_buff *tail = NULL;
          struct sk_buff *fskb = skb_shinfo(skb)->frag_list;
          unsigned int mss = skb_shinfo(skb)->gso_size;
          unsigned int doffset = skb->data - skb_mac_header(skb);
          unsigned int offset = doffset;
          unsigned int headroom;
          unsigned int len;
          int sg = !!(features & NETIF_F_SG);
          int nfrags = skb_shinfo(skb)->nr_frags;
          int err = -ENOMEM;
          int i = 0;
          int pos;
  
          __skb_push(skb, doffset);
          headroom = skb_headroom(skb);
          pos = skb_headlen(skb);
  
          do {
                  struct sk_buff *nskb;
                  skb_frag_t *frag;
                  int hsize;
                  int size;
  
                  len = skb->len - offset;
                  if (len > mss)
                          len = mss;
  
                  hsize = skb_headlen(skb) - offset;
                  if (hsize < 0)
                          hsize = 0;
                  if (hsize > len || !sg)
                          hsize = len;
  
                  if (!hsize && i >= nfrags) {
                          BUG_ON(fskb->len != len);
  
                          pos += len;
                          nskb = skb_clone(fskb, GFP_ATOMIC);
                          fskb = fskb->next;
  
                          if (unlikely(!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(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, skb);
                  nskb->mac_len = skb->mac_len;
  
                  /* nskb and skb might have different headroom */
                  if (nskb->ip_summed == CHECKSUM_PARTIAL)
                          nskb->csum_start += skb_headroom(nskb) - headroom;
  
                  skb_reset_mac_header(nskb);
                  skb_set_network_header(nskb, skb->mac_len);
                  nskb->transport_header = (nskb->network_header +
                                            skb_network_header_len(skb));
                  skb_copy_from_linear_data(skb, nskb->data, doffset);
  
                  if (fskb != skb_shinfo(skb)->frag_list)
                          continue;
  
                  if (!sg) {
                          nskb->ip_summed = CHECKSUM_NONE;
                          nskb->csum = skb_copy_and_csum_bits(skb, offset,
                                                              skb_put(nskb, len),
                                                              len, 0);
                          continue;
                  }
  
                  frag = skb_shinfo(nskb)->frags;
  
                  skb_copy_from_linear_data_offset(skb, offset,
                                                   skb_put(nskb, hsize), hsize);
  
                  while (pos < offset + len && i < nfrags) {
                          *frag = skb_shinfo(skb)->frags[i];
                          __skb_frag_ref(frag);
                          size = skb_frag_size(frag);
  
                          if (pos < offset) {
                                  frag->page_offset += offset - pos;
                                  skb_frag_size_sub(frag, offset - pos);
                          }
  
                          skb_shinfo(nskb)->nr_frags++;
  
                          if (pos + size <= offset + len) {
                                  i++;
                                  pos += size;
                          } else {
                                  skb_frag_size_sub(frag, pos + size - (offset + len));
                                  goto skip_fraglist;
                          }
  
                          frag++;
                  }
  
                  if (pos < offset + len) {
                          struct sk_buff *fskb2 = fskb;
  
                          BUG_ON(pos + fskb->len != offset + len);
  
                          pos += fskb->len;
                          fskb = fskb->next;
  
                          if (fskb2->next) {
                                  fskb2 = skb_clone(fskb2, GFP_ATOMIC);
                                  if (!fskb2)
                                          goto err;
                          } else
                                  skb_get(fskb2);
  
                          SKB_FRAG_ASSERT(nskb);
                          skb_shinfo(nskb)->frag_list = fskb2;
                  }
  
  skip_fraglist:
                  nskb->data_len = len - hsize;
                  nskb->len += nskb->data_len;
                  nskb->truesize += nskb->data_len;
          } while ((offset += len) < skb->len);
  
          return segs;
  
  err:
          while ((skb = segs)) {
                  segs = skb->next;
                  kfree_skb(skb);
          }
          return ERR_PTR(err);
  }
  EXPORT_SYMBOL_GPL(skb_segment);
  
  int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
  {
          struct sk_buff *p = *head;
          struct sk_buff *nskb;
          struct skb_shared_info *skbinfo = skb_shinfo(skb);
          struct skb_shared_info *pinfo = skb_shinfo(p);
          unsigned int headroom;
          unsigned int len = skb_gro_len(skb);
          unsigned int offset = skb_gro_offset(skb);
          unsigned int headlen = skb_headlen(skb);
          unsigned int delta_truesize;
  
          if (p->len + len >= 65536)
                  return -E2BIG;
  
          if (pinfo->frag_list)
                  goto merge;
          else if (headlen <= offset) {
                  skb_frag_t *frag;
                  skb_frag_t *frag2;
                  int i = skbinfo->nr_frags;
                  int nr_frags = pinfo->nr_frags + i;
  
                  offset -= headlen;
  
                  if (nr_frags > MAX_SKB_FRAGS)
                          return -E2BIG;
  
                  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)
                          return -E2BIG;
  
                  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;
          } else if (skb_gro_len(p) != pinfo->gso_size)
                  return -E2BIG;
  
          headroom = skb_headroom(p);
          nskb = alloc_skb(headroom + skb_gro_offset(p), GFP_ATOMIC);
          if (unlikely(!nskb))
                  return -ENOMEM;
  
          __copy_skb_header(nskb, p);
          nskb->mac_len = p->mac_len;
  
          skb_reserve(nskb, headroom);
          __skb_put(nskb, skb_gro_offset(p));
  
          skb_set_mac_header(nskb, skb_mac_header(p) - p->data);
          skb_set_network_header(nskb, skb_network_offset(p));
          skb_set_transport_header(nskb, skb_transport_offset(p));
  
          __skb_pull(p, skb_gro_offset(p));
          memcpy(skb_mac_header(nskb), skb_mac_header(p),
                 p->data - skb_mac_header(p));
  
          skb_shinfo(nskb)->frag_list = p;
          skb_shinfo(nskb)->gso_size = pinfo->gso_size;
          pinfo->gso_size = 0;
          skb_header_release(p);
          NAPI_GRO_CB(nskb)->last = p;
  
          nskb->data_len += p->len;
          nskb->truesize += p->truesize;
          nskb->len += p->len;
  
          *head = nskb;
          nskb->next = p->next;
          p->next = NULL;
  
          p = nskb;
  
  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);
  
          NAPI_GRO_CB(p)->last->next = skb;
          NAPI_GRO_CB(p)->last = skb;
          skb_header_release(skb);
  
  done:
          NAPI_GRO_CB(p)->count++;
          p->data_len += len;
          p->truesize += delta_truesize;
          p->len += len;
  
          NAPI_GRO_CB(skb)->same_flow = 1;
          return 0;
  }
  EXPORT_SYMBOL_GPL(skb_gro_receive);
  
  void __init skb_init(void)
  {
          skbuff_head_cache = kmem_cache_create("skbuff_head_cache",
                                                sizeof(struct sk_buff),
                                                0,
                                                SLAB_HWCACHE_ALIGN|SLAB_PANIC,
                                                NULL);
          skbuff_fclone_cache = kmem_cache_create("skbuff_fclone_cache",
                                                  (2*sizeof(struct sk_buff)) +
                                                  sizeof(atomic_t),
                                                  0,
                                                  SLAB_HWCACHE_ALIGN|SLAB_PANIC,
                                                  NULL);
  }
  
  /**
   *      skb_to_sgvec - Fill a scatter-gather list from a socket buffer
   *      @skb: Socket buffer containing the buffers to be mapped
   *      @sg: The scatter-gather list to map into
   *      @offset: The offset into the buffer's contents to start mapping
   *      @len: Length of buffer space to be mapped
   *
   *      Fill the specified scatter-gather list with mappings/pointers into a
   *      region of the buffer space attached to a socket buffer.
   */
  static int
  __skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int len)
  {
          int start = skb_headlen(skb);
          int i, copy = start - offset;
          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;
  }
  
  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)
  {
          int len = skb->len;
  
          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, len);
          return 0;
  }
  EXPORT_SYMBOL(sock_queue_err_skb);
  
  void skb_tstamp_tx(struct sk_buff *orig_skb,
                  struct skb_shared_hwtstamps *hwtstamps)
  {
          struct sock *sk = orig_skb->sk;
          struct sock_exterr_skb *serr;
          struct sk_buff *skb;
          int err;
  
          if (!sk)
                  return;
  
          skb = skb_clone(orig_skb, GFP_ATOMIC);
          if (!skb)
                  return;
  
          if (hwtstamps) {
                  *skb_hwtstamps(skb) =
                          *hwtstamps;
          } else {
                  /*
                   * no hardware time stamps available,
                   * so keep the shared tx_flags and only
                   * store software time stamp
                   */
                  skb->tstamp = ktime_get_real();
          }
  
          serr = SKB_EXT_ERR(skb);
          memset(serr, 0, sizeof(*serr));
          serr->ee.ee_errno = ENOMSG;
          serr->ee.ee_origin = SO_EE_ORIGIN_TIMESTAMPING;
  
          err = sock_queue_err_skb(sk, skb);
  
          if (err)
                  kfree_skb(skb);
  }
  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;
  
          err = sock_queue_err_skb(sk, skb);
          if (err)
                  kfree_skb(skb);
  }
  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;
          return true;
  }
  EXPORT_SYMBOL_GPL(skb_partial_csum_set);
  
  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)) {
                  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);