text: #ifndef __BACKPORT_SKBUFF_H
  #define __BACKPORT_SKBUFF_H
  #include_next <linux/skbuff.h>
  #include <linux/version.h>
  #include <generated/utsrelease.h>
  
  #if LINUX_VERSION_IS_LESS(3,4,0) && \
        (RHEL_RELEASE_CODE < RHEL_RELEASE_VERSION(6,4)) && \
        !(defined(CONFIG_SUSE_KERNEL) && LINUX_VERSION_IS_GEQ(3,0,0))
  #define skb_add_rx_frag(skb, i, page, off, size, truesize) \
  	skb_add_rx_frag(skb, i, page, off, size)
  #endif
  
  #if LINUX_VERSION_IS_LESS(3,3,0)
  #define __pskb_copy LINUX_BACKPORT(__pskb_copy)
  extern struct sk_buff *__pskb_copy(struct sk_buff *skb,
  				   int headroom, gfp_t gfp_mask);
  
  #define skb_complete_wifi_ack LINUX_BACKPORT(skb_complete_wifi_ack)
  static inline void skb_complete_wifi_ack(struct sk_buff *skb, bool acked)
  {
  	WARN_ON(1);
  }
  
  /* define to 0 so checks for it are always false */
  #define SKBTX_WIFI_STATUS 0
  #elif LINUX_VERSION_IS_LESS(3,18,0)
  #define skb_complete_wifi_ack LINUX_BACKPORT(skb_complete_wifi_ack)
  void skb_complete_wifi_ack(struct sk_buff *skb, bool acked);
  #endif
  
  #if LINUX_VERSION_IS_LESS(3,2,0)
  #include <linux/dma-mapping.h>
  
  /* mask skb_frag_page as RHEL6 backports this */
  #define skb_frag_page LINUX_BACKPORT(skb_frag_page)
  static inline struct page *skb_frag_page(const skb_frag_t *frag)
  {
  	return frag->page;
  }
  
  #define skb_frag_size LINUX_BACKPORT(skb_frag_size)
  static inline unsigned int skb_frag_size(const skb_frag_t *frag)
  {
  	return frag->size;
  }
  
  /* mask skb_frag_dma_map as RHEL6 backports this */
  #define skb_frag_dma_map LINUX_BACKPORT(skb_frag_dma_map)
  static inline dma_addr_t skb_frag_dma_map(struct device *dev,
  					  const skb_frag_t *frag,
  					  size_t offset, size_t size,
  					  enum dma_data_direction dir)
  {
  	return dma_map_page(dev, skb_frag_page(frag),
  			    frag->page_offset + offset, size, dir);
  }
  #endif
  
  #if LINUX_VERSION_IS_LESS(3,1,0)
  /* mask __netdev_alloc_skb_ip_align as RHEL6 backports this */
  #define __netdev_alloc_skb_ip_align(a,b,c) compat__netdev_alloc_skb_ip_align(a,b,c)
  static inline struct sk_buff *__netdev_alloc_skb_ip_align(struct net_device *dev,
  							  unsigned int length, gfp_t gfp)
  {
  	struct sk_buff *skb = __netdev_alloc_skb(dev, length + NET_IP_ALIGN, gfp);
  
  	if (NET_IP_ALIGN && skb)
  		skb_reserve(skb, NET_IP_ALIGN);
  	return skb;
  }
  #endif
  
  #ifndef skb_walk_frags
  #define skb_walk_frags(skb, iter)	\
  	for (iter = skb_shinfo(skb)->frag_list; iter; iter = iter->next)
  #endif
  
  #if LINUX_VERSION_IS_LESS(3,2,0)
  #define skb_frag_size_sub LINUX_BACKPORT(skb_frag_size_sub)
  static inline void skb_frag_size_sub(skb_frag_t *frag, int delta)
  {
  	frag->size -= delta;
  }
  
  /**
   * skb_frag_address - gets the address of the data contained in a paged fragment
   * @frag: the paged fragment buffer
   *
   * Returns the address of the data within @frag. The page must already
   * be mapped.
   */
  #define skb_frag_address LINUX_BACKPORT(skb_frag_address)
  static inline void *skb_frag_address(const skb_frag_t *frag)
  {
  	return page_address(skb_frag_page(frag)) + frag->page_offset;
  }
  #endif /* LINUX_VERSION_IS_LESS(3,2,0) */
  
  #if LINUX_VERSION_IS_LESS(3,9,0)
  #ifndef NETDEV_FRAG_PAGE_MAX_ORDER
  #define NETDEV_FRAG_PAGE_MAX_ORDER get_order(32768)
  #endif
  #ifndef NETDEV_FRAG_PAGE_MAX_SIZE
  #define NETDEV_FRAG_PAGE_MAX_SIZE  (PAGE_SIZE << NETDEV_FRAG_PAGE_MAX_ORDER)
  #endif
  #endif /* LINUX_VERSION_IS_LESS(3,9,0) */
  
  #if LINUX_VERSION_IS_LESS(3,9,0)
  #define skb_unclone LINUX_BACKPORT(skb_unclone)
  static inline int skb_unclone(struct sk_buff *skb, gfp_t pri)
  {
  	might_sleep_if(pri & __GFP_WAIT);
  	if (skb_cloned(skb))
  		return pskb_expand_head(skb, 0, 0, pri);
         return 0;
  }
  #endif
  
  #if LINUX_VERSION_IS_LESS(3,2,0)
  
  #define skb_frag_address_safe LINUX_BACKPORT(skb_frag_address_safe)
  /**
   * skb_frag_address_safe - gets the address of the data contained in a paged fragment
   * @frag: the paged fragment buffer
   *
   * Returns the address of the data within @frag. Checks that the page
   * is mapped and returns %NULL otherwise.
   */
  static inline void *skb_frag_address_safe(const skb_frag_t *frag)
  {
  	void *ptr = page_address(skb_frag_page(frag));
  	if (unlikely(!ptr))
  		return NULL;
  
  	return ptr + frag->page_offset;
  }
  #endif /* LINUX_VERSION_IS_LESS(3,2,0) */
  
  #if LINUX_VERSION_IS_LESS(3,14,0) && \
      RHEL_RELEASE_CODE < RHEL_RELEASE_VERSION(7,0) && \
      !(LINUX_VERSION_CODE == KERNEL_VERSION(3,13,11) && UTS_UBUNTU_RELEASE_ABI > 30)
  /*
   * Packet hash types specify the type of hash in skb_set_hash.
   *
   * Hash types refer to the protocol layer addresses which are used to
   * construct a packet's hash. The hashes are used to differentiate or identify
   * flows of the protocol layer for the hash type. Hash types are either
   * layer-2 (L2), layer-3 (L3), or layer-4 (L4).
   *
   * Properties of hashes:
   *
   * 1) Two packets in different flows have different hash values
   * 2) Two packets in the same flow should have the same hash value
   *
   * A hash at a higher layer is considered to be more specific. A driver should
   * set the most specific hash possible.
   *
   * A driver cannot indicate a more specific hash than the layer at which a hash
   * was computed. For instance an L3 hash cannot be set as an L4 hash.
   *
   * A driver may indicate a hash level which is less specific than the
   * actual layer the hash was computed on. For instance, a hash computed
   * at L4 may be considered an L3 hash. This should only be done if the
   * driver can't unambiguously determine that the HW computed the hash at
   * the higher layer. Note that the "should" in the second property above
   * permits this.
   */
  enum pkt_hash_types {
  	PKT_HASH_TYPE_NONE,	/* Undefined type */
  	PKT_HASH_TYPE_L2,	/* Input: src_MAC, dest_MAC */
  	PKT_HASH_TYPE_L3,	/* Input: src_IP, dst_IP */
  	PKT_HASH_TYPE_L4,	/* Input: src_IP, dst_IP, src_port, dst_port */
  };
  
  static inline void
  skb_set_hash(struct sk_buff *skb, __u32 hash, enum pkt_hash_types type)
  {
  #if LINUX_VERSION_IS_GEQ(3,2,0) /* 4031ae6edb */
  	skb->l4_rxhash = (type == PKT_HASH_TYPE_L4);
  #endif
  #if LINUX_VERSION_IS_GEQ(3,4,0) /* bdeab99191 */
  	skb->rxhash = hash;
  #endif
  }
  #endif /* LINUX_VERSION_IS_LESS(3,14,0) */
  
  #if LINUX_VERSION_IS_LESS(3,16,0)
  #define __pskb_copy_fclone LINUX_BACKPORT(__pskb_copy_fclone)
  static inline struct sk_buff *__pskb_copy_fclone(struct sk_buff *skb,
  						 int headroom, gfp_t gfp_mask,
  						 bool fclone)
  {
  	return __pskb_copy(skb, headroom, gfp_mask);
  }
  #endif
  
  #if LINUX_VERSION_IS_LESS(3,18,0)
  #define skb_clone_sk LINUX_BACKPORT(skb_clone_sk)
  struct sk_buff *skb_clone_sk(struct sk_buff *skb);
  #endif
  
  static inline bool skb_xmit_more(struct sk_buff *skb)
  {
  #if LINUX_VERSION_IS_LESS(3,18,0)
  	return false;
  #else
  	return skb->xmit_more;
  #endif
  }
  
  #if LINUX_VERSION_IS_LESS(3,19,0)
  /**
   * __dev_alloc_pages - allocate page for network Rx
   * @gfp_mask: allocation priority. Set __GFP_NOMEMALLOC if not for network Rx
   * @order: size of the allocation
   *
   * Allocate a new page.
   *
   * %NULL is returned if there is no free memory.
  */
  #define __dev_alloc_pages LINUX_BACKPORT(__dev_alloc_pages)
  static inline struct page *__dev_alloc_pages(gfp_t gfp_mask,
  					     unsigned int order)
  {
  	/* This piece of code contains several assumptions.
  	 * 1.  This is for device Rx, therefor a cold page is preferred.
  	 * 2.  The expectation is the user wants a compound page.
  	 * 3.  If requesting a order 0 page it will not be compound
  	 *     due to the check to see if order has a value in prep_new_page
  	 * 4.  __GFP_MEMALLOC is ignored if __GFP_NOMEMALLOC is set due to
  	 *     code in gfp_to_alloc_flags that should be enforcing this.
  	 */
  	gfp_mask |= __GFP_COLD | __GFP_COMP;
  #if LINUX_VERSION_IS_GEQ(3,6,0)
  	gfp_mask |= __GFP_MEMALLOC;
  #endif
  
  	return alloc_pages_node(NUMA_NO_NODE, gfp_mask, order);
  }
  
  #define dev_alloc_pages LINUX_BACKPORT(dev_alloc_pages)
  static inline struct page *dev_alloc_pages(unsigned int order)
  {
  	return __dev_alloc_pages(GFP_ATOMIC, order);
  }
  
  /**
   * __dev_alloc_page - allocate a page for network Rx
   * @gfp_mask: allocation priority. Set __GFP_NOMEMALLOC if not for network Rx
   *
   * Allocate a new page.
   *
   * %NULL is returned if there is no free memory.
   */
  #define __dev_alloc_page LINUX_BACKPORT(__dev_alloc_page)
  static inline struct page *__dev_alloc_page(gfp_t gfp_mask)
  {
  	return __dev_alloc_pages(gfp_mask, 0);
  }
  
  #define dev_alloc_page LINUX_BACKPORT(dev_alloc_page)
  static inline struct page *dev_alloc_page(void)
  {
  	return __dev_alloc_page(GFP_ATOMIC);
  }
  #endif /* LINUX_VERSION_IS_LESS(3,19,0) */
  
  #if LINUX_VERSION_IS_LESS(3,19,0)
  #define skb_copy_datagram_msg LINUX_BACKPORT(skb_copy_datagram_msg)
  static inline int skb_copy_datagram_msg(const struct sk_buff *from, int offset,
  					struct msghdr *msg, int size)
  {
  	return skb_copy_datagram_iovec(from, offset, msg->msg_iov, size);
  }
  
  #define memcpy_from_msg LINUX_BACKPORT(memcpy_from_msg)
  static inline int memcpy_from_msg(void *data, struct msghdr *msg, int len)
  {
  	return memcpy_fromiovec(data, msg->msg_iov, len);
  }
  
  /**
   *	skb_put_padto - increase size and pad an skbuff up to a minimal size
   *	@skb: buffer to pad
   *	@len: minimal length
   *
   *	Pads up a buffer to ensure the trailing bytes exist and are
   *	blanked. If the buffer already contains sufficient data it
   *	is untouched. Otherwise it is extended. Returns zero on
   *	success. The skb is freed on error.
   */
  #define skb_put_padto LINUX_BACKPORT(skb_put_padto)
  static inline int skb_put_padto(struct sk_buff *skb, unsigned int len)
  {
  	unsigned int size = skb->len;
  
  	if (unlikely(size < len)) {
  		len -= size;
  		if (skb_pad(skb, len))
  			return -ENOMEM;
  		__skb_put(skb, len);
  	}
  	return 0;
  }
  
  #define skb_ensure_writable LINUX_BACKPORT(skb_ensure_writable)
  int skb_ensure_writable(struct sk_buff *skb, int write_len);
  
  #endif /* LINUX_VERSION_IS_LESS(3,19,0) */
  
  #if LINUX_VERSION_IS_LESS(4,2,0)
  static inline void skb_free_frag(void *data)
  {
  	put_page(virt_to_head_page(data));
  }
  
  #if LINUX_VERSION_IS_LESS(3,3,0)
  
  static inline u32 skb_get_hash_perturb(struct sk_buff *skb, u32 key)
  {
  	return 0;
  }
  
  #else
  #include <net/flow_keys.h>
  #include <linux/jhash.h>
  
  static inline u32 skb_get_hash_perturb(struct sk_buff *skb, u32 key)
  {
  	struct flow_keys keys;
  
  	skb_flow_dissect(skb, &keys);
  	return jhash_3words((__force u32)keys.dst,
  			    (__force u32)keys.src ^ keys.ip_proto,
  			    (__force u32)keys.ports, key);
  }
  #endif /* LINUX_VERSION_IS_LESS(3,3,0) */
  #endif /* LINUX_VERSION_IS_LESS(4,2,0) */
  
  #if LINUX_VERSION_IS_LESS(4,13,0)
  static inline void *backport_skb_put(struct sk_buff *skb, unsigned int len)
  {
  	return skb_put(skb, len);
  }
  #define skb_put LINUX_BACKPORT(skb_put)
  
  static inline void *backport_skb_push(struct sk_buff *skb, unsigned int len)
  {
  	return skb_push(skb, len);
  }
  #define skb_push LINUX_BACKPORT(skb_push)
  
  static inline void *backport___skb_push(struct sk_buff *skb, unsigned int len)
  {
  	return __skb_push(skb, len);
  }
  #define __skb_push LINUX_BACKPORT(__skb_push)
  
  static inline void *skb_put_zero(struct sk_buff *skb, unsigned int len)
  {
  	void *tmp = skb_put(skb, len);
  
  	memset(tmp, 0, len);
  
  	return tmp;
  }
  
  static inline void *skb_put_data(struct sk_buff *skb, const void *data,
  				 unsigned int len)
  {
  	void *tmp = skb_put(skb, len);
  
  	memcpy(tmp, data, len);
  
  	return tmp;
  }
  
  static inline void skb_put_u8(struct sk_buff *skb, u8 val)
  {
  	*(u8 *)skb_put(skb, 1) = val;
  }
  #endif
  
  #if LINUX_VERSION_IS_LESS(4,20,0)
  static inline struct sk_buff *__skb_peek(const struct sk_buff_head *list_)
  {
  	return list_->next;
  }
  #endif
  
  #endif /* __BACKPORT_SKBUFF_H */
  