#ifndef _LINUX_LIST_NULLS_H
  #define _LINUX_LIST_NULLS_H

  #include <linux/poison.h>
  #include <linux/const.h>

  /*
   * Special version of lists, where end of list is not a NULL pointer,
   * but a 'nulls' marker, which can have many different values.
   * (up to 2^31 different values guaranteed on all platforms)
   *
   * In the standard hlist, termination of a list is the NULL pointer.
   * In this special 'nulls' variant, we use the fact that objects stored in
   * a list are aligned on a word (4 or 8 bytes alignment).
   * We therefore use the last significant bit of 'ptr' :
   * Set to 1 : This is a 'nulls' end-of-list marker (ptr >> 1)
   * Set to 0 : This is a pointer to some object (ptr)
   */
  
  struct hlist_nulls_head {
  	struct hlist_nulls_node *first;
  };
  
  struct hlist_nulls_node {
  	struct hlist_nulls_node *next, **pprev;
  };

  #define NULLS_MARKER(value) (1UL | (((long)value) << 1))

  #define INIT_HLIST_NULLS_HEAD(ptr, nulls) \

  	((ptr)->first = (struct hlist_nulls_node *) NULLS_MARKER(nulls))

  
  #define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
  /**
   * ptr_is_a_nulls - Test if a ptr is a nulls
   * @ptr: ptr to be tested
   *
   */
  static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
  {
  	return ((unsigned long)ptr & 1);
  }
  
  /**
   * get_nulls_value - Get the 'nulls' value of the end of chain
   * @ptr: end of chain
   *
   * Should be called only if is_a_nulls(ptr);
   */
  static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
  {
  	return ((unsigned long)ptr) >> 1;
  }
  
  static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
  {
  	return !h->pprev;
  }
  
  static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
  {
  	return is_a_nulls(h->first);
  }

  static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
  					struct hlist_nulls_head *h)
  {
  	struct hlist_nulls_node *first = h->first;
  
  	n->next = first;
  	n->pprev = &h->first;
  	h->first = n;
  	if (!is_a_nulls(first))
  		first->pprev = &n->next;
  }

  static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
  {
  	struct hlist_nulls_node *next = n->next;
  	struct hlist_nulls_node **pprev = n->pprev;

  
  	WRITE_ONCE(*pprev, next);

  	if (!is_a_nulls(next))
  		next->pprev = pprev;
  }

  static inline void hlist_nulls_del(struct hlist_nulls_node *n)
  {
  	__hlist_nulls_del(n);
  	n->pprev = LIST_POISON2;
  }

  /**
   * hlist_nulls_for_each_entry	- iterate over list of given type
   * @tpos:	the type * to use as a loop cursor.
   * @pos:	the &struct hlist_node to use as a loop cursor.
   * @head:	the head for your list.
   * @member:	the name of the hlist_node within the struct.
   *
   */
  #define hlist_nulls_for_each_entry(tpos, pos, head, member)		       \
  	for (pos = (head)->first;					       \
  	     (!is_a_nulls(pos)) &&					       \
  		({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
  	     pos = pos->next)
  
  /**
   * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
   * @tpos:	the type * to use as a loop cursor.
   * @pos:	the &struct hlist_node to use as a loop cursor.
   * @member:	the name of the hlist_node within the struct.
   *
   */
  #define hlist_nulls_for_each_entry_from(tpos, pos, member)	\
  	for (; (!is_a_nulls(pos)) && 				\
  		({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
  	     pos = pos->next)
  
  #endif