#ifndef LLIST_H
  #define LLIST_H
  /*
   * Lock-less NULL terminated single linked list
   *
   * If there are multiple producers and multiple consumers, llist_add
   * can be used in producers and llist_del_all can be used in
   * consumers.  They can work simultaneously without lock.  But
   * llist_del_first can not be used here.  Because llist_del_first
   * depends on list->first->next does not changed if list->first is not
   * changed during its operation, but llist_del_first, llist_add,
   * llist_add (or llist_del_all, llist_add, llist_add) sequence in
   * another consumer may violate that.
   *
   * If there are multiple producers and one consumer, llist_add can be
   * used in producers and llist_del_all or llist_del_first can be used
   * in the consumer.
   *
   * This can be summarized as follow:
   *
   *           |   add    | del_first |  del_all
   * add       |    -     |     -     |     -
   * del_first |          |     L     |     L
   * del_all   |          |           |     -
   *
   * Where "-" stands for no lock is needed, while "L" stands for lock
   * is needed.
   *
   * The list entries deleted via llist_del_all can be traversed with
   * traversing function such as llist_for_each etc.  But the list
   * entries can not be traversed safely before deleted from the list.
   * The order of deleted entries is from the newest to the oldest added
   * one.  If you want to traverse from the oldest to the newest, you
   * must reverse the order by yourself before traversing.
   *
   * The basic atomic operation of this list is cmpxchg on long.  On
   * architectures that don't have NMI-safe cmpxchg implementation, the
   * list can NOT be used in NMI handler.  So code uses the list in NMI
   * handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
   */
  
  struct llist_head {
  	struct llist_node *first;
  };
  
  struct llist_node {
  	struct llist_node *next;
  };
  
  #define LLIST_HEAD_INIT(name)	{ NULL }
  #define LLIST_HEAD(name)	struct llist_head name = LLIST_HEAD_INIT(name)
  
  /**
   * init_llist_head - initialize lock-less list head
   * @head:	the head for your lock-less list
   */
  static inline void init_llist_head(struct llist_head *list)
  {
  	list->first = NULL;
  }
  
  /**
   * llist_entry - get the struct of this entry
   * @ptr:	the &struct llist_node pointer.
   * @type:	the type of the struct this is embedded in.
   * @member:	the name of the llist_node within the struct.
   */
  #define llist_entry(ptr, type, member)		\
  	container_of(ptr, type, member)
  
  /**
   * llist_for_each - iterate over some deleted entries of a lock-less list
   * @pos:	the &struct llist_node to use as a loop cursor
   * @node:	the first entry of deleted list entries
   *
   * In general, some entries of the lock-less list can be traversed
   * safely only after being deleted from list, so start with an entry
   * instead of list head.
   *
   * If being used on entries deleted from lock-less list directly, the
   * traverse order is from the newest to the oldest added entry.  If
   * you want to traverse from the oldest to the newest, you must
   * reverse the order by yourself before traversing.
   */
  #define llist_for_each(pos, node)			\
  	for ((pos) = (node); pos; (pos) = (pos)->next)
  
  /**
   * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type
   * @pos:	the type * to use as a loop cursor.
   * @node:	the fist entry of deleted list entries.
   * @member:	the name of the llist_node with the struct.
   *
   * In general, some entries of the lock-less list can be traversed
   * safely only after being removed from list, so start with an entry
   * instead of list head.
   *
   * If being used on entries deleted from lock-less list directly, the
   * traverse order is from the newest to the oldest added entry.  If
   * you want to traverse from the oldest to the newest, you must
   * reverse the order by yourself before traversing.
   */
  #define llist_for_each_entry(pos, node, member)				\
  	for ((pos) = llist_entry((node), typeof(*(pos)), member);	\
  	     &(pos)->member != NULL;					\
  	     (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
  
  /**
   * llist_empty - tests whether a lock-less list is empty
   * @head:	the list to test
   *
   * Not guaranteed to be accurate or up to date.  Just a quick way to
   * test whether the list is empty without deleting something from the
   * list.
   */
  static inline int llist_empty(const struct llist_head *head)
  {
  	return ACCESS_ONCE(head->first) == NULL;
  }
  
  void llist_add(struct llist_node *new, struct llist_head *head);
  void llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
  		     struct llist_head *head);
  struct llist_node *llist_del_first(struct llist_head *head);
  struct llist_node *llist_del_all(struct llist_head *head);
  #endif /* LLIST_H */