/******************************************************************************
 * This file is part of linux project
 * From https://github.com/torvalds/linux/include/list.h
 *
 * 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.
 *
 * Note that the GPL places important restrictions on "derived works", yet
 * it does not provide a detailed definition of that term.  To avoid      
 * misunderstandings, we consider an application to constitute a          
 * "derivative work" for the purpose of this license if it does any of the
 * following:                                                             
 * 1. Integrates source code from Skylark project
 * 2. Integrates/includes/aggregates Skylark into a proprietary executable
 *    installer, such as those produced by InstallShield.
 * 3. Links to a library or executes a program that does any of the above.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * Here is a recipe to cook list.h for user space program
 *
 * 1. copy list.h from linux/include/list.h
 * 2. remove
 *     - #ifdef __KERNE__ and its #endif
 *     - all #include line
 *     - prefetch() and rcu related functions
 * 3. add macro CONTAINER_OF
 *
 * - hua.andy@gmail.com
 */

#ifndef _LINUX_LIST_H
#define _LINUX_LIST_H

#include <stdbool.h>
/* for offsetof defined */
#include <stddef.h>  

#if defined(__GNUC__)
#define CONTAINER_OF(ptr, type, member)                                                            \
    ({                                                                                             \
        const typeof(((type *) 0)->member) *__mptr = (const typeof(((type *) 0)->member) *) (ptr); \
        (type *) ((char *) __mptr - offsetof(type, member));                                       \
    })
#else
#define CONTAINER_OF(ptr, type, member) ((type *) ((char *) (ptr) - offsetof(type, member)))
#endif

/*
 * Simple doubly linked list implementation.
 *
 * Some of the internal functions ("__xxx") are useful when
 * manipulating whole lists rather than single entries, as
 * sometimes we already know the next/prev entries and we can
 * generate better code by using them directly rather than
 * using the generic single-entry routines.
 */

struct list_head
{
    struct list_head *next, *prev;
};

/*
 * Double linked lists with a single pointer list head.
 * Mostly useful for hash tables where the two pointer list head is
 * too wasteful.
 * You lose the ability to access the tail in O(1).
 */

struct hlist_head
{
    struct hlist_node *first;
};

struct hlist_node
{
    struct hlist_node *next, **pprev;
};

#define WRITE_ONCE(_var_, _val_) (_var_) = (_val_)
#define READ_ONCE(_var_) (_var_)

/* 断开节点后指向不可访问地址 */
#define LIST_POISON1 ((void *) 0x100)
#define LIST_POISON2 ((void *) 0x122)

#define LIST_HEAD_INIT(name) \
    {                        \
        &(name), &(name)     \
    }

#define LIST_HEAD(name) struct list_head name = LIST_HEAD_INIT(name)

/**
 * list_entry - get the struct for this entry
 * @ptr:    the &struct list_head pointer.
 * @type:    the type of the struct this is embedded in.
 * @member:    the name of the list_head within the struct.
 */
#define list_entry(ptr, type, member) CONTAINER_OF(ptr, type, member)

/**
 * list_first_entry - get the first element from a list
 * @ptr:    the list head to take the element from.
 * @type:    the type of the struct this is embedded in.
 * @member:    the name of the list_head within the struct.
 *
 * Note, that list is expected to be not empty.
 */
#define list_first_entry(ptr, type, member) list_entry((ptr)->next, type, member)

/**
 * list_last_entry - get the last element from a list
 * @ptr:    the list head to take the element from.
 * @type:    the type of the struct this is embedded in.
 * @member:    the name of the list_head within the struct.
 *
 * Note, that list is expected to be not empty.
 */
#define list_last_entry(ptr, type, member) list_entry((ptr)->prev, type, member)

/**
 * list_first_entry_or_null - get the first element from a list
 * @ptr:    the list head to take the element from.
 * @type:    the type of the struct this is embedded in.
 * @member:    the name of the list_head within the struct.
 *
 * Note that if the list is empty, it returns NULL.
 */
#define list_first_entry_or_null(ptr, type, member) (!list_empty(ptr) ? list_first_entry(ptr, type, member) : NULL)

/**
 * list_next_entry - get the next element in list
 * @p_node:    the type * to cursor
 * @member:    the name of the list_head within the struct.
 */
#define list_next_entry(p_node, type, member) list_entry((p_node)->member.next, type, member)

/**
 * list_prev_entry - get the prev element in list
 * @p_node:    the type * to cursor
 * @member:    the name of the list_head within the struct.
 */
#define list_prev_entry(p_node, type, member) list_entry((p_node)->member.prev, type, member)

/**
 * list_for_each    -    iterate over a list
 * @p_node:    the &struct list_head to use as a loop cursor.
 * @head:    the head for your list.
 */
#define list_for_each(p_node, head) for (p_node = (head)->next; p_node != (head); p_node = p_node->next)

/**
 * list_for_each_prev    -    iterate over a list backwards
 * @p_node:    the &struct list_head to use as a loop cursor.
 * @head:    the head for your list.
 */
#define list_for_each_prev(p_node, head) for (p_node = (head)->prev; p_node != (head); p_node = p_node->prev)

/**
 * list_for_each_safe - iterate over a list safe against removal of list entry
 * @p_node:    the &struct list_head to use as a loop cursor.
 * @n:        another &struct list_head to use as temporary storage
 * @head:    the head for your list.
 */
#define list_for_each_safe(p_node, n, head) \
    for (p_node = (head)->next, n = p_node->next; p_node != (head); p_node = n, n = p_node->next)

/**
 * list_for_each_prev_safe - iterate over a list backwards safe against removal of list entry
 * @p_node:    the &struct list_head to use as a loop cursor.
 * @n:        another &struct list_head to use as temporary storage
 * @head:    the head for your list.
 */
#define list_for_each_prev_safe(p_node, n, head) \
    for (p_node = (head)->prev, n = p_node->prev; p_node != (head); p_node = n, n = p_node->prev)

/**
 * list_for_each_entry    -    iterate over list of given type
 * @p_node:    the type * to use as a loop cursor.
 * @head:    the head for your list.
 * @member:    the name of the list_head within the struct.
 */
#define list_for_each_entry(p_node, head, type, member) \
    for (p_node = list_first_entry(head, type, member); &p_node->member != (head); p_node = list_next_entry(p_node, type, member))

/**
 * list_for_each_entry_reverse - iterate backwards over list of given type.
 * @p_node:    the type * to use as a loop cursor.
 * @head:    the head for your list.
 * @member:    the name of the list_head within the struct.
 */
#define list_for_each_entry_reverse(p_node, head, member) \
    for (p_node = list_last_entry(head, typeof(*p_node), member); &p_node->member != (head); p_node = list_prev_entry(p_node, member))

/**
 * list_prepare_entry - prepare a p_node entry for use in list_for_each_entry_continue()
 * @p_node:    the type * to use as a start point
 * @head:    the head of the list
 * @member:    the name of the list_head within the struct.
 *
 * Prepares a p_node entry for use as a start point in list_for_each_entry_continue().
 */
#define list_prepare_entry(p_node, head, member) ((p_node) ?: list_entry(head, typeof(*p_node), member))

/**
 * list_for_each_entry_continue - continue iteration over list of given type
 * @p_node:    the type * to use as a loop cursor.
 * @head:    the head for your list.
 * @member:    the name of the list_head within the struct.
 *
 * Continue to iterate over list of given type, continuing after
 * the current position.
 */
#define list_for_each_entry_continue(p_node, head, member) \
    for (p_node = list_next_entry(p_node, member); &p_node->member != (head); p_node = list_next_entry(p_node, member))

/**
 * list_for_each_entry_continue_reverse - iterate backwards from the given point
 * @p_node:    the type * to use as a loop cursor.
 * @head:    the head for your list.
 * @member:    the name of the list_head within the struct.
 *
 * Start to iterate over list of given type backwards, continuing after
 * the current position.
 */
#define list_for_each_entry_continue_reverse(p_node, head, member) \
    for (p_node = list_prev_entry(p_node, member); &p_node->member != (head); p_node = list_prev_entry(p_node, member))

/**
 * list_for_each_entry_from - iterate over list of given type from the current point
 * @p_node:    the type * to use as a loop cursor.
 * @head:    the head for your list.
 * @member:    the name of the list_head within the struct.
 *
 * Iterate over list of given type, continuing from current position.
 */
#define list_for_each_entry_from(p_node, head, member) \
    for (; &p_node->member != (head); p_node = list_next_entry(p_node, member))

/**
 * list_for_each_entry_safe - iterate over list of given type safe against removal of list entry
 * @p_node:    the type * to use as a loop cursor.
 * @n:        another type * to use as temporary storage
 * @head:    the head for your list.
 * @member:    the name of the list_head within the struct.
 */
#define list_for_each_entry_safe(p_node, n, head, type, member)                                                               \
    for (p_node = list_first_entry(head, type, member), n = list_next_entry(p_node, type, member); &p_node->member != (head); \
         p_node = n, n = list_next_entry(n, type, member))

/**
 * list_for_each_entry_safe_continue - continue list iteration safe against removal
 * @p_node:    the type * to use as a loop cursor.
 * @n:        another type * to use as temporary storage
 * @head:    the head for your list.
 * @member:    the name of the list_head within the struct.
 *
 * Iterate over list of given type, continuing after current point,
 * safe against removal of list entry.
 */
#define list_for_each_entry_safe_continue(p_node, n, head, member)                                                 \
    for (p_node = list_next_entry(p_node, member), n = list_next_entry(p_node, member); &p_node->member != (head); \
         p_node = n, n = list_next_entry(n, member))

/**
 * list_for_each_entry_safe_from - iterate over list from current point safe against removal
 * @p_node:    the type * to use as a loop cursor.
 * @n:        another type * to use as temporary storage
 * @head:    the head for your list.
 * @member:    the name of the list_head within the struct.
 *
 * Iterate over list of given type from current point, safe against
 * removal of list entry.
 */
#define list_for_each_entry_safe_from(p_node, n, head, member) \
    for (n = list_next_entry(p_node, member); &p_node->member != (head); p_node = n, n = list_next_entry(n, member))

/**
 * list_for_each_entry_safe_reverse - iterate backwards over list safe against removal
 * @p_node:    the type * to use as a loop cursor.
 * @n:        another type * to use as temporary storage
 * @head:    the head for your list.
 * @member:    the name of the list_head within the struct.
 *
 * Iterate backwards over list of given type, safe against removal
 * of list entry.
 */
#define list_for_each_entry_safe_reverse(p_node, n, head, type, member)                                                      \
    for (p_node = list_last_entry(head, type, member), n = list_prev_entry(p_node, type, member); &p_node->member != (head); \
         p_node = n, n = list_prev_entry(n, type, member))

/**
 * list_safe_reset_next - reset a stale list_for_each_entry_safe loop
 * @p_node:    the loop cursor used in the list_for_each_entry_safe loop
 * @n:        temporary storage used in list_for_each_entry_safe
 * @member:    the name of the list_head within the struct.
 *
 * list_safe_reset_next is not safe to use in general if the list may be
 * modified concurrently (eg. the lock is dropped in the loop body). An
 * exception to this is if the cursor element (p_node) is pinned in the list,
 * and list_safe_reset_next is called after re-taking the lock and before
 * completing the current iteration of the loop body.
 */
#define list_safe_reset_next(p_node, n, member) n = list_next_entry(p_node, member)

#define list_for_not_found(p_node, head, type, member) (&(p_node->member) == head)

#define HLIST_HEAD_INIT \
    {                   \
        .first = NULL   \
    }
#define HLIST_HEAD(name) struct hlist_head name = { .first = NULL }
#define INIT_HLIST_HEAD(ptr) ((ptr)->first = NULL)

#define hlist_entry(ptr, type, member) container_of(ptr, type, member)

#define hlist_for_each(pos, head) for (pos = (head)->first; pos; pos = pos->next)

#define hlist_for_each_safe(pos, n, head)                     \
    for (pos = (head)->first; pos && ({ n = pos->next; 1; }); \
         pos = n)

#define hlist_entry_safe(ptr, type, member)                  \
    ({                                                       \
        typeof(ptr) ____ptr = (ptr);                         \
        ____ptr ? hlist_entry(____ptr, type, member) : NULL; \
    })

/**
 * hlist_for_each_entry    - iterate over list of given type
 * @pos:    the type * to use as a loop cursor.
 * @head:    the head for your list.
 * @member:    the name of the hlist_node within the struct.
 */
#define hlist_for_each_entry(pos, head, member)                              \
    for (pos = hlist_entry_safe((head)->first, typeof(*(pos)), member); pos; \
         pos = hlist_entry_safe((pos)->member.next, typeof(*(pos)), member))

/**
 * hlist_for_each_entry_continue - iterate over a hlist continuing after current point
 * @pos:    the type * to use as a loop cursor.
 * @member:    the name of the hlist_node within the struct.
 */
#define hlist_for_each_entry_continue(pos, member)                                \
    for (pos = hlist_entry_safe((pos)->member.next, typeof(*(pos)), member); pos; \
         pos = hlist_entry_safe((pos)->member.next, typeof(*(pos)), member))

/**
 * hlist_for_each_entry_from - iterate over a hlist continuing from current point
 * @pos:    the type * to use as a loop cursor.
 * @member:    the name of the hlist_node within the struct.
 */
#define hlist_for_each_entry_from(pos, member) for (; pos; pos = hlist_entry_safe((pos)->member.next, typeof(*(pos)), member))

/**
 * hlist_for_each_entry_safe - iterate over list of given type safe against removal of list entry
 * @pos:    the type * to use as a loop cursor.
 * @n:        a &struct hlist_node to use as temporary storage
 * @head:    the head for your list.
 * @member:    the name of the hlist_node within the struct.
 */
#define hlist_for_each_entry_safe(pos, n, head, member)              \
    for (pos = hlist_entry_safe((head)->first, typeof(*pos), member);\
         pos && ({ n = pos->member.next; 1; });                         \
         pos = hlist_entry_safe(n, typeof(*pos), member))

#ifdef __cplusplus
extern "C"
{
#endif

static inline void INIT_LIST_HEAD(struct list_head *list)
{
    WRITE_ONCE(list->next, list);
    list->prev = list;
}

/*
 * Insert a _new entry between two known consecutive entries.
 *
 * This is only for internal list manipulation where we know
 * the prev/next entries already!
 */
static inline void __list_add(struct list_head *_new, struct list_head *prev, struct list_head *next)
{
    next->prev = _new;
    _new->next = next;
    _new->prev = prev;
    WRITE_ONCE(prev->next, _new);
}

/**
 * list_add - add a _new entry
 * @_new: _new entry to be added
 * @head: list head to add it after
 *
 * Insert a _new entry after the specified head.
 * This is good for implementing stacks.
 */
static inline void list_add(struct list_head *_new, struct list_head *head) { __list_add(_new, head, head->next); }

/**
 * list_add_tail - add a _new entry
 * @_new: _new entry to be added
 * @head: list head to add it before
 *
 * Insert a _new entry before the specified head.
 * This is useful for implementing queues.
 */
static inline void list_add_tail(struct list_head *_new, struct list_head *head) { __list_add(_new, head->prev, head); }

/*
 * Delete a list entry by making the prev/next entries
 * point to each other.
 *
 * This is only for internal list manipulation where we know
 * the prev/next entries already!
 */
static inline void __list_del(struct list_head *prev, struct list_head *next)
{
    next->prev = prev;
    WRITE_ONCE(prev->next, next);
}

/*
 * Delete a list entry and clear the 'prev' pointer.
 *
 * This is a special-purpose list clearing method used in the networking code
 * for lists allocated as per-cpu, where we don't want to incur the extra
 * WRITE_ONCE() overhead of a regular list_del_init(). The code that uses this
 * needs to check the node 'prev' pointer instead of calling list_empty().
 */
static inline void __list_del_clearprev(struct list_head *entry)
{
    __list_del(entry->prev, entry->next);
    entry->prev = NULL;
}

static inline void __list_del_entry(struct list_head *entry) { __list_del(entry->prev, entry->next); }

/**
 * list_del - deletes entry from list.
 * @entry: the element to delete from the list.
 * Note: list_empty() on entry does not return true after this, the entry is
 * in an undefined state.
 */
static inline void list_del(struct list_head *entry)
{
    __list_del_entry(entry);
    entry->next = (struct list_head *) LIST_POISON1;
    entry->prev = (struct list_head *) LIST_POISON2;
}

/**
 * list_replace - replace old entry by _new one
 * @old : the element to be replaced
 * @_new : the _new element to insert
 *
 * If @old was empty, it will be overwritten.
 */
static inline void list_replace(struct list_head *old, struct list_head *_new)
{
    _new->next = old->next;
    _new->next->prev = _new;
    _new->prev = old->prev;
    _new->prev->next = _new;
}

/**
 * list_replace_init - replace old entry by _new one and initialize the old one
 * @old : the element to be replaced
 * @_new : the _new element to insert
 *
 * If @old was empty, it will be overwritten.
 */
static inline void list_replace_init(struct list_head *old, struct list_head *_new)
{
    list_replace(old, _new);
    INIT_LIST_HEAD(old);
}

/**
 * list_swap - replace entry1 with entry2 and re-add entry1 at entry2's position
 * @entry1: the location to place entry2
 * @entry2: the location to place entry1
 */
static inline void list_swap(struct list_head *entry1, struct list_head *entry2)
{
    struct list_head *pos = entry2->prev;

    list_del(entry2);
    list_replace(entry1, entry2);
    if (pos == entry1) pos = entry2;
    list_add(entry1, pos);
}

/**
 * list_del_init - deletes entry from list and reinitialize it.
 * @entry: the element to delete from the list.
 */
static inline void list_del_init(struct list_head *entry)
{
    __list_del_entry(entry);
    INIT_LIST_HEAD(entry);
}

/**
 * list_move - delete from one list and add as another's head
 * @list: the entry to move
 * @head: the head that will precede our entry
 */
static inline void list_move(struct list_head *list, struct list_head *head)
{
    __list_del_entry(list);
    list_add(list, head);
}

/**
 * list_move_tail - delete from one list and add as another's tail
 * @list: the entry to move
 * @head: the head that will follow our entry
 */
static inline void list_move_tail(struct list_head *list, struct list_head *head)
{
    __list_del_entry(list);
    list_add_tail(list, head);
}

/**
 * list_bulk_move_tail - move a subsection of a list to its tail
 * @head: the head that will follow our entry
 * @first: first entry to move
 * @last: last entry to move, can be the same as first
 *
 * Move all entries between @first and including @last before @head.
 * All three entries must belong to the same linked list.
 */
static inline void list_bulk_move_tail(struct list_head *head, struct list_head *first, struct list_head *last)
{
    first->prev->next = last->next;
    last->next->prev = first->prev;

    head->prev->next = first;
    first->prev = head->prev;

    last->next = head;
    head->prev = last;
}

/**
 * list_is_first -- tests whether @list is the first entry in list @head
 * @list: the entry to test
 * @head: the head of the list
 */
static inline int list_is_first(const struct list_head *list, const struct list_head *head) { return list->prev == head; }

/**
 * list_is_last - tests whether @list is the last entry in list @head
 * @list: the entry to test
 * @head: the head of the list
 */
static inline int list_is_last(const struct list_head *list, const struct list_head *head) { return list->next == head; }

/**
 * list_empty - tests whether a list is empty
 * @head: the list to test.
 */
static inline int list_empty(const struct list_head *head) { return READ_ONCE(head->next) == head; }

/**
 * list_rotate_left - rotate the list to the left
 * @head: the head of the list
 */
static inline void list_rotate_left(struct list_head *head)
{
    struct list_head *first;

    if (!list_empty(head))
    {
        first = head->next;
        list_move_tail(first, head);
    }
}

/**
 * list_rotate_to_front() - Rotate list to specific item.
 * @list: The desired _new front of the list.
 * @head: The head of the list.
 *
 * Rotates list so that @list becomes the _new front of the list.
 */
static inline void list_rotate_to_front(struct list_head *list, struct list_head *head)
{
    /*
     * Deletes the list head from the list denoted by @head and
     * places it as the tail of @list, this effectively rotates the
     * list so that @list is at the front.
     */
    list_move_tail(head, list);
}

/**
 * list_is_singular - tests whether a list has just one entry.
 * @head: the list to test.
 */
static inline int list_is_singular(const struct list_head *head) { return !list_empty(head) && (head->next == head->prev); }

static inline void __list_cut_position(struct list_head *list, struct list_head *head, struct list_head *entry)
{
    struct list_head *new_first = entry->next;
    list->next = head->next;
    list->next->prev = list;
    list->prev = entry;
    entry->next = list;
    head->next = new_first;
    new_first->prev = head;
}

/**
 * list_cut_position - cut a list into two
 * @list: a _new list to add all removed entries
 * @head: a list with entries
 * @entry: an entry within head, could be the head itself
 *    and if so we won't cut the list
 *
 * This helper moves the initial part of @head, up to and
 * including @entry, from @head to @list. You should
 * pass on @entry an element you know is on @head. @list
 * should be an empty list or a list you do not care about
 * losing its data.
 *
 */
static inline void list_cut_position(struct list_head *list, struct list_head *head, struct list_head *entry)
{
    if (list_empty(head)) return;
    if (list_is_singular(head) && (head->next != entry && head != entry)) return;
    if (entry == head)
        INIT_LIST_HEAD(list);
    else
        __list_cut_position(list, head, entry);
}

/**
 * list_cut_before - cut a list into two, before given entry
 * @list: a _new list to add all removed entries
 * @head: a list with entries
 * @entry: an entry within head, could be the head itself
 *
 * This helper moves the initial part of @head, up to but
 * excluding @entry, from @head to @list.  You should pass
 * in @entry an element you know is on @head.  @list should
 * be an empty list or a list you do not care about losing
 * its data.
 * If @entry == @head, all entries on @head are moved to
 * @list.
 */
static inline void list_cut_before(struct list_head *list, struct list_head *head, struct list_head *entry)
{
    if (head->next == entry)
    {
        INIT_LIST_HEAD(list);
        return;
    }
    list->next = head->next;
    list->next->prev = list;
    list->prev = entry->prev;
    list->prev->next = list;
    head->next = entry;
    entry->prev = head;
}

static inline void __list_splice(const struct list_head *list, struct list_head *prev, struct list_head *next)
{
    struct list_head *first = list->next;
    struct list_head *last = list->prev;

    first->prev = prev;
    prev->next = first;

    last->next = next;
    next->prev = last;
}

/**
 * list_splice - join two lists, this is designed for stacks
 * @list: the _new list to add.
 * @head: the place to add it in the first list.
 */
static inline void list_splice(const struct list_head *list, struct list_head *head)
{
    if (!list_empty(list)) __list_splice(list, head, head->next);
}

/**
 * list_splice_tail - join two lists, each list being a queue
 * @list: the _new list to add.
 * @head: the place to add it in the first list.
 */
static inline void list_splice_tail(struct list_head *list, struct list_head *head)
{
    if (!list_empty(list)) __list_splice(list, head->prev, head);
}

/**
 * list_splice_init - join two lists and reinitialise the emptied list.
 * @list: the _new list to add.
 * @head: the place to add it in the first list.
 *
 * The list at @list is reinitialised
 */
static inline void list_splice_init(struct list_head *list, struct list_head *head)
{
    if (!list_empty(list))
    {
        __list_splice(list, head, head->next);
        INIT_LIST_HEAD(list);
    }
}

/**
 * list_splice_tail_init - join two lists and reinitialise the emptied list
 * @list: the _new list to add.
 * @head: the place to add it in the first list.
 *
 * Each of the lists is a queue.
 * The list at @list is reinitialised
 */
static inline void list_splice_tail_init(struct list_head *list, struct list_head *head)
{
    if (!list_empty(list))
    {
        __list_splice(list, head->prev, head);
        INIT_LIST_HEAD(list);
    }
}

static inline void INIT_HLIST_NODE(struct hlist_node *h)
{
    h->next = NULL;
    h->pprev = NULL;
}

/**
 * hlist_unhashed - Has node been removed from list and reinitialized?
 * @h: Node to be checked
 *
 * Not that not all removal functions will leave a node in unhashed
 * state.  For example, hlist_nulls_del_init_rcu() does leave the
 * node in unhashed state, but hlist_nulls_del() does not.
 */
static inline int hlist_unhashed(const struct hlist_node *h) { return !h->pprev; }

/**
 * hlist_unhashed_lockless - Version of hlist_unhashed for lockless use
 * @h: Node to be checked
 *
 * This variant of hlist_unhashed() must be used in lockless contexts
 * to avoid potential load-tearing.  The READ_ONCE() is paired with the
 * various WRITE_ONCE() in hlist helpers that are defined below.
 */
static inline int hlist_unhashed_lockless(const struct hlist_node *h) { return !READ_ONCE(h->pprev); }

/**
 * hlist_empty - Is the specified hlist_head structure an empty hlist?
 * @h: Structure to check.
 */
static inline int hlist_empty(const struct hlist_head *h) { return !READ_ONCE(h->first); }

static inline void __hlist_del(struct hlist_node *n)
{
    struct hlist_node *next = n->next;
    struct hlist_node **pprev = n->pprev;

    WRITE_ONCE(*pprev, next);
    if (next) WRITE_ONCE(next->pprev, pprev);
}

/**
 * hlist_del - Delete the specified hlist_node from its list
 * @n: Node to delete.
 *
 * Note that this function leaves the node in hashed state.  Use
 * hlist_del_init() or similar instead to unhash @n.
 */
static inline void hlist_del(struct hlist_node *n)
{
    __hlist_del(n);
    n->next = (struct hlist_node *) LIST_POISON1;
    n->pprev = (struct hlist_node **) LIST_POISON2;
}

/**
 * hlist_del_init - Delete the specified hlist_node from its list and initialize
 * @n: Node to delete.
 *
 * Note that this function leaves the node in unhashed state.
 */
static inline void hlist_del_init(struct hlist_node *n)
{
    if (!hlist_unhashed(n))
    {
        __hlist_del(n);
        INIT_HLIST_NODE(n);
    }
}

/**
 * hlist_add_head - add a _new entry at the beginning of the hlist
 * @n: _new entry to be added
 * @h: hlist head to add it after
 *
 * Insert a _new entry after the specified head.
 * This is good for implementing stacks.
 */
static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
{
    struct hlist_node *first = h->first;
    WRITE_ONCE(n->next, first);
    if (first) WRITE_ONCE(first->pprev, &n->next);
    WRITE_ONCE(h->first, n);
    WRITE_ONCE(n->pprev, &h->first);
}

/**
 * hlist_add_before - add a _new entry before the one specified
 * @n: _new entry to be added
 * @next: hlist node to add it before, which must be non-NULL
 */
static inline void hlist_add_before(struct hlist_node *n, struct hlist_node *next)
{
    WRITE_ONCE(n->pprev, next->pprev);
    WRITE_ONCE(n->next, next);
    WRITE_ONCE(next->pprev, &n->next);
    WRITE_ONCE(*(n->pprev), n);
}

/**
 * hlist_add_behing - add a _new entry after the one specified
 * @n: _new entry to be added
 * @prev: hlist node to add it after, which must be non-NULL
 */
static inline void hlist_add_behind(struct hlist_node *n, struct hlist_node *prev)
{
    WRITE_ONCE(n->next, prev->next);
    WRITE_ONCE(prev->next, n);
    WRITE_ONCE(n->pprev, &prev->next);

    if (n->next) WRITE_ONCE(n->next->pprev, &n->next);
}

/**
 * hlist_add_fake - create a fake hlist consisting of a single headless node
 * @n: Node to make a fake list out of
 *
 * This makes @n appear to be its own predecessor on a headless hlist.
 * The point of this is to allow things like hlist_del() to work correctly
 * in cases where there is no list.
 */
static inline void hlist_add_fake(struct hlist_node *n) { n->pprev = &n->next; }

/**
 * hlist_fake: Is this node a fake hlist?
 * @h: Node to check for being a self-referential fake hlist.
 */
static inline bool hlist_fake(struct hlist_node *h) { return h->pprev == &h->next; }

/**
 * hlist_is_singular_node - is node the only element of the specified hlist?
 * @n: Node to check for singularity.
 * @h: Header for potentially singular list.
 *
 * Check whether the node is the only node of the head without
 * accessing head, thus avoiding unnecessary cache misses.
 */
static inline bool hlist_is_singular_node(struct hlist_node *n, struct hlist_head *h)
{
    return !n->next && n->pprev == &h->first;
}

/**
 * hlist_move_list - Move an hlist
 * @old: hlist_head for old list.
 * @_new: hlist_head for _new list.
 *
 * Move a list from one list head to another. Fixup the pprev
 * reference of the first entry if it exists.
 */
static inline void hlist_move_list(struct hlist_head *old, struct hlist_head *_new)
{
    _new->first = old->first;
    if (_new->first) _new->first->pprev = &_new->first;
    old->first = NULL;
}

#ifdef __cplusplus
}
#endif

#endif
