/* SPDX-License-Identifier: GPL-2.0 */

/*
 * Copied from the Linux kernel source tree, version 2.6.13.
 *
 * Licensed under the GPL v2 as per the whole kernel source tree.
 *
 */

/** \file list.h doubly linked list implementation */

#include <stddef.h> /* offsetof */

/** get the struct this entry is embedded in */
#define container_of(ptr, type, member) ({                      \
	const typeof( ((type *)0)->member ) *__mptr = (ptr);    \
	(type *)( (char *)__mptr - offsetof(type,member) );})

/**
 * Non-NULL pointers that will result in page faults under normal
 * circumstances, used to verify that nobody uses non-initialized list entries.
 * Used for poisoning the \a next pointer of struct list_head.
 */
#define LIST_POISON1  ((void *) 0x00100100)
/** Non-null pointer, used for poisoning the \a prev pointer of struct
 * list_head
 */
#define LIST_POISON2  ((void *) 0x00200200)

/** Simple doubly linked list implementation. */
struct list_head {
	/** pointer to the next list entry */
	struct list_head *next;
	/** pointer to the previous list entry */
	struct list_head *prev;
};

/** Define an initialized list head. */
#define INITIALIZED_LIST_HEAD(name) struct list_head name = { &(name), &(name) }


/** must be called before using any other list functions */
#define INIT_LIST_HEAD(ptr) do { \
	(ptr)->next = (ptr); (ptr)->prev = (ptr); \
} while (0)


/*
 * 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.
 */


/*
 * 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;
	prev->next = new;
}

/**
 * add a new entry
 *
 * \param new new entry to be added
 * \param 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);
}

/**
 * add a new entry
 *
 * \param new new entry to be added
 * \param 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;
	prev->next = next;
}

/**
 * Delete entry from list.
 *
 * \param 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->prev, entry->next);
	entry->next = LIST_POISON1;
	entry->prev = LIST_POISON2;
}

/**
 * delete from one list and add as another's head
 *
 * \param list: the entry to move
 * \param head: the head that will precede our entry
 */
static inline void list_move(struct list_head *list, struct list_head *head)
{
        __list_del(list->prev, list->next);
        _list_add(list, head);
}

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

/**
 * get the struct for this entry
 *
 * \param ptr the &struct list_head pointer.
 * \param type the type of the struct this is embedded in.
 * \param member the name of the list_struct within the struct.
 */
#define list_entry(ptr, type, member) \
	container_of(ptr, type, member)

/**
 * iterate over list of given type
 *
 * \param pos the type * to use as a loop counter.
 * \param head the head for your list.
 * \param member the name of the list_struct within the struct.
 */
#define list_for_each_entry(pos, head, member)				\
	for (pos = list_entry((head)->next, typeof(*pos), member);	\
	     &pos->member != (head); 	\
	     pos = list_entry(pos->member.next, typeof(*pos), member))

/**
 * iterate over list of given type safe against removal of list entry
 *
 * \param pos the type * to use as a loop counter.
 * \param n another type * to use as temporary storage
 * \param head the head for your list.
 * \param member the name of the list_struct within the struct.
 */
#define list_for_each_entry_safe(pos, n, head, member)			\
	for (pos = list_entry((head)->next, typeof(*pos), member),	\
		n = list_entry(pos->member.next, typeof(*pos), member);	\
	     &pos->member != (head); 					\
	     pos = n, n = list_entry(n->member.next, typeof(*n), member))
/**
 * iterate backwards over list of given type safe against removal of list entry
 * \param pos the type * to use as a loop counter.
 * \param n another type * to use as temporary storage
 * \param head the head for your list.
 * \param member the name of the list_struct within the struct.
 */
#define list_for_each_entry_safe_reverse(pos, n, head, member)		\
	for (pos = list_entry((head)->prev, typeof(*pos), member),	\
		n = list_entry(pos->member.prev, typeof(*pos), member);	\
	     &pos->member != (head); 					\
	     pos = n, n = list_entry(n->member.prev, typeof(*n), member))

/**
 * Get the first element from a list
 * \param ptr the list head to take the element from.
 * \param type The type of the struct this is embedded in.
 * \param member The name of the list_struct 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)

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