path: root/lib/freebsd-queue.h

// SPDX-License-Identifier: BSD-3-Clause
/*-
 * Copyright (c) 1991, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 *	@(#)queue.h	8.5 (Berkeley) 8/20/94
 * $FreeBSD$
 */

#ifndef _SYS_QUEUE_H_
#define	_SYS_QUEUE_H_

#ifdef __cplusplus
extern "C" {
#endif

/*
 * This file defines four types of data structures: singly-linked lists,
 * singly-linked tail queues, lists and tail queues.
 *
 * A singly-linked list is headed by a single forward pointer. The elements
 * are singly linked for minimum space and pointer manipulation overhead at
 * the expense of O(n) removal for arbitrary elements. New elements can be
 * added to the list after an existing element or at the head of the list.
 * Elements being removed from the head of the list should use the explicit
 * macro for this purpose for optimum efficiency. A singly-linked list may
 * only be traversed in the forward direction.  Singly-linked lists are ideal
 * for applications with large datasets and few or no removals or for
 * implementing a LIFO queue.
 *
 * A singly-linked tail queue is headed by a pair of pointers, one to the
 * head of the list and the other to the tail of the list. The elements are
 * singly linked for minimum space and pointer manipulation overhead at the
 * expense of O(n) removal for arbitrary elements. New elements can be added
 * to the list after an existing element, at the head of the list, or at the
 * end of the list. Elements being removed from the head of the tail queue
 * should use the explicit macro for this purpose for optimum efficiency.
 * A singly-linked tail queue may only be traversed in the forward direction.
 * Singly-linked tail queues are ideal for applications with large datasets
 * and few or no removals or for implementing a FIFO queue.
 *
 * A list is headed by a single forward pointer (or an array of forward
 * pointers for a hash table header). The elements are doubly linked
 * so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before
 * or after an existing element or at the head of the list. A list
 * may only be traversed in the forward direction.
 *
 * A tail queue is headed by a pair of pointers, one to the head of the
 * list and the other to the tail of the list. The elements are doubly
 * linked so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before or
 * after an existing element, at the head of the list, or at the end of
 * the list. A tail queue may be traversed in either direction.
 *
 * For details on the use of these macros, see the queue(3) manual page.
 *
 *
 *				SLIST	LIST	STAILQ	TAILQ
 * _HEAD			+	+	+	+
 * _HEAD_INITIALIZER		+	+	+	+
 * _ENTRY			+	+	+	+
 * _INIT			+	+	+	+
 * _EMPTY			+	+	+	+
 * _FIRST			+	+	+	+
 * _NEXT			+	+	+	+
 * _PREV			-	-	-	+
 * _LAST			-	-	+	+
 * _FOREACH			+	+	+	+
 * _FOREACH_SAFE		+	+	+	+
 * _FOREACH_REVERSE		-	-	-	+
 * _FOREACH_REVERSE_SAFE	-	-	-	+
 * _INSERT_HEAD			+	+	+	+
 * _INSERT_BEFORE		-	+	-	+
 * _INSERT_AFTER		+	+	+	+
 * _INSERT_TAIL			-	-	+	+
 * _CONCAT			-	-	+	+
 * _REMOVE_AFTER		+	-	+	-
 * _REMOVE_HEAD			+	-	+	-
 * _REMOVE			+	+	+	+
 * _SWAP			+	+	+	+
 *
 */
#ifdef QUEUE_MACRO_DEBUG
/* Store the last 2 places the queue element or head was altered */
struct qm_trace {
	char *lastfile;
	int lastline;
	char *prevfile;
	int prevline;
};

#define	TRACEBUF	struct qm_trace trace;
#define	TRASHIT(x)	do {(x) = (void *)-1;} while (0)
#define	QMD_SAVELINK(name, link)	void **name = (void *)&(link)

#define QMD_TRACE_HEAD(head)                                                   \
	do {                                                                   \
		(head)->trace.prevline = (head)->trace.lastline;               \
		(head)->trace.prevfile = (head)->trace.lastfile;               \
		(head)->trace.lastline = __LINE__;                             \
		(head)->trace.lastfile = __FILE__;                             \
	} while (0)

#define QMD_TRACE_ELEM(elem)                                                   \
	do {                                                                   \
		(elem)->trace.prevline = (elem)->trace.lastline;               \
		(elem)->trace.prevfile = (elem)->trace.lastfile;               \
		(elem)->trace.lastline = __LINE__;                             \
		(elem)->trace.lastfile = __FILE__;                             \
	} while (0)

#else
#define	QMD_TRACE_ELEM(elem)
#define	QMD_TRACE_HEAD(head)
#define	QMD_SAVELINK(name, link)
#define	TRACEBUF
#define	TRASHIT(x)
#endif /* QUEUE_MACRO_DEBUG */

/*
 * Singly-linked List declarations.
 */
#define SLIST_HEAD(name, type)                                                 \
	struct name {                                                          \
		struct type *slh_first; /* first element */                    \
	}

#define SLIST_HEAD_INITIALIZER(head)                                           \
	{                                                                      \
		NULL                                                           \
	}

#define SLIST_ENTRY(type)                                                      \
	struct {                                                               \
		struct type *sle_next; /* next element */                      \
	}

/*
 * Singly-linked List functions.
 */
#define	SLIST_EMPTY(head)	((head)->slh_first == NULL)

#define	SLIST_FIRST(head)	((head)->slh_first)

#define SLIST_FOREACH(var, head, field)                                        \
	for ((var) = SLIST_FIRST((head)); (var);                               \
	     (var) = SLIST_NEXT((var), field))

#define SLIST_FOREACH_SAFE(var, head, field, tvar)                             \
	for ((var) = SLIST_FIRST((head));                                      \
	     (var) && ((tvar) = SLIST_NEXT((var), field), 1); (var) = (tvar))

#define SLIST_FOREACH_PREVPTR(var, varp, head, field)                          \
	for ((varp) = &SLIST_FIRST((head)); ((var) = *(varp)) != NULL;         \
	     (varp) = &SLIST_NEXT((var), field))

#define SLIST_INIT(head)                                                       \
	do {                                                                   \
		SLIST_FIRST((head)) = NULL;                                    \
	} while (0)

#define SLIST_INSERT_AFTER(slistelm, elm, field)                               \
	do {                                                                   \
		SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);      \
		SLIST_NEXT((slistelm), field) = (elm);                         \
	} while (0)

#define SLIST_INSERT_HEAD(head, elm, field)                                    \
	do {                                                                   \
		SLIST_NEXT((elm), field) = SLIST_FIRST((head));                \
		SLIST_FIRST((head)) = (elm);                                   \
	} while (0)

#define	SLIST_NEXT(elm, field)	((elm)->field.sle_next)

#define SLIST_REMOVE(head, elm, type, field)                                   \
	do {                                                                   \
		QMD_SAVELINK(oldnext, (elm)->field.sle_next);                  \
		if (SLIST_FIRST((head)) == (elm)) {                            \
			SLIST_REMOVE_HEAD((head), field);                      \
		} else {                                                       \
			struct type *curelm = SLIST_FIRST((head));             \
			while (SLIST_NEXT(curelm, field) != (elm))             \
				curelm = SLIST_NEXT(curelm, field);            \
			SLIST_REMOVE_AFTER(curelm, field);                     \
		}                                                              \
		TRASHIT(*oldnext);                                             \
	} while (0)

#define SLIST_REMOVE_AFTER(elm, field)                                         \
	do {                                                                   \
		SLIST_NEXT(elm, field) =                                       \
			SLIST_NEXT(SLIST_NEXT(elm, field), field);             \
	} while (0)

#define SLIST_REMOVE_HEAD(head, field)                                         \
	do {                                                                   \
		SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);  \
	} while (0)

#define SLIST_SWAP(head1, head2, type)                                         \
	do {                                                                   \
		struct type *swap_first = SLIST_FIRST(head1);                  \
		SLIST_FIRST(head1) = SLIST_FIRST(head2);                       \
		SLIST_FIRST(head2) = swap_first;                               \
	} while (0)

/*
 * Singly-linked Tail queue declarations.
 */
#define STAILQ_HEAD(name, type)                                                \
	struct name {                                                          \
		struct type *stqh_first; /* first element */                   \
		struct type **stqh_last; /* addr of last next element */       \
	}

#define STAILQ_HEAD_INITIALIZER(head)                                          \
	{                                                                      \
		NULL, &(head).stqh_first                                       \
	}

#define STAILQ_ENTRY(type)                                                     \
	struct {                                                               \
		struct type *stqe_next; /* next element */                     \
	}

/*
 * Singly-linked Tail queue functions.
 */
#define STAILQ_CONCAT(head1, head2)                                            \
	do {                                                                   \
		if (!STAILQ_EMPTY((head2))) {                                  \
			*(head1)->stqh_last = (head2)->stqh_first;             \
			(head1)->stqh_last = (head2)->stqh_last;               \
			STAILQ_INIT((head2));                                  \
		}                                                              \
	} while (0)

#define	STAILQ_EMPTY(head)	((head)->stqh_first == NULL)

#define	STAILQ_FIRST(head)	((head)->stqh_first)

#define STAILQ_FOREACH(var, head, field)                                       \
	for ((var) = STAILQ_FIRST((head)); (var);                              \
	     (var) = STAILQ_NEXT((var), field))


#define STAILQ_FOREACH_SAFE(var, head, field, tvar)                            \
	for ((var) = STAILQ_FIRST((head));                                     \
	     (var) && ((tvar) = STAILQ_NEXT((var), field), 1); (var) = (tvar))

#define STAILQ_INIT(head)                                                      \
	do {                                                                   \
		STAILQ_FIRST((head)) = NULL;                                   \
		(head)->stqh_last = &STAILQ_FIRST((head));                     \
	} while (0)

#define STAILQ_INSERT_AFTER(head, tqelm, elm, field)                           \
	do {                                                                   \
		if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field))  \
		    == NULL)                                                   \
			(head)->stqh_last = &STAILQ_NEXT((elm), field);        \
		STAILQ_NEXT((tqelm), field) = (elm);                           \
	} while (0)

#define STAILQ_INSERT_HEAD(head, elm, field)                                   \
	do {                                                                   \
		if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head)))         \
		    == NULL)                                                   \
			(head)->stqh_last = &STAILQ_NEXT((elm), field);        \
		STAILQ_FIRST((head)) = (elm);                                  \
	} while (0)

#define STAILQ_INSERT_TAIL(head, elm, field)                                   \
	do {                                                                   \
		STAILQ_NEXT((elm), field) = NULL;                              \
		*(head)->stqh_last = (elm);                                    \
		(head)->stqh_last = &STAILQ_NEXT((elm), field);                \
	} while (0)

#define STAILQ_LAST(head, type, field)                                         \
	(STAILQ_EMPTY((head))                                                  \
		 ? NULL                                                        \
		 : ((struct type *)(void *)((char *)((head)->stqh_last)        \
					    - offsetof(struct type, field))))

#define	STAILQ_NEXT(elm, field)	((elm)->field.stqe_next)

#define STAILQ_REMOVE(head, elm, type, field)                                  \
	do {                                                                   \
		QMD_SAVELINK(oldnext, (elm)->field.stqe_next);                 \
		if (STAILQ_FIRST((head)) == (elm)) {                           \
			STAILQ_REMOVE_HEAD((head), field);                     \
		} else {                                                       \
			struct type *curelm = STAILQ_FIRST((head));            \
			while (STAILQ_NEXT(curelm, field) != (elm))            \
				curelm = STAILQ_NEXT(curelm, field);           \
			STAILQ_REMOVE_AFTER(head, curelm, field);              \
		}                                                              \
		TRASHIT(*oldnext);                                             \
	} while (0)

#define STAILQ_REMOVE_AFTER(head, elm, field)                                  \
	do {                                                                   \
		if ((STAILQ_NEXT(elm, field) =                                 \
			     STAILQ_NEXT(STAILQ_NEXT(elm, field), field))      \
		    == NULL)                                                   \
			(head)->stqh_last = &STAILQ_NEXT((elm), field);        \
	} while (0)

#define STAILQ_REMOVE_HEAD(head, field)                                        \
	do {                                                                   \
		if ((STAILQ_FIRST((head)) =                                    \
			     STAILQ_NEXT(STAILQ_FIRST((head)), field))         \
		    == NULL)                                                   \
			(head)->stqh_last = &STAILQ_FIRST((head));             \
	} while (0)

#define STAILQ_SWAP(head1, head2, type)                                        \
	do {                                                                   \
		struct type *swap_first = STAILQ_FIRST(head1);                 \
		struct type **swap_last = (head1)->stqh_last;                  \
		STAILQ_FIRST(head1) = STAILQ_FIRST(head2);                     \
		(head1)->stqh_last = (head2)->stqh_last;                       \
		STAILQ_FIRST(head2) = swap_first;                              \
		(head2)->stqh_last = swap_last;                                \
		if (STAILQ_EMPTY(head1))                                       \
			(head1)->stqh_last = &STAILQ_FIRST(head1);             \
		if (STAILQ_EMPTY(head2))                                       \
			(head2)->stqh_last = &STAILQ_FIRST(head2);             \
	} while (0)


/*
 * List declarations.
 */
#define LIST_HEAD(name, type)                                                  \
	struct name {                                                          \
		struct type *lh_first; /* first element */                     \
	}

#define LIST_HEAD_INITIALIZER(head)                                            \
	{                                                                      \
		NULL                                                           \
	}

#define LIST_ENTRY(type)                                                       \
	struct {                                                               \
		struct type *le_next;  /* next element */                      \
		struct type **le_prev; /* address of previous next element */  \
	}

/*
 * List functions.
 */

#if (defined(_KERNEL) && defined(INVARIANTS))
#define QMD_LIST_CHECK_HEAD(head, field)                                       \
	do {                                                                   \
		if (LIST_FIRST((head)) != NULL                                 \
		    && LIST_FIRST((head))->field.le_prev                       \
			       != &LIST_FIRST((head)))                         \
			panic("Bad list head %p first->prev != head", (head)); \
	} while (0)

#define QMD_LIST_CHECK_NEXT(elm, field)                                        \
	do {                                                                   \
		if (LIST_NEXT((elm), field) != NULL                            \
		    && LIST_NEXT((elm), field)->field.le_prev                  \
			       != &((elm)->field.le_next))                     \
			panic("Bad link elm %p next->prev != elm", (elm));     \
	} while (0)

#define QMD_LIST_CHECK_PREV(elm, field)                                        \
	do {                                                                   \
		if (*(elm)->field.le_prev != (elm))                            \
			panic("Bad link elm %p prev->next != elm", (elm));     \
	} while (0)
#else
#define	QMD_LIST_CHECK_HEAD(head, field)
#define	QMD_LIST_CHECK_NEXT(elm, field)
#define	QMD_LIST_CHECK_PREV(elm, field)
#endif /* (_KERNEL && INVARIANTS) */

#define	LIST_EMPTY(head)	((head)->lh_first == NULL)

#define	LIST_FIRST(head)	((head)->lh_first)

#define LIST_FOREACH(var, head, field)                                         \
	for ((var) = LIST_FIRST((head)); (var); (var) = LIST_NEXT((var), field))

#define LIST_FOREACH_SAFE(var, head, field, tvar)                              \
	for ((var) = LIST_FIRST((head));                                       \
	     (var) && ((tvar) = LIST_NEXT((var), field), 1); (var) = (tvar))

#define LIST_INIT(head)                                                        \
	do {                                                                   \
		LIST_FIRST((head)) = NULL;                                     \
	} while (0)

#define LIST_INSERT_AFTER(listelm, elm, field)                                 \
	do {                                                                   \
		QMD_LIST_CHECK_NEXT(listelm, field);                           \
		if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field))    \
		    != NULL)                                                   \
			LIST_NEXT((listelm), field)->field.le_prev =           \
				&LIST_NEXT((elm), field);                      \
		LIST_NEXT((listelm), field) = (elm);                           \
		(elm)->field.le_prev = &LIST_NEXT((listelm), field);           \
	} while (0)

#define LIST_INSERT_BEFORE(listelm, elm, field)                                \
	do {                                                                   \
		QMD_LIST_CHECK_PREV(listelm, field);                           \
		(elm)->field.le_prev = (listelm)->field.le_prev;               \
		LIST_NEXT((elm), field) = (listelm);                           \
		*(listelm)->field.le_prev = (elm);                             \
		(listelm)->field.le_prev = &LIST_NEXT((elm), field);           \
	} while (0)

#define LIST_INSERT_HEAD(head, elm, field)                                     \
	do {                                                                   \
		QMD_LIST_CHECK_HEAD((head), field);                            \
		if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)    \
			LIST_FIRST((head))->field.le_prev =                    \
				&LIST_NEXT((elm), field);                      \
		LIST_FIRST((head)) = (elm);                                    \
		(elm)->field.le_prev = &LIST_FIRST((head));                    \
	} while (0)

#define	LIST_NEXT(elm, field)	((elm)->field.le_next)

#define LIST_REMOVE(elm, field)                                                \
	do {                                                                   \
		QMD_SAVELINK(oldnext, (elm)->field.le_next);                   \
		QMD_SAVELINK(oldprev, (elm)->field.le_prev);                   \
		QMD_LIST_CHECK_NEXT(elm, field);                               \
		QMD_LIST_CHECK_PREV(elm, field);                               \
		if (LIST_NEXT((elm), field) != NULL)                           \
			LIST_NEXT((elm), field)->field.le_prev =               \
				(elm)->field.le_prev;                          \
		*(elm)->field.le_prev = LIST_NEXT((elm), field);               \
		TRASHIT(*oldnext);                                             \
		TRASHIT(*oldprev);                                             \
	} while (0)

#define LIST_SWAP(head1, head2, type, field)                                   \
	do {                                                                   \
		struct type *swap_tmp = LIST_FIRST((head1));                   \
		LIST_FIRST((head1)) = LIST_FIRST((head2));                     \
		LIST_FIRST((head2)) = swap_tmp;                                \
		if ((swap_tmp = LIST_FIRST((head1))) != NULL)                  \
			swap_tmp->field.le_prev = &LIST_FIRST((head1));        \
		if ((swap_tmp = LIST_FIRST((head2))) != NULL)                  \
			swap_tmp->field.le_prev = &LIST_FIRST((head2));        \
	} while (0)

/*
 * Tail queue declarations.
 */
#define TAILQ_HEAD(name, type)                                                 \
	struct name {                                                          \
		struct type *tqh_first; /* first element */                    \
		struct type **tqh_last; /* addr of last next element */        \
		TRACEBUF                                                       \
	}

#define TAILQ_HEAD_INITIALIZER(head)                                           \
	{                                                                      \
		NULL, &(head).tqh_first                                        \
	}

#define TAILQ_ENTRY(type)                                                      \
	struct {                                                               \
		struct type *tqe_next;  /* next element */                     \
		struct type **tqe_prev; /* address of previous next element */ \
		TRACEBUF                                                       \
	}

/*
 * Tail queue functions.
 */
#if (defined(_KERNEL) && defined(INVARIANTS))
#define QMD_TAILQ_CHECK_HEAD(head, field)                                      \
	do {                                                                   \
		if (!TAILQ_EMPTY(head)                                         \
		    && TAILQ_FIRST((head))->field.tqe_prev                     \
			       != &TAILQ_FIRST((head)))                        \
			panic("Bad tailq head %p first->prev != head",         \
			      (head));                                         \
	} while (0)

#define QMD_TAILQ_CHECK_TAIL(head, field)                                      \
	do {                                                                   \
		if (*(head)->tqh_last != NULL)                                 \
			panic("Bad tailq NEXT(%p->tqh_last) != NULL", (head)); \
	} while (0)

#define QMD_TAILQ_CHECK_NEXT(elm, field)                                       \
	do {                                                                   \
		if (TAILQ_NEXT((elm), field) != NULL                           \
		    && TAILQ_NEXT((elm), field)->field.tqe_prev                \
			       != &((elm)->field.tqe_next))                    \
			panic("Bad link elm %p next->prev != elm", (elm));     \
	} while (0)

#define QMD_TAILQ_CHECK_PREV(elm, field)                                       \
	do {                                                                   \
		if (*(elm)->field.tqe_prev != (elm))                           \
			panic("Bad link elm %p prev->next != elm", (elm));     \
	} while (0)
#else
#define	QMD_TAILQ_CHECK_HEAD(head, field)
#define	QMD_TAILQ_CHECK_TAIL(head, headname)
#define	QMD_TAILQ_CHECK_NEXT(elm, field)
#define	QMD_TAILQ_CHECK_PREV(elm, field)
#endif /* (_KERNEL && INVARIANTS) */

#define TAILQ_CONCAT(head1, head2, field)                                      \
	do {                                                                   \
		if (!TAILQ_EMPTY(head2)) {                                     \
			*(head1)->tqh_last = (head2)->tqh_first;               \
			(head2)->tqh_first->field.tqe_prev =                   \
				(head1)->tqh_last;                             \
			(head1)->tqh_last = (head2)->tqh_last;                 \
			TAILQ_INIT((head2));                                   \
			QMD_TRACE_HEAD(head1);                                 \
			QMD_TRACE_HEAD(head2);                                 \
		}                                                              \
	} while (0)

#define	TAILQ_EMPTY(head)	((head)->tqh_first == NULL)

#define	TAILQ_FIRST(head)	((head)->tqh_first)

#define TAILQ_FOREACH(var, head, field)                                        \
	for ((var) = TAILQ_FIRST((head)); (var);                               \
	     (var) = TAILQ_NEXT((var), field))

#define TAILQ_FOREACH_SAFE(var, head, field, tvar)                             \
	for ((var) = TAILQ_FIRST((head));                                      \
	     (var) && ((tvar) = TAILQ_NEXT((var), field), 1); (var) = (tvar))

#define TAILQ_FOREACH_REVERSE(var, head, headname, field)                      \
	for ((var) = TAILQ_LAST((head), headname); (var);                      \
	     (var) = TAILQ_PREV((var), headname, field))

#define TAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar)           \
	for ((var) = TAILQ_LAST((head), headname);                             \
	     (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);        \
	     (var) = (tvar))

#define TAILQ_INIT(head)                                                       \
	do {                                                                   \
		TAILQ_FIRST((head)) = NULL;                                    \
		(head)->tqh_last = &TAILQ_FIRST((head));                       \
		QMD_TRACE_HEAD(head);                                          \
	} while (0)

#define TAILQ_INSERT_AFTER(head, listelm, elm, field)                          \
	do {                                                                   \
		QMD_TAILQ_CHECK_NEXT(listelm, field);                          \
		if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field))  \
		    != NULL)                                                   \
			TAILQ_NEXT((elm), field)->field.tqe_prev =             \
				&TAILQ_NEXT((elm), field);                     \
		else {                                                         \
			(head)->tqh_last = &TAILQ_NEXT((elm), field);          \
			QMD_TRACE_HEAD(head);                                  \
		}                                                              \
		TAILQ_NEXT((listelm), field) = (elm);                          \
		(elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);         \
		QMD_TRACE_ELEM(&(elm)->field);                                 \
		QMD_TRACE_ELEM(&listelm->field);                               \
	} while (0)

#define TAILQ_INSERT_BEFORE(listelm, elm, field)                               \
	do {                                                                   \
		QMD_TAILQ_CHECK_PREV(listelm, field);                          \
		(elm)->field.tqe_prev = (listelm)->field.tqe_prev;             \
		TAILQ_NEXT((elm), field) = (listelm);                          \
		*(listelm)->field.tqe_prev = (elm);                            \
		(listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);         \
		QMD_TRACE_ELEM(&(elm)->field);                                 \
		QMD_TRACE_ELEM(&listelm->field);                               \
	} while (0)

#define TAILQ_INSERT_HEAD(head, elm, field)                                    \
	do {                                                                   \
		QMD_TAILQ_CHECK_HEAD(head, field);                             \
		if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)  \
			TAILQ_FIRST((head))->field.tqe_prev =                  \
				&TAILQ_NEXT((elm), field);                     \
		else                                                           \
			(head)->tqh_last = &TAILQ_NEXT((elm), field);          \
		TAILQ_FIRST((head)) = (elm);                                   \
		(elm)->field.tqe_prev = &TAILQ_FIRST((head));                  \
		QMD_TRACE_HEAD(head);                                          \
		QMD_TRACE_ELEM(&(elm)->field);                                 \
	} while (0)

#define TAILQ_INSERT_TAIL(head, elm, field)                                    \
	do {                                                                   \
		QMD_TAILQ_CHECK_TAIL(head, field);                             \
		TAILQ_NEXT((elm), field) = NULL;                               \
		(elm)->field.tqe_prev = (head)->tqh_last;                      \
		*(head)->tqh_last = (elm);                                     \
		(head)->tqh_last = &TAILQ_NEXT((elm), field);                  \
		QMD_TRACE_HEAD(head);                                          \
		QMD_TRACE_ELEM(&(elm)->field);                                 \
	} while (0)

#define TAILQ_LAST(head, headname)                                             \
	(*(((struct headname *)((head)->tqh_last))->tqh_last))

#define	TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)

#define TAILQ_PREV(elm, headname, field)                                       \
	(*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))

#define TAILQ_REMOVE(head, elm, field)                                         \
	do {                                                                   \
		QMD_SAVELINK(oldnext, (elm)->field.tqe_next);                  \
		QMD_SAVELINK(oldprev, (elm)->field.tqe_prev);                  \
		QMD_TAILQ_CHECK_NEXT(elm, field);                              \
		QMD_TAILQ_CHECK_PREV(elm, field);                              \
		if ((TAILQ_NEXT((elm), field)) != NULL)                        \
			TAILQ_NEXT((elm), field)->field.tqe_prev =             \
				(elm)->field.tqe_prev;                         \
		else {                                                         \
			(head)->tqh_last = (elm)->field.tqe_prev;              \
			QMD_TRACE_HEAD(head);                                  \
		}                                                              \
		*(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);             \
		TRASHIT(*oldnext);                                             \
		TRASHIT(*oldprev);                                             \
		QMD_TRACE_ELEM(&(elm)->field);                                 \
	} while (0)

#define TAILQ_SWAP(head1, head2, type, field)                                  \
	do {                                                                   \
		struct type *swap_first = (head1)->tqh_first;                  \
		struct type **swap_last = (head1)->tqh_last;                   \
		(head1)->tqh_first = (head2)->tqh_first;                       \
		(head1)->tqh_last = (head2)->tqh_last;                         \
		(head2)->tqh_first = swap_first;                               \
		(head2)->tqh_last = swap_last;                                 \
		if ((swap_first = (head1)->tqh_first) != NULL)                 \
			swap_first->field.tqe_prev = &(head1)->tqh_first;      \
		else                                                           \
			(head1)->tqh_last = &(head1)->tqh_first;               \
		if ((swap_first = (head2)->tqh_first) != NULL)                 \
			swap_first->field.tqe_prev = &(head2)->tqh_first;      \
		else                                                           \
			(head2)->tqh_last = &(head2)->tqh_first;               \
	} while (0)

#ifdef __cplusplus
}
#endif

#endif /* !_SYS_QUEUE_H_ */