queue.h

/*
 * Copyright (c) 1991, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)queue.h	8.5 (Berkeley) 8/20/94
 */

#ifndef _SYS_QUEUE_H_
#define _SYS_QUEUE_H_

/*
 * This file defines five types of data structures: singly-linked lists,
 * lists, simple queues, tail queues, and circular 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 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 simple queue is headed by a pair of pointers, one the head of the
 * list and the other to the tail of the list. The elements are singly
 * linked to save space, so elements can only be removed from the
 * head of the list. 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. A simple queue 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.
 *
 * A circle 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 circle queue may be traversed in either direction, but has a more
 * complex end of list detection.
 *
 * For details on the use of these macros, see the queue(3) manual page.
 */

/*
 * List definitions.
 */
#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.
 */
#define LIST_INIT(head)          \
	do                           \
	{                            \
		(head)->lh_first = NULL; \
	} while (/*CONSTCOND*/ 0)

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

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

#define LIST_INSERT_HEAD(head, elm, field)                           \
	do                                                               \
	{                                                                \
		if (((elm)->field.le_next = (head)->lh_first) != NULL)       \
			(head)->lh_first->field.le_prev = &(elm)->field.le_next; \
		(head)->lh_first = (elm);                                    \
		(elm)->field.le_prev = &(head)->lh_first;                    \
	} while (/*CONSTCOND*/ 0)

#define LIST_REMOVE(elm, field)                       \
	do                                                \
	{                                                 \
		if ((elm)->field.le_next != NULL)             \
			(elm)->field.le_next->field.le_prev =     \
				(elm)->field.le_prev;                 \
		*(elm)->field.le_prev = (elm)->field.le_next; \
	} while (/*CONSTCOND*/ 0)

#define LIST_FOREACH(var, head, field) \
	for ((var) = ((head)->lh_first);   \
		 (var);                        \
		 (var) = ((var)->field.le_next))

/*
 * List access methods.
 */
#define LIST_EMPTY(head) ((head)->lh_first == NULL)
#define LIST_FIRST(head) ((head)->lh_first)
#define LIST_NEXT(elm, field) ((elm)->field.le_next)

/*
 * Singly-linked List definitions.
 */
#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_INIT(head)          \
	do                            \
	{                             \
		(head)->slh_first = NULL; \
	} while (/*CONSTCOND*/ 0)

#define SLIST_INSERT_AFTER(slistelm, elm, field)            \
	do                                                      \
	{                                                       \
		(elm)->field.sle_next = (slistelm)->field.sle_next; \
		(slistelm)->field.sle_next = (elm);                 \
	} while (/*CONSTCOND*/ 0)

#define SLIST_INSERT_HEAD(head, elm, field)        \
	do                                             \
	{                                              \
		(elm)->field.sle_next = (head)->slh_first; \
		(head)->slh_first = (elm);                 \
	} while (/*CONSTCOND*/ 0)

#define SLIST_REMOVE_HEAD(head, field)                         \
	do                                                         \
	{                                                          \
		(head)->slh_first = (head)->slh_first->field.sle_next; \
	} while (/*CONSTCOND*/ 0)

#define SLIST_REMOVE(head, elm, type, field)            \
	do                                                  \
	{                                                   \
		if ((head)->slh_first == (elm))                 \
		{                                               \
			SLIST_REMOVE_HEAD((head), field);           \
		}                                               \
		else                                            \
		{                                               \
			struct type *curelm = (head)->slh_first;    \
			while (curelm->field.sle_next != (elm))     \
				curelm = curelm->field.sle_next;        \
			curelm->field.sle_next =                    \
				curelm->field.sle_next->field.sle_next; \
		}                                               \
	} while (/*CONSTCOND*/ 0)

#define SLIST_FOREACH(var, head, field) \
	for ((var) = (head)->slh_first; (var); (var) = (var)->field.sle_next)

/*
 * Singly-linked List access methods.
 */
#define SLIST_EMPTY(head) ((head)->slh_first == NULL)
#define SLIST_FIRST(head) ((head)->slh_first)
#define SLIST_NEXT(elm, field) ((elm)->field.sle_next)

/*
 * 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_INIT(head)                        \
	do                                           \
	{                                            \
		(head)->stqh_first = NULL;               \
		(head)->stqh_last = &(head)->stqh_first; \
	} while (/*CONSTCOND*/ 0)

#define STAILQ_INSERT_HEAD(head, elm, field)                       \
	do                                                             \
	{                                                              \
		if (((elm)->field.stqe_next = (head)->stqh_first) == NULL) \
			(head)->stqh_last = &(elm)->field.stqe_next;           \
		(head)->stqh_first = (elm);                                \
	} while (/*CONSTCOND*/ 0)

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

#define STAILQ_INSERT_AFTER(head, listelm, elm, field)                     \
	do                                                                     \
	{                                                                      \
		if (((elm)->field.stqe_next = (listelm)->field.stqe_next) == NULL) \
			(head)->stqh_last = &(elm)->field.stqe_next;                   \
		(listelm)->field.stqe_next = (elm);                                \
	} while (/*CONSTCOND*/ 0)

#define STAILQ_REMOVE_HEAD(head, field)                                         \
	do                                                                          \
	{                                                                           \
		if (((head)->stqh_first = (head)->stqh_first->field.stqe_next) == NULL) \
			(head)->stqh_last = &(head)->stqh_first;                            \
	} while (/*CONSTCOND*/ 0)

#define STAILQ_REMOVE(head, elm, type, field)                           \
	do                                                                  \
	{                                                                   \
		if ((head)->stqh_first == (elm))                                \
		{                                                               \
			STAILQ_REMOVE_HEAD((head), field);                          \
		}                                                               \
		else                                                            \
		{                                                               \
			struct type *curelm = (head)->stqh_first;                   \
			while (curelm->field.stqe_next != (elm))                    \
				curelm = curelm->field.stqe_next;                       \
			if ((curelm->field.stqe_next =                              \
					 curelm->field.stqe_next->field.stqe_next) == NULL) \
				(head)->stqh_last = &(curelm)->field.stqe_next;         \
		}                                                               \
	} while (/*CONSTCOND*/ 0)

#define STAILQ_FOREACH(var, head, field) \
	for ((var) = ((head)->stqh_first);   \
		 (var);                          \
		 (var) = ((var)->field.stqe_next))

#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 (/*CONSTCOND*/ 0)

/*
 * Singly-linked Tail queue access methods.
 */
#define STAILQ_EMPTY(head) ((head)->stqh_first == NULL)
#define STAILQ_FIRST(head) ((head)->stqh_first)
#define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)

/*
 * Simple queue definitions.
 */
#define SIMPLEQ_HEAD(name, type)                                \
	struct name                                                 \
	{                                                           \
		struct type *sqh_first; /* first element */             \
		struct type **sqh_last; /* addr of last next element */ \
	}

#define SIMPLEQ_HEAD_INITIALIZER(head) \
	{                                  \
		NULL, &(head).sqh_first        \
	}

#define SIMPLEQ_ENTRY(type)                       \
	struct                                        \
	{                                             \
		struct type *sqe_next; /* next element */ \
	}

/*
 * Simple queue functions.
 */
#define SIMPLEQ_INIT(head)                     \
	do                                         \
	{                                          \
		(head)->sqh_first = NULL;              \
		(head)->sqh_last = &(head)->sqh_first; \
	} while (/*CONSTCOND*/ 0)

#define SIMPLEQ_INSERT_HEAD(head, elm, field)                    \
	do                                                           \
	{                                                            \
		if (((elm)->field.sqe_next = (head)->sqh_first) == NULL) \
			(head)->sqh_last = &(elm)->field.sqe_next;           \
		(head)->sqh_first = (elm);                               \
	} while (/*CONSTCOND*/ 0)

#define SIMPLEQ_INSERT_TAIL(head, elm, field)      \
	do                                             \
	{                                              \
		(elm)->field.sqe_next = NULL;              \
		*(head)->sqh_last = (elm);                 \
		(head)->sqh_last = &(elm)->field.sqe_next; \
	} while (/*CONSTCOND*/ 0)

#define SIMPLEQ_INSERT_AFTER(head, listelm, elm, field)                  \
	do                                                                   \
	{                                                                    \
		if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL) \
			(head)->sqh_last = &(elm)->field.sqe_next;                   \
		(listelm)->field.sqe_next = (elm);                               \
	} while (/*CONSTCOND*/ 0)

#define SIMPLEQ_REMOVE_HEAD(head, field)                                     \
	do                                                                       \
	{                                                                        \
		if (((head)->sqh_first = (head)->sqh_first->field.sqe_next) == NULL) \
			(head)->sqh_last = &(head)->sqh_first;                           \
	} while (/*CONSTCOND*/ 0)

#define SIMPLEQ_REMOVE(head, elm, type, field)                        \
	do                                                                \
	{                                                                 \
		if ((head)->sqh_first == (elm))                               \
		{                                                             \
			SIMPLEQ_REMOVE_HEAD((head), field);                       \
		}                                                             \
		else                                                          \
		{                                                             \
			struct type *curelm = (head)->sqh_first;                  \
			while (curelm->field.sqe_next != (elm))                   \
				curelm = curelm->field.sqe_next;                      \
			if ((curelm->field.sqe_next =                             \
					 curelm->field.sqe_next->field.sqe_next) == NULL) \
				(head)->sqh_last = &(curelm)->field.sqe_next;         \
		}                                                             \
	} while (/*CONSTCOND*/ 0)

#define SIMPLEQ_FOREACH(var, head, field) \
	for ((var) = ((head)->sqh_first);     \
		 (var);                           \
		 (var) = ((var)->field.sqe_next))

/*
 * Simple queue access methods.
 */
#define SIMPLEQ_EMPTY(head) ((head)->sqh_first == NULL)
#define SIMPLEQ_FIRST(head) ((head)->sqh_first)
#define SIMPLEQ_NEXT(elm, field) ((elm)->field.sqe_next)

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

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

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

/*
 * Tail queue functions.
 */
#define TAILQ_INIT(head)                       \
	do                                         \
	{                                          \
		(head)->tqh_first = NULL;              \
		(head)->tqh_last = &(head)->tqh_first; \
	} while (/*CONSTCOND*/ 0)

#define TAILQ_INSERT_HEAD(head, elm, field)                      \
	do                                                           \
	{                                                            \
		if (((elm)->field.tqe_next = (head)->tqh_first) != NULL) \
			(head)->tqh_first->field.tqe_prev =                  \
				&(elm)->field.tqe_next;                          \
		else                                                     \
			(head)->tqh_last = &(elm)->field.tqe_next;           \
		(head)->tqh_first = (elm);                               \
		(elm)->field.tqe_prev = &(head)->tqh_first;              \
	} while (/*CONSTCOND*/ 0)

#define TAILQ_INSERT_TAIL(head, elm, field)        \
	do                                             \
	{                                              \
		(elm)->field.tqe_next = NULL;              \
		(elm)->field.tqe_prev = (head)->tqh_last;  \
		*(head)->tqh_last = (elm);                 \
		(head)->tqh_last = &(elm)->field.tqe_next; \
	} while (/*CONSTCOND*/ 0)

#define TAILQ_INSERT_AFTER(head, listelm, elm, field)                    \
	do                                                                   \
	{                                                                    \
		if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL) \
			(elm)->field.tqe_next->field.tqe_prev =                      \
				&(elm)->field.tqe_next;                                  \
		else                                                             \
			(head)->tqh_last = &(elm)->field.tqe_next;                   \
		(listelm)->field.tqe_next = (elm);                               \
		(elm)->field.tqe_prev = &(listelm)->field.tqe_next;              \
	} while (/*CONSTCOND*/ 0)

#define TAILQ_INSERT_BEFORE(listelm, elm, field)            \
	do                                                      \
	{                                                       \
		(elm)->field.tqe_prev = (listelm)->field.tqe_prev;  \
		(elm)->field.tqe_next = (listelm);                  \
		*(listelm)->field.tqe_prev = (elm);                 \
		(listelm)->field.tqe_prev = &(elm)->field.tqe_next; \
	} while (/*CONSTCOND*/ 0)

#define TAILQ_REMOVE(head, elm, field)                  \
	do                                                  \
	{                                                   \
		if (((elm)->field.tqe_next) != NULL)            \
			(elm)->field.tqe_next->field.tqe_prev =     \
				(elm)->field.tqe_prev;                  \
		else                                            \
			(head)->tqh_last = (elm)->field.tqe_prev;   \
		*(elm)->field.tqe_prev = (elm)->field.tqe_next; \
	} while (/*CONSTCOND*/ 0)

#define TAILQ_FOREACH(var, head, field) \
	for ((var) = ((head)->tqh_first);   \
		 (var);                         \
		 (var) = ((var)->field.tqe_next))

#define TAILQ_FOREACH_REVERSE(var, head, headname, field)                \
	for ((var) = (*(((struct headname *)((head)->tqh_last))->tqh_last)); \
		 (var);                                                          \
		 (var) = (*(((struct headname *)((var)->field.tqe_prev))->tqh_last)))

#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));                                    \
		}                                                           \
	} while (/*CONSTCOND*/ 0)

/*
 * Tail queue access methods.
 */
#define TAILQ_EMPTY(head) ((head)->tqh_first == NULL)
#define TAILQ_FIRST(head) ((head)->tqh_first)
#define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)

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

/*
 * Circular queue definitions.
 */
#define CIRCLEQ_HEAD(name, type)                    \
	struct name                                     \
	{                                               \
		struct type *cqh_first; /* first element */ \
		struct type *cqh_last;	/* last element */  \
	}

#define CIRCLEQ_HEAD_INITIALIZER(head) \
	{                                  \
		(void *)&head, (void *)&head   \
	}

#define CIRCLEQ_ENTRY(type)                           \
	struct                                            \
	{                                                 \
		struct type *cqe_next; /* next element */     \
		struct type *cqe_prev; /* previous element */ \
	}

/*
 * Circular queue functions.
 */
#define CIRCLEQ_INIT(head)                  \
	do                                      \
	{                                       \
		(head)->cqh_first = (void *)(head); \
		(head)->cqh_last = (void *)(head);  \
	} while (/*CONSTCOND*/ 0)

#define CIRCLEQ_INSERT_AFTER(head, listelm, elm, field)        \
	do                                                         \
	{                                                          \
		(elm)->field.cqe_next = (listelm)->field.cqe_next;     \
		(elm)->field.cqe_prev = (listelm);                     \
		if ((listelm)->field.cqe_next == (void *)(head))       \
			(head)->cqh_last = (elm);                          \
		else                                                   \
			(listelm)->field.cqe_next->field.cqe_prev = (elm); \
		(listelm)->field.cqe_next = (elm);                     \
	} while (/*CONSTCOND*/ 0)

#define CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field)       \
	do                                                         \
	{                                                          \
		(elm)->field.cqe_next = (listelm);                     \
		(elm)->field.cqe_prev = (listelm)->field.cqe_prev;     \
		if ((listelm)->field.cqe_prev == (void *)(head))       \
			(head)->cqh_first = (elm);                         \
		else                                                   \
			(listelm)->field.cqe_prev->field.cqe_next = (elm); \
		(listelm)->field.cqe_prev = (elm);                     \
	} while (/*CONSTCOND*/ 0)

#define CIRCLEQ_INSERT_HEAD(head, elm, field)          \
	do                                                 \
	{                                                  \
		(elm)->field.cqe_next = (head)->cqh_first;     \
		(elm)->field.cqe_prev = (void *)(head);        \
		if ((head)->cqh_last == (void *)(head))        \
			(head)->cqh_last = (elm);                  \
		else                                           \
			(head)->cqh_first->field.cqe_prev = (elm); \
		(head)->cqh_first = (elm);                     \
	} while (/*CONSTCOND*/ 0)

#define CIRCLEQ_INSERT_TAIL(head, elm, field)         \
	do                                                \
	{                                                 \
		(elm)->field.cqe_next = (void *)(head);       \
		(elm)->field.cqe_prev = (head)->cqh_last;     \
		if ((head)->cqh_first == (void *)(head))      \
			(head)->cqh_first = (elm);                \
		else                                          \
			(head)->cqh_last->field.cqe_next = (elm); \
		(head)->cqh_last = (elm);                     \
	} while (/*CONSTCOND*/ 0)

#define CIRCLEQ_REMOVE(head, elm, field)               \
	do                                                 \
	{                                                  \
		if ((elm)->field.cqe_next == (void *)(head))   \
			(head)->cqh_last = (elm)->field.cqe_prev;  \
		else                                           \
			(elm)->field.cqe_next->field.cqe_prev =    \
				(elm)->field.cqe_prev;                 \
		if ((elm)->field.cqe_prev == (void *)(head))   \
			(head)->cqh_first = (elm)->field.cqe_next; \
		else                                           \
			(elm)->field.cqe_prev->field.cqe_next =    \
				(elm)->field.cqe_next;                 \
	} while (/*CONSTCOND*/ 0)

#define CIRCLEQ_FOREACH(var, head, field) \
	for ((var) = ((head)->cqh_first);     \
		 (var) != (const void *)(head);   \
		 (var) = ((var)->field.cqe_next))

#define CIRCLEQ_FOREACH_REVERSE(var, head, field) \
	for ((var) = ((head)->cqh_last);              \
		 (var) != (const void *)(head);           \
		 (var) = ((var)->field.cqe_prev))

/*
 * Circular queue access methods.
 */
#define CIRCLEQ_EMPTY(head) ((head)->cqh_first == (void *)(head))
#define CIRCLEQ_FIRST(head) ((head)->cqh_first)
#define CIRCLEQ_LAST(head) ((head)->cqh_last)
#define CIRCLEQ_NEXT(elm, field) ((elm)->field.cqe_next)
#define CIRCLEQ_PREV(elm, field) ((elm)->field.cqe_prev)

#define CIRCLEQ_LOOP_NEXT(head, elm, field)    \
	(((elm)->field.cqe_next == (void *)(head)) \
		 ? ((head)->cqh_first)                 \
		 : (elm->field.cqe_next))
#define CIRCLEQ_LOOP_PREV(head, elm, field)    \
	(((elm)->field.cqe_prev == (void *)(head)) \
		 ? ((head)->cqh_last)                  \
		 : (elm->field.cqe_prev))

#endif /* sys/queue.h */