text: /*	$NetBSD: queue.h,v 1.68 2014/11/19 08:10:01 uebayasi Exp $	*/
  
  /*
   * 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
   */
  
   /*
    * ASG_LK: MODIFICATION HISTORY
    * ==================================================================================
    * TAG          |   DATE (DD/MM/YYYY)    |   JIRA    |   DESCRIPTION
    * ==================================================================================
    * ASG_LK01         22/04/2021              -           SYSTEM-C Equivalent
    * ==================================================================================
   */
  
  #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.
   */
  
  /*
   * Include the definition of NULL only on NetBSD because sys/null.h
   * is not available elsewhere.  This conditional makes the header
   * portable and it can simply be dropped verbatim into any system.
   * The caveat is that on other systems some other header
   * must provide NULL before the macros can be used.
   */
  #ifdef __NetBSD__
  #include <sys/null.h>
  #endif
  
  #if defined(QUEUEDEBUG)
  # if defined(_KERNEL)
  #  define QUEUEDEBUG_ABORT(...) panic(__VA_ARGS__)
  # else
  #  include <err.h>
  #  define QUEUEDEBUG_ABORT(...) err(1, __VA_ARGS__)
  # endif
  #endif
  
  /*
   * 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 access methods.
   */
  #define	SLIST_FIRST(head)	((head)->slh_first)
  #define	SLIST_END(head)		NULL
  #define	SLIST_EMPTY(head)	((head)->slh_first == NULL)
  #define	SLIST_NEXT(elm, field)	((elm)->field.sle_next)
  
  #define	SLIST_FOREACH(var, head, field)					\
  	for((var) = (head)->slh_first;					\
  	    (var) != SLIST_END(head);					\
  	    (var) = (var)->field.sle_next)
  
  #define	SLIST_FOREACH_SAFE(var, head, field, tvar)			\
  	for ((var) = SLIST_FIRST((head));				\
  	    (var) != SLIST_END(head) &&					\
  	    ((tvar) = SLIST_NEXT((var), field), 1);			\
  	    (var) = (tvar))
  
  /*
   * Singly-linked List functions.
   */
  #define	SLIST_INIT(head) do {						\
  	(head)->slh_first = SLIST_END(head);				\
  } 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_AFTER(slistelm, field) do {			\
  	(slistelm)->field.sle_next =					\
  	    SLIST_NEXT(SLIST_NEXT((slistelm), field), field);		\
  } 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)
  
  
  /*
   * 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 access methods.
   */
  #define	LIST_FIRST(head)		((head)->lh_first)
  #define	LIST_END(head)			NULL
  #define	LIST_EMPTY(head)		((head)->lh_first == LIST_END(head))
  #define	LIST_NEXT(elm, field)		((elm)->field.le_next)
  
  #define	LIST_FOREACH(var, head, field)					\
  	for ((var) = ((head)->lh_first);				\
  	    (var) != LIST_END(head);					\
  	    (var) = ((var)->field.le_next))
  
  #define	LIST_FOREACH_SAFE(var, head, field, tvar)			\
  	for ((var) = LIST_FIRST((head));				\
  	    (var) != LIST_END(head) &&					\
  	    ((tvar) = LIST_NEXT((var), field), 1);			\
  	    (var) = (tvar))
  
  #define	LIST_MOVE(head1, head2) do {					\
  	LIST_INIT((head2));						\
  	if (!LIST_EMPTY((head1))) {					\
  		(head2)->lh_first = (head1)->lh_first;			\
  		LIST_INIT((head1));					\
  	}								\
  } while (/*CONSTCOND*/0)
  
  /*
   * List functions.
   */
  #if defined(QUEUEDEBUG)
  #define	QUEUEDEBUG_LIST_INSERT_HEAD(head, elm, field)			\
  	if ((head)->lh_first &&						\
  	    (head)->lh_first->field.le_prev != &(head)->lh_first)	\
  		QUEUEDEBUG_ABORT("LIST_INSERT_HEAD %p %s:%d", (head),	\
  		    __FILE__, __LINE__);
  #define	QUEUEDEBUG_LIST_OP(elm, field)					\
  	if ((elm)->field.le_next &&					\
  	    (elm)->field.le_next->field.le_prev !=			\
  	    &(elm)->field.le_next)					\
  		QUEUEDEBUG_ABORT("LIST_* forw %p %s:%d", (elm),		\
  		    __FILE__, __LINE__);				\
  	if (*(elm)->field.le_prev != (elm))				\
  		QUEUEDEBUG_ABORT("LIST_* back %p %s:%d", (elm),		\
  		    __FILE__, __LINE__);
  #define	QUEUEDEBUG_LIST_POSTREMOVE(elm, field)				\
  	(elm)->field.le_next = (void *)1L;				\
  	(elm)->field.le_prev = (void *)1L;
  #else
  #define	QUEUEDEBUG_LIST_INSERT_HEAD(head, elm, field)
  #define	QUEUEDEBUG_LIST_OP(elm, field)
  #define	QUEUEDEBUG_LIST_POSTREMOVE(elm, field)
  #endif
  
  #define	LIST_INIT(head) do {						\
  	(head)->lh_first = LIST_END(head);				\
  } while (/*CONSTCOND*/0)
  
  #define	LIST_INSERT_AFTER(listelm, elm, field) do {			\
  	QUEUEDEBUG_LIST_OP((listelm), field)				\
  	if (((elm)->field.le_next = (listelm)->field.le_next) != 	\
  	    LIST_END(head))						\
  		(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 {			\
  	QUEUEDEBUG_LIST_OP((listelm), field)				\
  	(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 {				\
  	QUEUEDEBUG_LIST_INSERT_HEAD((head), (elm), field)		\
  	if (((elm)->field.le_next = (head)->lh_first) != LIST_END(head))\
  		(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 {					\
  	QUEUEDEBUG_LIST_OP((elm), field)				\
  	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;			\
  	QUEUEDEBUG_LIST_POSTREMOVE((elm), field)			\
  } while (/*CONSTCOND*/0)
  
  #define LIST_REPLACE(elm, elm2, field) do {				\
  	if (((elm2)->field.le_next = (elm)->field.le_next) != NULL)	\
  		(elm2)->field.le_next->field.le_prev =			\
  		    &(elm2)->field.le_next;				\
  	(elm2)->field.le_prev = (elm)->field.le_prev;			\
  	*(elm2)->field.le_prev = (elm2);				\
  	QUEUEDEBUG_LIST_POSTREMOVE((elm), field)			\
  } while (/*CONSTCOND*/0)
  
  /*
   * 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 access methods.
   */
  #define	SIMPLEQ_FIRST(head)		((head)->sqh_first)
  #define	SIMPLEQ_END(head)		NULL
  #define	SIMPLEQ_EMPTY(head)		((head)->sqh_first == SIMPLEQ_END(head))
  #define	SIMPLEQ_NEXT(elm, field)	((elm)->field.sqe_next)
  
  #define	SIMPLEQ_FOREACH(var, head, field)				\
  	for ((var) = ((head)->sqh_first);				\
  	    (var) != SIMPLEQ_END(head);					\
  	    (var) = ((var)->field.sqe_next))
  
  #define	SIMPLEQ_FOREACH_SAFE(var, head, field, next)			\
  	for ((var) = ((head)->sqh_first);				\
  	    (var) != SIMPLEQ_END(head) &&				\
  	    ((next = ((var)->field.sqe_next)), 1);			\
  	    (var) = (next))
  
  /*
   * 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_AFTER(head, elm, field) do {			\
  	if (((elm)->field.sqe_next = (elm)->field.sqe_next->field.sqe_next) \
  	    == NULL)							\
  		(head)->sqh_last = &(elm)->field.sqe_next;		\
  } 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_CONCAT(head1, head2) do {				\
  	if (!SIMPLEQ_EMPTY((head2))) {					\
  		*(head1)->sqh_last = (head2)->sqh_first;		\
  		(head1)->sqh_last = (head2)->sqh_last;		\
  		SIMPLEQ_INIT((head2));					\
  	}								\
  } while (/*CONSTCOND*/0)
  
  #define	SIMPLEQ_LAST(head, type, field)					\
  	(SIMPLEQ_EMPTY((head)) ?						\
  		NULL :							\
  	        ((struct type *)(void *)				\
  		((char *)((head)->sqh_last) - offsetof(struct type, field))))
  
  /*
   * 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)					\
  	{ TAILQ_END(head), &(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 access methods.
   */
  #define	TAILQ_FIRST(head)		((head)->tqh_first)
  #define	TAILQ_END(head)			(NULL)
  #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))
  #define	TAILQ_EMPTY(head)		(TAILQ_FIRST(head) == TAILQ_END(head))
  
  
  #define	TAILQ_FOREACH(var, head, field)					\
  	for ((var) = ((head)->tqh_first);				\
  	    (var) != TAILQ_END(head);					\
  	    (var) = ((var)->field.tqe_next))
  
  #define	TAILQ_FOREACH_SAFE(var, head, field, next)			\
  	for ((var) = ((head)->tqh_first);				\
  	    (var) != TAILQ_END(head) &&					\
  	    ((next) = TAILQ_NEXT(var, field), 1); (var) = (next))
  
  #define	TAILQ_FOREACH_REVERSE(var, head, headname, field)		\
  	for ((var) = (*(((struct headname *)((head)->tqh_last))->tqh_last));\
  	    (var) != TAILQ_END(head);					\
  	    (var) = (*(((struct headname *)((var)->field.tqe_prev))->tqh_last)))
  
  #define	TAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, prev)	\
  	for ((var) = TAILQ_LAST((head), headname);			\
  	    (var) != TAILQ_END(head) && 				\
  	    ((prev) = TAILQ_PREV((var), headname, field), 1); (var) = (prev))
  
  /*
   * Tail queue functions.
   */
  #if defined(QUEUEDEBUG)
  #define	QUEUEDEBUG_TAILQ_INSERT_HEAD(head, elm, field)			\
  	if ((head)->tqh_first &&					\
  	    (head)->tqh_first->field.tqe_prev != &(head)->tqh_first)	\
  		QUEUEDEBUG_ABORT("TAILQ_INSERT_HEAD %p %s:%d", (head),	\
  		    __FILE__, __LINE__);
  #define	QUEUEDEBUG_TAILQ_INSERT_TAIL(head, elm, field)			\
  	if (*(head)->tqh_last != NULL)					\
  		QUEUEDEBUG_ABORT("TAILQ_INSERT_TAIL %p %s:%d", (head),	\
  		    __FILE__, __LINE__);
  #define	QUEUEDEBUG_TAILQ_OP(elm, field)					\
  	if ((elm)->field.tqe_next &&					\
  	    (elm)->field.tqe_next->field.tqe_prev !=			\
  	    &(elm)->field.tqe_next)					\
  		QUEUEDEBUG_ABORT("TAILQ_* forw %p %s:%d", (elm),	\
  		    __FILE__, __LINE__);				\
  	if (*(elm)->field.tqe_prev != (elm))				\
  		QUEUEDEBUG_ABORT("TAILQ_* back %p %s:%d", (elm),	\
  		    __FILE__, __LINE__);
  #define	QUEUEDEBUG_TAILQ_PREREMOVE(head, elm, field)			\
  	if ((elm)->field.tqe_next == NULL &&				\
  	    (head)->tqh_last != &(elm)->field.tqe_next)			\
  		QUEUEDEBUG_ABORT("TAILQ_PREREMOVE head %p elm %p %s:%d",\
  		    (head), (elm), __FILE__, __LINE__);
  #define	QUEUEDEBUG_TAILQ_POSTREMOVE(elm, field)				\
  	(elm)->field.tqe_next = (void *)1L;				\
  	(elm)->field.tqe_prev = (void *)1L;
  #else
  #define	QUEUEDEBUG_TAILQ_INSERT_HEAD(head, elm, field)
  #define	QUEUEDEBUG_TAILQ_INSERT_TAIL(head, elm, field)
  #define	QUEUEDEBUG_TAILQ_OP(elm, field)
  #define	QUEUEDEBUG_TAILQ_PREREMOVE(head, elm, field)
  #define	QUEUEDEBUG_TAILQ_POSTREMOVE(elm, field)
  #endif
  
  #define	TAILQ_INIT(head) do {						\
  	(head)->tqh_first = TAILQ_END(head);				\
  	(head)->tqh_last = &(head)->tqh_first;				\
  } while (/*CONSTCOND*/0)
  
  #define	TAILQ_INSERT_HEAD(head, elm, field) do {			\
  	QUEUEDEBUG_TAILQ_INSERT_HEAD((head), (elm), field)		\
  	if (((elm)->field.tqe_next = (head)->tqh_first) != TAILQ_END(head))\
  		(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 {			\
  	QUEUEDEBUG_TAILQ_INSERT_TAIL((head), (elm), field)		\
  	(elm)->field.tqe_next = TAILQ_END(head);			\
  	(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 {		\
  	QUEUEDEBUG_TAILQ_OP((listelm), field)				\
  	if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != 	\
  	    TAILQ_END(head))						\
  		(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 {			\
  	QUEUEDEBUG_TAILQ_OP((listelm), field)				\
  	(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 {				\
  	QUEUEDEBUG_TAILQ_PREREMOVE((head), (elm), field)		\
  	QUEUEDEBUG_TAILQ_OP((elm), field)				\
  	if (((elm)->field.tqe_next) != TAILQ_END(head))			\
  		(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;			\
  	QUEUEDEBUG_TAILQ_POSTREMOVE((elm), field);			\
  } while (/*CONSTCOND*/0)
  
  #define TAILQ_REPLACE(head, elm, elm2, field) do {			\
          if (((elm2)->field.tqe_next = (elm)->field.tqe_next) != 	\
  	    TAILQ_END(head))   						\
                  (elm2)->field.tqe_next->field.tqe_prev =		\
                      &(elm2)->field.tqe_next;				\
          else								\
                  (head)->tqh_last = &(elm2)->field.tqe_next;		\
          (elm2)->field.tqe_prev = (elm)->field.tqe_prev;			\
          *(elm2)->field.tqe_prev = (elm2);				\
  	QUEUEDEBUG_TAILQ_POSTREMOVE((elm), field);			\
  } while (/*CONSTCOND*/0)
  
  #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)
  
  /*
   * 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 access methods.
   */
  #define	STAILQ_FIRST(head)	((head)->stqh_first)
  #define	STAILQ_END(head)	NULL
  #define	STAILQ_NEXT(elm, field)	((elm)->field.stqe_next)
  #define	STAILQ_EMPTY(head)	(STAILQ_FIRST(head) == STAILQ_END(head))
  
  /*
   * 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_FOREACH_SAFE(var, head, field, tvar)			\
  	for ((var) = STAILQ_FIRST((head));				\
  	    (var) && ((tvar) = STAILQ_NEXT((var), field), 1);		\
  	    (var) = (tvar))
  
  #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)
  
  #define	STAILQ_LAST(head, type, field)					\
  	(STAILQ_EMPTY((head)) ?						\
  		NULL :							\
  	        ((struct type *)(void *)				\
  		((char *)((head)->stqh_last) - offsetof(struct type, field))))
  
  
  #ifndef _KERNEL
  /*
   * Circular queue definitions. Do not use. We still keep the macros
   * for compatibility but because of pointer aliasing issues their use
   * is discouraged!
   */
  
  /*
   * __launder_type():  We use this ugly hack to work around the the compiler
   * noticing that two types may not alias each other and elide tests in code.
   * We hit this in the CIRCLEQ macros when comparing 'struct name *' and
   * 'struct type *' (see CIRCLEQ_HEAD()).  Modern compilers (such as GCC
   * 4.8) declare these comparisons as always false, causing the code to
   * not run as designed.
   *
   * This hack is only to be used for comparisons and thus can be fully const.
   * Do not use for assignment.
   *
   * If we ever choose to change the ABI of the CIRCLEQ macros, we could fix
   * this by changing the head/tail sentinal values, but see the note above
   * this one.
   */
  #ifdef _MSC_VER
  #define __launder_type(x)  ((const void *)(x))
  #else
  static inline const void * __launder_type(const void *);
  static inline const void *
  __launder_type(const void *__x)
  {
  #ifdef SYSC							/* ASG_LK01: SYSTEM-C Equivalent */
  	__asm ("" : "+r" (__x));
  #else								/* ASG_LK01: SYSTEM-C Equivalent */
  	__asm __volatile("" : "+r" (__x));
  #endif								/* ASG_LK01: SYSTEM-C Equivalent */
  	return __x;
  }
  #endif
  
  #if defined(QUEUEDEBUG)
  #define QUEUEDEBUG_CIRCLEQ_HEAD(head, field)				\
  	if ((head)->cqh_first != CIRCLEQ_ENDC(head) &&			\
  	    (head)->cqh_first->field.cqe_prev != CIRCLEQ_ENDC(head))	\
  		QUEUEDEBUG_ABORT("CIRCLEQ head forw %p %s:%d", (head),	\
  		      __FILE__, __LINE__);				\
  	if ((head)->cqh_last != CIRCLEQ_ENDC(head) &&			\
  	    (head)->cqh_last->field.cqe_next != CIRCLEQ_ENDC(head))	\
  		QUEUEDEBUG_ABORT("CIRCLEQ head back %p %s:%d", (head),	\
  		      __FILE__, __LINE__);
  #define QUEUEDEBUG_CIRCLEQ_ELM(head, elm, field)			\
  	if ((elm)->field.cqe_next == CIRCLEQ_ENDC(head)) {		\
  		if ((head)->cqh_last != (elm))				\
  			QUEUEDEBUG_ABORT("CIRCLEQ elm last %p %s:%d",	\
  			    (elm), __FILE__, __LINE__);			\
  	} else {							\
  		if ((elm)->field.cqe_next->field.cqe_prev != (elm))	\
  			QUEUEDEBUG_ABORT("CIRCLEQ elm forw %p %s:%d",	\
  			    (elm), __FILE__, __LINE__);			\
  	}								\
  	if ((elm)->field.cqe_prev == CIRCLEQ_ENDC(head)) {		\
  		if ((head)->cqh_first != (elm))				\
  			QUEUEDEBUG_ABORT("CIRCLEQ elm first %p %s:%d",	\
  			    (elm), __FILE__, __LINE__);			\
  	} else {							\
  		if ((elm)->field.cqe_prev->field.cqe_next != (elm))	\
  			QUEUEDEBUG_ABORT("CIRCLEQ elm prev %p %s:%d",	\
  			    (elm), __FILE__, __LINE__);			\
  	}
  #define QUEUEDEBUG_CIRCLEQ_POSTREMOVE(elm, field)			\
  	(elm)->field.cqe_next = (void *)1L;				\
  	(elm)->field.cqe_prev = (void *)1L;
  #else
  #define QUEUEDEBUG_CIRCLEQ_HEAD(head, field)
  #define QUEUEDEBUG_CIRCLEQ_ELM(head, elm, field)
  #define QUEUEDEBUG_CIRCLEQ_POSTREMOVE(elm, field)
  #endif
  
  #define	CIRCLEQ_HEAD(name, type)					\
  struct name {								\
  	struct type *cqh_first;		/* first element */		\
  	struct type *cqh_last;		/* last element */		\
  }
  
  #define	CIRCLEQ_HEAD_INITIALIZER(head)					\
  	{ CIRCLEQ_END(&head), CIRCLEQ_END(&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 = CIRCLEQ_END(head);				\
  	(head)->cqh_last = CIRCLEQ_END(head);				\
  } while (/*CONSTCOND*/0)
  
  #define	CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {		\
  	QUEUEDEBUG_CIRCLEQ_HEAD((head), field)				\
  	QUEUEDEBUG_CIRCLEQ_ELM((head), (listelm), field)		\
  	(elm)->field.cqe_next = (listelm)->field.cqe_next;		\
  	(elm)->field.cqe_prev = (listelm);				\
  	if ((listelm)->field.cqe_next == CIRCLEQ_ENDC(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 {		\
  	QUEUEDEBUG_CIRCLEQ_HEAD((head), field)				\
  	QUEUEDEBUG_CIRCLEQ_ELM((head), (listelm), field)		\
  	(elm)->field.cqe_next = (listelm);				\
  	(elm)->field.cqe_prev = (listelm)->field.cqe_prev;		\
  	if ((listelm)->field.cqe_prev == CIRCLEQ_ENDC(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 {			\
  	QUEUEDEBUG_CIRCLEQ_HEAD((head), field)				\
  	(elm)->field.cqe_next = (head)->cqh_first;			\
  	(elm)->field.cqe_prev = CIRCLEQ_END(head);			\
  	if ((head)->cqh_last == CIRCLEQ_ENDC(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 {			\
  	QUEUEDEBUG_CIRCLEQ_HEAD((head), field)				\
  	(elm)->field.cqe_next = CIRCLEQ_END(head);			\
  	(elm)->field.cqe_prev = (head)->cqh_last;			\
  	if ((head)->cqh_first == CIRCLEQ_ENDC(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 {				\
  	QUEUEDEBUG_CIRCLEQ_HEAD((head), field)				\
  	QUEUEDEBUG_CIRCLEQ_ELM((head), (elm), field)			\
  	if ((elm)->field.cqe_next == CIRCLEQ_ENDC(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 == CIRCLEQ_ENDC(head))		\
  		(head)->cqh_first = (elm)->field.cqe_next;		\
  	else								\
  		(elm)->field.cqe_prev->field.cqe_next =			\
  		    (elm)->field.cqe_next;				\
  	QUEUEDEBUG_CIRCLEQ_POSTREMOVE((elm), field)			\
  } while (/*CONSTCOND*/0)
  
  #define	CIRCLEQ_FOREACH(var, head, field)				\
  	for ((var) = ((head)->cqh_first);				\
  		(var) != CIRCLEQ_ENDC(head);				\
  		(var) = ((var)->field.cqe_next))
  
  #define	CIRCLEQ_FOREACH_REVERSE(var, head, field)			\
  	for ((var) = ((head)->cqh_last);				\
  		(var) != CIRCLEQ_ENDC(head);				\
  		(var) = ((var)->field.cqe_prev))
  
  /*
   * Circular queue access methods.
   */
  #define	CIRCLEQ_FIRST(head)		((head)->cqh_first)
  #define	CIRCLEQ_LAST(head)		((head)->cqh_last)
  /* For comparisons */
  #define	CIRCLEQ_ENDC(head)		(__launder_type(head))
  /* For assignments */
  #define	CIRCLEQ_END(head)		((void *)(head))
  #define	CIRCLEQ_NEXT(elm, field)	((elm)->field.cqe_next)
  #define	CIRCLEQ_PREV(elm, field)	((elm)->field.cqe_prev)
  #define	CIRCLEQ_EMPTY(head)						\
      (CIRCLEQ_FIRST(head) == CIRCLEQ_ENDC(head))
  
  #define CIRCLEQ_LOOP_NEXT(head, elm, field)				\
  	(((elm)->field.cqe_next == CIRCLEQ_ENDC(head))			\
  	    ? ((head)->cqh_first)					\
  	    : (elm->field.cqe_next))
  #define CIRCLEQ_LOOP_PREV(head, elm, field)				\
  	(((elm)->field.cqe_prev == CIRCLEQ_ENDC(head))			\
  	    ? ((head)->cqh_last)					\
  	    : (elm->field.cqe_prev))
  #endif /* !_KERNEL */
  
  #endif	/* !_SYS_QUEUE_H_ */
  