text: /*-
   * 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.
   * 4. 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.
   *
   */
  
  #ifndef _USER_QUEUE_H_
  #define	_USER_QUEUE_H_
  
  /*
   * 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 }
  
  #if defined(_WIN32)
  #if defined(SLIST_ENTRY)
  #undef SLIST_ENTRY
  #endif
  #endif
  
  #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(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", (void *)(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", (void *)(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", (void *)(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 /* (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(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", (void *)(head));	\
  } while (0)
  
  #define	QMD_TAILQ_CHECK_TAIL(head, field) do {					\
  	if (*(head)->tqh_last != NULL)						\
  	    	panic("Bad tailq NEXT(%p->tqh_last) != NULL", (void *)(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", (void *)(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", (void *)(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 /* (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)
  
  #endif /* !_SYS_QUEUE_H_ */
  