/*
 * 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 */