/*  $OpenBSD: queue.h,v 1.38 2013/07/03 15:05:21 fgsch Exp $  */

/*  $NetBSD: queue.h,v 1.11 1996/05/16 05:17:14 mycroft 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

 */

#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 before or 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.

 */

#if defined(QUEUE_MACRO_DEBUG) || (defined(_KERNEL) && defined(DIAGNOSTIC))

#define _Q_INVALIDATE(a) (a) = ((void *)-1)

#else

#define _Q_INVALIDATE(a)

#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) (SLIST_FIRST(head) == SLIST_END(head))

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

#define SLIST_FOREACH(var, head, field)         \

    for((var) = SLIST_FIRST(head);          \

        (var) != SLIST_END(head);         \

        (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))

/*

 * Singly-linked List functions.

 */

#define SLIST_INIT(head) do {           \

    SLIST_FIRST(head) = SLIST_END(head);        \

} while(0)

#define SLIST_INSERT_AFTER(slistelm, elm, field) do {     \

    (elm)->field.sle_next = (slistelm)->field.sle_next;   \

    (slistelm)->field.sle_next = (elm);       \

} while (0)

#define SLIST_INSERT_HEAD(head, elm, field) do {      \

    (elm)->field.sle_next = (head)->slh_first;      \

    (head)->slh_first = (elm);          \

} while (0)

#define SLIST_REMOVE_AFTER(elm, field) do {       \

    (elm)->field.sle_next = (elm)->field.sle_next->field.sle_next;  \

} while (0)

#define SLIST_REMOVE_HEAD(head, field) do {       \

    (head)->slh_first = (head)->slh_first->field.sle_next;    \

} while (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;   \

        _Q_INVALIDATE((elm)->field.sle_next);     \

    }               \

} while (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)    (LIST_FIRST(head) == LIST_END(head))

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

#define LIST_FOREACH(var, head, field)          \

    for((var) = LIST_FIRST(head);         \

        (var)!= LIST_END(head);         \

        (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))

/*

 * List functions.

 */

#define LIST_INIT(head) do {           \

    LIST_FIRST(head) = LIST_END(head);       \

} while (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 (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 (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 (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;     \

    _Q_INVALIDATE((elm)->field.le_prev);        \

    _Q_INVALIDATE((elm)->field.le_next);        \

} while (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);        \

    _Q_INVALIDATE((elm)->field.le_prev);        \

    _Q_INVALIDATE((elm)->field.le_next);        \

} while (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)     (SIMPLEQ_FIRST(head) == SIMPLEQ_END(head))

#define SIMPLEQ_NEXT(elm, field)    ((elm)->field.sqe_next)

#define SIMPLEQ_FOREACH(var, head, field)       \

    for((var) = SIMPLEQ_FIRST(head);        \

        (var) != SIMPLEQ_END(head);         \

        (var) = SIMPLEQ_NEXT(var, field))

#define SIMPLEQ_FOREACH_SAFE(var, head, field, tvar)      \

    for ((var) = SIMPLEQ_FIRST(head);       \

        (var) && ((tvar) = SIMPLEQ_NEXT(var, field), 1);   \

        (var) = (tvar))

/*

 * Simple queue functions.

 */

#define SIMPLEQ_INIT(head) do {           \

    (head)->sqh_first = NULL;         \

    (head)->sqh_last = &(head)->sqh_first;        \

} while (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 (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 (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 (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 (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 (0)

/*

 * XOR Simple queue definitions.

 */

#define XSIMPLEQ_HEAD(name, type)         \

struct name {               \

    struct type *sqx_first; /* first element */     \

    struct type **sqx_last; /* addr of last next element */   \

    unsigned long sqx_cookie;         \

}

#define XSIMPLEQ_ENTRY(type)            \

struct {                \

    struct type *sqx_next;  /* next element */      \

}

/*

 * XOR Simple queue access methods.

 */

#define XSIMPLEQ_XOR(head, ptr)     ((__typeof(ptr))((head)->sqx_cookie ^ \

                    (unsigned long)(ptr)))

#define XSIMPLEQ_FIRST(head)      XSIMPLEQ_XOR(head, ((head)->sqx_first))

#define XSIMPLEQ_END(head)      NULL

#define XSIMPLEQ_EMPTY(head)      (XSIMPLEQ_FIRST(head) == XSIMPLEQ_END(head))

#define XSIMPLEQ_NEXT(head, elm, field)    XSIMPLEQ_XOR(head, ((elm)->field.sqx_next))

#define XSIMPLEQ_FOREACH(var, head, field)        \

    for ((var) = XSIMPLEQ_FIRST(head);        \

        (var) != XSIMPLEQ_END(head);        \

        (var) = XSIMPLEQ_NEXT(head, var, field))

#define XSIMPLEQ_FOREACH_SAFE(var, head, field, tvar)     \

    for ((var) = XSIMPLEQ_FIRST(head);        \

        (var) && ((tvar) = XSIMPLEQ_NEXT(head, var, field), 1); \

        (var) = (tvar))

/*

 * XOR Simple queue functions.

 */

#define XSIMPLEQ_INIT(head) do {          \

    arc4random_buf(&(head)->sqx_cookie, sizeof((head)->sqx_cookie)); \

    (head)->sqx_first = XSIMPLEQ_XOR(head, NULL);     \

    (head)->sqx_last = XSIMPLEQ_XOR(head, &(head)->sqx_first);  \

} while (0)

#define XSIMPLEQ_INSERT_HEAD(head, elm, field) do {     \

    if (((elm)->field.sqx_next = (head)->sqx_first) ==    \

        XSIMPLEQ_XOR(head, NULL))         \

        (head)->sqx_last = XSIMPLEQ_XOR(head, &(elm)->field.sqx_next); \

    (head)->sqx_first = XSIMPLEQ_XOR(head, (elm));      \

} while (0)

#define XSIMPLEQ_INSERT_TAIL(head, elm, field) do {     \

    (elm)->field.sqx_next = XSIMPLEQ_XOR(head, NULL);   \

    *(XSIMPLEQ_XOR(head, (head)->sqx_last)) = XSIMPLEQ_XOR(head, (elm)); \

    (head)->sqx_last = XSIMPLEQ_XOR(head, &(elm)->field.sqx_next);  \

} while (0)

#define XSIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do {   \

    if (((elm)->field.sqx_next = (listelm)->field.sqx_next) ==  \

        XSIMPLEQ_XOR(head, NULL))         \

        (head)->sqx_last = XSIMPLEQ_XOR(head, &(elm)->field.sqx_next); \

    (listelm)->field.sqx_next = XSIMPLEQ_XOR(head, (elm));    \

} while (0)

#define XSIMPLEQ_REMOVE_HEAD(head, field) do {        \

    if (((head)->sqx_first = XSIMPLEQ_XOR(head,     \

        (head)->sqx_first)->field.sqx_next) == XSIMPLEQ_XOR(head, NULL)) \

        (head)->sqx_last = XSIMPLEQ_XOR(head, &(head)->sqx_first); \

} while (0)

#define XSIMPLEQ_REMOVE_AFTER(head, elm, field) do {      \

    if (((elm)->field.sqx_next = XSIMPLEQ_XOR(head,     \

        (elm)->field.sqx_next)->field.sqx_next)     \

        == XSIMPLEQ_XOR(head, NULL))        \

        (head)->sqx_last =          \

            XSIMPLEQ_XOR(head, &(elm)->field.sqx_next);   \

} while (0)

/*

 * Tail queue definitions.

 */

#define TAILQ_HEAD(name, type)            \

struct name {               \

    struct type *tqh_first; /* first element */     \

    struct type **tqh_last; /* addr of last next element */   \

}

#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 */  \

}

/* 

 * 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))

/* XXX */

#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) = TAILQ_FIRST(head);         \

        (var) != TAILQ_END(head);         \

        (var) = TAILQ_NEXT(var, field))

#define TAILQ_FOREACH_SAFE(var, head, field, tvar)      \

    for ((var) = TAILQ_FIRST(head);         \

        (var) != TAILQ_END(head) &&         \

        ((tvar) = TAILQ_NEXT(var, field), 1);     \

        (var) = (tvar))

#define TAILQ_FOREACH_REVERSE(var, head, headname, field)   \

    for((var) = TAILQ_LAST(head, headname);       \

        (var) != TAILQ_END(head);         \

        (var) = TAILQ_PREV(var, headname, field))

#define TAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar)  \

    for ((var) = TAILQ_LAST(head, headname);      \

        (var) != TAILQ_END(head) &&         \

        ((tvar) = TAILQ_PREV(var, headname, field), 1);   \

        (var) = (tvar))

/*

 * Tail queue functions.

 */

#define TAILQ_INIT(head) do {           \

    (head)->tqh_first = NULL;         \

    (head)->tqh_last = &(head)->tqh_first;        \

} while (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 (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 (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 (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 (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;     \

    _Q_INVALIDATE((elm)->field.tqe_prev);       \

    _Q_INVALIDATE((elm)->field.tqe_next);       \

} while (0)

#define TAILQ_REPLACE(head, elm, elm2, field) do {      \

    if (((elm2)->field.tqe_next = (elm)->field.tqe_next) != NULL) \

        (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);       \

    _Q_INVALIDATE((elm)->field.tqe_prev);       \

    _Q_INVALIDATE((elm)->field.tqe_next);       \

} while (0)

/*

 * 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)          \

    { 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 access methods 

 */

#define CIRCLEQ_FIRST(head)   ((head)->cqh_first)

#define CIRCLEQ_LAST(head)    ((head)->cqh_last)

#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_END(head))

#define CIRCLEQ_FOREACH(var, head, field)       \

    for((var) = CIRCLEQ_FIRST(head);        \

        (var) != CIRCLEQ_END(head);         \

        (var) = CIRCLEQ_NEXT(var, field))

#define CIRCLEQ_FOREACH_SAFE(var, head, field, tvar)      \

    for ((var) = CIRCLEQ_FIRST(head);       \

        (var) != CIRCLEQ_END(head) &&       \

        ((tvar) = CIRCLEQ_NEXT(var, field), 1);     \

        (var) = (tvar))

#define CIRCLEQ_FOREACH_REVERSE(var, head, field)     \

    for((var) = CIRCLEQ_LAST(head);         \

        (var) != CIRCLEQ_END(head);         \

        (var) = CIRCLEQ_PREV(var, field))

#define CIRCLEQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar)  \

    for ((var) = CIRCLEQ_LAST(head, headname);      \

        (var) != CIRCLEQ_END(head) &&         \

        ((tvar) = CIRCLEQ_PREV(var, headname, field), 1);   \

        (var) = (tvar))

/*

 * Circular queue functions.

 */

#define CIRCLEQ_INIT(head) do {           \

    (head)->cqh_first = CIRCLEQ_END(head);        \

    (head)->cqh_last = CIRCLEQ_END(head);       \

} while (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 == CIRCLEQ_END(head))   \

        (head)->cqh_last = (elm);       \

    else                \

        (listelm)->field.cqe_next->field.cqe_prev = (elm);  \

    (listelm)->field.cqe_next = (elm);        \

} while (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 == CIRCLEQ_END(head))   \

        (head)->cqh_first = (elm);        \

    else                \

        (listelm)->field.cqe_prev->field.cqe_next = (elm);  \

    (listelm)->field.cqe_prev = (elm);        \

} while (0)

#define CIRCLEQ_INSERT_HEAD(head, elm, field) do {      \

    (elm)->field.cqe_next = (head)->cqh_first;      \

    (elm)->field.cqe_prev = CIRCLEQ_END(head);      \

    if ((head)->cqh_last == CIRCLEQ_END(head))      \

        (head)->cqh_last = (elm);       \

    else                \

        (head)->cqh_first->field.cqe_prev = (elm);    \

    (head)->cqh_first = (elm);          \

} while (0)

#define CIRCLEQ_INSERT_TAIL(head, elm, field) do {      \

    (elm)->field.cqe_next = CIRCLEQ_END(head);      \

    (elm)->field.cqe_prev = (head)->cqh_last;     \

    if ((head)->cqh_first == CIRCLEQ_END(head))     \

        (head)->cqh_first = (elm);        \

    else                \

        (head)->cqh_last->field.cqe_next = (elm);   \

    (head)->cqh_last = (elm);         \

} while (0)

#define CIRCLEQ_REMOVE(head, elm, field) do {       \

    if ((elm)->field.cqe_next == CIRCLEQ_END(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_END(head))     \

        (head)->cqh_first = (elm)->field.cqe_next;    \

    else                \

        (elm)->field.cqe_prev->field.cqe_next =     \

            (elm)->field.cqe_next;        \

    _Q_INVALIDATE((elm)->field.cqe_prev);       \

    _Q_INVALIDATE((elm)->field.cqe_next);       \

} while (0)

#define CIRCLEQ_REPLACE(head, elm, elm2, field) do {      \

    if (((elm2)->field.cqe_next = (elm)->field.cqe_next) ==   \

        CIRCLEQ_END(head))            \

        (head)->cqh_last = (elm2);        \

    else                \

        (elm2)->field.cqe_next->field.cqe_prev = (elm2);  \

    if (((elm2)->field.cqe_prev = (elm)->field.cqe_prev) ==   \

        CIRCLEQ_END(head))            \

        (head)->cqh_first = (elm2);       \

    else                \

        (elm2)->field.cqe_prev->field.cqe_next = (elm2);  \

    _Q_INVALIDATE((elm)->field.cqe_prev);       \

    _Q_INVALIDATE((elm)->field.cqe_next);       \

} while (0)

#endif  /* !_SYS_QUEUE_H_ */