/*
 * 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.
 *                      SLIST   LIST    STAILQ  TAILQ   CIRCLEQ
 * _HEAD                +       +       +       +       +
 * _HEAD_INITIALIZER    +       +       +       +       +
 * _ENTRY               +       +       +       +       +
 * _INIT                +       +       +       +       +
 * _EMPTY               +       +       +       +       +
 * _FIRST               +       +       +       +       +
 * _NEXT                +       +       +       +       +
 * _PREV                -       -       -       +       +
 * _LAST                -       -       +       +       +
 * _FOREACH             +       +       +       +       +
 * _FOREACH_REVERSE     -       -       -       +       +
 * _INSERT_HEAD         +       +       +       +       +
 * _INSERT_BEFORE       -       +       -       +       +
 * _INSERT_AFTER        +       +       +       +       +
 * _INSERT_TAIL         -       -       +       +       +
 * _REMOVE_HEAD         +       -       +       -       -
 * _REMOVE              +       +       +       +       +
 */

/*
 * 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 */
