/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * 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.
 */

#ifndef _SYS_QUEUE_H_
#define _SYS_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 be traversed in either 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.
 *
 * Below is a summary of implemented functions where:
 *  +  means the macro is available
 *  -  means the macro is not available
 *  s  means the macro is available but is slow (runs in O(n) time)
 *
 *				SLIST	LIST	STAILQ	TAILQ
 * _HEAD			+	+	+	+
 * _CLASS_HEAD			+	+	+	+
 * _HEAD_INITIALIZER		+	+	+	+
 * _ENTRY			+	+	+	+
 * _CLASS_ENTRY			+	+	+	+
 * _INIT			+	+	+	+
 * _EMPTY			+	+	+	+
 * _END				+	+	+	+
 * _FIRST			+	+	+	+
 * _NEXT			+	+	+	+
 * _PREV			-	+	-	+
 * _LAST			-	-	+	+
 * _LAST_FAST			-	-	-	+
 * _FOREACH			+	+	+	+
 * _FOREACH_FROM		+	+	+	+
 * _FOREACH_SAFE		+	+	+	+
 * _FOREACH_FROM_SAFE		+	+	+	+
 * _FOREACH_REVERSE		-	-	-	+
 * _FOREACH_REVERSE_FROM	-	-	-	+
 * _FOREACH_REVERSE_SAFE	-	-	-	+
 * _FOREACH_REVERSE_FROM_SAFE	-	-	-	+
 * _INSERT_HEAD			+	+	+	+
 * _INSERT_BEFORE		-	+	-	+
 * _INSERT_AFTER		+	+	+	+
 * _INSERT_TAIL			-	-	+	+
 * _CONCAT			s	s	+	+
 * _REMOVE_AFTER		+	-	+	-
 * _REMOVE_HEAD			+	+	+	+
 * _REMOVE			s	+	s	+
 * _REPLACE			-	+	-	+
 * _SWAP			+	+	+	+
 *
 */
#ifdef QUEUE_MACRO_DEBUG
#warn Use QUEUE_MACRO_DEBUG_TRACE and / or QUEUE_MACRO_DEBUG_TRASH
#define QUEUE_MACRO_DEBUG_TRACE
#define QUEUE_MACRO_DEBUG_TRASH
#endif

#ifdef QUEUE_MACRO_DEBUG_TRACE
/* Store the last 2 places the queue element or head was altered */
struct qm_trace {
  unsigned long lastline;
  unsigned long prevline;
  const char   *lastfile;
  const char   *prevfile;
};

#define TRACEBUF             struct qm_trace trace;
#define TRACEBUF_INITIALIZER {__LINE__, 0, __FILE__, NULL},

#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 /* !QUEUE_MACRO_DEBUG_TRACE */
#define QMD_TRACE_ELEM(elem)
#define QMD_TRACE_HEAD(head)
#define TRACEBUF
#define TRACEBUF_INITIALIZER
#endif /* QUEUE_MACRO_DEBUG_TRACE */

#ifdef QUEUE_MACRO_DEBUG_TRASH
#define QMD_SAVELINK(name, link) void **name = (void *)&(link)
#define TRASHIT(x)    \
  do {                \
    (x) = (void *)-1; \
  } while (0)
#define QMD_IS_TRASHED(x) ((x) == (void *)(intptr_t)-1)
#else /* !QUEUE_MACRO_DEBUG_TRASH */
#define QMD_SAVELINK(name, link)
#define TRASHIT(x)
#define QMD_IS_TRASHED(x) 0
#endif /* QUEUE_MACRO_DEBUG_TRASH */

#ifdef __cplusplus
/*
 * In C++ there can be structure lists and class lists:
 */
#define QUEUE_TYPEOF(type) type
#else
#define QUEUE_TYPEOF(type) struct type
#endif

/*
 * Singly-linked List declarations.
 */
#define SLIST_HEAD(name, type)                  \
  struct name {                                 \
    struct type *slh_first; /* first element */ \
  }

#define SLIST_CLASS_HEAD(name, type)           \
  struct name {                                \
    class type *slh_first; /* first element */ \
  }

#define SLIST_HEAD_INITIALIZER(head) {NULL}

#define SLIST_ENTRY(type)                     \
  struct {                                    \
    struct type *sle_next; /* next element */ \
  }

#define SLIST_CLASS_ENTRY(type)              \
  struct {                                   \
    class type *sle_next; /* next element */ \
  }

/*
 * Singly-linked List functions.
 */
#if (defined(_KERNEL) && defined(INVARIANTS))
#define QMD_SLIST_CHECK_PREVPTR(prevp, elm)                             \
  do {                                                                  \
    if (*(prevp) != (elm))                                              \
      panic("Bad prevptr *(%p) == %p != %p", (prevp), *(prevp), (elm)); \
  } while (0)
#else
#define QMD_SLIST_CHECK_PREVPTR(prevp, elm)
#endif

#define SLIST_CONCAT(head1, head2, type, field)              \
  do {                                                       \
    QUEUE_TYPEOF(type) *curelm = SLIST_FIRST(head1);         \
    if (curelm == NULL) {                                    \
      if ((SLIST_FIRST(head1) = SLIST_FIRST(head2)) != NULL) \
        SLIST_INIT(head2);                                   \
    } else if (SLIST_FIRST(head2) != NULL) {                 \
      while (SLIST_NEXT(curelm, field) != NULL)              \
        curelm = SLIST_NEXT(curelm, field);                  \
      SLIST_NEXT(curelm, field) = SLIST_FIRST(head2);        \
      SLIST_INIT(head2);                                     \
    }                                                        \
  } while (0)

#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_FROM(var, head, field)                 \
  for ((var) = ((var) ? (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_FROM_SAFE(var, head, field, tvar) \
  for ((var) = ((var) ? (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 {                                                \
    if (SLIST_FIRST((head)) == (elm)) {               \
      SLIST_REMOVE_HEAD((head), field);               \
    } else {                                          \
      QUEUE_TYPEOF(type) *curelm = SLIST_FIRST(head); \
      while (SLIST_NEXT(curelm, field) != (elm))      \
        curelm = SLIST_NEXT(curelm, field);           \
      SLIST_REMOVE_AFTER(curelm, field);              \
    }                                                 \
  } while (0)

#define SLIST_REMOVE_AFTER(elm, field)                                  \
  do {                                                                  \
    QMD_SAVELINK(oldnext, SLIST_NEXT(elm, field)->field.sle_next);      \
    SLIST_NEXT(elm, field) = SLIST_NEXT(SLIST_NEXT(elm, field), field); \
    TRASHIT(*oldnext);                                                  \
  } while (0)

#define SLIST_REMOVE_HEAD(head, field)                            \
  do {                                                            \
    QMD_SAVELINK(oldnext, SLIST_FIRST(head)->field.sle_next);     \
    SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field); \
    TRASHIT(*oldnext);                                            \
  } while (0)

#define SLIST_REMOVE_PREVPTR(prevp, elm, field) \
  do {                                          \
    QMD_SLIST_CHECK_PREVPTR(prevp, elm);        \
    *(prevp) = SLIST_NEXT(elm, field);          \
    TRASHIT((elm)->field.sle_next);             \
  } while (0)

#define SLIST_SWAP(head1, head2, type)                   \
  do {                                                   \
    QUEUE_TYPEOF(type) *swap_first = SLIST_FIRST(head1); \
    SLIST_FIRST(head1)             = SLIST_FIRST(head2); \
    SLIST_FIRST(head2)             = swap_first;         \
  } while (0)

#define SLIST_END(head) NULL

/*
 * 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_CLASS_HEAD(name, type)                        \
  struct name {                                              \
    class type  *stqh_first; /* first element */             \
    class 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 */ \
  }

#define STAILQ_CLASS_ENTRY(type)              \
  struct {                                    \
    class 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_FROM(var, head, field)                 \
  for ((var) = ((var) ? (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_FOREACH_FROM_SAFE(var, head, field, tvar) \
  for ((var) = ((var) ? (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                              \
                        : __containerof((head)->stqh_last,  \
                                        QUEUE_TYPEOF(type), \
                                        field.stqe_next))

#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 {                                           \
      QUEUE_TYPEOF(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 {                                                    \
    QUEUE_TYPEOF(type) *swap_first = STAILQ_FIRST(head1); \
    QUEUE_TYPEOF(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)

#define STAILQ_END(head) NULL

/*
 * List declarations.
 */
#define LIST_HEAD(name, type)                  \
  struct name {                                \
    struct type *lh_first; /* first element */ \
  }

#define LIST_CLASS_HEAD(name, type)           \
  struct name {                               \
    class 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 */ \
  }

#define LIST_CLASS_ENTRY(type)                                   \
  struct {                                                       \
    class type  *le_next; /* next element */                     \
    class type **le_prev; /* address of previous next element */ \
  }

/*
 * List functions.
 */

#if (defined(_KERNEL) && defined(INVARIANTS))
/*
 * QMD_LIST_CHECK_HEAD(LIST_HEAD *head, LIST_ENTRY NAME)
 *
 * If the list is non-empty, validates that the first element of the list
 * points back at 'head.'
 */
#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", (head));      \
  } while (0)

/*
 * QMD_LIST_CHECK_NEXT(TYPE *elm, LIST_ENTRY NAME)
 *
 * If an element follows 'elm' in the list, validates that the next element
 * points back at 'elm.'
 */
#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", (elm));                   \
  } while (0)

/*
 * QMD_LIST_CHECK_PREV(TYPE *elm, LIST_ENTRY NAME)
 *
 * Validates that the previous element (or head of the list) points to 'elm.'
 */
#define QMD_LIST_CHECK_PREV(elm, field)                  \
  do {                                                   \
    if (*(elm)->field.le_prev != (elm))                  \
      panic("Bad link elm %p prev->next != elm", (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 /* (_KERNEL && INVARIANTS) */

#define LIST_CONCAT(head1, head2, type, field)                      \
  do {                                                              \
    QUEUE_TYPEOF(type) *curelm = LIST_FIRST(head1);                 \
    if (curelm == NULL) {                                           \
      if ((LIST_FIRST(head1) = LIST_FIRST(head2)) != NULL) {        \
        LIST_FIRST(head2)->field.le_prev = &LIST_FIRST((head1));    \
        LIST_INIT(head2);                                           \
      }                                                             \
    } else if (LIST_FIRST(head2) != NULL) {                         \
      while (LIST_NEXT(curelm, field) != NULL)                      \
        curelm = LIST_NEXT(curelm, field);                          \
      LIST_NEXT(curelm, field)         = LIST_FIRST(head2);         \
      LIST_FIRST(head2)->field.le_prev = &LIST_NEXT(curelm, field); \
      LIST_INIT(head2);                                             \
    }                                                               \
  } while (0)

#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_FROM(var, head, field)                 \
  for ((var) = ((var) ? (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_FOREACH_FROM_SAFE(var, head, field, tvar) \
  for ((var) = ((var) ? (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_PREV(elm, head, type, field)      \
  ((elm)->field.le_prev == &LIST_FIRST((head)) \
       ? NULL                                  \
       : __containerof(                        \
             (elm)->field.le_prev, QUEUE_TYPEOF(type), field.le_next))

#define LIST_REMOVE_HEAD(head, field) LIST_REMOVE(LIST_FIRST(head), field)

#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_REPLACE(elm, elm2, 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);                                    \
    LIST_NEXT((elm2), field) = LIST_NEXT((elm), field);                 \
    if (LIST_NEXT((elm2), field) != NULL)                               \
      LIST_NEXT((elm2), field)->field.le_prev = &(elm2)->field.le_next; \
    (elm2)->field.le_prev  = (elm)->field.le_prev;                      \
    *(elm2)->field.le_prev = (elm2);                                    \
    TRASHIT(*oldnext);                                                  \
    TRASHIT(*oldprev);                                                  \
  } while (0)

#define LIST_SWAP(head1, head2, type, field)            \
  do {                                                  \
    QUEUE_TYPEOF(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)

#define LIST_END(head) NULL

/*
 * 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_CLASS_HEAD(name, type)                        \
  struct name {                                             \
    class type  *tqh_first; /* first element */             \
    class type **tqh_last;  /* addr of last next element */ \
    TRACEBUF                                                \
  }

#define TAILQ_HEAD_INITIALIZER(head) \
  {NULL, &(head).tqh_first, TRACEBUF_INITIALIZER}

#define TAILQ_ENTRY(type)                                          \
  struct {                                                         \
    struct type  *tqe_next; /* next element */                     \
    struct type **tqe_prev; /* address of previous next element */ \
    TRACEBUF                                                       \
  }

#define TAILQ_CLASS_ENTRY(type)                                   \
  struct {                                                        \
    class type  *tqe_next; /* next element */                     \
    class type **tqe_prev; /* address of previous next element */ \
    TRACEBUF                                                      \
  }

/*
 * Tail queue functions.
 */
#if (defined(_KERNEL) && defined(INVARIANTS))
/*
 * QMD_TAILQ_CHECK_HEAD(TAILQ_HEAD *head, TAILQ_ENTRY NAME)
 *
 * If the tailq is non-empty, validates that the first element of the tailq
 * points back at 'head.'
 */
#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", (head));        \
  } while (0)

/*
 * QMD_TAILQ_CHECK_TAIL(TAILQ_HEAD *head, TAILQ_ENTRY NAME)
 *
 * Validates that the tail of the tailq is a pointer to pointer to NULL.
 */
#define QMD_TAILQ_CHECK_TAIL(head, field)                    \
  do {                                                       \
    if (*(head)->tqh_last != NULL)                           \
      panic("Bad tailq NEXT(%p->tqh_last) != NULL", (head)); \
  } while (0)

/*
 * QMD_TAILQ_CHECK_NEXT(TYPE *elm, TAILQ_ENTRY NAME)
 *
 * If an element follows 'elm' in the tailq, validates that the next element
 * points back at 'elm.'
 */
#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", (elm));                      \
  } while (0)

/*
 * QMD_TAILQ_CHECK_PREV(TYPE *elm, TAILQ_ENTRY NAME)
 *
 * Validates that the previous element (or head of the tailq) points to 'elm.'
 */
#define QMD_TAILQ_CHECK_PREV(elm, field)                 \
  do {                                                   \
    if (*(elm)->field.tqe_prev != (elm))                 \
      panic("Bad link elm %p prev->next != elm", (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 /* (_KERNEL && 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_FROM(var, head, field)                 \
  for ((var) = ((var) ? (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_FROM_SAFE(var, head, field, tvar) \
  for ((var) = ((var) ? (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_FROM(var, head, headname, field)        \
  for ((var) = ((var) ? (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_FOREACH_REVERSE_FROM_SAFE(var, head, headname, field, tvar) \
  for ((var) = ((var) ? (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))

/*
 * The FAST function is fast in that it causes no data access other
 * then the access to the head. The standard LAST function above
 * will cause a data access of both the element you want and
 * the previous element. FAST is very useful for instances when
 * you may want to prefetch the last data element.
 */
#define TAILQ_LAST_FAST(head, type, field) \
  (TAILQ_EMPTY(head)                       \
       ? NULL                              \
       : __containerof((head)->tqh_last, QUEUE_TYPEOF(type), field.tqe_next))

#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_PREV_FAST(elm, head, type, field) \
  ((elm)->field.tqe_prev == &(head)->tqh_first  \
       ? NULL                                   \
       : __containerof(                         \
             (elm)->field.tqe_prev, QUEUE_TYPEOF(type), field.tqe_next))

#define TAILQ_REMOVE_HEAD(head, field) \
  TAILQ_REMOVE(head, TAILQ_FIRST(head), field)

#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_REPLACE(head, elm, elm2, 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);                                      \
    TAILQ_NEXT((elm2), field) = TAILQ_NEXT((elm), field);                  \
    if (TAILQ_NEXT((elm2), field) != TAILQ_END(head))                      \
      TAILQ_NEXT((elm2), field)->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);                                      \
    TRASHIT(*oldnext);                                                     \
    TRASHIT(*oldprev);                                                     \
    QMD_TRACE_ELEM(&(elm)->field);                                         \
  } while (0)

#define TAILQ_SWAP(head1, head2, type, field)            \
  do {                                                   \
    QUEUE_TYPEOF(type) *swap_first = (head1)->tqh_first; \
    QUEUE_TYPEOF(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)

#define TAILQ_END(head) NULL

#endif /* !_SYS_QUEUE_H_ */
