rough framework

[lemu] / bsd_queue.h

/*      $OpenBSD: queue.h,v 1.46 2020/12/30 13:33:12 millert 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 BSD_QUEUE_H
#define BSD_QUEUE_H

// #include <sys/_null.h>

/*
 * This file defines five types of data structures: singly-linked lists,
 * lists, simple queues, tail queues and XOR simple 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 to 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.
 *
 * An XOR simple queue is used in the same way as a regular simple queue.
 * The difference is that the head structure also includes a "cookie" that
 * is XOR'd with the queue pointer (first, last or next) to generate the
 * real pointer value.
 *
 * 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_INVALID ((void *)-1)
#define _Q_INVALIDATE(a) (a) = _Q_INVALID
#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) {                                              \
        SLIST_FIRST(head) = SLIST_END(head);                            \
}

#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)

#define SIMPLEQ_CONCAT(head1, head2) do {                               \
        if (!SIMPLEQ_EMPTY((head2))) {                                  \
                *(head1)->sqh_last = (head2)->sqh_first;                \
                (head1)->sqh_last = (head2)->sqh_last;                  \
                SIMPLEQ_INIT((head2));                                  \
        }                                                               \
} 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)

#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 (0)

/*
 * Singly-linked Tail queue declarations.
 */
#define STAILQ_HEAD(name, type)                                         \
struct name {                                                           \
        struct type *stqh_first;        /* first element */             \
        struct type **stqh_last;        /* addr of last next element */ \
}

#define STAILQ_HEAD_INITIALIZER(head)                                   \
        { NULL, &(head).stqh_first }

#define STAILQ_ENTRY(type)                                              \
struct {                                                                \
        struct type *stqe_next; /* next element */                      \
}

/*
 * Singly-linked Tail queue access methods.
 */
#define STAILQ_FIRST(head)      ((head)->stqh_first)
#define STAILQ_END(head)        NULL
#define STAILQ_EMPTY(head)      (STAILQ_FIRST(head) == STAILQ_END(head))
#define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)

#define STAILQ_FOREACH(var, head, field)                                \
        for ((var) = STAILQ_FIRST(head);                                \
            (var) != STAILQ_END(head);                                  \
            (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))

/*
 * Singly-linked Tail queue functions.
 */
#define STAILQ_INIT(head) do {                                          \
        STAILQ_FIRST((head)) = NULL;                                    \
        (head)->stqh_last = &STAILQ_FIRST((head));                      \
} 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_INSERT_AFTER(head, listelm, elm, field) do {             \
        if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((elm), field)) == NULL)\
                (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
        STAILQ_NEXT((elm), field) = (elm);                              \
} 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_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, elm, type, field) do {                      \
        if (STAILQ_FIRST((head)) == (elm)) {                            \
                STAILQ_REMOVE_HEAD((head), field);                      \
        } else {                                                        \
                struct type *curelm = (head)->stqh_first;               \
                while (STAILQ_NEXT(curelm, field) != (elm))             \
                        curelm = STAILQ_NEXT(curelm, field);            \
                STAILQ_REMOVE_AFTER(head, curelm, field);               \
        }                                                               \
} while (0)

#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_LAST(head, type, field)                                  \
        (STAILQ_EMPTY((head)) ? NULL :                                  \
                ((struct type *)(void *)                                \
                ((char *)((head)->stqh_last) - offsetof(struct type, field))))

#endif  /* !BSD_QUEUE_H */