user_queue.h

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/*-
 * 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.
 * 4. 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 _USER_QUEUE_H_
#define _USER_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 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.
 *
 * For details on the use of these macros, see the queue(3) manual page.
 *
 *
 *              SLIST   LIST    STAILQ  TAILQ
 * _HEAD            +   +   +   +
 * _HEAD_INITIALIZER        +   +   +   +
 * _ENTRY           +   +   +   +
 * _INIT            +   +   +   +
 * _EMPTY           +   +   +   +
 * _FIRST           +   +   +   +
 * _NEXT            +   +   +   +
 * _PREV            -   -   -   +
 * _LAST            -   -   +   +
 * _FOREACH         +   +   +   +
 * _FOREACH_SAFE        +   +   +   +
 * _FOREACH_REVERSE     -   -   -   +
 * _FOREACH_REVERSE_SAFE    -   -   -   +
 * _INSERT_HEAD         +   +   +   +
 * _INSERT_BEFORE       -   +   -   +
 * _INSERT_AFTER        +   +   +   +
 * _INSERT_TAIL         -   -   +   +
 * _CONCAT          -   -   +   +
 * _REMOVE_AFTER        +   -   +   -
 * _REMOVE_HEAD         +   -   +   -
 * _REMOVE          +   +   +   +
 * _SWAP            +   +   +   +
 *
 */
#ifdef QUEUE_MACRO_DEBUG
/* Store the last 2 places the queue element or head was altered */
struct qm_trace {
    char * lastfile;
    int lastline;
    char * prevfile;
    int prevline;
};

#define TRACEBUF    struct qm_trace trace;
#define TRASHIT(x)  do {(x) = (void *)-1;} while (0)
#define QMD_SAVELINK(name, link)    void **name = (void *)&(link)

#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
#define QMD_TRACE_ELEM(elem)
#define QMD_TRACE_HEAD(head)
#define QMD_SAVELINK(name, link)
#define TRACEBUF
#define TRASHIT(x)
#endif  /* QUEUE_MACRO_DEBUG */

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

#define SLIST_HEAD_INITIALIZER(head)                    \
    { NULL }

#if defined (__Userspace_os_Windows)
#if defined (SLIST_ENTRY)
#undef SLIST_ENTRY
#endif
#endif

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

/*
 * Singly-linked List functions.
 */
#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_SAFE(var, head, field, tvar)          \
    for ((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 {           \
    QMD_SAVELINK(oldnext, (elm)->field.sle_next);           \
    if (SLIST_FIRST((head)) == (elm)) {             \
        SLIST_REMOVE_HEAD((head), field);           \
    }                               \
    else {                              \
        struct type *curelm = SLIST_FIRST((head));      \
        while (SLIST_NEXT(curelm, field) != (elm))      \
            curelm = SLIST_NEXT(curelm, field);     \
        SLIST_REMOVE_AFTER(curelm, field);          \
    }                               \
    TRASHIT(*oldnext);                      \
} while (0)

#define SLIST_REMOVE_AFTER(elm, field) do {             \
    SLIST_NEXT(elm, field) =                    \
        SLIST_NEXT(SLIST_NEXT(elm, field), field);          \
} while (0)

#define SLIST_REMOVE_HEAD(head, field) do {             \
    SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);   \
} while (0)

#define SLIST_SWAP(head1, head2, type) do {             \
    struct type *swap_first = SLIST_FIRST(head1);           \
    SLIST_FIRST(head1) = SLIST_FIRST(head2);            \
    SLIST_FIRST(head2) = swap_first;                \
} 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 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_SAFE(var, head, field, tvar)         \
    for ((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 :                          \
            ((struct type *)(void *)                \
        ((char *)((head)->stqh_last) - __offsetof(struct type, field))))

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


/*
 * List declarations.
 */
#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.
 */

#if defined(INVARIANTS)
#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", (void *)(head));  \
} while (0)

#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", (void *)(elm));  \
} while (0)

#define QMD_LIST_CHECK_PREV(elm, field) do {                    \
    if (*(elm)->field.le_prev != (elm))                 \
        panic("Bad link elm %p prev->next != elm", (void *)(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 /* (INVARIANTS) */

#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_SAFE(var, head, field, tvar)           \
    for ((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_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_SWAP(head1, head2, type, field) do {           \
    struct 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)

/*
 * 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_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 */  \
    TRACEBUF                            \
}

/*
 * Tail queue functions.
 */
#if defined(INVARIANTS)
#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", (void *)(head)); \
} while (0)

#define QMD_TAILQ_CHECK_TAIL(head, field) do {                  \
    if (*(head)->tqh_last != NULL)                      \
            panic("Bad tailq NEXT(%p->tqh_last) != NULL", (void *)(head));  \
} while (0)

#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", (void *)(elm));  \
} while (0)

#define QMD_TAILQ_CHECK_PREV(elm, field) do {                   \
    if (*(elm)->field.tqe_prev != (elm))                    \
        panic("Bad link elm %p prev->next != elm", (void *)(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 /* (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_SAFE(var, head, field, tvar)          \
    for ((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_SAFE(var, head, headname, field, tvar)    \
    for ((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))

#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_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_SWAP(head1, head2, type, field) do {          \
    struct type *swap_first = (head1)->tqh_first;           \
    struct 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)

#endif /* !_SYS_QUEUE_H_ */