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  1. /*
  2.  * Copyright (c) 1991, 1993
  3.  *    The Regents of the University of California.  All rights reserved.
  4.  *
  5.  * Redistribution and use in source and binary forms, with or without
  6.  * modification, are permitted provided that the following conditions
  7.  * are met:
  8.  * 1. Redistributions of source code must retain the above copyright
  9.  *    notice, this list of conditions and the following disclaimer.
  10.  * 2. Redistributions in binary form must reproduce the above copyright
  11.  *    notice, this list of conditions and the following disclaimer in the
  12.  *    documentation and/or other materials provided with the distribution.
  13.  * 3. Neither the name of the University nor the names of its contributors
  14.  *    may be used to endorse or promote products derived from this software
  15.  *    without specific prior written permission.
  16.  *
  17.  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  18.  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19.  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20.  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  21.  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22.  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23.  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24.  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25.  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26.  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27.  * SUCH DAMAGE.
  28.  *
  29.  *    @(#)queue.h    8.5 (Berkeley) 8/20/94
  30.  */
  31.  
  32. #ifndef    _SYS_QUEUE_H_
  33. #define    _SYS_QUEUE_H_
  34.  
  35. /*
  36.  * This file defines five types of data structures: singly-linked lists,
  37.  * lists, simple queues, tail queues, and circular queues.
  38.  *
  39.  * A singly-linked list is headed by a single forward pointer. The
  40.  * elements are singly linked for minimum space and pointer manipulation
  41.  * overhead at the expense of O(n) removal for arbitrary elements. New
  42.  * elements can be added to the list after an existing element or at the
  43.  * head of the list.  Elements being removed from the head of the list
  44.  * should use the explicit macro for this purpose for optimum
  45.  * efficiency. A singly-linked list may only be traversed in the forward
  46.  * direction.  Singly-linked lists are ideal for applications with large
  47.  * datasets and few or no removals or for implementing a LIFO queue.
  48.  *
  49.  * A list is headed by a single forward pointer (or an array of forward
  50.  * pointers for a hash table header). The elements are doubly linked
  51.  * so that an arbitrary element can be removed without a need to
  52.  * traverse the list. New elements can be added to the list before
  53.  * or after an existing element or at the head of the list. A list
  54.  * may only be traversed in the forward direction.
  55.  *
  56.  * A simple queue is headed by a pair of pointers, one the head of the
  57.  * list and the other to the tail of the list. The elements are singly
  58.  * linked to save space, so elements can only be removed from the
  59.  * head of the list. New elements can be added to the list after
  60.  * an existing element, at the head of the list, or at the end of the
  61.  * list. A simple queue may only be traversed in the forward direction.
  62.  *
  63.  * A tail queue is headed by a pair of pointers, one to the head of the
  64.  * list and the other to the tail of the list. The elements are doubly
  65.  * linked so that an arbitrary element can be removed without a need to
  66.  * traverse the list. New elements can be added to the list before or
  67.  * after an existing element, at the head of the list, or at the end of
  68.  * the list. A tail queue may be traversed in either direction.
  69.  *
  70.  * A circle queue is headed by a pair of pointers, one to the head of the
  71.  * list and the other to the tail of the list. The elements are doubly
  72.  * linked so that an arbitrary element can be removed without a need to
  73.  * traverse the list. New elements can be added to the list before or after
  74.  * an existing element, at the head of the list, or at the end of the list.
  75.  * A circle queue may be traversed in either direction, but has a more
  76.  * complex end of list detection.
  77.  *
  78.  * For details on the use of these macros, see the queue(3) manual page.
  79.  */
  80.  
  81. /*
  82.  * List definitions.
  83.  */
  84. #define    LIST_HEAD(name, type)                        \
  85. struct name {                                \
  86.     struct type *lh_first;    /* first element */            \
  87. }
  88.  
  89. #define    LIST_HEAD_INITIALIZER(head)                    \
  90.     { NULL }
  91.  
  92. #define    LIST_ENTRY(type)                        \
  93. struct {                                \
  94.     struct type *le_next;    /* next element */            \
  95.     struct type **le_prev;    /* address of previous next element */    \
  96. }
  97.  
  98. /*
  99.  * List functions.
  100.  */
  101. #define    LIST_INIT(head) do {                        \
  102.     (head)->lh_first = NULL;                    \
  103. } while (/*CONSTCOND*/0)
  104.  
  105. #define    LIST_INSERT_AFTER(listelm, elm, field) do {            \
  106.     if (((elm)->field.le_next = (listelm)->field.le_next) != NULL)    \
  107.         (listelm)->field.le_next->field.le_prev =        \
  108.             &(elm)->field.le_next;                \
  109.     (listelm)->field.le_next = (elm);                \
  110.     (elm)->field.le_prev = &(listelm)->field.le_next;        \
  111. } while (/*CONSTCOND*/0)
  112.  
  113. #define    LIST_INSERT_BEFORE(listelm, elm, field) do {            \
  114.     (elm)->field.le_prev = (listelm)->field.le_prev;        \
  115.     (elm)->field.le_next = (listelm);                \
  116.     *(listelm)->field.le_prev = (elm);                \
  117.     (listelm)->field.le_prev = &(elm)->field.le_next;        \
  118. } while (/*CONSTCOND*/0)
  119.  
  120. #define    LIST_INSERT_HEAD(head, elm, field) do {                \
  121.     if (((elm)->field.le_next = (head)->lh_first) != NULL)        \
  122.         (head)->lh_first->field.le_prev = &(elm)->field.le_next;\
  123.     (head)->lh_first = (elm);                    \
  124.     (elm)->field.le_prev = &(head)->lh_first;            \
  125. } while (/*CONSTCOND*/0)
  126.  
  127. #define    LIST_REMOVE(elm, field) do {                    \
  128.     if ((elm)->field.le_next != NULL)                \
  129.         (elm)->field.le_next->field.le_prev =             \
  130.             (elm)->field.le_prev;                \
  131.     *(elm)->field.le_prev = (elm)->field.le_next;            \
  132. } while (/*CONSTCOND*/0)
  133.  
  134. #define    LIST_FOREACH(var, head, field)                    \
  135.     for ((var) = ((head)->lh_first);                \
  136.         (var);                            \
  137.         (var) = ((var)->field.le_next))
  138.  
  139. /*
  140.  * List access methods.
  141.  */
  142. #define    LIST_EMPTY(head)        ((head)->lh_first == NULL)
  143. #define    LIST_FIRST(head)        ((head)->lh_first)
  144. #define    LIST_NEXT(elm, field)        ((elm)->field.le_next)
  145.  
  146.  
  147. /*
  148.  * Singly-linked List definitions.
  149.  */
  150. #define    SLIST_HEAD(name, type)                        \
  151. struct name {                                \
  152.     struct type *slh_first;    /* first element */            \
  153. }
  154.  
  155. #define    SLIST_HEAD_INITIALIZER(head)                    \
  156.     { NULL }
  157.  
  158. #define    SLIST_ENTRY(type)                        \
  159. struct {                                \
  160.     struct type *sle_next;    /* next element */            \
  161. }
  162.  
  163. /*
  164.  * Singly-linked List functions.
  165.  */
  166. #define    SLIST_INIT(head) do {                        \
  167.     (head)->slh_first = NULL;                    \
  168. } while (/*CONSTCOND*/0)
  169.  
  170. #define    SLIST_INSERT_AFTER(slistelm, elm, field) do {            \
  171.     (elm)->field.sle_next = (slistelm)->field.sle_next;        \
  172.     (slistelm)->field.sle_next = (elm);                \
  173. } while (/*CONSTCOND*/0)
  174.  
  175. #define    SLIST_INSERT_HEAD(head, elm, field) do {            \
  176.     (elm)->field.sle_next = (head)->slh_first;            \
  177.     (head)->slh_first = (elm);                    \
  178. } while (/*CONSTCOND*/0)
  179.  
  180. #define    SLIST_REMOVE_HEAD(head, field) do {                \
  181.     (head)->slh_first = (head)->slh_first->field.sle_next;        \
  182. } while (/*CONSTCOND*/0)
  183.  
  184. #define    SLIST_REMOVE(head, elm, type, field) do {            \
  185.     if ((head)->slh_first == (elm)) {                \
  186.         SLIST_REMOVE_HEAD((head), field);            \
  187.     }                                \
  188.     else {                                \
  189.         struct type *curelm = (head)->slh_first;        \
  190.         while(curelm->field.sle_next != (elm))            \
  191.             curelm = curelm->field.sle_next;        \
  192.         curelm->field.sle_next =                \
  193.             curelm->field.sle_next->field.sle_next;        \
  194.     }                                \
  195. } while (/*CONSTCOND*/0)
  196.  
  197. #define    SLIST_FOREACH(var, head, field)                    \
  198.     for((var) = (head)->slh_first; (var); (var) = (var)->field.sle_next)
  199.  
  200. /*
  201.  * Singly-linked List access methods.
  202.  */
  203. #define    SLIST_EMPTY(head)    ((head)->slh_first == NULL)
  204. #define    SLIST_FIRST(head)    ((head)->slh_first)
  205. #define    SLIST_NEXT(elm, field)    ((elm)->field.sle_next)
  206.  
  207.  
  208. /*
  209.  * Singly-linked Tail queue declarations.
  210.  */
  211. #define    STAILQ_HEAD(name, type)                    \
  212. struct name {                                \
  213.     struct type *stqh_first;    /* first element */            \
  214.     struct type **stqh_last;    /* addr of last next element */        \
  215. }
  216.  
  217. #define    STAILQ_HEAD_INITIALIZER(head)                    \
  218.     { NULL, &(head).stqh_first }
  219.  
  220. #define    STAILQ_ENTRY(type)                        \
  221. struct {                                \
  222.     struct type *stqe_next;    /* next element */            \
  223. }
  224.  
  225. /*
  226.  * Singly-linked Tail queue functions.
  227.  */
  228. #define    STAILQ_INIT(head) do {                        \
  229.     (head)->stqh_first = NULL;                    \
  230.     (head)->stqh_last = &(head)->stqh_first;                \
  231. } while (/*CONSTCOND*/0)
  232.  
  233. #define    STAILQ_INSERT_HEAD(head, elm, field) do {            \
  234.     if (((elm)->field.stqe_next = (head)->stqh_first) == NULL)    \
  235.         (head)->stqh_last = &(elm)->field.stqe_next;        \
  236.     (head)->stqh_first = (elm);                    \
  237. } while (/*CONSTCOND*/0)
  238.  
  239. #define    STAILQ_INSERT_TAIL(head, elm, field) do {            \
  240.     (elm)->field.stqe_next = NULL;                    \
  241.     *(head)->stqh_last = (elm);                    \
  242.     (head)->stqh_last = &(elm)->field.stqe_next;            \
  243. } while (/*CONSTCOND*/0)
  244.  
  245. #define    STAILQ_INSERT_AFTER(head, listelm, elm, field) do {        \
  246.     if (((elm)->field.stqe_next = (listelm)->field.stqe_next) == NULL)\
  247.         (head)->stqh_last = &(elm)->field.stqe_next;        \
  248.     (listelm)->field.stqe_next = (elm);                \
  249. } while (/*CONSTCOND*/0)
  250.  
  251. #define    STAILQ_REMOVE_HEAD(head, field) do {                \
  252.     if (((head)->stqh_first = (head)->stqh_first->field.stqe_next) == NULL) \
  253.         (head)->stqh_last = &(head)->stqh_first;            \
  254. } while (/*CONSTCOND*/0)
  255.  
  256. #define    STAILQ_REMOVE(head, elm, type, field) do {            \
  257.     if ((head)->stqh_first == (elm)) {                \
  258.         STAILQ_REMOVE_HEAD((head), field);            \
  259.     } else {                            \
  260.         struct type *curelm = (head)->stqh_first;        \
  261.         while (curelm->field.stqe_next != (elm))            \
  262.             curelm = curelm->field.stqe_next;        \
  263.         if ((curelm->field.stqe_next =                \
  264.             curelm->field.stqe_next->field.stqe_next) == NULL) \
  265.                 (head)->stqh_last = &(curelm)->field.stqe_next; \
  266.     }                                \
  267. } while (/*CONSTCOND*/0)
  268.  
  269. #define    STAILQ_FOREACH(var, head, field)                \
  270.     for ((var) = ((head)->stqh_first);                \
  271.         (var);                            \
  272.         (var) = ((var)->field.stqe_next))
  273.  
  274. /*
  275.  * Singly-linked Tail queue access methods.
  276.  */
  277. #define    STAILQ_EMPTY(head)    ((head)->stqh_first == NULL)
  278. #define    STAILQ_FIRST(head)    ((head)->stqh_first)
  279. #define    STAILQ_NEXT(elm, field)    ((elm)->field.stqe_next)
  280.  
  281.  
  282. /*
  283.  * Simple queue definitions.
  284.  */
  285. #define    SIMPLEQ_HEAD(name, type)                    \
  286. struct name {                                \
  287.     struct type *sqh_first;    /* first element */            \
  288.     struct type **sqh_last;    /* addr of last next element */        \
  289. }
  290.  
  291. #define    SIMPLEQ_HEAD_INITIALIZER(head)                    \
  292.     { NULL, &(head).sqh_first }
  293.  
  294. #define    SIMPLEQ_ENTRY(type)                        \
  295. struct {                                \
  296.     struct type *sqe_next;    /* next element */            \
  297. }
  298.  
  299. /*
  300.  * Simple queue functions.
  301.  */
  302. #define    SIMPLEQ_INIT(head) do {                        \
  303.     (head)->sqh_first = NULL;                    \
  304.     (head)->sqh_last = &(head)->sqh_first;                \
  305. } while (/*CONSTCOND*/0)
  306.  
  307. #define    SIMPLEQ_INSERT_HEAD(head, elm, field) do {            \
  308.     if (((elm)->field.sqe_next = (head)->sqh_first) == NULL)    \
  309.         (head)->sqh_last = &(elm)->field.sqe_next;        \
  310.     (head)->sqh_first = (elm);                    \
  311. } while (/*CONSTCOND*/0)
  312.  
  313. #define    SIMPLEQ_INSERT_TAIL(head, elm, field) do {            \
  314.     (elm)->field.sqe_next = NULL;                    \
  315.     *(head)->sqh_last = (elm);                    \
  316.     (head)->sqh_last = &(elm)->field.sqe_next;            \
  317. } while (/*CONSTCOND*/0)
  318.  
  319. #define    SIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do {        \
  320.     if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL)\
  321.         (head)->sqh_last = &(elm)->field.sqe_next;        \
  322.     (listelm)->field.sqe_next = (elm);                \
  323. } while (/*CONSTCOND*/0)
  324.  
  325. #define    SIMPLEQ_REMOVE_HEAD(head, field) do {                \
  326.     if (((head)->sqh_first = (head)->sqh_first->field.sqe_next) == NULL) \
  327.         (head)->sqh_last = &(head)->sqh_first;            \
  328. } while (/*CONSTCOND*/0)
  329.  
  330. #define    SIMPLEQ_REMOVE(head, elm, type, field) do {            \
  331.     if ((head)->sqh_first == (elm)) {                \
  332.         SIMPLEQ_REMOVE_HEAD((head), field);            \
  333.     } else {                            \
  334.         struct type *curelm = (head)->sqh_first;        \
  335.         while (curelm->field.sqe_next != (elm))            \
  336.             curelm = curelm->field.sqe_next;        \
  337.         if ((curelm->field.sqe_next =                \
  338.             curelm->field.sqe_next->field.sqe_next) == NULL) \
  339.                 (head)->sqh_last = &(curelm)->field.sqe_next; \
  340.     }                                \
  341. } while (/*CONSTCOND*/0)
  342.  
  343. #define    SIMPLEQ_FOREACH(var, head, field)                \
  344.     for ((var) = ((head)->sqh_first);                \
  345.         (var);                            \
  346.         (var) = ((var)->field.sqe_next))
  347.  
  348. /*
  349.  * Simple queue access methods.
  350.  */
  351. #define    SIMPLEQ_EMPTY(head)        ((head)->sqh_first == NULL)
  352. #define    SIMPLEQ_FIRST(head)        ((head)->sqh_first)
  353. #define    SIMPLEQ_NEXT(elm, field)    ((elm)->field.sqe_next)
  354.  
  355.  
  356. /*
  357.  * Tail queue definitions.
  358.  */
  359. #define    _TAILQ_HEAD(name, type, qual)                    \
  360. struct name {                                \
  361.     qual type *tqh_first;        /* first element */        \
  362.     qual type *qual *tqh_last;    /* addr of last next element */    \
  363. }
  364. #define TAILQ_HEAD(name, type)    _TAILQ_HEAD(name, struct type,)
  365.  
  366. #define    TAILQ_HEAD_INITIALIZER(head)                    \
  367.     { NULL, &(head).tqh_first }
  368.  
  369. #define    _TAILQ_ENTRY(type, qual)                    \
  370. struct {                                \
  371.     qual type *tqe_next;        /* next element */        \
  372.     qual type *qual *tqe_prev;    /* address of previous next element */\
  373. }
  374. #define TAILQ_ENTRY(type)    _TAILQ_ENTRY(struct type,)
  375.  
  376. /*
  377.  * Tail queue functions.
  378.  */
  379. #define    TAILQ_INIT(head) do {                        \
  380.     (head)->tqh_first = NULL;                    \
  381.     (head)->tqh_last = &(head)->tqh_first;                \
  382. } while (/*CONSTCOND*/0)
  383.  
  384. #define    TAILQ_INSERT_HEAD(head, elm, field) do {            \
  385.     if (((elm)->field.tqe_next = (head)->tqh_first) != NULL)    \
  386.         (head)->tqh_first->field.tqe_prev =            \
  387.             &(elm)->field.tqe_next;                \
  388.     else                                \
  389.         (head)->tqh_last = &(elm)->field.tqe_next;        \
  390.     (head)->tqh_first = (elm);                    \
  391.     (elm)->field.tqe_prev = &(head)->tqh_first;            \
  392. } while (/*CONSTCOND*/0)
  393.  
  394. #define    TAILQ_INSERT_TAIL(head, elm, field) do {            \
  395.     (elm)->field.tqe_next = NULL;                    \
  396.     (elm)->field.tqe_prev = (head)->tqh_last;            \
  397.     *(head)->tqh_last = (elm);                    \
  398.     (head)->tqh_last = &(elm)->field.tqe_next;            \
  399. } while (/*CONSTCOND*/0)
  400.  
  401. #define    TAILQ_INSERT_AFTER(head, listelm, elm, field) do {        \
  402.     if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)\
  403.         (elm)->field.tqe_next->field.tqe_prev =         \
  404.             &(elm)->field.tqe_next;                \
  405.     else                                \
  406.         (head)->tqh_last = &(elm)->field.tqe_next;        \
  407.     (listelm)->field.tqe_next = (elm);                \
  408.     (elm)->field.tqe_prev = &(listelm)->field.tqe_next;        \
  409. } while (/*CONSTCOND*/0)
  410.  
  411. #define    TAILQ_INSERT_BEFORE(listelm, elm, field) do {            \
  412.     (elm)->field.tqe_prev = (listelm)->field.tqe_prev;        \
  413.     (elm)->field.tqe_next = (listelm);                \
  414.     *(listelm)->field.tqe_prev = (elm);                \
  415.     (listelm)->field.tqe_prev = &(elm)->field.tqe_next;        \
  416. } while (/*CONSTCOND*/0)
  417.  
  418. #define    TAILQ_REMOVE(head, elm, field) do {                \
  419.     if (((elm)->field.tqe_next) != NULL)                \
  420.         (elm)->field.tqe_next->field.tqe_prev =         \
  421.             (elm)->field.tqe_prev;                \
  422.     else                                \
  423.         (head)->tqh_last = (elm)->field.tqe_prev;        \
  424.     *(elm)->field.tqe_prev = (elm)->field.tqe_next;            \
  425. } while (/*CONSTCOND*/0)
  426.  
  427. #define    TAILQ_FOREACH(var, head, field)                    \
  428.     for ((var) = ((head)->tqh_first);                \
  429.         (var);                            \
  430.         (var) = ((var)->field.tqe_next))
  431.  
  432. #define    TAILQ_FOREACH_REVERSE(var, head, headname, field)        \
  433.     for ((var) = (*(((struct headname *)((head)->tqh_last))->tqh_last));    \
  434.         (var);                            \
  435.         (var) = (*(((struct headname *)((var)->field.tqe_prev))->tqh_last)))
  436.  
  437. /*
  438.  * Tail queue access methods.
  439.  */
  440. #define    TAILQ_EMPTY(head)        ((head)->tqh_first == NULL)
  441. #define    TAILQ_FIRST(head)        ((head)->tqh_first)
  442. #define    TAILQ_NEXT(elm, field)        ((elm)->field.tqe_next)
  443.  
  444. #define    TAILQ_LAST(head, headname) \
  445.     (*(((struct headname *)((head)->tqh_last))->tqh_last))
  446. #define    TAILQ_PREV(elm, headname, field) \
  447.     (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
  448.  
  449.  
  450. /*
  451.  * Circular queue definitions.
  452.  */
  453. #define    CIRCLEQ_HEAD(name, type)                    \
  454. struct name {                                \
  455.     struct type *cqh_first;        /* first element */        \
  456.     struct type *cqh_last;        /* last element */        \
  457. }
  458.  
  459. #define    CIRCLEQ_HEAD_INITIALIZER(head)                    \
  460.     { (void *)&head, (void *)&head }
  461.  
  462. #define    CIRCLEQ_ENTRY(type)                        \
  463. struct {                                \
  464.     struct type *cqe_next;        /* next element */        \
  465.     struct type *cqe_prev;        /* previous element */        \
  466. }
  467.  
  468. /*
  469.  * Circular queue functions.
  470.  */
  471. #define    CIRCLEQ_INIT(head) do {                        \
  472.     (head)->cqh_first = (void *)(head);                \
  473.     (head)->cqh_last = (void *)(head);                \
  474. } while (/*CONSTCOND*/0)
  475.  
  476. #define    CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {        \
  477.     (elm)->field.cqe_next = (listelm)->field.cqe_next;        \
  478.     (elm)->field.cqe_prev = (listelm);                \
  479.     if ((listelm)->field.cqe_next == (void *)(head))        \
  480.         (head)->cqh_last = (elm);                \
  481.     else                                \
  482.         (listelm)->field.cqe_next->field.cqe_prev = (elm);    \
  483.     (listelm)->field.cqe_next = (elm);                \
  484. } while (/*CONSTCOND*/0)
  485.  
  486. #define    CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do {        \
  487.     (elm)->field.cqe_next = (listelm);                \
  488.     (elm)->field.cqe_prev = (listelm)->field.cqe_prev;        \
  489.     if ((listelm)->field.cqe_prev == (void *)(head))        \
  490.         (head)->cqh_first = (elm);                \
  491.     else                                \
  492.         (listelm)->field.cqe_prev->field.cqe_next = (elm);    \
  493.     (listelm)->field.cqe_prev = (elm);                \
  494. } while (/*CONSTCOND*/0)
  495.  
  496. #define    CIRCLEQ_INSERT_HEAD(head, elm, field) do {            \
  497.     (elm)->field.cqe_next = (head)->cqh_first;            \
  498.     (elm)->field.cqe_prev = (void *)(head);                \
  499.     if ((head)->cqh_last == (void *)(head))                \
  500.         (head)->cqh_last = (elm);                \
  501.     else                                \
  502.         (head)->cqh_first->field.cqe_prev = (elm);        \
  503.     (head)->cqh_first = (elm);                    \
  504. } while (/*CONSTCOND*/0)
  505.  
  506. #define    CIRCLEQ_INSERT_TAIL(head, elm, field) do {            \
  507.     (elm)->field.cqe_next = (void *)(head);                \
  508.     (elm)->field.cqe_prev = (head)->cqh_last;            \
  509.     if ((head)->cqh_first == (void *)(head))            \
  510.         (head)->cqh_first = (elm);                \
  511.     else                                \
  512.         (head)->cqh_last->field.cqe_next = (elm);        \
  513.     (head)->cqh_last = (elm);                    \
  514. } while (/*CONSTCOND*/0)
  515.  
  516. #define    CIRCLEQ_REMOVE(head, elm, field) do {                \
  517.     if ((elm)->field.cqe_next == (void *)(head))            \
  518.         (head)->cqh_last = (elm)->field.cqe_prev;        \
  519.     else                                \
  520.         (elm)->field.cqe_next->field.cqe_prev =            \
  521.             (elm)->field.cqe_prev;                \
  522.     if ((elm)->field.cqe_prev == (void *)(head))            \
  523.         (head)->cqh_first = (elm)->field.cqe_next;        \
  524.     else                                \
  525.         (elm)->field.cqe_prev->field.cqe_next =            \
  526.             (elm)->field.cqe_next;                \
  527. } while (/*CONSTCOND*/0)
  528.  
  529. #define    CIRCLEQ_FOREACH(var, head, field)                \
  530.     for ((var) = ((head)->cqh_first);                \
  531.         (var) != (const void *)(head);                \
  532.         (var) = ((var)->field.cqe_next))
  533.  
  534. #define    CIRCLEQ_FOREACH_REVERSE(var, head, field)            \
  535.     for ((var) = ((head)->cqh_last);                \
  536.         (var) != (const void *)(head);                \
  537.         (var) = ((var)->field.cqe_prev))
  538.  
  539. /*
  540.  * Circular queue access methods.
  541.  */
  542. #define    CIRCLEQ_EMPTY(head)        ((head)->cqh_first == (void *)(head))
  543. #define    CIRCLEQ_FIRST(head)        ((head)->cqh_first)
  544. #define    CIRCLEQ_LAST(head)        ((head)->cqh_last)
  545. #define    CIRCLEQ_NEXT(elm, field)    ((elm)->field.cqe_next)
  546. #define    CIRCLEQ_PREV(elm, field)    ((elm)->field.cqe_prev)
  547.  
  548. #define CIRCLEQ_LOOP_NEXT(head, elm, field)                \
  549.     (((elm)->field.cqe_next == (void *)(head))            \
  550.         ? ((head)->cqh_first)                    \
  551.         : (elm->field.cqe_next))
  552. #define CIRCLEQ_LOOP_PREV(head, elm, field)                \
  553.     (((elm)->field.cqe_prev == (void *)(head))            \
  554.         ? ((head)->cqh_last)                    \
  555.         : (elm->field.cqe_prev))
  556.  
  557. #endif    /* sys/queue.h */
  558.