The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/sys/queue.h

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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  * 4. 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  * $FreeBSD: releng/7.4/sys/sys/queue.h 204395 2010-02-27 04:02:40Z emaste $
   31  */
   32 
   33 #ifndef _SYS_QUEUE_H_
   34 #define _SYS_QUEUE_H_
   35 
   36 #include <sys/cdefs.h>
   37 
   38 /*
   39  * This file defines four types of data structures: singly-linked lists,
   40  * singly-linked tail queues, lists and tail queues.
   41  *
   42  * A singly-linked list is headed by a single forward pointer. The elements
   43  * are singly linked for minimum space and pointer manipulation overhead at
   44  * the expense of O(n) removal for arbitrary elements. New elements can be
   45  * added to the list after an existing element or at the head of the list.
   46  * Elements being removed from the head of the list should use the explicit
   47  * macro for this purpose for optimum efficiency. A singly-linked list may
   48  * only be traversed in the forward direction.  Singly-linked lists are ideal
   49  * for applications with large datasets and few or no removals or for
   50  * implementing a LIFO queue.
   51  *
   52  * A singly-linked tail queue is headed by a pair of pointers, one to the
   53  * head of the list and the other to the tail of the list. The elements are
   54  * singly linked for minimum space and pointer manipulation overhead at the
   55  * expense of O(n) removal for arbitrary elements. New elements can be added
   56  * to the list after an existing element, at the head of the list, or at the
   57  * end of the list. Elements being removed from the head of the tail queue
   58  * should use the explicit macro for this purpose for optimum efficiency.
   59  * A singly-linked tail queue may only be traversed in the forward direction.
   60  * Singly-linked tail queues are ideal for applications with large datasets
   61  * and few or no removals or for implementing a FIFO queue.
   62  *
   63  * A list is headed by a single forward pointer (or an array of forward
   64  * pointers for a hash table header). The elements are doubly linked
   65  * 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
   67  * or after an existing element or at the head of the list. A list
   68  * may only be traversed in the forward direction.
   69  *
   70  * A tail 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
   74  * after an existing element, at the head of the list, or at the end of
   75  * the list. A tail queue may be traversed in either direction.
   76  *
   77  * For details on the use of these macros, see the queue(3) manual page.
   78  *
   79  *
   80  *                              SLIST   LIST    STAILQ  TAILQ
   81  * _HEAD                        +       +       +       +
   82  * _HEAD_INITIALIZER            +       +       +       +
   83  * _ENTRY                       +       +       +       +
   84  * _INIT                        +       +       +       +
   85  * _EMPTY                       +       +       +       +
   86  * _FIRST                       +       +       +       +
   87  * _NEXT                        +       +       +       +
   88  * _PREV                        -       -       -       +
   89  * _LAST                        -       -       +       +
   90  * _FOREACH                     +       +       +       +
   91  * _FOREACH_SAFE                +       +       +       +
   92  * _FOREACH_REVERSE             -       -       -       +
   93  * _FOREACH_REVERSE_SAFE        -       -       -       +
   94  * _INSERT_HEAD                 +       +       +       +
   95  * _INSERT_BEFORE               -       +       -       +
   96  * _INSERT_AFTER                +       +       +       +
   97  * _INSERT_TAIL                 -       -       +       +
   98  * _CONCAT                      -       -       +       +
   99  * _REMOVE_AFTER                +       -       +       -
  100  * _REMOVE_HEAD                 +       -       +       -
  101  * _REMOVE                      +       +       +       +
  102  *
  103  */
  104 #ifdef QUEUE_MACRO_DEBUG
  105 /* Store the last 2 places the queue element or head was altered */
  106 struct qm_trace {
  107         char * lastfile;
  108         int lastline;
  109         char * prevfile;
  110         int prevline;
  111 };
  112 
  113 #define TRACEBUF        struct qm_trace trace;
  114 #define TRASHIT(x)      do {(x) = (void *)-1;} while (0)
  115 #define QMD_SAVELINK(name, link)        void **name = (void *)&(link)
  116 
  117 #define QMD_TRACE_HEAD(head) do {                                       \
  118         (head)->trace.prevline = (head)->trace.lastline;                \
  119         (head)->trace.prevfile = (head)->trace.lastfile;                \
  120         (head)->trace.lastline = __LINE__;                              \
  121         (head)->trace.lastfile = __FILE__;                              \
  122 } while (0)
  123 
  124 #define QMD_TRACE_ELEM(elem) do {                                       \
  125         (elem)->trace.prevline = (elem)->trace.lastline;                \
  126         (elem)->trace.prevfile = (elem)->trace.lastfile;                \
  127         (elem)->trace.lastline = __LINE__;                              \
  128         (elem)->trace.lastfile = __FILE__;                              \
  129 } while (0)
  130 
  131 #else
  132 #define QMD_TRACE_ELEM(elem)
  133 #define QMD_TRACE_HEAD(head)
  134 #define QMD_SAVELINK(name, link)
  135 #define TRACEBUF
  136 #define TRASHIT(x)
  137 #endif  /* QUEUE_MACRO_DEBUG */
  138 
  139 /*
  140  * Singly-linked List declarations.
  141  */
  142 #define SLIST_HEAD(name, type)                                          \
  143 struct name {                                                           \
  144         struct type *slh_first; /* first element */                     \
  145 }
  146 
  147 #define SLIST_HEAD_INITIALIZER(head)                                    \
  148         { NULL }
  149 
  150 #define SLIST_ENTRY(type)                                               \
  151 struct {                                                                \
  152         struct type *sle_next;  /* next element */                      \
  153 }
  154 
  155 /*
  156  * Singly-linked List functions.
  157  */
  158 #define SLIST_EMPTY(head)       ((head)->slh_first == NULL)
  159 
  160 #define SLIST_FIRST(head)       ((head)->slh_first)
  161 
  162 #define SLIST_FOREACH(var, head, field)                                 \
  163         for ((var) = SLIST_FIRST((head));                               \
  164             (var);                                                      \
  165             (var) = SLIST_NEXT((var), field))
  166 
  167 #define SLIST_FOREACH_SAFE(var, head, field, tvar)                      \
  168         for ((var) = SLIST_FIRST((head));                               \
  169             (var) && ((tvar) = SLIST_NEXT((var), field), 1);            \
  170             (var) = (tvar))
  171 
  172 #define SLIST_FOREACH_PREVPTR(var, varp, head, field)                   \
  173         for ((varp) = &SLIST_FIRST((head));                             \
  174             ((var) = *(varp)) != NULL;                                  \
  175             (varp) = &SLIST_NEXT((var), field))
  176 
  177 #define SLIST_INIT(head) do {                                           \
  178         SLIST_FIRST((head)) = NULL;                                     \
  179 } while (0)
  180 
  181 #define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
  182         SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);       \
  183         SLIST_NEXT((slistelm), field) = (elm);                          \
  184 } while (0)
  185 
  186 #define SLIST_INSERT_HEAD(head, elm, field) do {                        \
  187         SLIST_NEXT((elm), field) = SLIST_FIRST((head));                 \
  188         SLIST_FIRST((head)) = (elm);                                    \
  189 } while (0)
  190 
  191 #define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)
  192 
  193 #define SLIST_REMOVE(head, elm, type, field) do {                       \
  194         QMD_SAVELINK(oldnext, (elm)->field.sle_next);                   \
  195         if (SLIST_FIRST((head)) == (elm)) {                             \
  196                 SLIST_REMOVE_HEAD((head), field);                       \
  197         }                                                               \
  198         else {                                                          \
  199                 struct type *curelm = SLIST_FIRST((head));              \
  200                 while (SLIST_NEXT(curelm, field) != (elm))              \
  201                         curelm = SLIST_NEXT(curelm, field);             \
  202                 SLIST_REMOVE_AFTER(curelm, field);                      \
  203         }                                                               \
  204         TRASHIT(*oldnext);                                              \
  205 } while (0)
  206 
  207 #define SLIST_REMOVE_AFTER(elm, field) do {                             \
  208         SLIST_NEXT(elm, field) =                                        \
  209             SLIST_NEXT(SLIST_NEXT(elm, field), field);                  \
  210 } while (0)
  211 
  212 #define SLIST_REMOVE_HEAD(head, field) do {                             \
  213         SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);   \
  214 } while (0)
  215 
  216 /*
  217  * Singly-linked Tail queue declarations.
  218  */
  219 #define STAILQ_HEAD(name, type)                                         \
  220 struct name {                                                           \
  221         struct type *stqh_first;/* first element */                     \
  222         struct type **stqh_last;/* addr of last next element */         \
  223 }
  224 
  225 #define STAILQ_HEAD_INITIALIZER(head)                                   \
  226         { NULL, &(head).stqh_first }
  227 
  228 #define STAILQ_ENTRY(type)                                              \
  229 struct {                                                                \
  230         struct type *stqe_next; /* next element */                      \
  231 }
  232 
  233 /*
  234  * Singly-linked Tail queue functions.
  235  */
  236 #define STAILQ_CONCAT(head1, head2) do {                                \
  237         if (!STAILQ_EMPTY((head2))) {                                   \
  238                 *(head1)->stqh_last = (head2)->stqh_first;              \
  239                 (head1)->stqh_last = (head2)->stqh_last;                \
  240                 STAILQ_INIT((head2));                                   \
  241         }                                                               \
  242 } while (0)
  243 
  244 #define STAILQ_EMPTY(head)      ((head)->stqh_first == NULL)
  245 
  246 #define STAILQ_FIRST(head)      ((head)->stqh_first)
  247 
  248 #define STAILQ_FOREACH(var, head, field)                                \
  249         for((var) = STAILQ_FIRST((head));                               \
  250            (var);                                                       \
  251            (var) = STAILQ_NEXT((var), field))
  252 
  253 
  254 #define STAILQ_FOREACH_SAFE(var, head, field, tvar)                     \
  255         for ((var) = STAILQ_FIRST((head));                              \
  256             (var) && ((tvar) = STAILQ_NEXT((var), field), 1);           \
  257             (var) = (tvar))
  258 
  259 #define STAILQ_INIT(head) do {                                          \
  260         STAILQ_FIRST((head)) = NULL;                                    \
  261         (head)->stqh_last = &STAILQ_FIRST((head));                      \
  262 } while (0)
  263 
  264 #define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {               \
  265         if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
  266                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
  267         STAILQ_NEXT((tqelm), field) = (elm);                            \
  268 } while (0)
  269 
  270 #define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
  271         if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL) \
  272                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
  273         STAILQ_FIRST((head)) = (elm);                                   \
  274 } while (0)
  275 
  276 #define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
  277         STAILQ_NEXT((elm), field) = NULL;                               \
  278         *(head)->stqh_last = (elm);                                     \
  279         (head)->stqh_last = &STAILQ_NEXT((elm), field);                 \
  280 } while (0)
  281 
  282 #define STAILQ_LAST(head, type, field)                                  \
  283         (STAILQ_EMPTY((head)) ?                                         \
  284                 NULL :                                                  \
  285                 ((struct type *)(void *)                                \
  286                 ((char *)((head)->stqh_last) - __offsetof(struct type, field))))
  287 
  288 #define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
  289 
  290 #define STAILQ_REMOVE(head, elm, type, field) do {                      \
  291         QMD_SAVELINK(oldnext, (elm)->field.stqe_next);                  \
  292         if (STAILQ_FIRST((head)) == (elm)) {                            \
  293                 STAILQ_REMOVE_HEAD((head), field);                      \
  294         }                                                               \
  295         else {                                                          \
  296                 struct type *curelm = STAILQ_FIRST((head));             \
  297                 while (STAILQ_NEXT(curelm, field) != (elm))             \
  298                         curelm = STAILQ_NEXT(curelm, field);            \
  299                 STAILQ_REMOVE_AFTER(head, curelm, field);               \
  300         }                                                               \
  301         TRASHIT(*oldnext);                                              \
  302 } while (0)
  303 
  304 #define STAILQ_REMOVE_HEAD(head, field) do {                            \
  305         if ((STAILQ_FIRST((head)) =                                     \
  306              STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL)         \
  307                 (head)->stqh_last = &STAILQ_FIRST((head));              \
  308 } while (0)
  309 
  310 #define STAILQ_REMOVE_AFTER(head, elm, field) do {                      \
  311         if ((STAILQ_NEXT(elm, field) =                                  \
  312              STAILQ_NEXT(STAILQ_NEXT(elm, field), field)) == NULL)      \
  313                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
  314 } while (0)
  315 
  316 /*
  317  * List declarations.
  318  */
  319 #define LIST_HEAD(name, type)                                           \
  320 struct name {                                                           \
  321         struct type *lh_first;  /* first element */                     \
  322 }
  323 
  324 #define LIST_HEAD_INITIALIZER(head)                                     \
  325         { NULL }
  326 
  327 #define LIST_ENTRY(type)                                                \
  328 struct {                                                                \
  329         struct type *le_next;   /* next element */                      \
  330         struct type **le_prev;  /* address of previous next element */  \
  331 }
  332 
  333 /*
  334  * List functions.
  335  */
  336 
  337 #if (defined(_KERNEL) && defined(INVARIANTS))
  338 #define QMD_LIST_CHECK_HEAD(head, field) do {                           \
  339         if (LIST_FIRST((head)) != NULL &&                               \
  340             LIST_FIRST((head))->field.le_prev !=                        \
  341              &LIST_FIRST((head)))                                       \
  342                 panic("Bad list head %p first->prev != head", (head));  \
  343 } while (0)
  344 
  345 #define QMD_LIST_CHECK_NEXT(elm, field) do {                            \
  346         if (LIST_NEXT((elm), field) != NULL &&                          \
  347             LIST_NEXT((elm), field)->field.le_prev !=                   \
  348              &((elm)->field.le_next))                                   \
  349                 panic("Bad link elm %p next->prev != elm", (elm));      \
  350 } while (0)
  351 
  352 #define QMD_LIST_CHECK_PREV(elm, field) do {                            \
  353         if (*(elm)->field.le_prev != (elm))                             \
  354                 panic("Bad link elm %p prev->next != elm", (elm));      \
  355 } while (0)
  356 #else
  357 #define QMD_LIST_CHECK_HEAD(head, field)
  358 #define QMD_LIST_CHECK_NEXT(elm, field)
  359 #define QMD_LIST_CHECK_PREV(elm, field)
  360 #endif /* (_KERNEL && INVARIANTS) */
  361 
  362 #define LIST_EMPTY(head)        ((head)->lh_first == NULL)
  363 
  364 #define LIST_FIRST(head)        ((head)->lh_first)
  365 
  366 #define LIST_FOREACH(var, head, field)                                  \
  367         for ((var) = LIST_FIRST((head));                                \
  368             (var);                                                      \
  369             (var) = LIST_NEXT((var), field))
  370 
  371 #define LIST_FOREACH_SAFE(var, head, field, tvar)                       \
  372         for ((var) = LIST_FIRST((head));                                \
  373             (var) && ((tvar) = LIST_NEXT((var), field), 1);             \
  374             (var) = (tvar))
  375 
  376 #define LIST_INIT(head) do {                                            \
  377         LIST_FIRST((head)) = NULL;                                      \
  378 } while (0)
  379 
  380 #define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
  381         QMD_LIST_CHECK_NEXT(listelm, field);                            \
  382         if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
  383                 LIST_NEXT((listelm), field)->field.le_prev =            \
  384                     &LIST_NEXT((elm), field);                           \
  385         LIST_NEXT((listelm), field) = (elm);                            \
  386         (elm)->field.le_prev = &LIST_NEXT((listelm), field);            \
  387 } while (0)
  388 
  389 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
  390         QMD_LIST_CHECK_PREV(listelm, field);                            \
  391         (elm)->field.le_prev = (listelm)->field.le_prev;                \
  392         LIST_NEXT((elm), field) = (listelm);                            \
  393         *(listelm)->field.le_prev = (elm);                              \
  394         (listelm)->field.le_prev = &LIST_NEXT((elm), field);            \
  395 } while (0)
  396 
  397 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
  398         QMD_LIST_CHECK_HEAD((head), field);                             \
  399         if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)     \
  400                 LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
  401         LIST_FIRST((head)) = (elm);                                     \
  402         (elm)->field.le_prev = &LIST_FIRST((head));                     \
  403 } while (0)
  404 
  405 #define LIST_NEXT(elm, field)   ((elm)->field.le_next)
  406 
  407 #define LIST_REMOVE(elm, field) do {                                    \
  408         QMD_SAVELINK(oldnext, (elm)->field.le_next);                    \
  409         QMD_SAVELINK(oldprev, (elm)->field.le_prev);                    \
  410         QMD_LIST_CHECK_NEXT(elm, field);                                \
  411         QMD_LIST_CHECK_PREV(elm, field);                                \
  412         if (LIST_NEXT((elm), field) != NULL)                            \
  413                 LIST_NEXT((elm), field)->field.le_prev =                \
  414                     (elm)->field.le_prev;                               \
  415         *(elm)->field.le_prev = LIST_NEXT((elm), field);                \
  416         TRASHIT(*oldnext);                                              \
  417         TRASHIT(*oldprev);                                              \
  418 } while (0)
  419 
  420 /*
  421  * Tail queue declarations.
  422  */
  423 #define TAILQ_HEAD(name, type)                                          \
  424 struct name {                                                           \
  425         struct type *tqh_first; /* first element */                     \
  426         struct type **tqh_last; /* addr of last next element */         \
  427         TRACEBUF                                                        \
  428 }
  429 
  430 #define TAILQ_HEAD_INITIALIZER(head)                                    \
  431         { NULL, &(head).tqh_first }
  432 
  433 #define TAILQ_ENTRY(type)                                               \
  434 struct {                                                                \
  435         struct type *tqe_next;  /* next element */                      \
  436         struct type **tqe_prev; /* address of previous next element */  \
  437         TRACEBUF                                                        \
  438 }
  439 
  440 /*
  441  * Tail queue functions.
  442  */
  443 #if (defined(_KERNEL) && defined(INVARIANTS))
  444 #define QMD_TAILQ_CHECK_HEAD(head, field) do {                          \
  445         if (!TAILQ_EMPTY(head) &&                                       \
  446             TAILQ_FIRST((head))->field.tqe_prev !=                      \
  447              &TAILQ_FIRST((head)))                                      \
  448                 panic("Bad tailq head %p first->prev != head", (head)); \
  449 } while (0)
  450 
  451 #define QMD_TAILQ_CHECK_TAIL(head, field) do {                          \
  452         if (*(head)->tqh_last != NULL)                                  \
  453                 panic("Bad tailq NEXT(%p->tqh_last) != NULL", (head));  \
  454 } while (0)
  455 
  456 #define QMD_TAILQ_CHECK_NEXT(elm, field) do {                           \
  457         if (TAILQ_NEXT((elm), field) != NULL &&                         \
  458             TAILQ_NEXT((elm), field)->field.tqe_prev !=                 \
  459              &((elm)->field.tqe_next))                                  \
  460                 panic("Bad link elm %p next->prev != elm", (elm));      \
  461 } while (0)
  462 
  463 #define QMD_TAILQ_CHECK_PREV(elm, field) do {                           \
  464         if (*(elm)->field.tqe_prev != (elm))                            \
  465                 panic("Bad link elm %p prev->next != elm", (elm));      \
  466 } while (0)
  467 #else
  468 #define QMD_TAILQ_CHECK_HEAD(head, field)
  469 #define QMD_TAILQ_CHECK_TAIL(head, headname)
  470 #define QMD_TAILQ_CHECK_NEXT(elm, field)
  471 #define QMD_TAILQ_CHECK_PREV(elm, field)
  472 #endif /* (_KERNEL && INVARIANTS) */
  473 
  474 #define TAILQ_CONCAT(head1, head2, field) do {                          \
  475         if (!TAILQ_EMPTY(head2)) {                                      \
  476                 *(head1)->tqh_last = (head2)->tqh_first;                \
  477                 (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last; \
  478                 (head1)->tqh_last = (head2)->tqh_last;                  \
  479                 TAILQ_INIT((head2));                                    \
  480                 QMD_TRACE_HEAD(head1);                                  \
  481                 QMD_TRACE_HEAD(head2);                                  \
  482         }                                                               \
  483 } while (0)
  484 
  485 #define TAILQ_EMPTY(head)       ((head)->tqh_first == NULL)
  486 
  487 #define TAILQ_FIRST(head)       ((head)->tqh_first)
  488 
  489 #define TAILQ_FOREACH(var, head, field)                                 \
  490         for ((var) = TAILQ_FIRST((head));                               \
  491             (var);                                                      \
  492             (var) = TAILQ_NEXT((var), field))
  493 
  494 #define TAILQ_FOREACH_SAFE(var, head, field, tvar)                      \
  495         for ((var) = TAILQ_FIRST((head));                               \
  496             (var) && ((tvar) = TAILQ_NEXT((var), field), 1);            \
  497             (var) = (tvar))
  498 
  499 #define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
  500         for ((var) = TAILQ_LAST((head), headname);                      \
  501             (var);                                                      \
  502             (var) = TAILQ_PREV((var), headname, field))
  503 
  504 #define TAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar)    \
  505         for ((var) = TAILQ_LAST((head), headname);                      \
  506             (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);  \
  507             (var) = (tvar))
  508 
  509 #define TAILQ_INIT(head) do {                                           \
  510         TAILQ_FIRST((head)) = NULL;                                     \
  511         (head)->tqh_last = &TAILQ_FIRST((head));                        \
  512         QMD_TRACE_HEAD(head);                                           \
  513 } while (0)
  514 
  515 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
  516         QMD_TAILQ_CHECK_NEXT(listelm, field);                           \
  517         if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
  518                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
  519                     &TAILQ_NEXT((elm), field);                          \
  520         else {                                                          \
  521                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
  522                 QMD_TRACE_HEAD(head);                                   \
  523         }                                                               \
  524         TAILQ_NEXT((listelm), field) = (elm);                           \
  525         (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);          \
  526         QMD_TRACE_ELEM(&(elm)->field);                                  \
  527         QMD_TRACE_ELEM(&listelm->field);                                \
  528 } while (0)
  529 
  530 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
  531         QMD_TAILQ_CHECK_PREV(listelm, field);                           \
  532         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
  533         TAILQ_NEXT((elm), field) = (listelm);                           \
  534         *(listelm)->field.tqe_prev = (elm);                             \
  535         (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);          \
  536         QMD_TRACE_ELEM(&(elm)->field);                                  \
  537         QMD_TRACE_ELEM(&listelm->field);                                \
  538 } while (0)
  539 
  540 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
  541         QMD_TAILQ_CHECK_HEAD(head, field);                              \
  542         if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)   \
  543                 TAILQ_FIRST((head))->field.tqe_prev =                   \
  544                     &TAILQ_NEXT((elm), field);                          \
  545         else                                                            \
  546                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
  547         TAILQ_FIRST((head)) = (elm);                                    \
  548         (elm)->field.tqe_prev = &TAILQ_FIRST((head));                   \
  549         QMD_TRACE_HEAD(head);                                           \
  550         QMD_TRACE_ELEM(&(elm)->field);                                  \
  551 } while (0)
  552 
  553 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
  554         QMD_TAILQ_CHECK_TAIL(head, field);                              \
  555         TAILQ_NEXT((elm), field) = NULL;                                \
  556         (elm)->field.tqe_prev = (head)->tqh_last;                       \
  557         *(head)->tqh_last = (elm);                                      \
  558         (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
  559         QMD_TRACE_HEAD(head);                                           \
  560         QMD_TRACE_ELEM(&(elm)->field);                                  \
  561 } while (0)
  562 
  563 #define TAILQ_LAST(head, headname)                                      \
  564         (*(((struct headname *)((head)->tqh_last))->tqh_last))
  565 
  566 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
  567 
  568 #define TAILQ_PREV(elm, headname, field)                                \
  569         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
  570 
  571 #define TAILQ_REMOVE(head, elm, field) do {                             \
  572         QMD_SAVELINK(oldnext, (elm)->field.tqe_next);                   \
  573         QMD_SAVELINK(oldprev, (elm)->field.tqe_prev);                   \
  574         QMD_TAILQ_CHECK_NEXT(elm, field);                               \
  575         QMD_TAILQ_CHECK_PREV(elm, field);                               \
  576         if ((TAILQ_NEXT((elm), field)) != NULL)                         \
  577                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
  578                     (elm)->field.tqe_prev;                              \
  579         else {                                                          \
  580                 (head)->tqh_last = (elm)->field.tqe_prev;               \
  581                 QMD_TRACE_HEAD(head);                                   \
  582         }                                                               \
  583         *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);              \
  584         TRASHIT(*oldnext);                                              \
  585         TRASHIT(*oldprev);                                              \
  586         QMD_TRACE_ELEM(&(elm)->field);                                  \
  587 } while (0)
  588 
  589 
  590 #ifdef _KERNEL
  591 
  592 /*
  593  * XXX insque() and remque() are an old way of handling certain queues.
  594  * They bogusly assumes that all queue heads look alike.
  595  */
  596 
  597 struct quehead {
  598         struct quehead *qh_link;
  599         struct quehead *qh_rlink;
  600 };
  601 
  602 #ifdef __CC_SUPPORTS___INLINE
  603 
  604 static __inline void
  605 insque(void *a, void *b)
  606 {
  607         struct quehead *element = (struct quehead *)a,
  608                  *head = (struct quehead *)b;
  609 
  610         element->qh_link = head->qh_link;
  611         element->qh_rlink = head;
  612         head->qh_link = element;
  613         element->qh_link->qh_rlink = element;
  614 }
  615 
  616 static __inline void
  617 remque(void *a)
  618 {
  619         struct quehead *element = (struct quehead *)a;
  620 
  621         element->qh_link->qh_rlink = element->qh_rlink;
  622         element->qh_rlink->qh_link = element->qh_link;
  623         element->qh_rlink = 0;
  624 }
  625 
  626 #else /* !__CC_SUPPORTS___INLINE */
  627 
  628 void    insque(void *a, void *b);
  629 void    remque(void *a);
  630 
  631 #endif /* __CC_SUPPORTS___INLINE */
  632 
  633 #endif /* _KERNEL */
  634 
  635 #endif /* !_SYS_QUEUE_H_ */

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