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/8.1/sys/sys/queue.h 204392 2010-02-27 03:47:22Z 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 #define STAILQ_SWAP(head1, head2, type) do {                            \
  317         struct type *swap_first = STAILQ_FIRST(head1);                  \
  318         struct type **swap_last = (head1)->stqh_last;                   \
  319         STAILQ_FIRST(head1) = STAILQ_FIRST(head2);                      \
  320         (head1)->stqh_last = (head2)->stqh_last;                        \
  321         STAILQ_FIRST(head2) = swap_first;                               \
  322         (head2)->stqh_last = swap_last;                                 \
  323         if (STAILQ_EMPTY(head1))                                        \
  324                 (head1)->stqh_last = &STAILQ_FIRST(head1);              \
  325         if (STAILQ_EMPTY(head2))                                        \
  326                 (head2)->stqh_last = &STAILQ_FIRST(head2);              \
  327 } while (0)
  328 
  329 
  330 /*
  331  * List declarations.
  332  */
  333 #define LIST_HEAD(name, type)                                           \
  334 struct name {                                                           \
  335         struct type *lh_first;  /* first element */                     \
  336 }
  337 
  338 #define LIST_HEAD_INITIALIZER(head)                                     \
  339         { NULL }
  340 
  341 #define LIST_ENTRY(type)                                                \
  342 struct {                                                                \
  343         struct type *le_next;   /* next element */                      \
  344         struct type **le_prev;  /* address of previous next element */  \
  345 }
  346 
  347 /*
  348  * List functions.
  349  */
  350 
  351 #if (defined(_KERNEL) && defined(INVARIANTS))
  352 #define QMD_LIST_CHECK_HEAD(head, field) do {                           \
  353         if (LIST_FIRST((head)) != NULL &&                               \
  354             LIST_FIRST((head))->field.le_prev !=                        \
  355              &LIST_FIRST((head)))                                       \
  356                 panic("Bad list head %p first->prev != head", (head));  \
  357 } while (0)
  358 
  359 #define QMD_LIST_CHECK_NEXT(elm, field) do {                            \
  360         if (LIST_NEXT((elm), field) != NULL &&                          \
  361             LIST_NEXT((elm), field)->field.le_prev !=                   \
  362              &((elm)->field.le_next))                                   \
  363                 panic("Bad link elm %p next->prev != elm", (elm));      \
  364 } while (0)
  365 
  366 #define QMD_LIST_CHECK_PREV(elm, field) do {                            \
  367         if (*(elm)->field.le_prev != (elm))                             \
  368                 panic("Bad link elm %p prev->next != elm", (elm));      \
  369 } while (0)
  370 #else
  371 #define QMD_LIST_CHECK_HEAD(head, field)
  372 #define QMD_LIST_CHECK_NEXT(elm, field)
  373 #define QMD_LIST_CHECK_PREV(elm, field)
  374 #endif /* (_KERNEL && INVARIANTS) */
  375 
  376 #define LIST_EMPTY(head)        ((head)->lh_first == NULL)
  377 
  378 #define LIST_FIRST(head)        ((head)->lh_first)
  379 
  380 #define LIST_FOREACH(var, head, field)                                  \
  381         for ((var) = LIST_FIRST((head));                                \
  382             (var);                                                      \
  383             (var) = LIST_NEXT((var), field))
  384 
  385 #define LIST_FOREACH_SAFE(var, head, field, tvar)                       \
  386         for ((var) = LIST_FIRST((head));                                \
  387             (var) && ((tvar) = LIST_NEXT((var), field), 1);             \
  388             (var) = (tvar))
  389 
  390 #define LIST_INIT(head) do {                                            \
  391         LIST_FIRST((head)) = NULL;                                      \
  392 } while (0)
  393 
  394 #define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
  395         QMD_LIST_CHECK_NEXT(listelm, field);                            \
  396         if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
  397                 LIST_NEXT((listelm), field)->field.le_prev =            \
  398                     &LIST_NEXT((elm), field);                           \
  399         LIST_NEXT((listelm), field) = (elm);                            \
  400         (elm)->field.le_prev = &LIST_NEXT((listelm), field);            \
  401 } while (0)
  402 
  403 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
  404         QMD_LIST_CHECK_PREV(listelm, field);                            \
  405         (elm)->field.le_prev = (listelm)->field.le_prev;                \
  406         LIST_NEXT((elm), field) = (listelm);                            \
  407         *(listelm)->field.le_prev = (elm);                              \
  408         (listelm)->field.le_prev = &LIST_NEXT((elm), field);            \
  409 } while (0)
  410 
  411 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
  412         QMD_LIST_CHECK_HEAD((head), field);                             \
  413         if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)     \
  414                 LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
  415         LIST_FIRST((head)) = (elm);                                     \
  416         (elm)->field.le_prev = &LIST_FIRST((head));                     \
  417 } while (0)
  418 
  419 #define LIST_NEXT(elm, field)   ((elm)->field.le_next)
  420 
  421 #define LIST_REMOVE(elm, field) do {                                    \
  422         QMD_SAVELINK(oldnext, (elm)->field.le_next);                    \
  423         QMD_SAVELINK(oldprev, (elm)->field.le_prev);                    \
  424         QMD_LIST_CHECK_NEXT(elm, field);                                \
  425         QMD_LIST_CHECK_PREV(elm, field);                                \
  426         if (LIST_NEXT((elm), field) != NULL)                            \
  427                 LIST_NEXT((elm), field)->field.le_prev =                \
  428                     (elm)->field.le_prev;                               \
  429         *(elm)->field.le_prev = LIST_NEXT((elm), field);                \
  430         TRASHIT(*oldnext);                                              \
  431         TRASHIT(*oldprev);                                              \
  432 } while (0)
  433 
  434 #define LIST_SWAP(head1, head2, type, field) do {                       \
  435         struct type *swap_tmp = LIST_FIRST((head1));                    \
  436         LIST_FIRST((head1)) = LIST_FIRST((head2));                      \
  437         LIST_FIRST((head2)) = swap_tmp;                                 \
  438         if ((swap_tmp = LIST_FIRST((head1))) != NULL)                   \
  439                 swap_tmp->field.le_prev = &LIST_FIRST((head1));         \
  440         if ((swap_tmp = LIST_FIRST((head2))) != NULL)                   \
  441                 swap_tmp->field.le_prev = &LIST_FIRST((head2));         \
  442 } while (0)
  443 
  444 /*
  445  * Tail queue declarations.
  446  */
  447 #define TAILQ_HEAD(name, type)                                          \
  448 struct name {                                                           \
  449         struct type *tqh_first; /* first element */                     \
  450         struct type **tqh_last; /* addr of last next element */         \
  451         TRACEBUF                                                        \
  452 }
  453 
  454 #define TAILQ_HEAD_INITIALIZER(head)                                    \
  455         { NULL, &(head).tqh_first }
  456 
  457 #define TAILQ_ENTRY(type)                                               \
  458 struct {                                                                \
  459         struct type *tqe_next;  /* next element */                      \
  460         struct type **tqe_prev; /* address of previous next element */  \
  461         TRACEBUF                                                        \
  462 }
  463 
  464 /*
  465  * Tail queue functions.
  466  */
  467 #if (defined(_KERNEL) && defined(INVARIANTS))
  468 #define QMD_TAILQ_CHECK_HEAD(head, field) do {                          \
  469         if (!TAILQ_EMPTY(head) &&                                       \
  470             TAILQ_FIRST((head))->field.tqe_prev !=                      \
  471              &TAILQ_FIRST((head)))                                      \
  472                 panic("Bad tailq head %p first->prev != head", (head)); \
  473 } while (0)
  474 
  475 #define QMD_TAILQ_CHECK_TAIL(head, field) do {                          \
  476         if (*(head)->tqh_last != NULL)                                  \
  477                 panic("Bad tailq NEXT(%p->tqh_last) != NULL", (head));  \
  478 } while (0)
  479 
  480 #define QMD_TAILQ_CHECK_NEXT(elm, field) do {                           \
  481         if (TAILQ_NEXT((elm), field) != NULL &&                         \
  482             TAILQ_NEXT((elm), field)->field.tqe_prev !=                 \
  483              &((elm)->field.tqe_next))                                  \
  484                 panic("Bad link elm %p next->prev != elm", (elm));      \
  485 } while (0)
  486 
  487 #define QMD_TAILQ_CHECK_PREV(elm, field) do {                           \
  488         if (*(elm)->field.tqe_prev != (elm))                            \
  489                 panic("Bad link elm %p prev->next != elm", (elm));      \
  490 } while (0)
  491 #else
  492 #define QMD_TAILQ_CHECK_HEAD(head, field)
  493 #define QMD_TAILQ_CHECK_TAIL(head, headname)
  494 #define QMD_TAILQ_CHECK_NEXT(elm, field)
  495 #define QMD_TAILQ_CHECK_PREV(elm, field)
  496 #endif /* (_KERNEL && INVARIANTS) */
  497 
  498 #define TAILQ_CONCAT(head1, head2, field) do {                          \
  499         if (!TAILQ_EMPTY(head2)) {                                      \
  500                 *(head1)->tqh_last = (head2)->tqh_first;                \
  501                 (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last; \
  502                 (head1)->tqh_last = (head2)->tqh_last;                  \
  503                 TAILQ_INIT((head2));                                    \
  504                 QMD_TRACE_HEAD(head1);                                  \
  505                 QMD_TRACE_HEAD(head2);                                  \
  506         }                                                               \
  507 } while (0)
  508 
  509 #define TAILQ_EMPTY(head)       ((head)->tqh_first == NULL)
  510 
  511 #define TAILQ_FIRST(head)       ((head)->tqh_first)
  512 
  513 #define TAILQ_FOREACH(var, head, field)                                 \
  514         for ((var) = TAILQ_FIRST((head));                               \
  515             (var);                                                      \
  516             (var) = TAILQ_NEXT((var), field))
  517 
  518 #define TAILQ_FOREACH_SAFE(var, head, field, tvar)                      \
  519         for ((var) = TAILQ_FIRST((head));                               \
  520             (var) && ((tvar) = TAILQ_NEXT((var), field), 1);            \
  521             (var) = (tvar))
  522 
  523 #define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
  524         for ((var) = TAILQ_LAST((head), headname);                      \
  525             (var);                                                      \
  526             (var) = TAILQ_PREV((var), headname, field))
  527 
  528 #define TAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar)    \
  529         for ((var) = TAILQ_LAST((head), headname);                      \
  530             (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);  \
  531             (var) = (tvar))
  532 
  533 #define TAILQ_INIT(head) do {                                           \
  534         TAILQ_FIRST((head)) = NULL;                                     \
  535         (head)->tqh_last = &TAILQ_FIRST((head));                        \
  536         QMD_TRACE_HEAD(head);                                           \
  537 } while (0)
  538 
  539 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
  540         QMD_TAILQ_CHECK_NEXT(listelm, field);                           \
  541         if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
  542                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
  543                     &TAILQ_NEXT((elm), field);                          \
  544         else {                                                          \
  545                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
  546                 QMD_TRACE_HEAD(head);                                   \
  547         }                                                               \
  548         TAILQ_NEXT((listelm), field) = (elm);                           \
  549         (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);          \
  550         QMD_TRACE_ELEM(&(elm)->field);                                  \
  551         QMD_TRACE_ELEM(&listelm->field);                                \
  552 } while (0)
  553 
  554 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
  555         QMD_TAILQ_CHECK_PREV(listelm, field);                           \
  556         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
  557         TAILQ_NEXT((elm), field) = (listelm);                           \
  558         *(listelm)->field.tqe_prev = (elm);                             \
  559         (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);          \
  560         QMD_TRACE_ELEM(&(elm)->field);                                  \
  561         QMD_TRACE_ELEM(&listelm->field);                                \
  562 } while (0)
  563 
  564 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
  565         QMD_TAILQ_CHECK_HEAD(head, field);                              \
  566         if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)   \
  567                 TAILQ_FIRST((head))->field.tqe_prev =                   \
  568                     &TAILQ_NEXT((elm), field);                          \
  569         else                                                            \
  570                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
  571         TAILQ_FIRST((head)) = (elm);                                    \
  572         (elm)->field.tqe_prev = &TAILQ_FIRST((head));                   \
  573         QMD_TRACE_HEAD(head);                                           \
  574         QMD_TRACE_ELEM(&(elm)->field);                                  \
  575 } while (0)
  576 
  577 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
  578         QMD_TAILQ_CHECK_TAIL(head, field);                              \
  579         TAILQ_NEXT((elm), field) = NULL;                                \
  580         (elm)->field.tqe_prev = (head)->tqh_last;                       \
  581         *(head)->tqh_last = (elm);                                      \
  582         (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
  583         QMD_TRACE_HEAD(head);                                           \
  584         QMD_TRACE_ELEM(&(elm)->field);                                  \
  585 } while (0)
  586 
  587 #define TAILQ_LAST(head, headname)                                      \
  588         (*(((struct headname *)((head)->tqh_last))->tqh_last))
  589 
  590 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
  591 
  592 #define TAILQ_PREV(elm, headname, field)                                \
  593         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
  594 
  595 #define TAILQ_REMOVE(head, elm, field) do {                             \
  596         QMD_SAVELINK(oldnext, (elm)->field.tqe_next);                   \
  597         QMD_SAVELINK(oldprev, (elm)->field.tqe_prev);                   \
  598         QMD_TAILQ_CHECK_NEXT(elm, field);                               \
  599         QMD_TAILQ_CHECK_PREV(elm, field);                               \
  600         if ((TAILQ_NEXT((elm), field)) != NULL)                         \
  601                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
  602                     (elm)->field.tqe_prev;                              \
  603         else {                                                          \
  604                 (head)->tqh_last = (elm)->field.tqe_prev;               \
  605                 QMD_TRACE_HEAD(head);                                   \
  606         }                                                               \
  607         *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);              \
  608         TRASHIT(*oldnext);                                              \
  609         TRASHIT(*oldprev);                                              \
  610         QMD_TRACE_ELEM(&(elm)->field);                                  \
  611 } while (0)
  612 
  613 #define TAILQ_SWAP(head1, head2, type, field) do {                      \
  614         struct type *swap_first = (head1)->tqh_first;                   \
  615         struct type **swap_last = (head1)->tqh_last;                    \
  616         (head1)->tqh_first = (head2)->tqh_first;                        \
  617         (head1)->tqh_last = (head2)->tqh_last;                          \
  618         (head2)->tqh_first = swap_first;                                \
  619         (head2)->tqh_last = swap_last;                                  \
  620         if ((swap_first = (head1)->tqh_first) != NULL)                  \
  621                 swap_first->field.tqe_prev = &(head1)->tqh_first;       \
  622         else                                                            \
  623                 (head1)->tqh_last = &(head1)->tqh_first;                \
  624         if ((swap_first = (head2)->tqh_first) != NULL)                  \
  625                 swap_first->field.tqe_prev = &(head2)->tqh_first;       \
  626         else                                                            \
  627                 (head2)->tqh_last = &(head2)->tqh_first;                \
  628 } while (0)
  629 
  630 #endif /* !_SYS_QUEUE_H_ */

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