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/9.1/sys/sys/queue.h 221843 2011-05-13 15:49:23Z mdf $
   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  * _SWAP                        +       +       +       +
  103  *
  104  */
  105 #ifdef QUEUE_MACRO_DEBUG
  106 /* Store the last 2 places the queue element or head was altered */
  107 struct qm_trace {
  108         char * lastfile;
  109         int lastline;
  110         char * prevfile;
  111         int prevline;
  112 };
  113 
  114 #define TRACEBUF        struct qm_trace trace;
  115 #define TRASHIT(x)      do {(x) = (void *)-1;} while (0)
  116 #define QMD_SAVELINK(name, link)        void **name = (void *)&(link)
  117 
  118 #define QMD_TRACE_HEAD(head) do {                                       \
  119         (head)->trace.prevline = (head)->trace.lastline;                \
  120         (head)->trace.prevfile = (head)->trace.lastfile;                \
  121         (head)->trace.lastline = __LINE__;                              \
  122         (head)->trace.lastfile = __FILE__;                              \
  123 } while (0)
  124 
  125 #define QMD_TRACE_ELEM(elem) do {                                       \
  126         (elem)->trace.prevline = (elem)->trace.lastline;                \
  127         (elem)->trace.prevfile = (elem)->trace.lastfile;                \
  128         (elem)->trace.lastline = __LINE__;                              \
  129         (elem)->trace.lastfile = __FILE__;                              \
  130 } while (0)
  131 
  132 #else
  133 #define QMD_TRACE_ELEM(elem)
  134 #define QMD_TRACE_HEAD(head)
  135 #define QMD_SAVELINK(name, link)
  136 #define TRACEBUF
  137 #define TRASHIT(x)
  138 #endif  /* QUEUE_MACRO_DEBUG */
  139 
  140 /*
  141  * Singly-linked List declarations.
  142  */
  143 #define SLIST_HEAD(name, type)                                          \
  144 struct name {                                                           \
  145         struct type *slh_first; /* first element */                     \
  146 }
  147 
  148 #define SLIST_HEAD_INITIALIZER(head)                                    \
  149         { NULL }
  150 
  151 #define SLIST_ENTRY(type)                                               \
  152 struct {                                                                \
  153         struct type *sle_next;  /* next element */                      \
  154 }
  155 
  156 /*
  157  * Singly-linked List functions.
  158  */
  159 #define SLIST_EMPTY(head)       ((head)->slh_first == NULL)
  160 
  161 #define SLIST_FIRST(head)       ((head)->slh_first)
  162 
  163 #define SLIST_FOREACH(var, head, field)                                 \
  164         for ((var) = SLIST_FIRST((head));                               \
  165             (var);                                                      \
  166             (var) = SLIST_NEXT((var), field))
  167 
  168 #define SLIST_FOREACH_SAFE(var, head, field, tvar)                      \
  169         for ((var) = SLIST_FIRST((head));                               \
  170             (var) && ((tvar) = SLIST_NEXT((var), field), 1);            \
  171             (var) = (tvar))
  172 
  173 #define SLIST_FOREACH_PREVPTR(var, varp, head, field)                   \
  174         for ((varp) = &SLIST_FIRST((head));                             \
  175             ((var) = *(varp)) != NULL;                                  \
  176             (varp) = &SLIST_NEXT((var), field))
  177 
  178 #define SLIST_INIT(head) do {                                           \
  179         SLIST_FIRST((head)) = NULL;                                     \
  180 } while (0)
  181 
  182 #define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
  183         SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);       \
  184         SLIST_NEXT((slistelm), field) = (elm);                          \
  185 } while (0)
  186 
  187 #define SLIST_INSERT_HEAD(head, elm, field) do {                        \
  188         SLIST_NEXT((elm), field) = SLIST_FIRST((head));                 \
  189         SLIST_FIRST((head)) = (elm);                                    \
  190 } while (0)
  191 
  192 #define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)
  193 
  194 #define SLIST_REMOVE(head, elm, type, field) do {                       \
  195         QMD_SAVELINK(oldnext, (elm)->field.sle_next);                   \
  196         if (SLIST_FIRST((head)) == (elm)) {                             \
  197                 SLIST_REMOVE_HEAD((head), field);                       \
  198         }                                                               \
  199         else {                                                          \
  200                 struct type *curelm = SLIST_FIRST((head));              \
  201                 while (SLIST_NEXT(curelm, field) != (elm))              \
  202                         curelm = SLIST_NEXT(curelm, field);             \
  203                 SLIST_REMOVE_AFTER(curelm, field);                      \
  204         }                                                               \
  205         TRASHIT(*oldnext);                                              \
  206 } while (0)
  207 
  208 #define SLIST_REMOVE_AFTER(elm, field) do {                             \
  209         SLIST_NEXT(elm, field) =                                        \
  210             SLIST_NEXT(SLIST_NEXT(elm, field), field);                  \
  211 } while (0)
  212 
  213 #define SLIST_REMOVE_HEAD(head, field) do {                             \
  214         SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);   \
  215 } while (0)
  216 
  217 #define SLIST_SWAP(head1, head2, type) do {                             \
  218         struct type *swap_first = SLIST_FIRST(head1);                   \
  219         SLIST_FIRST(head1) = SLIST_FIRST(head2);                        \
  220         SLIST_FIRST(head2) = swap_first;                                \
  221 } while (0)
  222 
  223 /*
  224  * Singly-linked Tail queue declarations.
  225  */
  226 #define STAILQ_HEAD(name, type)                                         \
  227 struct name {                                                           \
  228         struct type *stqh_first;/* first element */                     \
  229         struct type **stqh_last;/* addr of last next element */         \
  230 }
  231 
  232 #define STAILQ_HEAD_INITIALIZER(head)                                   \
  233         { NULL, &(head).stqh_first }
  234 
  235 #define STAILQ_ENTRY(type)                                              \
  236 struct {                                                                \
  237         struct type *stqe_next; /* next element */                      \
  238 }
  239 
  240 /*
  241  * Singly-linked Tail queue functions.
  242  */
  243 #define STAILQ_CONCAT(head1, head2) do {                                \
  244         if (!STAILQ_EMPTY((head2))) {                                   \
  245                 *(head1)->stqh_last = (head2)->stqh_first;              \
  246                 (head1)->stqh_last = (head2)->stqh_last;                \
  247                 STAILQ_INIT((head2));                                   \
  248         }                                                               \
  249 } while (0)
  250 
  251 #define STAILQ_EMPTY(head)      ((head)->stqh_first == NULL)
  252 
  253 #define STAILQ_FIRST(head)      ((head)->stqh_first)
  254 
  255 #define STAILQ_FOREACH(var, head, field)                                \
  256         for((var) = STAILQ_FIRST((head));                               \
  257            (var);                                                       \
  258            (var) = STAILQ_NEXT((var), field))
  259 
  260 
  261 #define STAILQ_FOREACH_SAFE(var, head, field, tvar)                     \
  262         for ((var) = STAILQ_FIRST((head));                              \
  263             (var) && ((tvar) = STAILQ_NEXT((var), field), 1);           \
  264             (var) = (tvar))
  265 
  266 #define STAILQ_INIT(head) do {                                          \
  267         STAILQ_FIRST((head)) = NULL;                                    \
  268         (head)->stqh_last = &STAILQ_FIRST((head));                      \
  269 } while (0)
  270 
  271 #define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {               \
  272         if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
  273                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
  274         STAILQ_NEXT((tqelm), field) = (elm);                            \
  275 } while (0)
  276 
  277 #define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
  278         if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL) \
  279                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
  280         STAILQ_FIRST((head)) = (elm);                                   \
  281 } while (0)
  282 
  283 #define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
  284         STAILQ_NEXT((elm), field) = NULL;                               \
  285         *(head)->stqh_last = (elm);                                     \
  286         (head)->stqh_last = &STAILQ_NEXT((elm), field);                 \
  287 } while (0)
  288 
  289 #define STAILQ_LAST(head, type, field)                                  \
  290         (STAILQ_EMPTY((head)) ?                                         \
  291                 NULL :                                                  \
  292                 ((struct type *)(void *)                                \
  293                 ((char *)((head)->stqh_last) - __offsetof(struct type, field))))
  294 
  295 #define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
  296 
  297 #define STAILQ_REMOVE(head, elm, type, field) do {                      \
  298         QMD_SAVELINK(oldnext, (elm)->field.stqe_next);                  \
  299         if (STAILQ_FIRST((head)) == (elm)) {                            \
  300                 STAILQ_REMOVE_HEAD((head), field);                      \
  301         }                                                               \
  302         else {                                                          \
  303                 struct type *curelm = STAILQ_FIRST((head));             \
  304                 while (STAILQ_NEXT(curelm, field) != (elm))             \
  305                         curelm = STAILQ_NEXT(curelm, field);            \
  306                 STAILQ_REMOVE_AFTER(head, curelm, field);               \
  307         }                                                               \
  308         TRASHIT(*oldnext);                                              \
  309 } while (0)
  310 
  311 #define STAILQ_REMOVE_AFTER(head, elm, field) do {                      \
  312         if ((STAILQ_NEXT(elm, field) =                                  \
  313              STAILQ_NEXT(STAILQ_NEXT(elm, field), field)) == NULL)      \
  314                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
  315 } while (0)
  316 
  317 #define STAILQ_REMOVE_HEAD(head, field) do {                            \
  318         if ((STAILQ_FIRST((head)) =                                     \
  319              STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL)         \
  320                 (head)->stqh_last = &STAILQ_FIRST((head));              \
  321 } while (0)
  322 
  323 #define STAILQ_SWAP(head1, head2, type) do {                            \
  324         struct type *swap_first = STAILQ_FIRST(head1);                  \
  325         struct type **swap_last = (head1)->stqh_last;                   \
  326         STAILQ_FIRST(head1) = STAILQ_FIRST(head2);                      \
  327         (head1)->stqh_last = (head2)->stqh_last;                        \
  328         STAILQ_FIRST(head2) = swap_first;                               \
  329         (head2)->stqh_last = swap_last;                                 \
  330         if (STAILQ_EMPTY(head1))                                        \
  331                 (head1)->stqh_last = &STAILQ_FIRST(head1);              \
  332         if (STAILQ_EMPTY(head2))                                        \
  333                 (head2)->stqh_last = &STAILQ_FIRST(head2);              \
  334 } while (0)
  335 
  336 
  337 /*
  338  * List declarations.
  339  */
  340 #define LIST_HEAD(name, type)                                           \
  341 struct name {                                                           \
  342         struct type *lh_first;  /* first element */                     \
  343 }
  344 
  345 #define LIST_HEAD_INITIALIZER(head)                                     \
  346         { NULL }
  347 
  348 #define LIST_ENTRY(type)                                                \
  349 struct {                                                                \
  350         struct type *le_next;   /* next element */                      \
  351         struct type **le_prev;  /* address of previous next element */  \
  352 }
  353 
  354 /*
  355  * List functions.
  356  */
  357 
  358 #if (defined(_KERNEL) && defined(INVARIANTS))
  359 #define QMD_LIST_CHECK_HEAD(head, field) do {                           \
  360         if (LIST_FIRST((head)) != NULL &&                               \
  361             LIST_FIRST((head))->field.le_prev !=                        \
  362              &LIST_FIRST((head)))                                       \
  363                 panic("Bad list head %p first->prev != head", (head));  \
  364 } while (0)
  365 
  366 #define QMD_LIST_CHECK_NEXT(elm, field) do {                            \
  367         if (LIST_NEXT((elm), field) != NULL &&                          \
  368             LIST_NEXT((elm), field)->field.le_prev !=                   \
  369              &((elm)->field.le_next))                                   \
  370                 panic("Bad link elm %p next->prev != elm", (elm));      \
  371 } while (0)
  372 
  373 #define QMD_LIST_CHECK_PREV(elm, field) do {                            \
  374         if (*(elm)->field.le_prev != (elm))                             \
  375                 panic("Bad link elm %p prev->next != elm", (elm));      \
  376 } while (0)
  377 #else
  378 #define QMD_LIST_CHECK_HEAD(head, field)
  379 #define QMD_LIST_CHECK_NEXT(elm, field)
  380 #define QMD_LIST_CHECK_PREV(elm, field)
  381 #endif /* (_KERNEL && INVARIANTS) */
  382 
  383 #define LIST_EMPTY(head)        ((head)->lh_first == NULL)
  384 
  385 #define LIST_FIRST(head)        ((head)->lh_first)
  386 
  387 #define LIST_FOREACH(var, head, field)                                  \
  388         for ((var) = LIST_FIRST((head));                                \
  389             (var);                                                      \
  390             (var) = LIST_NEXT((var), field))
  391 
  392 #define LIST_FOREACH_SAFE(var, head, field, tvar)                       \
  393         for ((var) = LIST_FIRST((head));                                \
  394             (var) && ((tvar) = LIST_NEXT((var), field), 1);             \
  395             (var) = (tvar))
  396 
  397 #define LIST_INIT(head) do {                                            \
  398         LIST_FIRST((head)) = NULL;                                      \
  399 } while (0)
  400 
  401 #define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
  402         QMD_LIST_CHECK_NEXT(listelm, field);                            \
  403         if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
  404                 LIST_NEXT((listelm), field)->field.le_prev =            \
  405                     &LIST_NEXT((elm), field);                           \
  406         LIST_NEXT((listelm), field) = (elm);                            \
  407         (elm)->field.le_prev = &LIST_NEXT((listelm), field);            \
  408 } while (0)
  409 
  410 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
  411         QMD_LIST_CHECK_PREV(listelm, field);                            \
  412         (elm)->field.le_prev = (listelm)->field.le_prev;                \
  413         LIST_NEXT((elm), field) = (listelm);                            \
  414         *(listelm)->field.le_prev = (elm);                              \
  415         (listelm)->field.le_prev = &LIST_NEXT((elm), field);            \
  416 } while (0)
  417 
  418 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
  419         QMD_LIST_CHECK_HEAD((head), field);                             \
  420         if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)     \
  421                 LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
  422         LIST_FIRST((head)) = (elm);                                     \
  423         (elm)->field.le_prev = &LIST_FIRST((head));                     \
  424 } while (0)
  425 
  426 #define LIST_NEXT(elm, field)   ((elm)->field.le_next)
  427 
  428 #define LIST_REMOVE(elm, field) do {                                    \
  429         QMD_SAVELINK(oldnext, (elm)->field.le_next);                    \
  430         QMD_SAVELINK(oldprev, (elm)->field.le_prev);                    \
  431         QMD_LIST_CHECK_NEXT(elm, field);                                \
  432         QMD_LIST_CHECK_PREV(elm, field);                                \
  433         if (LIST_NEXT((elm), field) != NULL)                            \
  434                 LIST_NEXT((elm), field)->field.le_prev =                \
  435                     (elm)->field.le_prev;                               \
  436         *(elm)->field.le_prev = LIST_NEXT((elm), field);                \
  437         TRASHIT(*oldnext);                                              \
  438         TRASHIT(*oldprev);                                              \
  439 } while (0)
  440 
  441 #define LIST_SWAP(head1, head2, type, field) do {                       \
  442         struct type *swap_tmp = LIST_FIRST((head1));                    \
  443         LIST_FIRST((head1)) = LIST_FIRST((head2));                      \
  444         LIST_FIRST((head2)) = swap_tmp;                                 \
  445         if ((swap_tmp = LIST_FIRST((head1))) != NULL)                   \
  446                 swap_tmp->field.le_prev = &LIST_FIRST((head1));         \
  447         if ((swap_tmp = LIST_FIRST((head2))) != NULL)                   \
  448                 swap_tmp->field.le_prev = &LIST_FIRST((head2));         \
  449 } while (0)
  450 
  451 /*
  452  * Tail queue declarations.
  453  */
  454 #define TAILQ_HEAD(name, type)                                          \
  455 struct name {                                                           \
  456         struct type *tqh_first; /* first element */                     \
  457         struct type **tqh_last; /* addr of last next element */         \
  458         TRACEBUF                                                        \
  459 }
  460 
  461 #define TAILQ_HEAD_INITIALIZER(head)                                    \
  462         { NULL, &(head).tqh_first }
  463 
  464 #define TAILQ_ENTRY(type)                                               \
  465 struct {                                                                \
  466         struct type *tqe_next;  /* next element */                      \
  467         struct type **tqe_prev; /* address of previous next element */  \
  468         TRACEBUF                                                        \
  469 }
  470 
  471 /*
  472  * Tail queue functions.
  473  */
  474 #if (defined(_KERNEL) && defined(INVARIANTS))
  475 #define QMD_TAILQ_CHECK_HEAD(head, field) do {                          \
  476         if (!TAILQ_EMPTY(head) &&                                       \
  477             TAILQ_FIRST((head))->field.tqe_prev !=                      \
  478              &TAILQ_FIRST((head)))                                      \
  479                 panic("Bad tailq head %p first->prev != head", (head)); \
  480 } while (0)
  481 
  482 #define QMD_TAILQ_CHECK_TAIL(head, field) do {                          \
  483         if (*(head)->tqh_last != NULL)                                  \
  484                 panic("Bad tailq NEXT(%p->tqh_last) != NULL", (head));  \
  485 } while (0)
  486 
  487 #define QMD_TAILQ_CHECK_NEXT(elm, field) do {                           \
  488         if (TAILQ_NEXT((elm), field) != NULL &&                         \
  489             TAILQ_NEXT((elm), field)->field.tqe_prev !=                 \
  490              &((elm)->field.tqe_next))                                  \
  491                 panic("Bad link elm %p next->prev != elm", (elm));      \
  492 } while (0)
  493 
  494 #define QMD_TAILQ_CHECK_PREV(elm, field) do {                           \
  495         if (*(elm)->field.tqe_prev != (elm))                            \
  496                 panic("Bad link elm %p prev->next != elm", (elm));      \
  497 } while (0)
  498 #else
  499 #define QMD_TAILQ_CHECK_HEAD(head, field)
  500 #define QMD_TAILQ_CHECK_TAIL(head, headname)
  501 #define QMD_TAILQ_CHECK_NEXT(elm, field)
  502 #define QMD_TAILQ_CHECK_PREV(elm, field)
  503 #endif /* (_KERNEL && INVARIANTS) */
  504 
  505 #define TAILQ_CONCAT(head1, head2, field) do {                          \
  506         if (!TAILQ_EMPTY(head2)) {                                      \
  507                 *(head1)->tqh_last = (head2)->tqh_first;                \
  508                 (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last; \
  509                 (head1)->tqh_last = (head2)->tqh_last;                  \
  510                 TAILQ_INIT((head2));                                    \
  511                 QMD_TRACE_HEAD(head1);                                  \
  512                 QMD_TRACE_HEAD(head2);                                  \
  513         }                                                               \
  514 } while (0)
  515 
  516 #define TAILQ_EMPTY(head)       ((head)->tqh_first == NULL)
  517 
  518 #define TAILQ_FIRST(head)       ((head)->tqh_first)
  519 
  520 #define TAILQ_FOREACH(var, head, field)                                 \
  521         for ((var) = TAILQ_FIRST((head));                               \
  522             (var);                                                      \
  523             (var) = TAILQ_NEXT((var), field))
  524 
  525 #define TAILQ_FOREACH_SAFE(var, head, field, tvar)                      \
  526         for ((var) = TAILQ_FIRST((head));                               \
  527             (var) && ((tvar) = TAILQ_NEXT((var), field), 1);            \
  528             (var) = (tvar))
  529 
  530 #define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
  531         for ((var) = TAILQ_LAST((head), headname);                      \
  532             (var);                                                      \
  533             (var) = TAILQ_PREV((var), headname, field))
  534 
  535 #define TAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar)    \
  536         for ((var) = TAILQ_LAST((head), headname);                      \
  537             (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);  \
  538             (var) = (tvar))
  539 
  540 #define TAILQ_INIT(head) do {                                           \
  541         TAILQ_FIRST((head)) = NULL;                                     \
  542         (head)->tqh_last = &TAILQ_FIRST((head));                        \
  543         QMD_TRACE_HEAD(head);                                           \
  544 } while (0)
  545 
  546 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
  547         QMD_TAILQ_CHECK_NEXT(listelm, field);                           \
  548         if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
  549                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
  550                     &TAILQ_NEXT((elm), field);                          \
  551         else {                                                          \
  552                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
  553                 QMD_TRACE_HEAD(head);                                   \
  554         }                                                               \
  555         TAILQ_NEXT((listelm), field) = (elm);                           \
  556         (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);          \
  557         QMD_TRACE_ELEM(&(elm)->field);                                  \
  558         QMD_TRACE_ELEM(&listelm->field);                                \
  559 } while (0)
  560 
  561 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
  562         QMD_TAILQ_CHECK_PREV(listelm, field);                           \
  563         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
  564         TAILQ_NEXT((elm), field) = (listelm);                           \
  565         *(listelm)->field.tqe_prev = (elm);                             \
  566         (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);          \
  567         QMD_TRACE_ELEM(&(elm)->field);                                  \
  568         QMD_TRACE_ELEM(&listelm->field);                                \
  569 } while (0)
  570 
  571 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
  572         QMD_TAILQ_CHECK_HEAD(head, field);                              \
  573         if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)   \
  574                 TAILQ_FIRST((head))->field.tqe_prev =                   \
  575                     &TAILQ_NEXT((elm), field);                          \
  576         else                                                            \
  577                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
  578         TAILQ_FIRST((head)) = (elm);                                    \
  579         (elm)->field.tqe_prev = &TAILQ_FIRST((head));                   \
  580         QMD_TRACE_HEAD(head);                                           \
  581         QMD_TRACE_ELEM(&(elm)->field);                                  \
  582 } while (0)
  583 
  584 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
  585         QMD_TAILQ_CHECK_TAIL(head, field);                              \
  586         TAILQ_NEXT((elm), field) = NULL;                                \
  587         (elm)->field.tqe_prev = (head)->tqh_last;                       \
  588         *(head)->tqh_last = (elm);                                      \
  589         (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
  590         QMD_TRACE_HEAD(head);                                           \
  591         QMD_TRACE_ELEM(&(elm)->field);                                  \
  592 } while (0)
  593 
  594 #define TAILQ_LAST(head, headname)                                      \
  595         (*(((struct headname *)((head)->tqh_last))->tqh_last))
  596 
  597 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
  598 
  599 #define TAILQ_PREV(elm, headname, field)                                \
  600         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
  601 
  602 #define TAILQ_REMOVE(head, elm, field) do {                             \
  603         QMD_SAVELINK(oldnext, (elm)->field.tqe_next);                   \
  604         QMD_SAVELINK(oldprev, (elm)->field.tqe_prev);                   \
  605         QMD_TAILQ_CHECK_NEXT(elm, field);                               \
  606         QMD_TAILQ_CHECK_PREV(elm, field);                               \
  607         if ((TAILQ_NEXT((elm), field)) != NULL)                         \
  608                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
  609                     (elm)->field.tqe_prev;                              \
  610         else {                                                          \
  611                 (head)->tqh_last = (elm)->field.tqe_prev;               \
  612                 QMD_TRACE_HEAD(head);                                   \
  613         }                                                               \
  614         *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);              \
  615         TRASHIT(*oldnext);                                              \
  616         TRASHIT(*oldprev);                                              \
  617         QMD_TRACE_ELEM(&(elm)->field);                                  \
  618 } while (0)
  619 
  620 #define TAILQ_SWAP(head1, head2, type, field) do {                      \
  621         struct type *swap_first = (head1)->tqh_first;                   \
  622         struct type **swap_last = (head1)->tqh_last;                    \
  623         (head1)->tqh_first = (head2)->tqh_first;                        \
  624         (head1)->tqh_last = (head2)->tqh_last;                          \
  625         (head2)->tqh_first = swap_first;                                \
  626         (head2)->tqh_last = swap_last;                                  \
  627         if ((swap_first = (head1)->tqh_first) != NULL)                  \
  628                 swap_first->field.tqe_prev = &(head1)->tqh_first;       \
  629         else                                                            \
  630                 (head1)->tqh_last = &(head1)->tqh_first;                \
  631         if ((swap_first = (head2)->tqh_first) != NULL)                  \
  632                 swap_first->field.tqe_prev = &(head2)->tqh_first;       \
  633         else                                                            \
  634                 (head2)->tqh_last = &(head2)->tqh_first;                \
  635 } while (0)
  636 
  637 #endif /* !_SYS_QUEUE_H_ */

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