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/8.0/sys/sys/queue.h 192926 2009-05-27 19:28:04Z ed $
   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 
  116 #define QMD_TRACE_HEAD(head) do {                                       \
  117         (head)->trace.prevline = (head)->trace.lastline;                \
  118         (head)->trace.prevfile = (head)->trace.lastfile;                \
  119         (head)->trace.lastline = __LINE__;                              \
  120         (head)->trace.lastfile = __FILE__;                              \
  121 } while (0)
  122 
  123 #define QMD_TRACE_ELEM(elem) do {                                       \
  124         (elem)->trace.prevline = (elem)->trace.lastline;                \
  125         (elem)->trace.prevfile = (elem)->trace.lastfile;                \
  126         (elem)->trace.lastline = __LINE__;                              \
  127         (elem)->trace.lastfile = __FILE__;                              \
  128 } while (0)
  129 
  130 #else
  131 #define QMD_TRACE_ELEM(elem)
  132 #define QMD_TRACE_HEAD(head)
  133 #define TRACEBUF
  134 #define TRASHIT(x)
  135 #endif  /* QUEUE_MACRO_DEBUG */
  136 
  137 /*
  138  * Singly-linked List declarations.
  139  */
  140 #define SLIST_HEAD(name, type)                                          \
  141 struct name {                                                           \
  142         struct type *slh_first; /* first element */                     \
  143 }
  144 
  145 #define SLIST_HEAD_INITIALIZER(head)                                    \
  146         { NULL }
  147 
  148 #define SLIST_ENTRY(type)                                               \
  149 struct {                                                                \
  150         struct type *sle_next;  /* next element */                      \
  151 }
  152 
  153 /*
  154  * Singly-linked List functions.
  155  */
  156 #define SLIST_EMPTY(head)       ((head)->slh_first == NULL)
  157 
  158 #define SLIST_FIRST(head)       ((head)->slh_first)
  159 
  160 #define SLIST_FOREACH(var, head, field)                                 \
  161         for ((var) = SLIST_FIRST((head));                               \
  162             (var);                                                      \
  163             (var) = SLIST_NEXT((var), field))
  164 
  165 #define SLIST_FOREACH_SAFE(var, head, field, tvar)                      \
  166         for ((var) = SLIST_FIRST((head));                               \
  167             (var) && ((tvar) = SLIST_NEXT((var), field), 1);            \
  168             (var) = (tvar))
  169 
  170 #define SLIST_FOREACH_PREVPTR(var, varp, head, field)                   \
  171         for ((varp) = &SLIST_FIRST((head));                             \
  172             ((var) = *(varp)) != NULL;                                  \
  173             (varp) = &SLIST_NEXT((var), field))
  174 
  175 #define SLIST_INIT(head) do {                                           \
  176         SLIST_FIRST((head)) = NULL;                                     \
  177 } while (0)
  178 
  179 #define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
  180         SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);       \
  181         SLIST_NEXT((slistelm), field) = (elm);                          \
  182 } while (0)
  183 
  184 #define SLIST_INSERT_HEAD(head, elm, field) do {                        \
  185         SLIST_NEXT((elm), field) = SLIST_FIRST((head));                 \
  186         SLIST_FIRST((head)) = (elm);                                    \
  187 } while (0)
  188 
  189 #define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)
  190 
  191 #define SLIST_REMOVE(head, elm, type, field) do {                       \
  192         if (SLIST_FIRST((head)) == (elm)) {                             \
  193                 SLIST_REMOVE_HEAD((head), field);                       \
  194         }                                                               \
  195         else {                                                          \
  196                 struct type *curelm = SLIST_FIRST((head));              \
  197                 while (SLIST_NEXT(curelm, field) != (elm))              \
  198                         curelm = SLIST_NEXT(curelm, field);             \
  199                 SLIST_REMOVE_AFTER(curelm, field);                      \
  200         }                                                               \
  201         TRASHIT((elm)->field.sle_next);                                 \
  202 } while (0)
  203 
  204 #define SLIST_REMOVE_AFTER(elm, field) do {                             \
  205         SLIST_NEXT(elm, field) =                                        \
  206             SLIST_NEXT(SLIST_NEXT(elm, field), field);                  \
  207 } while (0)
  208 
  209 #define SLIST_REMOVE_HEAD(head, field) do {                             \
  210         SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);   \
  211 } while (0)
  212 
  213 /*
  214  * Singly-linked Tail queue declarations.
  215  */
  216 #define STAILQ_HEAD(name, type)                                         \
  217 struct name {                                                           \
  218         struct type *stqh_first;/* first element */                     \
  219         struct type **stqh_last;/* addr of last next element */         \
  220 }
  221 
  222 #define STAILQ_HEAD_INITIALIZER(head)                                   \
  223         { NULL, &(head).stqh_first }
  224 
  225 #define STAILQ_ENTRY(type)                                              \
  226 struct {                                                                \
  227         struct type *stqe_next; /* next element */                      \
  228 }
  229 
  230 /*
  231  * Singly-linked Tail queue functions.
  232  */
  233 #define STAILQ_CONCAT(head1, head2) do {                                \
  234         if (!STAILQ_EMPTY((head2))) {                                   \
  235                 *(head1)->stqh_last = (head2)->stqh_first;              \
  236                 (head1)->stqh_last = (head2)->stqh_last;                \
  237                 STAILQ_INIT((head2));                                   \
  238         }                                                               \
  239 } while (0)
  240 
  241 #define STAILQ_EMPTY(head)      ((head)->stqh_first == NULL)
  242 
  243 #define STAILQ_FIRST(head)      ((head)->stqh_first)
  244 
  245 #define STAILQ_FOREACH(var, head, field)                                \
  246         for((var) = STAILQ_FIRST((head));                               \
  247            (var);                                                       \
  248            (var) = STAILQ_NEXT((var), field))
  249 
  250 
  251 #define STAILQ_FOREACH_SAFE(var, head, field, tvar)                     \
  252         for ((var) = STAILQ_FIRST((head));                              \
  253             (var) && ((tvar) = STAILQ_NEXT((var), field), 1);           \
  254             (var) = (tvar))
  255 
  256 #define STAILQ_INIT(head) do {                                          \
  257         STAILQ_FIRST((head)) = NULL;                                    \
  258         (head)->stqh_last = &STAILQ_FIRST((head));                      \
  259 } while (0)
  260 
  261 #define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {               \
  262         if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
  263                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
  264         STAILQ_NEXT((tqelm), field) = (elm);                            \
  265 } while (0)
  266 
  267 #define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
  268         if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL) \
  269                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
  270         STAILQ_FIRST((head)) = (elm);                                   \
  271 } while (0)
  272 
  273 #define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
  274         STAILQ_NEXT((elm), field) = NULL;                               \
  275         *(head)->stqh_last = (elm);                                     \
  276         (head)->stqh_last = &STAILQ_NEXT((elm), field);                 \
  277 } while (0)
  278 
  279 #define STAILQ_LAST(head, type, field)                                  \
  280         (STAILQ_EMPTY((head)) ?                                         \
  281                 NULL :                                                  \
  282                 ((struct type *)(void *)                                \
  283                 ((char *)((head)->stqh_last) - __offsetof(struct type, field))))
  284 
  285 #define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
  286 
  287 #define STAILQ_REMOVE(head, elm, type, field) do {                      \
  288         if (STAILQ_FIRST((head)) == (elm)) {                            \
  289                 STAILQ_REMOVE_HEAD((head), field);                      \
  290         }                                                               \
  291         else {                                                          \
  292                 struct type *curelm = STAILQ_FIRST((head));             \
  293                 while (STAILQ_NEXT(curelm, field) != (elm))             \
  294                         curelm = STAILQ_NEXT(curelm, field);            \
  295                 STAILQ_REMOVE_AFTER(head, curelm, field);               \
  296         }                                                               \
  297         TRASHIT((elm)->field.stqe_next);                                \
  298 } while (0)
  299 
  300 #define STAILQ_REMOVE_HEAD(head, field) do {                            \
  301         if ((STAILQ_FIRST((head)) =                                     \
  302              STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL)         \
  303                 (head)->stqh_last = &STAILQ_FIRST((head));              \
  304 } while (0)
  305 
  306 #define STAILQ_REMOVE_AFTER(head, elm, field) do {                      \
  307         if ((STAILQ_NEXT(elm, field) =                                  \
  308              STAILQ_NEXT(STAILQ_NEXT(elm, field), field)) == NULL)      \
  309                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
  310 } while (0)
  311 
  312 #define STAILQ_SWAP(head1, head2, type) do {                            \
  313         struct type *swap_first = STAILQ_FIRST(head1);                  \
  314         struct type **swap_last = (head1)->stqh_last;                   \
  315         STAILQ_FIRST(head1) = STAILQ_FIRST(head2);                      \
  316         (head1)->stqh_last = (head2)->stqh_last;                        \
  317         STAILQ_FIRST(head2) = swap_first;                               \
  318         (head2)->stqh_last = swap_last;                                 \
  319         if (STAILQ_EMPTY(head1))                                        \
  320                 (head1)->stqh_last = &STAILQ_FIRST(head1);              \
  321         if (STAILQ_EMPTY(head2))                                        \
  322                 (head2)->stqh_last = &STAILQ_FIRST(head2);              \
  323 } while (0)
  324 
  325 
  326 /*
  327  * List declarations.
  328  */
  329 #define LIST_HEAD(name, type)                                           \
  330 struct name {                                                           \
  331         struct type *lh_first;  /* first element */                     \
  332 }
  333 
  334 #define LIST_HEAD_INITIALIZER(head)                                     \
  335         { NULL }
  336 
  337 #define LIST_ENTRY(type)                                                \
  338 struct {                                                                \
  339         struct type *le_next;   /* next element */                      \
  340         struct type **le_prev;  /* address of previous next element */  \
  341 }
  342 
  343 /*
  344  * List functions.
  345  */
  346 
  347 #if (defined(_KERNEL) && defined(INVARIANTS))
  348 #define QMD_LIST_CHECK_HEAD(head, field) do {                           \
  349         if (LIST_FIRST((head)) != NULL &&                               \
  350             LIST_FIRST((head))->field.le_prev !=                        \
  351              &LIST_FIRST((head)))                                       \
  352                 panic("Bad list head %p first->prev != head", (head));  \
  353 } while (0)
  354 
  355 #define QMD_LIST_CHECK_NEXT(elm, field) do {                            \
  356         if (LIST_NEXT((elm), field) != NULL &&                          \
  357             LIST_NEXT((elm), field)->field.le_prev !=                   \
  358              &((elm)->field.le_next))                                   \
  359                 panic("Bad link elm %p next->prev != elm", (elm));      \
  360 } while (0)
  361 
  362 #define QMD_LIST_CHECK_PREV(elm, field) do {                            \
  363         if (*(elm)->field.le_prev != (elm))                             \
  364                 panic("Bad link elm %p prev->next != elm", (elm));      \
  365 } while (0)
  366 #else
  367 #define QMD_LIST_CHECK_HEAD(head, field)
  368 #define QMD_LIST_CHECK_NEXT(elm, field)
  369 #define QMD_LIST_CHECK_PREV(elm, field)
  370 #endif /* (_KERNEL && INVARIANTS) */
  371 
  372 #define LIST_EMPTY(head)        ((head)->lh_first == NULL)
  373 
  374 #define LIST_FIRST(head)        ((head)->lh_first)
  375 
  376 #define LIST_FOREACH(var, head, field)                                  \
  377         for ((var) = LIST_FIRST((head));                                \
  378             (var);                                                      \
  379             (var) = LIST_NEXT((var), field))
  380 
  381 #define LIST_FOREACH_SAFE(var, head, field, tvar)                       \
  382         for ((var) = LIST_FIRST((head));                                \
  383             (var) && ((tvar) = LIST_NEXT((var), field), 1);             \
  384             (var) = (tvar))
  385 
  386 #define LIST_INIT(head) do {                                            \
  387         LIST_FIRST((head)) = NULL;                                      \
  388 } while (0)
  389 
  390 #define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
  391         QMD_LIST_CHECK_NEXT(listelm, field);                            \
  392         if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
  393                 LIST_NEXT((listelm), field)->field.le_prev =            \
  394                     &LIST_NEXT((elm), field);                           \
  395         LIST_NEXT((listelm), field) = (elm);                            \
  396         (elm)->field.le_prev = &LIST_NEXT((listelm), field);            \
  397 } while (0)
  398 
  399 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
  400         QMD_LIST_CHECK_PREV(listelm, field);                            \
  401         (elm)->field.le_prev = (listelm)->field.le_prev;                \
  402         LIST_NEXT((elm), field) = (listelm);                            \
  403         *(listelm)->field.le_prev = (elm);                              \
  404         (listelm)->field.le_prev = &LIST_NEXT((elm), field);            \
  405 } while (0)
  406 
  407 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
  408         QMD_LIST_CHECK_HEAD((head), field);                             \
  409         if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)     \
  410                 LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
  411         LIST_FIRST((head)) = (elm);                                     \
  412         (elm)->field.le_prev = &LIST_FIRST((head));                     \
  413 } while (0)
  414 
  415 #define LIST_NEXT(elm, field)   ((elm)->field.le_next)
  416 
  417 #define LIST_REMOVE(elm, field) do {                                    \
  418         QMD_LIST_CHECK_NEXT(elm, field);                                \
  419         QMD_LIST_CHECK_PREV(elm, field);                                \
  420         if (LIST_NEXT((elm), field) != NULL)                            \
  421                 LIST_NEXT((elm), field)->field.le_prev =                \
  422                     (elm)->field.le_prev;                               \
  423         *(elm)->field.le_prev = LIST_NEXT((elm), field);                \
  424         TRASHIT((elm)->field.le_next);                                  \
  425         TRASHIT((elm)->field.le_prev);                                  \
  426 } while (0)
  427 
  428 #define LIST_SWAP(head1, head2, type, field) do {                       \
  429         struct type *swap_tmp = LIST_FIRST((head1));                    \
  430         LIST_FIRST((head1)) = LIST_FIRST((head2));                      \
  431         LIST_FIRST((head2)) = swap_tmp;                                 \
  432         if ((swap_tmp = LIST_FIRST((head1))) != NULL)                   \
  433                 swap_tmp->field.le_prev = &LIST_FIRST((head1));         \
  434         if ((swap_tmp = LIST_FIRST((head2))) != NULL)                   \
  435                 swap_tmp->field.le_prev = &LIST_FIRST((head2));         \
  436 } while (0)
  437 
  438 /*
  439  * Tail queue declarations.
  440  */
  441 #define TAILQ_HEAD(name, type)                                          \
  442 struct name {                                                           \
  443         struct type *tqh_first; /* first element */                     \
  444         struct type **tqh_last; /* addr of last next element */         \
  445         TRACEBUF                                                        \
  446 }
  447 
  448 #define TAILQ_HEAD_INITIALIZER(head)                                    \
  449         { NULL, &(head).tqh_first }
  450 
  451 #define TAILQ_ENTRY(type)                                               \
  452 struct {                                                                \
  453         struct type *tqe_next;  /* next element */                      \
  454         struct type **tqe_prev; /* address of previous next element */  \
  455         TRACEBUF                                                        \
  456 }
  457 
  458 /*
  459  * Tail queue functions.
  460  */
  461 #if (defined(_KERNEL) && defined(INVARIANTS))
  462 #define QMD_TAILQ_CHECK_HEAD(head, field) do {                          \
  463         if (!TAILQ_EMPTY(head) &&                                       \
  464             TAILQ_FIRST((head))->field.tqe_prev !=                      \
  465              &TAILQ_FIRST((head)))                                      \
  466                 panic("Bad tailq head %p first->prev != head", (head)); \
  467 } while (0)
  468 
  469 #define QMD_TAILQ_CHECK_TAIL(head, field) do {                          \
  470         if (*(head)->tqh_last != NULL)                                  \
  471                 panic("Bad tailq NEXT(%p->tqh_last) != NULL", (head));  \
  472 } while (0)
  473 
  474 #define QMD_TAILQ_CHECK_NEXT(elm, field) do {                           \
  475         if (TAILQ_NEXT((elm), field) != NULL &&                         \
  476             TAILQ_NEXT((elm), field)->field.tqe_prev !=                 \
  477              &((elm)->field.tqe_next))                                  \
  478                 panic("Bad link elm %p next->prev != elm", (elm));      \
  479 } while (0)
  480 
  481 #define QMD_TAILQ_CHECK_PREV(elm, field) do {                           \
  482         if (*(elm)->field.tqe_prev != (elm))                            \
  483                 panic("Bad link elm %p prev->next != elm", (elm));      \
  484 } while (0)
  485 #else
  486 #define QMD_TAILQ_CHECK_HEAD(head, field)
  487 #define QMD_TAILQ_CHECK_TAIL(head, headname)
  488 #define QMD_TAILQ_CHECK_NEXT(elm, field)
  489 #define QMD_TAILQ_CHECK_PREV(elm, field)
  490 #endif /* (_KERNEL && INVARIANTS) */
  491 
  492 #define TAILQ_CONCAT(head1, head2, field) do {                          \
  493         if (!TAILQ_EMPTY(head2)) {                                      \
  494                 *(head1)->tqh_last = (head2)->tqh_first;                \
  495                 (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last; \
  496                 (head1)->tqh_last = (head2)->tqh_last;                  \
  497                 TAILQ_INIT((head2));                                    \
  498                 QMD_TRACE_HEAD(head1);                                  \
  499                 QMD_TRACE_HEAD(head2);                                  \
  500         }                                                               \
  501 } while (0)
  502 
  503 #define TAILQ_EMPTY(head)       ((head)->tqh_first == NULL)
  504 
  505 #define TAILQ_FIRST(head)       ((head)->tqh_first)
  506 
  507 #define TAILQ_FOREACH(var, head, field)                                 \
  508         for ((var) = TAILQ_FIRST((head));                               \
  509             (var);                                                      \
  510             (var) = TAILQ_NEXT((var), field))
  511 
  512 #define TAILQ_FOREACH_SAFE(var, head, field, tvar)                      \
  513         for ((var) = TAILQ_FIRST((head));                               \
  514             (var) && ((tvar) = TAILQ_NEXT((var), field), 1);            \
  515             (var) = (tvar))
  516 
  517 #define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
  518         for ((var) = TAILQ_LAST((head), headname);                      \
  519             (var);                                                      \
  520             (var) = TAILQ_PREV((var), headname, field))
  521 
  522 #define TAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar)    \
  523         for ((var) = TAILQ_LAST((head), headname);                      \
  524             (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);  \
  525             (var) = (tvar))
  526 
  527 #define TAILQ_INIT(head) do {                                           \
  528         TAILQ_FIRST((head)) = NULL;                                     \
  529         (head)->tqh_last = &TAILQ_FIRST((head));                        \
  530         QMD_TRACE_HEAD(head);                                           \
  531 } while (0)
  532 
  533 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
  534         QMD_TAILQ_CHECK_NEXT(listelm, field);                           \
  535         if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
  536                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
  537                     &TAILQ_NEXT((elm), field);                          \
  538         else {                                                          \
  539                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
  540                 QMD_TRACE_HEAD(head);                                   \
  541         }                                                               \
  542         TAILQ_NEXT((listelm), field) = (elm);                           \
  543         (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);          \
  544         QMD_TRACE_ELEM(&(elm)->field);                                  \
  545         QMD_TRACE_ELEM(&listelm->field);                                \
  546 } while (0)
  547 
  548 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
  549         QMD_TAILQ_CHECK_PREV(listelm, field);                           \
  550         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
  551         TAILQ_NEXT((elm), field) = (listelm);                           \
  552         *(listelm)->field.tqe_prev = (elm);                             \
  553         (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);          \
  554         QMD_TRACE_ELEM(&(elm)->field);                                  \
  555         QMD_TRACE_ELEM(&listelm->field);                                \
  556 } while (0)
  557 
  558 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
  559         QMD_TAILQ_CHECK_HEAD(head, field);                              \
  560         if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)   \
  561                 TAILQ_FIRST((head))->field.tqe_prev =                   \
  562                     &TAILQ_NEXT((elm), field);                          \
  563         else                                                            \
  564                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
  565         TAILQ_FIRST((head)) = (elm);                                    \
  566         (elm)->field.tqe_prev = &TAILQ_FIRST((head));                   \
  567         QMD_TRACE_HEAD(head);                                           \
  568         QMD_TRACE_ELEM(&(elm)->field);                                  \
  569 } while (0)
  570 
  571 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
  572         QMD_TAILQ_CHECK_TAIL(head, field);                              \
  573         TAILQ_NEXT((elm), field) = NULL;                                \
  574         (elm)->field.tqe_prev = (head)->tqh_last;                       \
  575         *(head)->tqh_last = (elm);                                      \
  576         (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
  577         QMD_TRACE_HEAD(head);                                           \
  578         QMD_TRACE_ELEM(&(elm)->field);                                  \
  579 } while (0)
  580 
  581 #define TAILQ_LAST(head, headname)                                      \
  582         (*(((struct headname *)((head)->tqh_last))->tqh_last))
  583 
  584 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
  585 
  586 #define TAILQ_PREV(elm, headname, field)                                \
  587         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
  588 
  589 #define TAILQ_REMOVE(head, elm, field) do {                             \
  590         QMD_TAILQ_CHECK_NEXT(elm, field);                               \
  591         QMD_TAILQ_CHECK_PREV(elm, field);                               \
  592         if ((TAILQ_NEXT((elm), field)) != NULL)                         \
  593                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
  594                     (elm)->field.tqe_prev;                              \
  595         else {                                                          \
  596                 (head)->tqh_last = (elm)->field.tqe_prev;               \
  597                 QMD_TRACE_HEAD(head);                                   \
  598         }                                                               \
  599         *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);              \
  600         TRASHIT((elm)->field.tqe_next);                                 \
  601         TRASHIT((elm)->field.tqe_prev);                                 \
  602         QMD_TRACE_ELEM(&(elm)->field);                                  \
  603 } while (0)
  604 
  605 #define TAILQ_SWAP(head1, head2, type, field) do {                      \
  606         struct type *swap_first = (head1)->tqh_first;                   \
  607         struct type **swap_last = (head1)->tqh_last;                    \
  608         (head1)->tqh_first = (head2)->tqh_first;                        \
  609         (head1)->tqh_last = (head2)->tqh_last;                          \
  610         (head2)->tqh_first = swap_first;                                \
  611         (head2)->tqh_last = swap_last;                                  \
  612         if ((swap_first = (head1)->tqh_first) != NULL)                  \
  613                 swap_first->field.tqe_prev = &(head1)->tqh_first;       \
  614         else                                                            \
  615                 (head1)->tqh_last = &(head1)->tqh_first;                \
  616         if ((swap_first = (head2)->tqh_first) != NULL)                  \
  617                 swap_first->field.tqe_prev = &(head2)->tqh_first;       \
  618         else                                                            \
  619                 (head2)->tqh_last = &(head2)->tqh_first;                \
  620 } while (0)
  621 
  622 #endif /* !_SYS_QUEUE_H_ */

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