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  * 3. All advertising materials mentioning features or use of this software
   14  *    must display the following acknowledgement:
   15  *      This product includes software developed by the University of
   16  *      California, Berkeley and its contributors.
   17  * 4. Neither the name of the University nor the names of its contributors
   18  *    may be used to endorse or promote products derived from this software
   19  *    without specific prior written permission.
   20  *
   21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   31  * SUCH DAMAGE.
   32  *
   33  *      @(#)queue.h     8.5 (Berkeley) 8/20/94
   34  * $FreeBSD: releng/5.2/sys/sys/queue.h 118904 2003-08-14 14:49:26Z kan $
   35  */
   36 
   37 #ifndef _SYS_QUEUE_H_
   38 #define _SYS_QUEUE_H_
   39 
   40 #include <sys/cdefs.h>
   41 
   42 /*
   43  * This file defines four types of data structures: singly-linked lists,
   44  * singly-linked tail queues, lists and tail queues.
   45  *
   46  * A singly-linked list is headed by a single forward pointer. The elements
   47  * are singly linked for minimum space and pointer manipulation overhead at
   48  * the expense of O(n) removal for arbitrary elements. New elements can be
   49  * added to the list after an existing element or at the head of the list.
   50  * Elements being removed from the head of the list should use the explicit
   51  * macro for this purpose for optimum efficiency. A singly-linked list may
   52  * only be traversed in the forward direction.  Singly-linked lists are ideal
   53  * for applications with large datasets and few or no removals or for
   54  * implementing a LIFO queue.
   55  *
   56  * A singly-linked tail queue is headed by a pair of pointers, one to the
   57  * head of the list and the other to the tail of the list. The elements are
   58  * singly linked for minimum space and pointer manipulation overhead at the
   59  * expense of O(n) removal for arbitrary elements. New elements can be added
   60  * to the list after an existing element, at the head of the list, or at the
   61  * end of the list. Elements being removed from the head of the tail queue
   62  * should use the explicit macro for this purpose for optimum efficiency.
   63  * A singly-linked tail queue may only be traversed in the forward direction.
   64  * Singly-linked tail queues are ideal for applications with large datasets
   65  * and few or no removals or for implementing a FIFO queue.
   66  *
   67  * A list is headed by a single forward pointer (or an array of forward
   68  * pointers for a hash table header). The elements are doubly linked
   69  * so that an arbitrary element can be removed without a need to
   70  * traverse the list. New elements can be added to the list before
   71  * or after an existing element or at the head of the list. A list
   72  * may only be traversed in the forward direction.
   73  *
   74  * A tail queue is headed by a pair of pointers, one to the head of the
   75  * list and the other to the tail of the list. The elements are doubly
   76  * linked so that an arbitrary element can be removed without a need to
   77  * traverse the list. New elements can be added to the list before or
   78  * after an existing element, at the head of the list, or at the end of
   79  * the list. A tail queue may be traversed in either direction.
   80  *
   81  * For details on the use of these macros, see the queue(3) manual page.
   82  *
   83  *
   84  *                              SLIST   LIST    STAILQ  TAILQ
   85  * _HEAD                        +       +       +       +
   86  * _HEAD_INITIALIZER            +       +       +       +
   87  * _ENTRY                       +       +       +       +
   88  * _INIT                        +       +       +       +
   89  * _EMPTY                       +       +       +       +
   90  * _FIRST                       +       +       +       +
   91  * _NEXT                        +       +       +       +
   92  * _PREV                        -       -       -       +
   93  * _LAST                        -       -       +       +
   94  * _FOREACH                     +       +       +       +
   95  * _FOREACH_SAFE                +       +       +       +
   96  * _FOREACH_REVERSE             -       -       -       +
   97  * _FOREACH_REVERSE_SAFE        -       -       -       +
   98  * _INSERT_HEAD                 +       +       +       +
   99  * _INSERT_BEFORE               -       +       -       +
  100  * _INSERT_AFTER                +       +       +       +
  101  * _INSERT_TAIL                 -       -       +       +
  102  * _CONCAT                      -       -       +       +
  103  * _REMOVE_HEAD                 +       -       +       -
  104  * _REMOVE                      +       +       +       +
  105  *
  106  */
  107 #define QUEUE_MACRO_DEBUG 0
  108 #if QUEUE_MACRO_DEBUG
  109 /* Store the last 2 places the queue element or head was altered */
  110 struct qm_trace {
  111         char * lastfile;
  112         int lastline;
  113         char * prevfile;
  114         int prevline;
  115 };
  116 
  117 #define TRACEBUF        struct qm_trace trace;
  118 #define TRASHIT(x)      do {(x) = (void *)-1;} while (0)
  119 
  120 #define QMD_TRACE_HEAD(head) do {                                       \
  121         (head)->trace.prevline = (head)->trace.lastline;                \
  122         (head)->trace.prevfile = (head)->trace.lastfile;                \
  123         (head)->trace.lastline = __LINE__;                              \
  124         (head)->trace.lastfile = __FILE__;                              \
  125 } while (0)
  126 
  127 #define QMD_TRACE_ELEM(elem) do {                                       \
  128         (elem)->trace.prevline = (elem)->trace.lastline;                \
  129         (elem)->trace.prevfile = (elem)->trace.lastfile;                \
  130         (elem)->trace.lastline = __LINE__;                              \
  131         (elem)->trace.lastfile = __FILE__;                              \
  132 } while (0)
  133 
  134 #else
  135 #define QMD_TRACE_ELEM(elem)
  136 #define QMD_TRACE_HEAD(head)
  137 #define TRACEBUF
  138 #define TRASHIT(x)
  139 #endif  /* QUEUE_MACRO_DEBUG */
  140 
  141 /*
  142  * Singly-linked List declarations.
  143  */
  144 #define SLIST_HEAD(name, type)                                          \
  145 struct name {                                                           \
  146         struct type *slh_first; /* first element */                     \
  147 }
  148 
  149 #define SLIST_HEAD_INITIALIZER(head)                                    \
  150         { NULL }
  151 
  152 #define SLIST_ENTRY(type)                                               \
  153 struct {                                                                \
  154         struct type *sle_next;  /* next element */                      \
  155 }
  156 
  157 /*
  158  * Singly-linked List functions.
  159  */
  160 #define SLIST_EMPTY(head)       ((head)->slh_first == NULL)
  161 
  162 #define SLIST_FIRST(head)       ((head)->slh_first)
  163 
  164 #define SLIST_FOREACH(var, head, field)                                 \
  165         for ((var) = SLIST_FIRST((head));                               \
  166             (var);                                                      \
  167             (var) = SLIST_NEXT((var), field))
  168 
  169 #define SLIST_FOREACH_SAFE(var, head, field, tvar)                      \
  170         for ((var) = SLIST_FIRST((head));                               \
  171             (var) && ((tvar) = SLIST_NEXT((var), field), 1);            \
  172             (var) = (tvar))
  173 
  174 #define SLIST_FOREACH_PREVPTR(var, varp, head, field)                   \
  175         for ((varp) = &SLIST_FIRST((head));                             \
  176             ((var) = *(varp)) != NULL;                                  \
  177             (varp) = &SLIST_NEXT((var), field))
  178 
  179 #define SLIST_INIT(head) do {                                           \
  180         SLIST_FIRST((head)) = NULL;                                     \
  181 } while (0)
  182 
  183 #define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
  184         SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);       \
  185         SLIST_NEXT((slistelm), field) = (elm);                          \
  186 } while (0)
  187 
  188 #define SLIST_INSERT_HEAD(head, elm, field) do {                        \
  189         SLIST_NEXT((elm), field) = SLIST_FIRST((head));                 \
  190         SLIST_FIRST((head)) = (elm);                                    \
  191 } while (0)
  192 
  193 #define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)
  194 
  195 #define SLIST_REMOVE(head, elm, type, field) do {                       \
  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_NEXT(curelm, field) =                             \
  204                     SLIST_NEXT(SLIST_NEXT(curelm, field), field);       \
  205         }                                                               \
  206 } while (0)
  207 
  208 #define SLIST_REMOVE_HEAD(head, field) do {                             \
  209         SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);   \
  210 } while (0)
  211 
  212 /*
  213  * Singly-linked Tail queue declarations.
  214  */
  215 #define STAILQ_HEAD(name, type)                                         \
  216 struct name {                                                           \
  217         struct type *stqh_first;/* first element */                     \
  218         struct type **stqh_last;/* addr of last next element */         \
  219 }
  220 
  221 #define STAILQ_HEAD_INITIALIZER(head)                                   \
  222         { NULL, &(head).stqh_first }
  223 
  224 #define STAILQ_ENTRY(type)                                              \
  225 struct {                                                                \
  226         struct type *stqe_next; /* next element */                      \
  227 }
  228 
  229 /*
  230  * Singly-linked Tail queue functions.
  231  */
  232 #define STAILQ_CONCAT(head1, head2) do {                                \
  233         if (!STAILQ_EMPTY((head2))) {                                   \
  234                 *(head1)->stqh_last = (head2)->stqh_first;              \
  235                 (head1)->stqh_last = (head2)->stqh_last;                \
  236                 STAILQ_INIT((head2));                                   \
  237         }                                                               \
  238 } while (0)
  239 
  240 #define STAILQ_EMPTY(head)      ((head)->stqh_first == NULL)
  241 
  242 #define STAILQ_FIRST(head)      ((head)->stqh_first)
  243 
  244 #define STAILQ_FOREACH(var, head, field)                                \
  245         for((var) = STAILQ_FIRST((head));                               \
  246            (var);                                                       \
  247            (var) = STAILQ_NEXT((var), field))
  248 
  249 
  250 #define STAILQ_FOREACH_SAFE(var, head, field, tvar)                     \
  251         for ((var) = STAILQ_FIRST((head));                              \
  252             (var) && ((tvar) = STAILQ_NEXT((var), field), 1);           \
  253             (var) = (tvar))
  254 
  255 #define STAILQ_INIT(head) do {                                          \
  256         STAILQ_FIRST((head)) = NULL;                                    \
  257         (head)->stqh_last = &STAILQ_FIRST((head));                      \
  258 } while (0)
  259 
  260 #define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {               \
  261         if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
  262                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
  263         STAILQ_NEXT((tqelm), field) = (elm);                            \
  264 } while (0)
  265 
  266 #define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
  267         if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL) \
  268                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
  269         STAILQ_FIRST((head)) = (elm);                                   \
  270 } while (0)
  271 
  272 #define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
  273         STAILQ_NEXT((elm), field) = NULL;                               \
  274         *(head)->stqh_last = (elm);                                     \
  275         (head)->stqh_last = &STAILQ_NEXT((elm), field);                 \
  276 } while (0)
  277 
  278 #define STAILQ_LAST(head, type, field)                                  \
  279         (STAILQ_EMPTY((head)) ?                                         \
  280                 NULL :                                                  \
  281                 ((struct type *)                                        \
  282                 ((char *)((head)->stqh_last) - __offsetof(struct type, field))))
  283 
  284 #define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
  285 
  286 #define STAILQ_REMOVE(head, elm, type, field) do {                      \
  287         if (STAILQ_FIRST((head)) == (elm)) {                            \
  288                 STAILQ_REMOVE_HEAD((head), field);                      \
  289         }                                                               \
  290         else {                                                          \
  291                 struct type *curelm = STAILQ_FIRST((head));             \
  292                 while (STAILQ_NEXT(curelm, field) != (elm))             \
  293                         curelm = STAILQ_NEXT(curelm, field);            \
  294                 if ((STAILQ_NEXT(curelm, field) =                       \
  295                      STAILQ_NEXT(STAILQ_NEXT(curelm, field), field)) == NULL)\
  296                         (head)->stqh_last = &STAILQ_NEXT((curelm), field);\
  297         }                                                               \
  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_HEAD_UNTIL(head, elm, field) do {                 \
  307         if ((STAILQ_FIRST((head)) = STAILQ_NEXT((elm), field)) == NULL) \
  308                 (head)->stqh_last = &STAILQ_FIRST((head));              \
  309 } while (0)
  310 
  311 /*
  312  * List declarations.
  313  */
  314 #define LIST_HEAD(name, type)                                           \
  315 struct name {                                                           \
  316         struct type *lh_first;  /* first element */                     \
  317 }
  318 
  319 #define LIST_HEAD_INITIALIZER(head)                                     \
  320         { NULL }
  321 
  322 #define LIST_ENTRY(type)                                                \
  323 struct {                                                                \
  324         struct type *le_next;   /* next element */                      \
  325         struct type **le_prev;  /* address of previous next element */  \
  326 }
  327 
  328 /*
  329  * List functions.
  330  */
  331 
  332 #define LIST_EMPTY(head)        ((head)->lh_first == NULL)
  333 
  334 #define LIST_FIRST(head)        ((head)->lh_first)
  335 
  336 #define LIST_FOREACH(var, head, field)                                  \
  337         for ((var) = LIST_FIRST((head));                                \
  338             (var);                                                      \
  339             (var) = LIST_NEXT((var), field))
  340 
  341 #define LIST_FOREACH_SAFE(var, head, field, tvar)                       \
  342         for ((var) = LIST_FIRST((head));                                \
  343             (var) && ((tvar) = LIST_NEXT((var), field), 1);             \
  344             (var) = (tvar))
  345 
  346 #define LIST_INIT(head) do {                                            \
  347         LIST_FIRST((head)) = NULL;                                      \
  348 } while (0)
  349 
  350 #define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
  351         if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
  352                 LIST_NEXT((listelm), field)->field.le_prev =            \
  353                     &LIST_NEXT((elm), field);                           \
  354         LIST_NEXT((listelm), field) = (elm);                            \
  355         (elm)->field.le_prev = &LIST_NEXT((listelm), field);            \
  356 } while (0)
  357 
  358 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
  359         (elm)->field.le_prev = (listelm)->field.le_prev;                \
  360         LIST_NEXT((elm), field) = (listelm);                            \
  361         *(listelm)->field.le_prev = (elm);                              \
  362         (listelm)->field.le_prev = &LIST_NEXT((elm), field);            \
  363 } while (0)
  364 
  365 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
  366         if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)     \
  367                 LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
  368         LIST_FIRST((head)) = (elm);                                     \
  369         (elm)->field.le_prev = &LIST_FIRST((head));                     \
  370 } while (0)
  371 
  372 #define LIST_NEXT(elm, field)   ((elm)->field.le_next)
  373 
  374 #define LIST_REMOVE(elm, field) do {                                    \
  375         if (LIST_NEXT((elm), field) != NULL)                            \
  376                 LIST_NEXT((elm), field)->field.le_prev =                \
  377                     (elm)->field.le_prev;                               \
  378         *(elm)->field.le_prev = LIST_NEXT((elm), field);                \
  379 } while (0)
  380 
  381 /*
  382  * Tail queue declarations.
  383  */
  384 #define TAILQ_HEAD(name, type)                                          \
  385 struct name {                                                           \
  386         struct type *tqh_first; /* first element */                     \
  387         struct type **tqh_last; /* addr of last next element */         \
  388         TRACEBUF                                                        \
  389 }
  390 
  391 #define TAILQ_HEAD_INITIALIZER(head)                                    \
  392         { NULL, &(head).tqh_first }
  393 
  394 #define TAILQ_ENTRY(type)                                               \
  395 struct {                                                                \
  396         struct type *tqe_next;  /* next element */                      \
  397         struct type **tqe_prev; /* address of previous next element */  \
  398         TRACEBUF                                                        \
  399 }
  400 
  401 /*
  402  * Tail queue functions.
  403  */
  404 #define TAILQ_CONCAT(head1, head2, field) do {                          \
  405         if (!TAILQ_EMPTY(head2)) {                                      \
  406                 *(head1)->tqh_last = (head2)->tqh_first;                \
  407                 (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last; \
  408                 (head1)->tqh_last = (head2)->tqh_last;                  \
  409                 TAILQ_INIT((head2));                                    \
  410                 QMD_TRACE_HEAD(head);                                   \
  411                 QMD_TRACE_HEAD(head2);                                  \
  412         }                                                               \
  413 } while (0)
  414 
  415 #define TAILQ_EMPTY(head)       ((head)->tqh_first == NULL)
  416 
  417 #define TAILQ_FIRST(head)       ((head)->tqh_first)
  418 
  419 #define TAILQ_FOREACH(var, head, field)                                 \
  420         for ((var) = TAILQ_FIRST((head));                               \
  421             (var);                                                      \
  422             (var) = TAILQ_NEXT((var), field))
  423 
  424 #define TAILQ_FOREACH_SAFE(var, head, field, tvar)                      \
  425         for ((var) = TAILQ_FIRST((head));                               \
  426             (var) && ((tvar) = TAILQ_NEXT((var), field), 1);            \
  427             (var) = (tvar))
  428 
  429 #define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
  430         for ((var) = TAILQ_LAST((head), headname);                      \
  431             (var);                                                      \
  432             (var) = TAILQ_PREV((var), headname, field))
  433 
  434 #define TAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar)    \
  435         for ((var) = TAILQ_LAST((head), headname);                      \
  436             (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);  \
  437             (var) = (tvar))
  438 
  439 #define TAILQ_INIT(head) do {                                           \
  440         TAILQ_FIRST((head)) = NULL;                                     \
  441         (head)->tqh_last = &TAILQ_FIRST((head));                        \
  442         QMD_TRACE_HEAD(head);                                           \
  443 } while (0)
  444 
  445 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
  446         if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
  447                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
  448                     &TAILQ_NEXT((elm), field);                          \
  449         else {                                                          \
  450                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
  451                 QMD_TRACE_HEAD(head);                                   \
  452         }                                                               \
  453         TAILQ_NEXT((listelm), field) = (elm);                           \
  454         (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);          \
  455         QMD_TRACE_ELEM(&(elm)->field);                                  \
  456         QMD_TRACE_ELEM(&listelm->field);                                \
  457 } while (0)
  458 
  459 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
  460         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
  461         TAILQ_NEXT((elm), field) = (listelm);                           \
  462         *(listelm)->field.tqe_prev = (elm);                             \
  463         (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);          \
  464         QMD_TRACE_ELEM(&(elm)->field);                                  \
  465         QMD_TRACE_ELEM(&listelm->field);                                \
  466 } while (0)
  467 
  468 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
  469         if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)   \
  470                 TAILQ_FIRST((head))->field.tqe_prev =                   \
  471                     &TAILQ_NEXT((elm), field);                          \
  472         else                                                            \
  473                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
  474         TAILQ_FIRST((head)) = (elm);                                    \
  475         (elm)->field.tqe_prev = &TAILQ_FIRST((head));                   \
  476         QMD_TRACE_HEAD(head);                                           \
  477         QMD_TRACE_ELEM(&(elm)->field);                                  \
  478 } while (0)
  479 
  480 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
  481         TAILQ_NEXT((elm), field) = NULL;                                \
  482         (elm)->field.tqe_prev = (head)->tqh_last;                       \
  483         *(head)->tqh_last = (elm);                                      \
  484         (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
  485         QMD_TRACE_HEAD(head);                                           \
  486         QMD_TRACE_ELEM(&(elm)->field);                                  \
  487 } while (0)
  488 
  489 #define TAILQ_LAST(head, headname)                                      \
  490         (*(((struct headname *)((head)->tqh_last))->tqh_last))
  491 
  492 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
  493 
  494 #define TAILQ_PREV(elm, headname, field)                                \
  495         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
  496 
  497 #define TAILQ_REMOVE(head, elm, field) do {                             \
  498         if ((TAILQ_NEXT((elm), field)) != NULL)                         \
  499                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
  500                     (elm)->field.tqe_prev;                              \
  501         else {                                                          \
  502                 (head)->tqh_last = (elm)->field.tqe_prev;               \
  503                 QMD_TRACE_HEAD(head);                                   \
  504         }                                                               \
  505         *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);              \
  506         TRASHIT((elm)->field.tqe_next);                                 \
  507         TRASHIT((elm)->field.tqe_prev);                                 \
  508         QMD_TRACE_ELEM(&(elm)->field);                                  \
  509 } while (0)
  510 
  511 
  512 #ifdef _KERNEL
  513 
  514 /*
  515  * XXX insque() and remque() are an old way of handling certain queues.
  516  * They bogusly assumes that all queue heads look alike.
  517  */
  518 
  519 struct quehead {
  520         struct quehead *qh_link;
  521         struct quehead *qh_rlink;
  522 };
  523 
  524 #ifdef  __GNUC__
  525 
  526 static __inline void
  527 insque(void *a, void *b)
  528 {
  529         struct quehead *element = (struct quehead *)a,
  530                  *head = (struct quehead *)b;
  531 
  532         element->qh_link = head->qh_link;
  533         element->qh_rlink = head;
  534         head->qh_link = element;
  535         element->qh_link->qh_rlink = element;
  536 }
  537 
  538 static __inline void
  539 remque(void *a)
  540 {
  541         struct quehead *element = (struct quehead *)a;
  542 
  543         element->qh_link->qh_rlink = element->qh_rlink;
  544         element->qh_rlink->qh_link = element->qh_link;
  545         element->qh_rlink = 0;
  546 }
  547 
  548 #else /* !__GNUC__ */
  549 
  550 void    insque(void *a, void *b);
  551 void    remque(void *a);
  552 
  553 #endif /* __GNUC__ */
  554 
  555 #endif /* _KERNEL */
  556 
  557 #endif /* !_SYS_QUEUE_H_ */

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