The Design and Implementation of the FreeBSD Operating System, Second Edition
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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: src/sys/sys/queue.h,v 1.10.2.5 1999/09/05 08:22:46 peter Exp $
   35  */
   36 
   37 #ifndef _SYS_QUEUE_H_
   38 #define _SYS_QUEUE_H_
   39 
   40 /*
   41  * This file defines five types of data structures: singly-linked lists,
   42  * slingly-linked tail queues, lists, tail queues, and circular queues.
   43  *
   44  * A singly-linked list is headed by a single forward pointer. The elements
   45  * are singly linked for minimum space and pointer manipulation overhead at
   46  * the expense of O(n) removal for arbitrary elements. New elements can be
   47  * added to the list after an existing element or at the head of the list.
   48  * Elements being removed from the head of the list should use the explicit
   49  * macro for this purpose for optimum efficiency. A singly-linked list may
   50  * only be traversed in the forward direction.  Singly-linked lists are ideal
   51  * for applications with large datasets and few or no removals or for
   52  * implementing a LIFO queue.
   53  *
   54  * A singly-linked tail queue is headed by a pair of pointers, one to the
   55  * head of the list and the other to the tail of the list. The elements are
   56  * singly linked for minimum space and pointer manipulation overhead at the
   57  * expense of O(n) removal for arbitrary elements. New elements can be added
   58  * to the list after an existing element, at the head of the list, or at the
   59  * end of the list. Elements being removed from the head of the tail queue
   60  * should use the explicit macro for this purpose for optimum efficiency.
   61  * A singly-linked tail queue may only be traversed in the forward direction.
   62  * Singly-linked tail queues are ideal for applications with large datasets
   63  * and few or no removals or for implementing a FIFO queue.
   64  *
   65  * A list is headed by a single forward pointer (or an array of forward
   66  * pointers for a hash table header). The elements are doubly linked
   67  * so that an arbitrary element can be removed without a need to
   68  * traverse the list. New elements can be added to the list before
   69  * or after an existing element or at the head of the list. A list
   70  * may only be traversed in the forward direction.
   71  *
   72  * A tail queue is headed by a pair of pointers, one to the head of the
   73  * list and the other to the tail of the list. The elements are doubly
   74  * linked so that an arbitrary element can be removed without a need to
   75  * traverse the list. New elements can be added to the list before or
   76  * after an existing element, at the head of the list, or at the end of
   77  * the list. A tail queue may only be traversed in the forward direction.
   78  *
   79  * A circle queue is headed by a pair of pointers, one to the head of the
   80  * list and the other to the tail of the list. The elements are doubly
   81  * linked so that an arbitrary element can be removed without a need to
   82  * traverse the list. New elements can be added to the list before or after
   83  * an existing element, at the head of the list, or at the end of the list.
   84  * A circle queue may be traversed in either direction, but has a more
   85  * complex end of list detection.
   86  *
   87  * For details on the use of these macros, see the queue(3) manual page.
   88  *
   89  *
   90  *                      SLIST   LIST    STAILQ  TAILQ   CIRCLEQ
   91  * _HEAD                +       +       +       +       +
   92  * _ENTRY               +       +       +       +       +
   93  * _INIT                +       +       +       +       +
   94  * _EMPTY               +       +       +       +       +
   95  * _FIRST               +       +       -       +       +
   96  * _NEXT                +       +       -       +       +
   97  * _PREV                -       -       -       +       +
   98  * _LAST                -       -       -       +       +
   99  * _FOREACH             +       +       -       +       -
  100  * _INSERT_HEAD         +       +       +       +       +
  101  * _INSERT_BEFORE       -       +       -       +       +
  102  * _INSERT_AFTER        +       +       +       +       +
  103  * _INSERT_TAIL         -       -       +       +       +
  104  * _REMOVE_HEAD         +       -       +       -       -
  105  * _REMOVE              +       +       +       +       +
  106  *
  107  */
  108 
  109 /*
  110  * Singly-linked List definitions.
  111  */
  112 #define SLIST_HEAD(name, type)                                          \
  113 struct name {                                                           \
  114         struct type *slh_first; /* first element */                     \
  115 }
  116  
  117 #define SLIST_ENTRY(type)                                               \
  118 struct {                                                                \
  119         struct type *sle_next;  /* next element */                      \
  120 }
  121  
  122 /*
  123  * Singly-linked List functions.
  124  */
  125 #define SLIST_EMPTY(head)       ((head)->slh_first == NULL)
  126 
  127 #define SLIST_FIRST(head)       ((head)->slh_first)
  128 
  129 #define SLIST_FOREACH(var, head, field)                                 \
  130         for((var) = (head)->slh_first; (var); (var) = (var)->field.sle_next)
  131 
  132 #define SLIST_INIT(head) {                                              \
  133         (head)->slh_first = NULL;                                       \
  134 }
  135 
  136 #define SLIST_INSERT_AFTER(slistelm, elm, field) do  {                  \
  137         (elm)->field.sle_next = (slistelm)->field.sle_next;             \
  138         (slistelm)->field.sle_next = (elm);                             \
  139 } while (0)
  140 
  141 #define SLIST_INSERT_HEAD(head, elm, field) do {                        \
  142         (elm)->field.sle_next = (head)->slh_first;                      \
  143         (head)->slh_first = (elm);                                      \
  144 } while (0)
  145 
  146 #define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)
  147 
  148 #define SLIST_REMOVE_HEAD(head, field) do {                             \
  149         (head)->slh_first = (head)->slh_first->field.sle_next;          \
  150 } while (0)
  151 
  152 #define SLIST_REMOVE(head, elm, type, field) do {                       \
  153         if ((head)->slh_first == (elm)) {                               \
  154                 SLIST_REMOVE_HEAD((head), field);                       \
  155         }                                                               \
  156         else {                                                          \
  157                 struct type *curelm = (head)->slh_first;                \
  158                 while( curelm->field.sle_next != (elm) )                \
  159                         curelm = curelm->field.sle_next;                \
  160                 curelm->field.sle_next =                                \
  161                     curelm->field.sle_next->field.sle_next;             \
  162         }                                                               \
  163 } while (0)
  164 
  165 /*
  166  * Singly-linked Tail queue definitions.
  167  */
  168 #define STAILQ_HEAD(name, type)                                         \
  169 struct name {                                                           \
  170         struct type *stqh_first;/* first element */                     \
  171         struct type **stqh_last;/* addr of last next element */         \
  172 }
  173 
  174 #define STAILQ_ENTRY(type)                                              \
  175 struct {                                                                \
  176         struct type *stqe_next; /* next element */                      \
  177 }
  178 
  179 /*
  180  * Singly-linked Tail queue functions.
  181  */
  182 #define STAILQ_EMPTY(head) ((head)->stqh_first == NULL)
  183 
  184 #define STAILQ_INIT(head) do {                                          \
  185         (head)->stqh_first = NULL;                                      \
  186         (head)->stqh_last = &(head)->stqh_first;                        \
  187 } while (0)
  188 
  189 #define STAILQ_FIRST(head)      ((head)->stqh_first)
  190 #define STAILQ_LAST(head)       (*(head)->stqh_last)
  191 
  192 #define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
  193         if (((elm)->field.stqe_next = (head)->stqh_first) == NULL)      \
  194                 (head)->stqh_last = &(elm)->field.stqe_next;            \
  195         (head)->stqh_first = (elm);                                     \
  196 } while (0)
  197 
  198 #define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
  199         (elm)->field.stqe_next = NULL;                                  \
  200         *(head)->stqh_last = (elm);                                     \
  201         (head)->stqh_last = &(elm)->field.stqe_next;                    \
  202 } while (0)
  203 
  204 #define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {               \
  205         if (((elm)->field.stqe_next = (tqelm)->field.stqe_next) == NULL)\
  206                 (head)->stqh_last = &(elm)->field.stqe_next;            \
  207         (tqelm)->field.stqe_next = (elm);                               \
  208 } while (0)
  209 
  210 #define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
  211 
  212 #define STAILQ_REMOVE_HEAD(head, field) do {                            \
  213         if (((head)->stqh_first =                                       \
  214              (head)->stqh_first->field.stqe_next) == NULL)              \
  215                 (head)->stqh_last = &(head)->stqh_first;                \
  216 } while (0)
  217 
  218 #define STAILQ_REMOVE(head, elm, type, field) do {                      \
  219         if ((head)->stqh_first == (elm)) {                              \
  220                 STAILQ_REMOVE_HEAD(head, field);                        \
  221         }                                                               \
  222         else {                                                          \
  223                 struct type *curelm = (head)->stqh_first;               \
  224                 while( curelm->field.stqe_next != (elm) )               \
  225                         curelm = curelm->field.stqe_next;               \
  226                 if((curelm->field.stqe_next =                           \
  227                     curelm->field.stqe_next->field.stqe_next) == NULL)  \
  228                         (head)->stqh_last = &(curelm)->field.stqe_next; \
  229         }                                                               \
  230 } while (0)
  231 
  232 /*
  233  * List definitions.
  234  */
  235 #define LIST_HEAD(name, type)                                           \
  236 struct name {                                                           \
  237         struct type *lh_first;  /* first element */                     \
  238 }
  239 
  240 #define LIST_ENTRY(type)                                                \
  241 struct {                                                                \
  242         struct type *le_next;   /* next element */                      \
  243         struct type **le_prev;  /* address of previous next element */  \
  244 }
  245 
  246 /*
  247  * List functions.
  248  */
  249 
  250 #define LIST_EMPTY(head) ((head)->lh_first == NULL)
  251 
  252 #define LIST_FIRST(head)        ((head)->lh_first)
  253 
  254 #define LIST_FOREACH(var, head, field)                                  \
  255         for((var) = (head)->lh_first; (var); (var) = (var)->field.le_next)
  256 
  257 #define LIST_INIT(head) do {                                            \
  258         (head)->lh_first = NULL;                                        \
  259 } while (0)
  260 
  261 #define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
  262         if (((elm)->field.le_next = (listelm)->field.le_next) != NULL)  \
  263                 (listelm)->field.le_next->field.le_prev =               \
  264                     &(elm)->field.le_next;                              \
  265         (listelm)->field.le_next = (elm);                               \
  266         (elm)->field.le_prev = &(listelm)->field.le_next;               \
  267 } while (0)
  268 
  269 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
  270         (elm)->field.le_prev = (listelm)->field.le_prev;                \
  271         (elm)->field.le_next = (listelm);                               \
  272         *(listelm)->field.le_prev = (elm);                              \
  273         (listelm)->field.le_prev = &(elm)->field.le_next;               \
  274 } while (0)
  275 
  276 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
  277         if (((elm)->field.le_next = (head)->lh_first) != NULL)          \
  278                 (head)->lh_first->field.le_prev = &(elm)->field.le_next;\
  279         (head)->lh_first = (elm);                                       \
  280         (elm)->field.le_prev = &(head)->lh_first;                       \
  281 } while (0)
  282 
  283 #define LIST_NEXT(elm, field)   ((elm)->field.le_next)
  284 
  285 #define LIST_REMOVE(elm, field) do {                                    \
  286         if ((elm)->field.le_next != NULL)                               \
  287                 (elm)->field.le_next->field.le_prev =                   \
  288                     (elm)->field.le_prev;                               \
  289         *(elm)->field.le_prev = (elm)->field.le_next;                   \
  290 } while (0)
  291 
  292 /*
  293  * Tail queue definitions.
  294  */
  295 #define TAILQ_HEAD(name, type)                                          \
  296 struct name {                                                           \
  297         struct type *tqh_first; /* first element */                     \
  298         struct type **tqh_last; /* addr of last next element */         \
  299 }
  300 
  301 #define TAILQ_HEAD_INITIALIZER(head)                                    \
  302         { NULL, &(head).tqh_first }
  303 
  304 #define TAILQ_ENTRY(type)                                               \
  305 struct {                                                                \
  306         struct type *tqe_next;  /* next element */                      \
  307         struct type **tqe_prev; /* address of previous next element */  \
  308 }
  309 
  310 /*
  311  * Tail queue functions.
  312  */
  313 #define TAILQ_EMPTY(head) ((head)->tqh_first == NULL)
  314 
  315 #define TAILQ_FOREACH(var, head, field)                                 \
  316         for (var = TAILQ_FIRST(head); var; var = TAILQ_NEXT(var, field))
  317 
  318 #define TAILQ_FIRST(head) ((head)->tqh_first)
  319 
  320 #define TAILQ_LAST(head, headname) \
  321         (*(((struct headname *)((head)->tqh_last))->tqh_last))
  322 
  323 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
  324 
  325 #define TAILQ_PREV(elm, headname, field) \
  326         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
  327 
  328 #define TAILQ_INIT(head) do {                                           \
  329         (head)->tqh_first = NULL;                                       \
  330         (head)->tqh_last = &(head)->tqh_first;                          \
  331 } while (0)
  332 
  333 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
  334         if (((elm)->field.tqe_next = (head)->tqh_first) != NULL)        \
  335                 (head)->tqh_first->field.tqe_prev =                     \
  336                     &(elm)->field.tqe_next;                             \
  337         else                                                            \
  338                 (head)->tqh_last = &(elm)->field.tqe_next;              \
  339         (head)->tqh_first = (elm);                                      \
  340         (elm)->field.tqe_prev = &(head)->tqh_first;                     \
  341 } while (0)
  342 
  343 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
  344         (elm)->field.tqe_next = NULL;                                   \
  345         (elm)->field.tqe_prev = (head)->tqh_last;                       \
  346         *(head)->tqh_last = (elm);                                      \
  347         (head)->tqh_last = &(elm)->field.tqe_next;                      \
  348 } while (0)
  349 
  350 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
  351         if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)\
  352                 (elm)->field.tqe_next->field.tqe_prev =                 \
  353                     &(elm)->field.tqe_next;                             \
  354         else                                                            \
  355                 (head)->tqh_last = &(elm)->field.tqe_next;              \
  356         (listelm)->field.tqe_next = (elm);                              \
  357         (elm)->field.tqe_prev = &(listelm)->field.tqe_next;             \
  358 } while (0)
  359 
  360 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
  361         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
  362         (elm)->field.tqe_next = (listelm);                              \
  363         *(listelm)->field.tqe_prev = (elm);                             \
  364         (listelm)->field.tqe_prev = &(elm)->field.tqe_next;             \
  365 } while (0)
  366 
  367 #define TAILQ_REMOVE(head, elm, field) do {                             \
  368         if (((elm)->field.tqe_next) != NULL)                            \
  369                 (elm)->field.tqe_next->field.tqe_prev =                 \
  370                     (elm)->field.tqe_prev;                              \
  371         else                                                            \
  372                 (head)->tqh_last = (elm)->field.tqe_prev;               \
  373         *(elm)->field.tqe_prev = (elm)->field.tqe_next;                 \
  374 } while (0)
  375 
  376 /*
  377  * Circular queue definitions.
  378  */
  379 #define CIRCLEQ_HEAD(name, type)                                        \
  380 struct name {                                                           \
  381         struct type *cqh_first;         /* first element */             \
  382         struct type *cqh_last;          /* last element */              \
  383 }
  384 
  385 #define CIRCLEQ_ENTRY(type)                                             \
  386 struct {                                                                \
  387         struct type *cqe_next;          /* next element */              \
  388         struct type *cqe_prev;          /* previous element */          \
  389 }
  390 
  391 /*
  392  * Circular queue functions.
  393  */
  394 #define CIRCLEQ_EMPTY(head) ((head)->cqh_first == (void *)(head))
  395 
  396 #define CIRCLEQ_FIRST(head) ((head)->cqh_first)
  397 
  398 #define CIRCLEQ_FOREACH(var, head, field)                               \
  399         for((var) = (head)->cqh_first;                                  \
  400             (var) != (void *)(head);                                    \
  401             (var) = (var)->field.cqe_next)
  402 
  403 #define CIRCLEQ_INIT(head) do {                                         \
  404         (head)->cqh_first = (void *)(head);                             \
  405         (head)->cqh_last = (void *)(head);                              \
  406 } while (0)
  407 
  408 #define CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {            \
  409         (elm)->field.cqe_next = (listelm)->field.cqe_next;              \
  410         (elm)->field.cqe_prev = (listelm);                              \
  411         if ((listelm)->field.cqe_next == (void *)(head))                \
  412                 (head)->cqh_last = (elm);                               \
  413         else                                                            \
  414                 (listelm)->field.cqe_next->field.cqe_prev = (elm);      \
  415         (listelm)->field.cqe_next = (elm);                              \
  416 } while (0)
  417 
  418 #define CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do {           \
  419         (elm)->field.cqe_next = (listelm);                              \
  420         (elm)->field.cqe_prev = (listelm)->field.cqe_prev;              \
  421         if ((listelm)->field.cqe_prev == (void *)(head))                \
  422                 (head)->cqh_first = (elm);                              \
  423         else                                                            \
  424                 (listelm)->field.cqe_prev->field.cqe_next = (elm);      \
  425         (listelm)->field.cqe_prev = (elm);                              \
  426 } while (0)
  427 
  428 #define CIRCLEQ_INSERT_HEAD(head, elm, field) do {                      \
  429         (elm)->field.cqe_next = (head)->cqh_first;                      \
  430         (elm)->field.cqe_prev = (void *)(head);                         \
  431         if ((head)->cqh_last == (void *)(head))                         \
  432                 (head)->cqh_last = (elm);                               \
  433         else                                                            \
  434                 (head)->cqh_first->field.cqe_prev = (elm);              \
  435         (head)->cqh_first = (elm);                                      \
  436 } while (0)
  437 
  438 #define CIRCLEQ_INSERT_TAIL(head, elm, field) do {                      \
  439         (elm)->field.cqe_next = (void *)(head);                         \
  440         (elm)->field.cqe_prev = (head)->cqh_last;                       \
  441         if ((head)->cqh_first == (void *)(head))                        \
  442                 (head)->cqh_first = (elm);                              \
  443         else                                                            \
  444                 (head)->cqh_last->field.cqe_next = (elm);               \
  445         (head)->cqh_last = (elm);                                       \
  446 } while (0)
  447 
  448 #define CIRCLEQ_LAST(head) ((head)->cqh_last)
  449 
  450 #define CIRCLEQ_NEXT(elm,field) ((elm)->field.cqe_next)
  451 
  452 #define CIRCLEQ_PREV(elm,field) ((elm)->field.cqe_prev)
  453 
  454 #define CIRCLEQ_REMOVE(head, elm, field) do {                           \
  455         if ((elm)->field.cqe_next == (void *)(head))                    \
  456                 (head)->cqh_last = (elm)->field.cqe_prev;               \
  457         else                                                            \
  458                 (elm)->field.cqe_next->field.cqe_prev =                 \
  459                     (elm)->field.cqe_prev;                              \
  460         if ((elm)->field.cqe_prev == (void *)(head))                    \
  461                 (head)->cqh_first = (elm)->field.cqe_next;              \
  462         else                                                            \
  463                 (elm)->field.cqe_prev->field.cqe_next =                 \
  464                     (elm)->field.cqe_next;                              \
  465 } while (0)
  466 
  467 #ifdef KERNEL
  468 
  469 /*
  470  * XXX insque() and remque() are an old way of handling certain queues.
  471  * They bogusly assumes that all queue heads look alike.
  472  */
  473 
  474 struct quehead {
  475         struct quehead *qh_link;
  476         struct quehead *qh_rlink;
  477 };
  478 
  479 #ifdef  __GNUC__
  480 
  481 static __inline void
  482 insque(void *a, void *b)
  483 {
  484         struct quehead *element = a, *head = b;
  485 
  486         element->qh_link = head->qh_link;
  487         element->qh_rlink = head;
  488         head->qh_link = element;
  489         element->qh_link->qh_rlink = element;
  490 }
  491 
  492 static __inline void
  493 remque(void *a)
  494 {
  495         struct quehead *element = a;
  496 
  497         element->qh_link->qh_rlink = element->qh_rlink;
  498         element->qh_rlink->qh_link = element->qh_link;
  499         element->qh_rlink = 0;
  500 }
  501 
  502 #else /* !__GNUC__ */
  503 
  504 void    insque __P((void *a, void *b));
  505 void    remque __P((void *a));
  506 
  507 #endif /* __GNUC__ */
  508 
  509 #endif /* KERNEL */
  510 
  511 #endif /* !_SYS_QUEUE_H_ */

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