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/10.4/sys/sys/queue.h 307534 2016-10-17 21:49:54Z mckusick $
   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 be traversed in either 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  * Below is a summary of implemented functions where:
   80  *  +  means the macro is available
   81  *  -  means the macro is not available
   82  *  s  means the macro is available but is slow (runs in O(n) time)
   83  *
   84  *                              SLIST   LIST    STAILQ  TAILQ
   85  * _HEAD                        +       +       +       +
   86  * _CLASS_HEAD                  +       +       +       +
   87  * _HEAD_INITIALIZER            +       +       +       +
   88  * _ENTRY                       +       +       +       +
   89  * _CLASS_ENTRY                 +       +       +       +
   90  * _INIT                        +       +       +       +
   91  * _EMPTY                       +       +       +       +
   92  * _FIRST                       +       +       +       +
   93  * _NEXT                        +       +       +       +
   94  * _PREV                        -       +       -       +
   95  * _LAST                        -       -       +       +
   96  * _FOREACH                     +       +       +       +
   97  * _FOREACH_FROM                +       +       +       +
   98  * _FOREACH_SAFE                +       +       +       +
   99  * _FOREACH_FROM_SAFE           +       +       +       +
  100  * _FOREACH_REVERSE             -       -       -       +
  101  * _FOREACH_REVERSE_FROM        -       -       -       +
  102  * _FOREACH_REVERSE_SAFE        -       -       -       +
  103  * _FOREACH_REVERSE_FROM_SAFE   -       -       -       +
  104  * _INSERT_HEAD                 +       +       +       +
  105  * _INSERT_BEFORE               -       +       -       +
  106  * _INSERT_AFTER                +       +       +       +
  107  * _INSERT_TAIL                 -       -       +       +
  108  * _CONCAT                      s       s       +       +
  109  * _REMOVE_AFTER                +       -       +       -
  110  * _REMOVE_HEAD                 +       -       +       -
  111  * _REMOVE                      s       +       s       +
  112  * _SWAP                        +       +       +       +
  113  *
  114  */
  115 #ifdef QUEUE_MACRO_DEBUG
  116 /* Store the last 2 places the queue element or head was altered */
  117 struct qm_trace {
  118         unsigned long    lastline;
  119         unsigned long    prevline;
  120         const char      *lastfile;
  121         const char      *prevfile;
  122 };
  123 
  124 #define TRACEBUF        struct qm_trace trace;
  125 #define TRACEBUF_INITIALIZER    { __LINE__, 0, __FILE__, NULL } ,
  126 #define TRASHIT(x)      do {(x) = (void *)-1;} while (0)
  127 #define QMD_SAVELINK(name, link)        void **name = (void *)&(link)
  128 
  129 #define QMD_TRACE_HEAD(head) do {                                       \
  130         (head)->trace.prevline = (head)->trace.lastline;                \
  131         (head)->trace.prevfile = (head)->trace.lastfile;                \
  132         (head)->trace.lastline = __LINE__;                              \
  133         (head)->trace.lastfile = __FILE__;                              \
  134 } while (0)
  135 
  136 #define QMD_TRACE_ELEM(elem) do {                                       \
  137         (elem)->trace.prevline = (elem)->trace.lastline;                \
  138         (elem)->trace.prevfile = (elem)->trace.lastfile;                \
  139         (elem)->trace.lastline = __LINE__;                              \
  140         (elem)->trace.lastfile = __FILE__;                              \
  141 } while (0)
  142 
  143 #else
  144 #define QMD_TRACE_ELEM(elem)
  145 #define QMD_TRACE_HEAD(head)
  146 #define QMD_SAVELINK(name, link)
  147 #define TRACEBUF
  148 #define TRACEBUF_INITIALIZER
  149 #define TRASHIT(x)
  150 #endif  /* QUEUE_MACRO_DEBUG */
  151 
  152 #ifdef __cplusplus
  153 /*
  154  * In C++ there can be structure lists and class lists:
  155  */
  156 #define QUEUE_TYPEOF(type) type
  157 #else
  158 #define QUEUE_TYPEOF(type) struct type
  159 #endif
  160 
  161 /*
  162  * Singly-linked List declarations.
  163  */
  164 #define SLIST_HEAD(name, type)                                          \
  165 struct name {                                                           \
  166         struct type *slh_first; /* first element */                     \
  167 }
  168 
  169 #define SLIST_CLASS_HEAD(name, type)                                    \
  170 struct name {                                                           \
  171         class type *slh_first;  /* first element */                     \
  172 }
  173 
  174 #define SLIST_HEAD_INITIALIZER(head)                                    \
  175         { NULL }
  176 
  177 #define SLIST_ENTRY(type)                                               \
  178 struct {                                                                \
  179         struct type *sle_next;  /* next element */                      \
  180 }
  181 
  182 #define SLIST_CLASS_ENTRY(type)                                         \
  183 struct {                                                                \
  184         class type *sle_next;           /* next element */              \
  185 }
  186 
  187 /*
  188  * Singly-linked List functions.
  189  */
  190 #define SLIST_CONCAT(head1, head2, type, field) do {                    \
  191         QUEUE_TYPEOF(type) *curelm = SLIST_FIRST(head1);                \
  192         if (curelm == NULL) {                                           \
  193                 if ((SLIST_FIRST(head1) = SLIST_FIRST(head2)) != NULL)  \
  194                         SLIST_INIT(head2);                              \
  195         } else if (SLIST_FIRST(head2) != NULL) {                        \
  196                 while (SLIST_NEXT(curelm, field) != NULL)               \
  197                         curelm = SLIST_NEXT(curelm, field);             \
  198                 SLIST_NEXT(curelm, field) = SLIST_FIRST(head2);         \
  199                 SLIST_INIT(head2);                                      \
  200         }                                                               \
  201 } while (0)
  202 
  203 #define SLIST_EMPTY(head)       ((head)->slh_first == NULL)
  204 
  205 #define SLIST_FIRST(head)       ((head)->slh_first)
  206 
  207 #define SLIST_FOREACH(var, head, field)                                 \
  208         for ((var) = SLIST_FIRST((head));                               \
  209             (var);                                                      \
  210             (var) = SLIST_NEXT((var), field))
  211 
  212 #define SLIST_FOREACH_FROM(var, head, field)                            \
  213         for ((var) = ((var) ? (var) : SLIST_FIRST((head)));             \
  214             (var);                                                      \
  215             (var) = SLIST_NEXT((var), field))
  216 
  217 #define SLIST_FOREACH_SAFE(var, head, field, tvar)                      \
  218         for ((var) = SLIST_FIRST((head));                               \
  219             (var) && ((tvar) = SLIST_NEXT((var), field), 1);            \
  220             (var) = (tvar))
  221 
  222 #define SLIST_FOREACH_FROM_SAFE(var, head, field, tvar)                 \
  223         for ((var) = ((var) ? (var) : SLIST_FIRST((head)));             \
  224             (var) && ((tvar) = SLIST_NEXT((var), field), 1);            \
  225             (var) = (tvar))
  226 
  227 #define SLIST_FOREACH_PREVPTR(var, varp, head, field)                   \
  228         for ((varp) = &SLIST_FIRST((head));                             \
  229             ((var) = *(varp)) != NULL;                                  \
  230             (varp) = &SLIST_NEXT((var), field))
  231 
  232 #define SLIST_INIT(head) do {                                           \
  233         SLIST_FIRST((head)) = NULL;                                     \
  234 } while (0)
  235 
  236 #define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
  237         SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);       \
  238         SLIST_NEXT((slistelm), field) = (elm);                          \
  239 } while (0)
  240 
  241 #define SLIST_INSERT_HEAD(head, elm, field) do {                        \
  242         SLIST_NEXT((elm), field) = SLIST_FIRST((head));                 \
  243         SLIST_FIRST((head)) = (elm);                                    \
  244 } while (0)
  245 
  246 #define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)
  247 
  248 #define SLIST_REMOVE(head, elm, type, field) do {                       \
  249         QMD_SAVELINK(oldnext, (elm)->field.sle_next);                   \
  250         if (SLIST_FIRST((head)) == (elm)) {                             \
  251                 SLIST_REMOVE_HEAD((head), field);                       \
  252         }                                                               \
  253         else {                                                          \
  254                 QUEUE_TYPEOF(type) *curelm = SLIST_FIRST(head);         \
  255                 while (SLIST_NEXT(curelm, field) != (elm))              \
  256                         curelm = SLIST_NEXT(curelm, field);             \
  257                 SLIST_REMOVE_AFTER(curelm, field);                      \
  258         }                                                               \
  259         TRASHIT(*oldnext);                                              \
  260 } while (0)
  261 
  262 #define SLIST_REMOVE_AFTER(elm, field) do {                             \
  263         SLIST_NEXT(elm, field) =                                        \
  264             SLIST_NEXT(SLIST_NEXT(elm, field), field);                  \
  265 } while (0)
  266 
  267 #define SLIST_REMOVE_HEAD(head, field) do {                             \
  268         SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);   \
  269 } while (0)
  270 
  271 #define SLIST_SWAP(head1, head2, type) do {                             \
  272         QUEUE_TYPEOF(type) *swap_first = SLIST_FIRST(head1);            \
  273         SLIST_FIRST(head1) = SLIST_FIRST(head2);                        \
  274         SLIST_FIRST(head2) = swap_first;                                \
  275 } while (0)
  276 
  277 /*
  278  * Singly-linked Tail queue declarations.
  279  */
  280 #define STAILQ_HEAD(name, type)                                         \
  281 struct name {                                                           \
  282         struct type *stqh_first;/* first element */                     \
  283         struct type **stqh_last;/* addr of last next element */         \
  284 }
  285 
  286 #define STAILQ_CLASS_HEAD(name, type)                                   \
  287 struct name {                                                           \
  288         class type *stqh_first; /* first element */                     \
  289         class type **stqh_last; /* addr of last next element */         \
  290 }
  291 
  292 #define STAILQ_HEAD_INITIALIZER(head)                                   \
  293         { NULL, &(head).stqh_first }
  294 
  295 #define STAILQ_ENTRY(type)                                              \
  296 struct {                                                                \
  297         struct type *stqe_next; /* next element */                      \
  298 }
  299 
  300 #define STAILQ_CLASS_ENTRY(type)                                        \
  301 struct {                                                                \
  302         class type *stqe_next;  /* next element */                      \
  303 }
  304 
  305 /*
  306  * Singly-linked Tail queue functions.
  307  */
  308 #define STAILQ_CONCAT(head1, head2) do {                                \
  309         if (!STAILQ_EMPTY((head2))) {                                   \
  310                 *(head1)->stqh_last = (head2)->stqh_first;              \
  311                 (head1)->stqh_last = (head2)->stqh_last;                \
  312                 STAILQ_INIT((head2));                                   \
  313         }                                                               \
  314 } while (0)
  315 
  316 #define STAILQ_EMPTY(head)      ((head)->stqh_first == NULL)
  317 
  318 #define STAILQ_FIRST(head)      ((head)->stqh_first)
  319 
  320 #define STAILQ_FOREACH(var, head, field)                                \
  321         for((var) = STAILQ_FIRST((head));                               \
  322            (var);                                                       \
  323            (var) = STAILQ_NEXT((var), field))
  324 
  325 #define STAILQ_FOREACH_FROM(var, head, field)                           \
  326         for ((var) = ((var) ? (var) : STAILQ_FIRST((head)));            \
  327            (var);                                                       \
  328            (var) = STAILQ_NEXT((var), field))
  329 
  330 #define STAILQ_FOREACH_SAFE(var, head, field, tvar)                     \
  331         for ((var) = STAILQ_FIRST((head));                              \
  332             (var) && ((tvar) = STAILQ_NEXT((var), field), 1);           \
  333             (var) = (tvar))
  334 
  335 #define STAILQ_FOREACH_FROM_SAFE(var, head, field, tvar)                \
  336         for ((var) = ((var) ? (var) : STAILQ_FIRST((head)));            \
  337             (var) && ((tvar) = STAILQ_NEXT((var), field), 1);           \
  338             (var) = (tvar))
  339 
  340 #define STAILQ_INIT(head) do {                                          \
  341         STAILQ_FIRST((head)) = NULL;                                    \
  342         (head)->stqh_last = &STAILQ_FIRST((head));                      \
  343 } while (0)
  344 
  345 #define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {               \
  346         if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
  347                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
  348         STAILQ_NEXT((tqelm), field) = (elm);                            \
  349 } while (0)
  350 
  351 #define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
  352         if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL) \
  353                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
  354         STAILQ_FIRST((head)) = (elm);                                   \
  355 } while (0)
  356 
  357 #define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
  358         STAILQ_NEXT((elm), field) = NULL;                               \
  359         *(head)->stqh_last = (elm);                                     \
  360         (head)->stqh_last = &STAILQ_NEXT((elm), field);                 \
  361 } while (0)
  362 
  363 #define STAILQ_LAST(head, type, field)                          \
  364         (STAILQ_EMPTY((head)) ? NULL :                          \
  365             __containerof((head)->stqh_last,                    \
  366             QUEUE_TYPEOF(type), field.stqe_next))
  367 
  368 #define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
  369 
  370 #define STAILQ_REMOVE(head, elm, type, field) do {                      \
  371         QMD_SAVELINK(oldnext, (elm)->field.stqe_next);                  \
  372         if (STAILQ_FIRST((head)) == (elm)) {                            \
  373                 STAILQ_REMOVE_HEAD((head), field);                      \
  374         }                                                               \
  375         else {                                                          \
  376                 QUEUE_TYPEOF(type) *curelm = STAILQ_FIRST(head);        \
  377                 while (STAILQ_NEXT(curelm, field) != (elm))             \
  378                         curelm = STAILQ_NEXT(curelm, field);            \
  379                 STAILQ_REMOVE_AFTER(head, curelm, field);               \
  380         }                                                               \
  381         TRASHIT(*oldnext);                                              \
  382 } while (0)
  383 
  384 #define STAILQ_REMOVE_AFTER(head, elm, field) do {                      \
  385         if ((STAILQ_NEXT(elm, field) =                                  \
  386              STAILQ_NEXT(STAILQ_NEXT(elm, field), field)) == NULL)      \
  387                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
  388 } while (0)
  389 
  390 #define STAILQ_REMOVE_HEAD(head, field) do {                            \
  391         if ((STAILQ_FIRST((head)) =                                     \
  392              STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL)         \
  393                 (head)->stqh_last = &STAILQ_FIRST((head));              \
  394 } while (0)
  395 
  396 #define STAILQ_SWAP(head1, head2, type) do {                            \
  397         QUEUE_TYPEOF(type) *swap_first = STAILQ_FIRST(head1);           \
  398         QUEUE_TYPEOF(type) **swap_last = (head1)->stqh_last;            \
  399         STAILQ_FIRST(head1) = STAILQ_FIRST(head2);                      \
  400         (head1)->stqh_last = (head2)->stqh_last;                        \
  401         STAILQ_FIRST(head2) = swap_first;                               \
  402         (head2)->stqh_last = swap_last;                                 \
  403         if (STAILQ_EMPTY(head1))                                        \
  404                 (head1)->stqh_last = &STAILQ_FIRST(head1);              \
  405         if (STAILQ_EMPTY(head2))                                        \
  406                 (head2)->stqh_last = &STAILQ_FIRST(head2);              \
  407 } while (0)
  408 
  409 
  410 /*
  411  * List declarations.
  412  */
  413 #define LIST_HEAD(name, type)                                           \
  414 struct name {                                                           \
  415         struct type *lh_first;  /* first element */                     \
  416 }
  417 
  418 #define LIST_CLASS_HEAD(name, type)                                     \
  419 struct name {                                                           \
  420         class type *lh_first;   /* first element */                     \
  421 }
  422 
  423 #define LIST_HEAD_INITIALIZER(head)                                     \
  424         { NULL }
  425 
  426 #define LIST_ENTRY(type)                                                \
  427 struct {                                                                \
  428         struct type *le_next;   /* next element */                      \
  429         struct type **le_prev;  /* address of previous next element */  \
  430 }
  431 
  432 #define LIST_CLASS_ENTRY(type)                                          \
  433 struct {                                                                \
  434         class type *le_next;    /* next element */                      \
  435         class type **le_prev;   /* address of previous next element */  \
  436 }
  437 
  438 /*
  439  * List functions.
  440  */
  441 
  442 #if (defined(_KERNEL) && defined(INVARIANTS))
  443 #define QMD_LIST_CHECK_HEAD(head, field) do {                           \
  444         if (LIST_FIRST((head)) != NULL &&                               \
  445             LIST_FIRST((head))->field.le_prev !=                        \
  446              &LIST_FIRST((head)))                                       \
  447                 panic("Bad list head %p first->prev != head", (head));  \
  448 } while (0)
  449 
  450 #define QMD_LIST_CHECK_NEXT(elm, field) do {                            \
  451         if (LIST_NEXT((elm), field) != NULL &&                          \
  452             LIST_NEXT((elm), field)->field.le_prev !=                   \
  453              &((elm)->field.le_next))                                   \
  454                 panic("Bad link elm %p next->prev != elm", (elm));      \
  455 } while (0)
  456 
  457 #define QMD_LIST_CHECK_PREV(elm, field) do {                            \
  458         if (*(elm)->field.le_prev != (elm))                             \
  459                 panic("Bad link elm %p prev->next != elm", (elm));      \
  460 } while (0)
  461 #else
  462 #define QMD_LIST_CHECK_HEAD(head, field)
  463 #define QMD_LIST_CHECK_NEXT(elm, field)
  464 #define QMD_LIST_CHECK_PREV(elm, field)
  465 #endif /* (_KERNEL && INVARIANTS) */
  466 
  467 #define LIST_CONCAT(head1, head2, type, field) do {                           \
  468         QUEUE_TYPEOF(type) *curelm = LIST_FIRST(head1);                       \
  469         if (curelm == NULL) {                                                 \
  470                 if ((LIST_FIRST(head1) = LIST_FIRST(head2)) != NULL) {        \
  471                         LIST_FIRST(head2)->field.le_prev =                    \
  472                             &LIST_FIRST((head1));                             \
  473                         LIST_INIT(head2);                                     \
  474                 }                                                             \
  475         } else if (LIST_FIRST(head2) != NULL) {                               \
  476                 while (LIST_NEXT(curelm, field) != NULL)                      \
  477                         curelm = LIST_NEXT(curelm, field);                    \
  478                 LIST_NEXT(curelm, field) = LIST_FIRST(head2);                 \
  479                 LIST_FIRST(head2)->field.le_prev = &LIST_NEXT(curelm, field); \
  480                 LIST_INIT(head2);                                             \
  481         }                                                                     \
  482 } while (0)
  483 
  484 #define LIST_EMPTY(head)        ((head)->lh_first == NULL)
  485 
  486 #define LIST_FIRST(head)        ((head)->lh_first)
  487 
  488 #define LIST_FOREACH(var, head, field)                                  \
  489         for ((var) = LIST_FIRST((head));                                \
  490             (var);                                                      \
  491             (var) = LIST_NEXT((var), field))
  492 
  493 #define LIST_FOREACH_FROM(var, head, field)                             \
  494         for ((var) = ((var) ? (var) : LIST_FIRST((head)));              \
  495             (var);                                                      \
  496             (var) = LIST_NEXT((var), field))
  497 
  498 #define LIST_FOREACH_SAFE(var, head, field, tvar)                       \
  499         for ((var) = LIST_FIRST((head));                                \
  500             (var) && ((tvar) = LIST_NEXT((var), field), 1);             \
  501             (var) = (tvar))
  502 
  503 #define LIST_FOREACH_FROM_SAFE(var, head, field, tvar)                  \
  504         for ((var) = ((var) ? (var) : LIST_FIRST((head)));              \
  505             (var) && ((tvar) = LIST_NEXT((var), field), 1);             \
  506             (var) = (tvar))
  507 
  508 #define LIST_INIT(head) do {                                            \
  509         LIST_FIRST((head)) = NULL;                                      \
  510 } while (0)
  511 
  512 #define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
  513         QMD_LIST_CHECK_NEXT(listelm, field);                            \
  514         if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
  515                 LIST_NEXT((listelm), field)->field.le_prev =            \
  516                     &LIST_NEXT((elm), field);                           \
  517         LIST_NEXT((listelm), field) = (elm);                            \
  518         (elm)->field.le_prev = &LIST_NEXT((listelm), field);            \
  519 } while (0)
  520 
  521 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
  522         QMD_LIST_CHECK_PREV(listelm, field);                            \
  523         (elm)->field.le_prev = (listelm)->field.le_prev;                \
  524         LIST_NEXT((elm), field) = (listelm);                            \
  525         *(listelm)->field.le_prev = (elm);                              \
  526         (listelm)->field.le_prev = &LIST_NEXT((elm), field);            \
  527 } while (0)
  528 
  529 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
  530         QMD_LIST_CHECK_HEAD((head), field);                             \
  531         if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)     \
  532                 LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
  533         LIST_FIRST((head)) = (elm);                                     \
  534         (elm)->field.le_prev = &LIST_FIRST((head));                     \
  535 } while (0)
  536 
  537 #define LIST_NEXT(elm, field)   ((elm)->field.le_next)
  538 
  539 #define LIST_PREV(elm, head, type, field)                       \
  540         ((elm)->field.le_prev == &LIST_FIRST((head)) ? NULL :   \
  541             __containerof((elm)->field.le_prev,                 \
  542             QUEUE_TYPEOF(type), field.le_next))
  543 
  544 #define LIST_REMOVE(elm, field) do {                                    \
  545         QMD_SAVELINK(oldnext, (elm)->field.le_next);                    \
  546         QMD_SAVELINK(oldprev, (elm)->field.le_prev);                    \
  547         QMD_LIST_CHECK_NEXT(elm, field);                                \
  548         QMD_LIST_CHECK_PREV(elm, field);                                \
  549         if (LIST_NEXT((elm), field) != NULL)                            \
  550                 LIST_NEXT((elm), field)->field.le_prev =                \
  551                     (elm)->field.le_prev;                               \
  552         *(elm)->field.le_prev = LIST_NEXT((elm), field);                \
  553         TRASHIT(*oldnext);                                              \
  554         TRASHIT(*oldprev);                                              \
  555 } while (0)
  556 
  557 #define LIST_SWAP(head1, head2, type, field) do {                       \
  558         QUEUE_TYPEOF(type) *swap_tmp = LIST_FIRST(head1);               \
  559         LIST_FIRST((head1)) = LIST_FIRST((head2));                      \
  560         LIST_FIRST((head2)) = swap_tmp;                                 \
  561         if ((swap_tmp = LIST_FIRST((head1))) != NULL)                   \
  562                 swap_tmp->field.le_prev = &LIST_FIRST((head1));         \
  563         if ((swap_tmp = LIST_FIRST((head2))) != NULL)                   \
  564                 swap_tmp->field.le_prev = &LIST_FIRST((head2));         \
  565 } while (0)
  566 
  567 /*
  568  * Tail queue declarations.
  569  */
  570 #define TAILQ_HEAD(name, type)                                          \
  571 struct name {                                                           \
  572         struct type *tqh_first; /* first element */                     \
  573         struct type **tqh_last; /* addr of last next element */         \
  574         TRACEBUF                                                        \
  575 }
  576 
  577 #define TAILQ_CLASS_HEAD(name, type)                                    \
  578 struct name {                                                           \
  579         class type *tqh_first;  /* first element */                     \
  580         class type **tqh_last;  /* addr of last next element */         \
  581         TRACEBUF                                                        \
  582 }
  583 
  584 #define TAILQ_HEAD_INITIALIZER(head)                                    \
  585         { NULL, &(head).tqh_first, TRACEBUF_INITIALIZER }
  586 
  587 #define TAILQ_ENTRY(type)                                               \
  588 struct {                                                                \
  589         struct type *tqe_next;  /* next element */                      \
  590         struct type **tqe_prev; /* address of previous next element */  \
  591         TRACEBUF                                                        \
  592 }
  593 
  594 #define TAILQ_CLASS_ENTRY(type)                                         \
  595 struct {                                                                \
  596         class type *tqe_next;   /* next element */                      \
  597         class type **tqe_prev;  /* address of previous next element */  \
  598         TRACEBUF                                                        \
  599 }
  600 
  601 /*
  602  * Tail queue functions.
  603  */
  604 #if (defined(_KERNEL) && defined(INVARIANTS))
  605 #define QMD_TAILQ_CHECK_HEAD(head, field) do {                          \
  606         if (!TAILQ_EMPTY(head) &&                                       \
  607             TAILQ_FIRST((head))->field.tqe_prev !=                      \
  608              &TAILQ_FIRST((head)))                                      \
  609                 panic("Bad tailq head %p first->prev != head", (head)); \
  610 } while (0)
  611 
  612 #define QMD_TAILQ_CHECK_TAIL(head, field) do {                          \
  613         if (*(head)->tqh_last != NULL)                                  \
  614                 panic("Bad tailq NEXT(%p->tqh_last) != NULL", (head));  \
  615 } while (0)
  616 
  617 #define QMD_TAILQ_CHECK_NEXT(elm, field) do {                           \
  618         if (TAILQ_NEXT((elm), field) != NULL &&                         \
  619             TAILQ_NEXT((elm), field)->field.tqe_prev !=                 \
  620              &((elm)->field.tqe_next))                                  \
  621                 panic("Bad link elm %p next->prev != elm", (elm));      \
  622 } while (0)
  623 
  624 #define QMD_TAILQ_CHECK_PREV(elm, field) do {                           \
  625         if (*(elm)->field.tqe_prev != (elm))                            \
  626                 panic("Bad link elm %p prev->next != elm", (elm));      \
  627 } while (0)
  628 #else
  629 #define QMD_TAILQ_CHECK_HEAD(head, field)
  630 #define QMD_TAILQ_CHECK_TAIL(head, headname)
  631 #define QMD_TAILQ_CHECK_NEXT(elm, field)
  632 #define QMD_TAILQ_CHECK_PREV(elm, field)
  633 #endif /* (_KERNEL && INVARIANTS) */
  634 
  635 #define TAILQ_CONCAT(head1, head2, field) do {                          \
  636         if (!TAILQ_EMPTY(head2)) {                                      \
  637                 *(head1)->tqh_last = (head2)->tqh_first;                \
  638                 (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last; \
  639                 (head1)->tqh_last = (head2)->tqh_last;                  \
  640                 TAILQ_INIT((head2));                                    \
  641                 QMD_TRACE_HEAD(head1);                                  \
  642                 QMD_TRACE_HEAD(head2);                                  \
  643         }                                                               \
  644 } while (0)
  645 
  646 #define TAILQ_EMPTY(head)       ((head)->tqh_first == NULL)
  647 
  648 #define TAILQ_FIRST(head)       ((head)->tqh_first)
  649 
  650 #define TAILQ_FOREACH(var, head, field)                                 \
  651         for ((var) = TAILQ_FIRST((head));                               \
  652             (var);                                                      \
  653             (var) = TAILQ_NEXT((var), field))
  654 
  655 #define TAILQ_FOREACH_FROM(var, head, field)                            \
  656         for ((var) = ((var) ? (var) : TAILQ_FIRST((head)));             \
  657             (var);                                                      \
  658             (var) = TAILQ_NEXT((var), field))
  659 
  660 #define TAILQ_FOREACH_SAFE(var, head, field, tvar)                      \
  661         for ((var) = TAILQ_FIRST((head));                               \
  662             (var) && ((tvar) = TAILQ_NEXT((var), field), 1);            \
  663             (var) = (tvar))
  664 
  665 #define TAILQ_FOREACH_FROM_SAFE(var, head, field, tvar)                 \
  666         for ((var) = ((var) ? (var) : TAILQ_FIRST((head)));             \
  667             (var) && ((tvar) = TAILQ_NEXT((var), field), 1);            \
  668             (var) = (tvar))
  669 
  670 #define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
  671         for ((var) = TAILQ_LAST((head), headname);                      \
  672             (var);                                                      \
  673             (var) = TAILQ_PREV((var), headname, field))
  674 
  675 #define TAILQ_FOREACH_REVERSE_FROM(var, head, headname, field)          \
  676         for ((var) = ((var) ? (var) : TAILQ_LAST((head), headname));    \
  677             (var);                                                      \
  678             (var) = TAILQ_PREV((var), headname, field))
  679 
  680 #define TAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar)    \
  681         for ((var) = TAILQ_LAST((head), headname);                      \
  682             (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);  \
  683             (var) = (tvar))
  684 
  685 #define TAILQ_FOREACH_REVERSE_FROM_SAFE(var, head, headname, field, tvar) \
  686         for ((var) = ((var) ? (var) : TAILQ_LAST((head), headname));    \
  687             (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);  \
  688             (var) = (tvar))
  689 
  690 #define TAILQ_INIT(head) do {                                           \
  691         TAILQ_FIRST((head)) = NULL;                                     \
  692         (head)->tqh_last = &TAILQ_FIRST((head));                        \
  693         QMD_TRACE_HEAD(head);                                           \
  694 } while (0)
  695 
  696 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
  697         QMD_TAILQ_CHECK_NEXT(listelm, field);                           \
  698         if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
  699                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
  700                     &TAILQ_NEXT((elm), field);                          \
  701         else {                                                          \
  702                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
  703                 QMD_TRACE_HEAD(head);                                   \
  704         }                                                               \
  705         TAILQ_NEXT((listelm), field) = (elm);                           \
  706         (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);          \
  707         QMD_TRACE_ELEM(&(elm)->field);                                  \
  708         QMD_TRACE_ELEM(&(listelm)->field);                              \
  709 } while (0)
  710 
  711 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
  712         QMD_TAILQ_CHECK_PREV(listelm, field);                           \
  713         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
  714         TAILQ_NEXT((elm), field) = (listelm);                           \
  715         *(listelm)->field.tqe_prev = (elm);                             \
  716         (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);          \
  717         QMD_TRACE_ELEM(&(elm)->field);                                  \
  718         QMD_TRACE_ELEM(&(listelm)->field);                              \
  719 } while (0)
  720 
  721 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
  722         QMD_TAILQ_CHECK_HEAD(head, field);                              \
  723         if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)   \
  724                 TAILQ_FIRST((head))->field.tqe_prev =                   \
  725                     &TAILQ_NEXT((elm), field);                          \
  726         else                                                            \
  727                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
  728         TAILQ_FIRST((head)) = (elm);                                    \
  729         (elm)->field.tqe_prev = &TAILQ_FIRST((head));                   \
  730         QMD_TRACE_HEAD(head);                                           \
  731         QMD_TRACE_ELEM(&(elm)->field);                                  \
  732 } while (0)
  733 
  734 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
  735         QMD_TAILQ_CHECK_TAIL(head, field);                              \
  736         TAILQ_NEXT((elm), field) = NULL;                                \
  737         (elm)->field.tqe_prev = (head)->tqh_last;                       \
  738         *(head)->tqh_last = (elm);                                      \
  739         (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
  740         QMD_TRACE_HEAD(head);                                           \
  741         QMD_TRACE_ELEM(&(elm)->field);                                  \
  742 } while (0)
  743 
  744 #define TAILQ_LAST(head, headname)                                      \
  745         (*(((struct headname *)((head)->tqh_last))->tqh_last))
  746 
  747 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
  748 
  749 #define TAILQ_PREV(elm, headname, field)                                \
  750         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
  751 
  752 #define TAILQ_REMOVE(head, elm, field) do {                             \
  753         QMD_SAVELINK(oldnext, (elm)->field.tqe_next);                   \
  754         QMD_SAVELINK(oldprev, (elm)->field.tqe_prev);                   \
  755         QMD_TAILQ_CHECK_NEXT(elm, field);                               \
  756         QMD_TAILQ_CHECK_PREV(elm, field);                               \
  757         if ((TAILQ_NEXT((elm), field)) != NULL)                         \
  758                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
  759                     (elm)->field.tqe_prev;                              \
  760         else {                                                          \
  761                 (head)->tqh_last = (elm)->field.tqe_prev;               \
  762                 QMD_TRACE_HEAD(head);                                   \
  763         }                                                               \
  764         *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);              \
  765         TRASHIT(*oldnext);                                              \
  766         TRASHIT(*oldprev);                                              \
  767         QMD_TRACE_ELEM(&(elm)->field);                                  \
  768 } while (0)
  769 
  770 #define TAILQ_SWAP(head1, head2, type, field) do {                      \
  771         QUEUE_TYPEOF(type) *swap_first = (head1)->tqh_first;            \
  772         QUEUE_TYPEOF(type) **swap_last = (head1)->tqh_last;             \
  773         (head1)->tqh_first = (head2)->tqh_first;                        \
  774         (head1)->tqh_last = (head2)->tqh_last;                          \
  775         (head2)->tqh_first = swap_first;                                \
  776         (head2)->tqh_last = swap_last;                                  \
  777         if ((swap_first = (head1)->tqh_first) != NULL)                  \
  778                 swap_first->field.tqe_prev = &(head1)->tqh_first;       \
  779         else                                                            \
  780                 (head1)->tqh_last = &(head1)->tqh_first;                \
  781         if ((swap_first = (head2)->tqh_first) != NULL)                  \
  782                 swap_first->field.tqe_prev = &(head2)->tqh_first;       \
  783         else                                                            \
  784                 (head2)->tqh_last = &(head2)->tqh_first;                \
  785 } while (0)
  786 
  787 #endif /* !_SYS_QUEUE_H_ */

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