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  * SPDX-License-Identifier: BSD-3-Clause
    3  *
    4  * Copyright (c) 1991, 1993
    5  *      The Regents of the University of California.  All rights reserved.
    6  *
    7  * Redistribution and use in source and binary forms, with or without
    8  * modification, are permitted provided that the following conditions
    9  * are met:
   10  * 1. Redistributions of source code must retain the above copyright
   11  *    notice, this list of conditions and the following disclaimer.
   12  * 2. Redistributions in binary form must reproduce the above copyright
   13  *    notice, this list of conditions and the following disclaimer in the
   14  *    documentation and/or other materials provided with the distribution.
   15  * 3. Neither the name of the University nor the names of its contributors
   16  *    may be used to endorse or promote products derived from this software
   17  *    without specific prior written permission.
   18  *
   19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   29  * SUCH DAMAGE.
   30  *
   31  *      @(#)queue.h     8.5 (Berkeley) 8/20/94
   32  * $FreeBSD$
   33  */
   34 
   35 #ifndef _SYS_QUEUE_H_
   36 #define _SYS_QUEUE_H_
   37 
   38 #include <sys/cdefs.h>
   39 
   40 /*
   41  * This file defines four types of data structures: singly-linked lists,
   42  * singly-linked tail queues, lists and tail 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 be traversed in either 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 be traversed in either direction.
   78  *
   79  * For details on the use of these macros, see the queue(3) manual page.
   80  *
   81  * Below is a summary of implemented functions where:
   82  *  +  means the macro is available
   83  *  -  means the macro is not available
   84  *  s  means the macro is available but is slow (runs in O(n) time)
   85  *
   86  *                              SLIST   LIST    STAILQ  TAILQ
   87  * _HEAD                        +       +       +       +
   88  * _CLASS_HEAD                  +       +       +       +
   89  * _HEAD_INITIALIZER            +       +       +       +
   90  * _ENTRY                       +       +       +       +
   91  * _CLASS_ENTRY                 +       +       +       +
   92  * _INIT                        +       +       +       +
   93  * _EMPTY                       +       +       +       +
   94  * _END                         +       +       +       +
   95  * _FIRST                       +       +       +       +
   96  * _NEXT                        +       +       +       +
   97  * _PREV                        -       +       -       +
   98  * _LAST                        -       -       +       +
   99  * _LAST_FAST                   -       -       -       +
  100  * _FOREACH                     +       +       +       +
  101  * _FOREACH_FROM                +       +       +       +
  102  * _FOREACH_SAFE                +       +       +       +
  103  * _FOREACH_FROM_SAFE           +       +       +       +
  104  * _FOREACH_REVERSE             -       -       -       +
  105  * _FOREACH_REVERSE_FROM        -       -       -       +
  106  * _FOREACH_REVERSE_SAFE        -       -       -       +
  107  * _FOREACH_REVERSE_FROM_SAFE   -       -       -       +
  108  * _INSERT_HEAD                 +       +       +       +
  109  * _INSERT_BEFORE               -       +       -       +
  110  * _INSERT_AFTER                +       +       +       +
  111  * _INSERT_TAIL                 -       -       +       +
  112  * _CONCAT                      s       s       +       +
  113  * _REMOVE_AFTER                +       -       +       -
  114  * _REMOVE_HEAD                 +       -       +       -
  115  * _REMOVE                      s       +       s       +
  116  * _SWAP                        +       +       +       +
  117  *
  118  */
  119 #ifdef QUEUE_MACRO_DEBUG
  120 #warn Use QUEUE_MACRO_DEBUG_TRACE and/or QUEUE_MACRO_DEBUG_TRASH
  121 #define QUEUE_MACRO_DEBUG_TRACE
  122 #define QUEUE_MACRO_DEBUG_TRASH
  123 #endif
  124 
  125 #ifdef QUEUE_MACRO_DEBUG_TRACE
  126 /* Store the last 2 places the queue element or head was altered */
  127 struct qm_trace {
  128         unsigned long    lastline;
  129         unsigned long    prevline;
  130         const char      *lastfile;
  131         const char      *prevfile;
  132 };
  133 
  134 #define TRACEBUF        struct qm_trace trace;
  135 #define TRACEBUF_INITIALIZER    { __LINE__, 0, __FILE__, NULL } ,
  136 
  137 #define QMD_TRACE_HEAD(head) do {                                       \
  138         (head)->trace.prevline = (head)->trace.lastline;                \
  139         (head)->trace.prevfile = (head)->trace.lastfile;                \
  140         (head)->trace.lastline = __LINE__;                              \
  141         (head)->trace.lastfile = __FILE__;                              \
  142 } while (0)
  143 
  144 #define QMD_TRACE_ELEM(elem) do {                                       \
  145         (elem)->trace.prevline = (elem)->trace.lastline;                \
  146         (elem)->trace.prevfile = (elem)->trace.lastfile;                \
  147         (elem)->trace.lastline = __LINE__;                              \
  148         (elem)->trace.lastfile = __FILE__;                              \
  149 } while (0)
  150 
  151 #else   /* !QUEUE_MACRO_DEBUG_TRACE */
  152 #define QMD_TRACE_ELEM(elem)
  153 #define QMD_TRACE_HEAD(head)
  154 #define TRACEBUF
  155 #define TRACEBUF_INITIALIZER
  156 #endif  /* QUEUE_MACRO_DEBUG_TRACE */
  157 
  158 #ifdef QUEUE_MACRO_DEBUG_TRASH
  159 #define QMD_SAVELINK(name, link)        void **name = (void *)&(link)
  160 #define TRASHIT(x)              do {(x) = (void *)-1;} while (0)
  161 #define QMD_IS_TRASHED(x)       ((x) == (void *)(intptr_t)-1)
  162 #else   /* !QUEUE_MACRO_DEBUG_TRASH */
  163 #define QMD_SAVELINK(name, link)
  164 #define TRASHIT(x)
  165 #define QMD_IS_TRASHED(x)       0
  166 #endif  /* QUEUE_MACRO_DEBUG_TRASH */
  167 
  168 #ifdef __cplusplus
  169 /*
  170  * In C++ there can be structure lists and class lists:
  171  */
  172 #define QUEUE_TYPEOF(type) type
  173 #else
  174 #define QUEUE_TYPEOF(type) struct type
  175 #endif
  176 
  177 /*
  178  * Singly-linked List declarations.
  179  */
  180 #define SLIST_HEAD(name, type)                                          \
  181 struct name {                                                           \
  182         struct type *slh_first; /* first element */                     \
  183 }
  184 
  185 #define SLIST_CLASS_HEAD(name, type)                                    \
  186 struct name {                                                           \
  187         class type *slh_first;  /* first element */                     \
  188 }
  189 
  190 #define SLIST_HEAD_INITIALIZER(head)                                    \
  191         { NULL }
  192 
  193 #define SLIST_ENTRY(type)                                               \
  194 struct {                                                                \
  195         struct type *sle_next;  /* next element */                      \
  196 }
  197 
  198 #define SLIST_CLASS_ENTRY(type)                                         \
  199 struct {                                                                \
  200         class type *sle_next;           /* next element */              \
  201 }
  202 
  203 /*
  204  * Singly-linked List functions.
  205  */
  206 #if (defined(_KERNEL) && defined(INVARIANTS))
  207 #define QMD_SLIST_CHECK_PREVPTR(prevp, elm) do {                        \
  208         if (*(prevp) != (elm))                                          \
  209                 panic("Bad prevptr *(%p) == %p != %p",                  \
  210                     (prevp), *(prevp), (elm));                          \
  211 } while (0)
  212 #else
  213 #define QMD_SLIST_CHECK_PREVPTR(prevp, elm)
  214 #endif
  215 
  216 #define SLIST_CONCAT(head1, head2, type, field) do {                    \
  217         QUEUE_TYPEOF(type) *curelm = SLIST_FIRST(head1);                \
  218         if (curelm == NULL) {                                           \
  219                 if ((SLIST_FIRST(head1) = SLIST_FIRST(head2)) != NULL)  \
  220                         SLIST_INIT(head2);                              \
  221         } else if (SLIST_FIRST(head2) != NULL) {                        \
  222                 while (SLIST_NEXT(curelm, field) != NULL)               \
  223                         curelm = SLIST_NEXT(curelm, field);             \
  224                 SLIST_NEXT(curelm, field) = SLIST_FIRST(head2);         \
  225                 SLIST_INIT(head2);                                      \
  226         }                                                               \
  227 } while (0)
  228 
  229 #define SLIST_EMPTY(head)       ((head)->slh_first == NULL)
  230 
  231 #define SLIST_FIRST(head)       ((head)->slh_first)
  232 
  233 #define SLIST_FOREACH(var, head, field)                                 \
  234         for ((var) = SLIST_FIRST((head));                               \
  235             (var);                                                      \
  236             (var) = SLIST_NEXT((var), field))
  237 
  238 #define SLIST_FOREACH_FROM(var, head, field)                            \
  239         for ((var) = ((var) ? (var) : SLIST_FIRST((head)));             \
  240             (var);                                                      \
  241             (var) = SLIST_NEXT((var), field))
  242 
  243 #define SLIST_FOREACH_SAFE(var, head, field, tvar)                      \
  244         for ((var) = SLIST_FIRST((head));                               \
  245             (var) && ((tvar) = SLIST_NEXT((var), field), 1);            \
  246             (var) = (tvar))
  247 
  248 #define SLIST_FOREACH_FROM_SAFE(var, head, field, tvar)                 \
  249         for ((var) = ((var) ? (var) : SLIST_FIRST((head)));             \
  250             (var) && ((tvar) = SLIST_NEXT((var), field), 1);            \
  251             (var) = (tvar))
  252 
  253 #define SLIST_FOREACH_PREVPTR(var, varp, head, field)                   \
  254         for ((varp) = &SLIST_FIRST((head));                             \
  255             ((var) = *(varp)) != NULL;                                  \
  256             (varp) = &SLIST_NEXT((var), field))
  257 
  258 #define SLIST_INIT(head) do {                                           \
  259         SLIST_FIRST((head)) = NULL;                                     \
  260 } while (0)
  261 
  262 #define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
  263         SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);       \
  264         SLIST_NEXT((slistelm), field) = (elm);                          \
  265 } while (0)
  266 
  267 #define SLIST_INSERT_HEAD(head, elm, field) do {                        \
  268         SLIST_NEXT((elm), field) = SLIST_FIRST((head));                 \
  269         SLIST_FIRST((head)) = (elm);                                    \
  270 } while (0)
  271 
  272 #define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)
  273 
  274 #define SLIST_REMOVE(head, elm, type, field) do {                       \
  275         if (SLIST_FIRST((head)) == (elm)) {                             \
  276                 SLIST_REMOVE_HEAD((head), field);                       \
  277         }                                                               \
  278         else {                                                          \
  279                 QUEUE_TYPEOF(type) *curelm = SLIST_FIRST(head);         \
  280                 while (SLIST_NEXT(curelm, field) != (elm))              \
  281                         curelm = SLIST_NEXT(curelm, field);             \
  282                 SLIST_REMOVE_AFTER(curelm, field);                      \
  283         }                                                               \
  284 } while (0)
  285 
  286 #define SLIST_REMOVE_AFTER(elm, field) do {                             \
  287         QMD_SAVELINK(oldnext, SLIST_NEXT(elm, field)->field.sle_next);  \
  288         SLIST_NEXT(elm, field) =                                        \
  289             SLIST_NEXT(SLIST_NEXT(elm, field), field);                  \
  290         TRASHIT(*oldnext);                                              \
  291 } while (0)
  292 
  293 #define SLIST_REMOVE_HEAD(head, field) do {                             \
  294         QMD_SAVELINK(oldnext, SLIST_FIRST(head)->field.sle_next);       \
  295         SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);   \
  296         TRASHIT(*oldnext);                                              \
  297 } while (0)
  298 
  299 #define SLIST_REMOVE_PREVPTR(prevp, elm, field) do {                    \
  300         QMD_SLIST_CHECK_PREVPTR(prevp, elm);                            \
  301         *(prevp) = SLIST_NEXT(elm, field);                              \
  302         TRASHIT((elm)->field.sle_next);                                 \
  303 } while (0)
  304 
  305 #define SLIST_SWAP(head1, head2, type) do {                             \
  306         QUEUE_TYPEOF(type) *swap_first = SLIST_FIRST(head1);            \
  307         SLIST_FIRST(head1) = SLIST_FIRST(head2);                        \
  308         SLIST_FIRST(head2) = swap_first;                                \
  309 } while (0)
  310 
  311 #define SLIST_END(head)         NULL
  312 
  313 /*
  314  * Singly-linked Tail queue declarations.
  315  */
  316 #define STAILQ_HEAD(name, type)                                         \
  317 struct name {                                                           \
  318         struct type *stqh_first;/* first element */                     \
  319         struct type **stqh_last;/* addr of last next element */         \
  320 }
  321 
  322 #define STAILQ_CLASS_HEAD(name, type)                                   \
  323 struct name {                                                           \
  324         class type *stqh_first; /* first element */                     \
  325         class type **stqh_last; /* addr of last next element */         \
  326 }
  327 
  328 #define STAILQ_HEAD_INITIALIZER(head)                                   \
  329         { NULL, &(head).stqh_first }
  330 
  331 #define STAILQ_ENTRY(type)                                              \
  332 struct {                                                                \
  333         struct type *stqe_next; /* next element */                      \
  334 }
  335 
  336 #define STAILQ_CLASS_ENTRY(type)                                        \
  337 struct {                                                                \
  338         class type *stqe_next;  /* next element */                      \
  339 }
  340 
  341 /*
  342  * Singly-linked Tail queue functions.
  343  */
  344 #define STAILQ_CONCAT(head1, head2) do {                                \
  345         if (!STAILQ_EMPTY((head2))) {                                   \
  346                 *(head1)->stqh_last = (head2)->stqh_first;              \
  347                 (head1)->stqh_last = (head2)->stqh_last;                \
  348                 STAILQ_INIT((head2));                                   \
  349         }                                                               \
  350 } while (0)
  351 
  352 #define STAILQ_EMPTY(head)      ((head)->stqh_first == NULL)
  353 
  354 #define STAILQ_FIRST(head)      ((head)->stqh_first)
  355 
  356 #define STAILQ_FOREACH(var, head, field)                                \
  357         for((var) = STAILQ_FIRST((head));                               \
  358            (var);                                                       \
  359            (var) = STAILQ_NEXT((var), field))
  360 
  361 #define STAILQ_FOREACH_FROM(var, head, field)                           \
  362         for ((var) = ((var) ? (var) : STAILQ_FIRST((head)));            \
  363            (var);                                                       \
  364            (var) = STAILQ_NEXT((var), field))
  365 
  366 #define STAILQ_FOREACH_SAFE(var, head, field, tvar)                     \
  367         for ((var) = STAILQ_FIRST((head));                              \
  368             (var) && ((tvar) = STAILQ_NEXT((var), field), 1);           \
  369             (var) = (tvar))
  370 
  371 #define STAILQ_FOREACH_FROM_SAFE(var, head, field, tvar)                \
  372         for ((var) = ((var) ? (var) : STAILQ_FIRST((head)));            \
  373             (var) && ((tvar) = STAILQ_NEXT((var), field), 1);           \
  374             (var) = (tvar))
  375 
  376 #define STAILQ_INIT(head) do {                                          \
  377         STAILQ_FIRST((head)) = NULL;                                    \
  378         (head)->stqh_last = &STAILQ_FIRST((head));                      \
  379 } while (0)
  380 
  381 #define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {               \
  382         if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
  383                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
  384         STAILQ_NEXT((tqelm), field) = (elm);                            \
  385 } while (0)
  386 
  387 #define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
  388         if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL) \
  389                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
  390         STAILQ_FIRST((head)) = (elm);                                   \
  391 } while (0)
  392 
  393 #define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
  394         STAILQ_NEXT((elm), field) = NULL;                               \
  395         *(head)->stqh_last = (elm);                                     \
  396         (head)->stqh_last = &STAILQ_NEXT((elm), field);                 \
  397 } while (0)
  398 
  399 #define STAILQ_LAST(head, type, field)                          \
  400         (STAILQ_EMPTY((head)) ? NULL :                          \
  401             __containerof((head)->stqh_last,                    \
  402             QUEUE_TYPEOF(type), field.stqe_next))
  403 
  404 #define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
  405 
  406 #define STAILQ_REMOVE(head, elm, type, field) do {                      \
  407         QMD_SAVELINK(oldnext, (elm)->field.stqe_next);                  \
  408         if (STAILQ_FIRST((head)) == (elm)) {                            \
  409                 STAILQ_REMOVE_HEAD((head), field);                      \
  410         }                                                               \
  411         else {                                                          \
  412                 QUEUE_TYPEOF(type) *curelm = STAILQ_FIRST(head);        \
  413                 while (STAILQ_NEXT(curelm, field) != (elm))             \
  414                         curelm = STAILQ_NEXT(curelm, field);            \
  415                 STAILQ_REMOVE_AFTER(head, curelm, field);               \
  416         }                                                               \
  417         TRASHIT(*oldnext);                                              \
  418 } while (0)
  419 
  420 #define STAILQ_REMOVE_AFTER(head, elm, field) do {                      \
  421         if ((STAILQ_NEXT(elm, field) =                                  \
  422              STAILQ_NEXT(STAILQ_NEXT(elm, field), field)) == NULL)      \
  423                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
  424 } while (0)
  425 
  426 #define STAILQ_REMOVE_HEAD(head, field) do {                            \
  427         if ((STAILQ_FIRST((head)) =                                     \
  428              STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL)         \
  429                 (head)->stqh_last = &STAILQ_FIRST((head));              \
  430 } while (0)
  431 
  432 #define STAILQ_SWAP(head1, head2, type) do {                            \
  433         QUEUE_TYPEOF(type) *swap_first = STAILQ_FIRST(head1);           \
  434         QUEUE_TYPEOF(type) **swap_last = (head1)->stqh_last;            \
  435         STAILQ_FIRST(head1) = STAILQ_FIRST(head2);                      \
  436         (head1)->stqh_last = (head2)->stqh_last;                        \
  437         STAILQ_FIRST(head2) = swap_first;                               \
  438         (head2)->stqh_last = swap_last;                                 \
  439         if (STAILQ_EMPTY(head1))                                        \
  440                 (head1)->stqh_last = &STAILQ_FIRST(head1);              \
  441         if (STAILQ_EMPTY(head2))                                        \
  442                 (head2)->stqh_last = &STAILQ_FIRST(head2);              \
  443 } while (0)
  444 
  445 #define STAILQ_END(head)        NULL
  446 
  447 
  448 /*
  449  * List declarations.
  450  */
  451 #define LIST_HEAD(name, type)                                           \
  452 struct name {                                                           \
  453         struct type *lh_first;  /* first element */                     \
  454 }
  455 
  456 #define LIST_CLASS_HEAD(name, type)                                     \
  457 struct name {                                                           \
  458         class type *lh_first;   /* first element */                     \
  459 }
  460 
  461 #define LIST_HEAD_INITIALIZER(head)                                     \
  462         { NULL }
  463 
  464 #define LIST_ENTRY(type)                                                \
  465 struct {                                                                \
  466         struct type *le_next;   /* next element */                      \
  467         struct type **le_prev;  /* address of previous next element */  \
  468 }
  469 
  470 #define LIST_CLASS_ENTRY(type)                                          \
  471 struct {                                                                \
  472         class type *le_next;    /* next element */                      \
  473         class type **le_prev;   /* address of previous next element */  \
  474 }
  475 
  476 /*
  477  * List functions.
  478  */
  479 
  480 #if (defined(_KERNEL) && defined(INVARIANTS))
  481 /*
  482  * QMD_LIST_CHECK_HEAD(LIST_HEAD *head, LIST_ENTRY NAME)
  483  *
  484  * If the list is non-empty, validates that the first element of the list
  485  * points back at 'head.'
  486  */
  487 #define QMD_LIST_CHECK_HEAD(head, field) do {                           \
  488         if (LIST_FIRST((head)) != NULL &&                               \
  489             LIST_FIRST((head))->field.le_prev !=                        \
  490              &LIST_FIRST((head)))                                       \
  491                 panic("Bad list head %p first->prev != head", (head));  \
  492 } while (0)
  493 
  494 /*
  495  * QMD_LIST_CHECK_NEXT(TYPE *elm, LIST_ENTRY NAME)
  496  *
  497  * If an element follows 'elm' in the list, validates that the next element
  498  * points back at 'elm.'
  499  */
  500 #define QMD_LIST_CHECK_NEXT(elm, field) do {                            \
  501         if (LIST_NEXT((elm), field) != NULL &&                          \
  502             LIST_NEXT((elm), field)->field.le_prev !=                   \
  503              &((elm)->field.le_next))                                   \
  504                 panic("Bad link elm %p next->prev != elm", (elm));      \
  505 } while (0)
  506 
  507 /*
  508  * QMD_LIST_CHECK_PREV(TYPE *elm, LIST_ENTRY NAME)
  509  *
  510  * Validates that the previous element (or head of the list) points to 'elm.'
  511  */
  512 #define QMD_LIST_CHECK_PREV(elm, field) do {                            \
  513         if (*(elm)->field.le_prev != (elm))                             \
  514                 panic("Bad link elm %p prev->next != elm", (elm));      \
  515 } while (0)
  516 #else
  517 #define QMD_LIST_CHECK_HEAD(head, field)
  518 #define QMD_LIST_CHECK_NEXT(elm, field)
  519 #define QMD_LIST_CHECK_PREV(elm, field)
  520 #endif /* (_KERNEL && INVARIANTS) */
  521 
  522 #define LIST_CONCAT(head1, head2, type, field) do {                           \
  523         QUEUE_TYPEOF(type) *curelm = LIST_FIRST(head1);                       \
  524         if (curelm == NULL) {                                                 \
  525                 if ((LIST_FIRST(head1) = LIST_FIRST(head2)) != NULL) {        \
  526                         LIST_FIRST(head2)->field.le_prev =                    \
  527                             &LIST_FIRST((head1));                             \
  528                         LIST_INIT(head2);                                     \
  529                 }                                                             \
  530         } else if (LIST_FIRST(head2) != NULL) {                               \
  531                 while (LIST_NEXT(curelm, field) != NULL)                      \
  532                         curelm = LIST_NEXT(curelm, field);                    \
  533                 LIST_NEXT(curelm, field) = LIST_FIRST(head2);                 \
  534                 LIST_FIRST(head2)->field.le_prev = &LIST_NEXT(curelm, field); \
  535                 LIST_INIT(head2);                                             \
  536         }                                                                     \
  537 } while (0)
  538 
  539 #define LIST_EMPTY(head)        ((head)->lh_first == NULL)
  540 
  541 #define LIST_FIRST(head)        ((head)->lh_first)
  542 
  543 #define LIST_FOREACH(var, head, field)                                  \
  544         for ((var) = LIST_FIRST((head));                                \
  545             (var);                                                      \
  546             (var) = LIST_NEXT((var), field))
  547 
  548 #define LIST_FOREACH_FROM(var, head, field)                             \
  549         for ((var) = ((var) ? (var) : LIST_FIRST((head)));              \
  550             (var);                                                      \
  551             (var) = LIST_NEXT((var), field))
  552 
  553 #define LIST_FOREACH_SAFE(var, head, field, tvar)                       \
  554         for ((var) = LIST_FIRST((head));                                \
  555             (var) && ((tvar) = LIST_NEXT((var), field), 1);             \
  556             (var) = (tvar))
  557 
  558 #define LIST_FOREACH_FROM_SAFE(var, head, field, tvar)                  \
  559         for ((var) = ((var) ? (var) : LIST_FIRST((head)));              \
  560             (var) && ((tvar) = LIST_NEXT((var), field), 1);             \
  561             (var) = (tvar))
  562 
  563 #define LIST_INIT(head) do {                                            \
  564         LIST_FIRST((head)) = NULL;                                      \
  565 } while (0)
  566 
  567 #define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
  568         QMD_LIST_CHECK_NEXT(listelm, field);                            \
  569         if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
  570                 LIST_NEXT((listelm), field)->field.le_prev =            \
  571                     &LIST_NEXT((elm), field);                           \
  572         LIST_NEXT((listelm), field) = (elm);                            \
  573         (elm)->field.le_prev = &LIST_NEXT((listelm), field);            \
  574 } while (0)
  575 
  576 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
  577         QMD_LIST_CHECK_PREV(listelm, field);                            \
  578         (elm)->field.le_prev = (listelm)->field.le_prev;                \
  579         LIST_NEXT((elm), field) = (listelm);                            \
  580         *(listelm)->field.le_prev = (elm);                              \
  581         (listelm)->field.le_prev = &LIST_NEXT((elm), field);            \
  582 } while (0)
  583 
  584 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
  585         QMD_LIST_CHECK_HEAD((head), field);                             \
  586         if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)     \
  587                 LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
  588         LIST_FIRST((head)) = (elm);                                     \
  589         (elm)->field.le_prev = &LIST_FIRST((head));                     \
  590 } while (0)
  591 
  592 #define LIST_NEXT(elm, field)   ((elm)->field.le_next)
  593 
  594 #define LIST_PREV(elm, head, type, field)                       \
  595         ((elm)->field.le_prev == &LIST_FIRST((head)) ? NULL :   \
  596             __containerof((elm)->field.le_prev,                 \
  597             QUEUE_TYPEOF(type), field.le_next))
  598 
  599 #define LIST_REMOVE(elm, field) do {                                    \
  600         QMD_SAVELINK(oldnext, (elm)->field.le_next);                    \
  601         QMD_SAVELINK(oldprev, (elm)->field.le_prev);                    \
  602         QMD_LIST_CHECK_NEXT(elm, field);                                \
  603         QMD_LIST_CHECK_PREV(elm, field);                                \
  604         if (LIST_NEXT((elm), field) != NULL)                            \
  605                 LIST_NEXT((elm), field)->field.le_prev =                \
  606                     (elm)->field.le_prev;                               \
  607         *(elm)->field.le_prev = LIST_NEXT((elm), field);                \
  608         TRASHIT(*oldnext);                                              \
  609         TRASHIT(*oldprev);                                              \
  610 } while (0)
  611 
  612 #define LIST_SWAP(head1, head2, type, field) do {                       \
  613         QUEUE_TYPEOF(type) *swap_tmp = LIST_FIRST(head1);               \
  614         LIST_FIRST((head1)) = LIST_FIRST((head2));                      \
  615         LIST_FIRST((head2)) = swap_tmp;                                 \
  616         if ((swap_tmp = LIST_FIRST((head1))) != NULL)                   \
  617                 swap_tmp->field.le_prev = &LIST_FIRST((head1));         \
  618         if ((swap_tmp = LIST_FIRST((head2))) != NULL)                   \
  619                 swap_tmp->field.le_prev = &LIST_FIRST((head2));         \
  620 } while (0)
  621 
  622 #define LIST_END(head)  NULL
  623 
  624 /*
  625  * Tail queue declarations.
  626  */
  627 #define TAILQ_HEAD(name, type)                                          \
  628 struct name {                                                           \
  629         struct type *tqh_first; /* first element */                     \
  630         struct type **tqh_last; /* addr of last next element */         \
  631         TRACEBUF                                                        \
  632 }
  633 
  634 #define TAILQ_CLASS_HEAD(name, type)                                    \
  635 struct name {                                                           \
  636         class type *tqh_first;  /* first element */                     \
  637         class type **tqh_last;  /* addr of last next element */         \
  638         TRACEBUF                                                        \
  639 }
  640 
  641 #define TAILQ_HEAD_INITIALIZER(head)                                    \
  642         { NULL, &(head).tqh_first, TRACEBUF_INITIALIZER }
  643 
  644 #define TAILQ_ENTRY(type)                                               \
  645 struct {                                                                \
  646         struct type *tqe_next;  /* next element */                      \
  647         struct type **tqe_prev; /* address of previous next element */  \
  648         TRACEBUF                                                        \
  649 }
  650 
  651 #define TAILQ_CLASS_ENTRY(type)                                         \
  652 struct {                                                                \
  653         class type *tqe_next;   /* next element */                      \
  654         class type **tqe_prev;  /* address of previous next element */  \
  655         TRACEBUF                                                        \
  656 }
  657 
  658 /*
  659  * Tail queue functions.
  660  */
  661 #if (defined(_KERNEL) && defined(INVARIANTS))
  662 /*
  663  * QMD_TAILQ_CHECK_HEAD(TAILQ_HEAD *head, TAILQ_ENTRY NAME)
  664  *
  665  * If the tailq is non-empty, validates that the first element of the tailq
  666  * points back at 'head.'
  667  */
  668 #define QMD_TAILQ_CHECK_HEAD(head, field) do {                          \
  669         if (!TAILQ_EMPTY(head) &&                                       \
  670             TAILQ_FIRST((head))->field.tqe_prev !=                      \
  671              &TAILQ_FIRST((head)))                                      \
  672                 panic("Bad tailq head %p first->prev != head", (head)); \
  673 } while (0)
  674 
  675 /*
  676  * QMD_TAILQ_CHECK_TAIL(TAILQ_HEAD *head, TAILQ_ENTRY NAME)
  677  *
  678  * Validates that the tail of the tailq is a pointer to pointer to NULL.
  679  */
  680 #define QMD_TAILQ_CHECK_TAIL(head, field) do {                          \
  681         if (*(head)->tqh_last != NULL)                                  \
  682                 panic("Bad tailq NEXT(%p->tqh_last) != NULL", (head));  \
  683 } while (0)
  684 
  685 /*
  686  * QMD_TAILQ_CHECK_NEXT(TYPE *elm, TAILQ_ENTRY NAME)
  687  *
  688  * If an element follows 'elm' in the tailq, validates that the next element
  689  * points back at 'elm.'
  690  */
  691 #define QMD_TAILQ_CHECK_NEXT(elm, field) do {                           \
  692         if (TAILQ_NEXT((elm), field) != NULL &&                         \
  693             TAILQ_NEXT((elm), field)->field.tqe_prev !=                 \
  694              &((elm)->field.tqe_next))                                  \
  695                 panic("Bad link elm %p next->prev != elm", (elm));      \
  696 } while (0)
  697 
  698 /*
  699  * QMD_TAILQ_CHECK_PREV(TYPE *elm, TAILQ_ENTRY NAME)
  700  *
  701  * Validates that the previous element (or head of the tailq) points to 'elm.'
  702  */
  703 #define QMD_TAILQ_CHECK_PREV(elm, field) do {                           \
  704         if (*(elm)->field.tqe_prev != (elm))                            \
  705                 panic("Bad link elm %p prev->next != elm", (elm));      \
  706 } while (0)
  707 #else
  708 #define QMD_TAILQ_CHECK_HEAD(head, field)
  709 #define QMD_TAILQ_CHECK_TAIL(head, headname)
  710 #define QMD_TAILQ_CHECK_NEXT(elm, field)
  711 #define QMD_TAILQ_CHECK_PREV(elm, field)
  712 #endif /* (_KERNEL && INVARIANTS) */
  713 
  714 #define TAILQ_CONCAT(head1, head2, field) do {                          \
  715         if (!TAILQ_EMPTY(head2)) {                                      \
  716                 *(head1)->tqh_last = (head2)->tqh_first;                \
  717                 (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last; \
  718                 (head1)->tqh_last = (head2)->tqh_last;                  \
  719                 TAILQ_INIT((head2));                                    \
  720                 QMD_TRACE_HEAD(head1);                                  \
  721                 QMD_TRACE_HEAD(head2);                                  \
  722         }                                                               \
  723 } while (0)
  724 
  725 #define TAILQ_EMPTY(head)       ((head)->tqh_first == NULL)
  726 
  727 #define TAILQ_FIRST(head)       ((head)->tqh_first)
  728 
  729 #define TAILQ_FOREACH(var, head, field)                                 \
  730         for ((var) = TAILQ_FIRST((head));                               \
  731             (var);                                                      \
  732             (var) = TAILQ_NEXT((var), field))
  733 
  734 #define TAILQ_FOREACH_FROM(var, head, field)                            \
  735         for ((var) = ((var) ? (var) : TAILQ_FIRST((head)));             \
  736             (var);                                                      \
  737             (var) = TAILQ_NEXT((var), field))
  738 
  739 #define TAILQ_FOREACH_SAFE(var, head, field, tvar)                      \
  740         for ((var) = TAILQ_FIRST((head));                               \
  741             (var) && ((tvar) = TAILQ_NEXT((var), field), 1);            \
  742             (var) = (tvar))
  743 
  744 #define TAILQ_FOREACH_FROM_SAFE(var, head, field, tvar)                 \
  745         for ((var) = ((var) ? (var) : TAILQ_FIRST((head)));             \
  746             (var) && ((tvar) = TAILQ_NEXT((var), field), 1);            \
  747             (var) = (tvar))
  748 
  749 #define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
  750         for ((var) = TAILQ_LAST((head), headname);                      \
  751             (var);                                                      \
  752             (var) = TAILQ_PREV((var), headname, field))
  753 
  754 #define TAILQ_FOREACH_REVERSE_FROM(var, head, headname, field)          \
  755         for ((var) = ((var) ? (var) : TAILQ_LAST((head), headname));    \
  756             (var);                                                      \
  757             (var) = TAILQ_PREV((var), headname, field))
  758 
  759 #define TAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar)    \
  760         for ((var) = TAILQ_LAST((head), headname);                      \
  761             (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);  \
  762             (var) = (tvar))
  763 
  764 #define TAILQ_FOREACH_REVERSE_FROM_SAFE(var, head, headname, field, tvar) \
  765         for ((var) = ((var) ? (var) : TAILQ_LAST((head), headname));    \
  766             (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);  \
  767             (var) = (tvar))
  768 
  769 #define TAILQ_INIT(head) do {                                           \
  770         TAILQ_FIRST((head)) = NULL;                                     \
  771         (head)->tqh_last = &TAILQ_FIRST((head));                        \
  772         QMD_TRACE_HEAD(head);                                           \
  773 } while (0)
  774 
  775 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
  776         QMD_TAILQ_CHECK_NEXT(listelm, field);                           \
  777         if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
  778                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
  779                     &TAILQ_NEXT((elm), field);                          \
  780         else {                                                          \
  781                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
  782                 QMD_TRACE_HEAD(head);                                   \
  783         }                                                               \
  784         TAILQ_NEXT((listelm), field) = (elm);                           \
  785         (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);          \
  786         QMD_TRACE_ELEM(&(elm)->field);                                  \
  787         QMD_TRACE_ELEM(&(listelm)->field);                              \
  788 } while (0)
  789 
  790 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
  791         QMD_TAILQ_CHECK_PREV(listelm, field);                           \
  792         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
  793         TAILQ_NEXT((elm), field) = (listelm);                           \
  794         *(listelm)->field.tqe_prev = (elm);                             \
  795         (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);          \
  796         QMD_TRACE_ELEM(&(elm)->field);                                  \
  797         QMD_TRACE_ELEM(&(listelm)->field);                              \
  798 } while (0)
  799 
  800 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
  801         QMD_TAILQ_CHECK_HEAD(head, field);                              \
  802         if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)   \
  803                 TAILQ_FIRST((head))->field.tqe_prev =                   \
  804                     &TAILQ_NEXT((elm), field);                          \
  805         else                                                            \
  806                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
  807         TAILQ_FIRST((head)) = (elm);                                    \
  808         (elm)->field.tqe_prev = &TAILQ_FIRST((head));                   \
  809         QMD_TRACE_HEAD(head);                                           \
  810         QMD_TRACE_ELEM(&(elm)->field);                                  \
  811 } while (0)
  812 
  813 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
  814         QMD_TAILQ_CHECK_TAIL(head, field);                              \
  815         TAILQ_NEXT((elm), field) = NULL;                                \
  816         (elm)->field.tqe_prev = (head)->tqh_last;                       \
  817         *(head)->tqh_last = (elm);                                      \
  818         (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
  819         QMD_TRACE_HEAD(head);                                           \
  820         QMD_TRACE_ELEM(&(elm)->field);                                  \
  821 } while (0)
  822 
  823 #define TAILQ_LAST(head, headname)                                      \
  824         (*(((struct headname *)((head)->tqh_last))->tqh_last))
  825 
  826 /*
  827  * The FAST function is fast in that it causes no data access other
  828  * then the access to the head. The standard LAST function above
  829  * will cause a data access of both the element you want and
  830  * the previous element. FAST is very useful for instances when
  831  * you may want to prefetch the last data element.
  832  */
  833 #define TAILQ_LAST_FAST(head, type, field)                      \
  834     (TAILQ_EMPTY(head) ? NULL : __containerof((head)->tqh_last, QUEUE_TYPEOF(type), field.tqe_next))
  835 
  836 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
  837 
  838 #define TAILQ_PREV(elm, headname, field)                                \
  839         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
  840 
  841 #define TAILQ_PREV_FAST(elm, head, type, field)                         \
  842     ((elm)->field.tqe_prev == &(head)->tqh_first ? NULL :               \
  843      __containerof((elm)->field.tqe_prev, QUEUE_TYPEOF(type), field.tqe_next))
  844 
  845 #define TAILQ_REMOVE(head, elm, field) do {                             \
  846         QMD_SAVELINK(oldnext, (elm)->field.tqe_next);                   \
  847         QMD_SAVELINK(oldprev, (elm)->field.tqe_prev);                   \
  848         QMD_TAILQ_CHECK_NEXT(elm, field);                               \
  849         QMD_TAILQ_CHECK_PREV(elm, field);                               \
  850         if ((TAILQ_NEXT((elm), field)) != NULL)                         \
  851                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
  852                     (elm)->field.tqe_prev;                              \
  853         else {                                                          \
  854                 (head)->tqh_last = (elm)->field.tqe_prev;               \
  855                 QMD_TRACE_HEAD(head);                                   \
  856         }                                                               \
  857         *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);              \
  858         TRASHIT(*oldnext);                                              \
  859         TRASHIT(*oldprev);                                              \
  860         QMD_TRACE_ELEM(&(elm)->field);                                  \
  861 } while (0)
  862 
  863 #define TAILQ_SWAP(head1, head2, type, field) do {                      \
  864         QUEUE_TYPEOF(type) *swap_first = (head1)->tqh_first;            \
  865         QUEUE_TYPEOF(type) **swap_last = (head1)->tqh_last;             \
  866         (head1)->tqh_first = (head2)->tqh_first;                        \
  867         (head1)->tqh_last = (head2)->tqh_last;                          \
  868         (head2)->tqh_first = swap_first;                                \
  869         (head2)->tqh_last = swap_last;                                  \
  870         if ((swap_first = (head1)->tqh_first) != NULL)                  \
  871                 swap_first->field.tqe_prev = &(head1)->tqh_first;       \
  872         else                                                            \
  873                 (head1)->tqh_last = &(head1)->tqh_first;                \
  874         if ((swap_first = (head2)->tqh_first) != NULL)                  \
  875                 swap_first->field.tqe_prev = &(head2)->tqh_first;       \
  876         else                                                            \
  877                 (head2)->tqh_last = &(head2)->tqh_first;                \
  878 } while (0)
  879 
  880 #define TAILQ_END(head)         NULL
  881 
  882 #endif /* !_SYS_QUEUE_H_ */

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