misc/sys/queue.h

   1 /*
   2  * Copyright (c) 1991, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. 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  */
  31
  32 #ifndef _SYS_QUEUE_H_
  33 #define _SYS_QUEUE_H_
  34
  35 /*
  36  * This file defines five types of data structures: singly-linked lists,
  37  * lists, simple queues, tail queues, and circular queues.
  38  *
  39  * A singly-linked list is headed by a single forward pointer. The
  40  * elements are singly linked for minimum space and pointer manipulation
  41  * overhead at the expense of O(n) removal for arbitrary elements. New
  42  * elements can be added to the list after an existing element or at the
  43  * head of the list.  Elements being removed from the head of the list
  44  * should use the explicit macro for this purpose for optimum
  45  * efficiency. A singly-linked list may only be traversed in the forward
  46  * direction.  Singly-linked lists are ideal for applications with large
  47  * datasets and few or no removals or for implementing a LIFO queue.
  48  *
  49  * A list is headed by a single forward pointer (or an array of forward
  50  * pointers for a hash table header). The elements are doubly linked
  51  * so that an arbitrary element can be removed without a need to
  52  * traverse the list. New elements can be added to the list before
  53  * or after an existing element or at the head of the list. A list
  54  * may only be traversed in the forward direction.
  55  *
  56  * A simple queue is headed by a pair of pointers, one the head of the
  57  * list and the other to the tail of the list. The elements are singly
  58  * linked to save space, so elements can only be removed from the
  59  * head of the list. New elements can be added to the list after
  60  * an existing element, at the head of the list, or at the end of the
  61  * list. A simple queue may only be traversed in the forward direction.
  62  *
  63  * A tail queue is headed by a pair of pointers, one to the head of the
  64  * list and the other to the tail of the list. The elements are doubly
  65  * linked 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 or
  67  * after an existing element, at the head of the list, or at the end of
  68  * the list. A tail queue may be traversed in either direction.
  69  *
  70  * A circle 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 after
  74  * an existing element, at the head of the list, or at the end of the list.
  75  * A circle queue may be traversed in either direction, but has a more
  76  * complex end of list detection.
  77  *
  78  * For details on the use of these macros, see the queue(3) manual page.
  79  */
  80
  81 /*
  82  * List definitions.
  83  */
  84 #define LIST_HEAD(name, type)                                           \
  85 struct name {                                                           \
  86         struct type *lh_first;  /* first element */                     \
  87 }
  88
  89 #define LIST_HEAD_INITIALIZER(head)                                     \
  90         { NULL }
  91
  92 #define LIST_ENTRY(type)                                                \
  93 struct {                                                                \
  94         struct type *le_next;   /* next element */                      \
  95         struct type **le_prev;  /* address of previous next element */  \
  96 }
  97
  98 /*
  99  * List functions.
 100  */
 101 #define LIST_INIT(head) do {                                            \
 102         (head)->lh_first = NULL;                                        \
 103 } while (/*CONSTCOND*/0)
 104
 105 #define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
 106         QUEUEDEBUG_LIST_OP((listelm), field)                            \
 107         if (((elm)->field.le_next = (listelm)->field.le_next) != NULL)  \
 108                 (listelm)->field.le_next->field.le_prev =               \
 109                     &(elm)->field.le_next;                              \
 110         (listelm)->field.le_next = (elm);                               \
 111         (elm)->field.le_prev = &(listelm)->field.le_next;               \
 112 } while (/*CONSTCOND*/0)
 113
 114 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
 115         QUEUEDEBUG_LIST_OP((listelm), field)                            \
 116         (elm)->field.le_prev = (listelm)->field.le_prev;                \
 117         (elm)->field.le_next = (listelm);                               \
 118         *(listelm)->field.le_prev = (elm);                              \
 119         (listelm)->field.le_prev = &(elm)->field.le_next;               \
 120 } while (/*CONSTCOND*/0)
 121
 122 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
 123         QUEUEDEBUG_LIST_INSERT_HEAD((head), (elm), field)               \
 124         if (((elm)->field.le_next = (head)->lh_first) != NULL)          \
 125                 (head)->lh_first->field.le_prev = &(elm)->field.le_next;\
 126         (head)->lh_first = (elm);                                       \
 127         (elm)->field.le_prev = &(head)->lh_first;                       \
 128 } while (/*CONSTCOND*/0)
 129
 130 #define LIST_REMOVE(elm, field) do {                                    \
 131         QUEUEDEBUG_LIST_OP((elm), field)                                \
 132         if ((elm)->field.le_next != NULL)                               \
 133                 (elm)->field.le_next->field.le_prev =                   \
 134                     (elm)->field.le_prev;                               \
 135         *(elm)->field.le_prev = (elm)->field.le_next;                   \
 136         QUEUEDEBUG_LIST_POSTREMOVE((elm), field)                        \
 137 } while (/*CONSTCOND*/0)
 138
 139 #define LIST_FOREACH(var, head, field)                                  \
 140         for ((var) = ((head)->lh_first);                                \
 141                 (var);                                                  \
 142                 (var) = ((var)->field.le_next))
 143
 144 /*
 145  * List access methods.
 146  */
 147 #define LIST_EMPTY(head)                ((head)->lh_first == NULL)
 148 #define LIST_FIRST(head)                ((head)->lh_first)
 149 #define LIST_NEXT(elm, field)           ((elm)->field.le_next)
 150
 151
 152 /*
 153  * Singly-linked List definitions.
 154  */
 155 #define SLIST_HEAD(name, type)                                          \
 156 struct name {                                                           \
 157         struct type *slh_first; /* first element */                     \
 158 }
 159
 160 #define SLIST_HEAD_INITIALIZER(head)                                    \
 161         { NULL }
 162
 163 #define SLIST_ENTRY(type)                                               \
 164 struct {                                                                \
 165         struct type *sle_next;  /* next element */                      \
 166 }
 167
 168 /*
 169  * Singly-linked List functions.
 170  */
 171 #define SLIST_INIT(head) do {                                           \
 172         (head)->slh_first = NULL;                                       \
 173 } while (/*CONSTCOND*/0)
 174
 175 #define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
 176         (elm)->field.sle_next = (slistelm)->field.sle_next;             \
 177         (slistelm)->field.sle_next = (elm);                             \
 178 } while (/*CONSTCOND*/0)
 179
 180 #define SLIST_INSERT_HEAD(head, elm, field) do {                        \
 181         (elm)->field.sle_next = (head)->slh_first;                      \
 182         (head)->slh_first = (elm);                                      \
 183 } while (/*CONSTCOND*/0)
 184
 185 #define SLIST_REMOVE_HEAD(head, field) do {                             \
 186         (head)->slh_first = (head)->slh_first->field.sle_next;          \
 187 } while (/*CONSTCOND*/0)
 188
 189 #define SLIST_REMOVE(head, elm, type, field) do {                       \
 190         if ((head)->slh_first == (elm)) {                               \
 191                 SLIST_REMOVE_HEAD((head), field);                       \
 192         }                                                               \
 193         else {                                                          \
 194                 struct type *curelm = (head)->slh_first;                \
 195                 while(curelm->field.sle_next != (elm))                  \
 196                         curelm = curelm->field.sle_next;                \
 197                 curelm->field.sle_next =                                \
 198                     curelm->field.sle_next->field.sle_next;             \
 199         }                                                               \
 200 } while (/*CONSTCOND*/0)
 201
 202 #define SLIST_FOREACH(var, head, field)                                 \
 203         for((var) = (head)->slh_first; (var); (var) = (var)->field.sle_next)
 204
 205 /*
 206  * Singly-linked List access methods.
 207  */
 208 #define SLIST_EMPTY(head)       ((head)->slh_first == NULL)
 209 #define SLIST_FIRST(head)       ((head)->slh_first)
 210 #define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)
 211
 212
 213 /*
 214  * Singly-linked Tail queue declarations.
 215  */
 216 #define STAILQ_HEAD(name, type)                                 \
 217 struct name {                                                           \
 218         struct type *stqh_first;        /* first element */                     \
 219         struct type **stqh_last;        /* addr of last next element */         \
 220 }
 221
 222 #define STAILQ_HEAD_INITIALIZER(head)                                   \
 223         { NULL, &(head).stqh_first }
 224
 225 #define STAILQ_ENTRY(type)                                              \
 226 struct {                                                                \
 227         struct type *stqe_next; /* next element */                      \
 228 }
 229
 230 /*
 231  * Singly-linked Tail queue functions.
 232  */
 233 #define STAILQ_INIT(head) do {                                          \
 234         (head)->stqh_first = NULL;                                      \
 235         (head)->stqh_last = &(head)->stqh_first;                                \
 236 } while (/*CONSTCOND*/0)
 237
 238 #define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
 239         if (((elm)->field.stqe_next = (head)->stqh_first) == NULL)      \
 240                 (head)->stqh_last = &(elm)->field.stqe_next;            \
 241         (head)->stqh_first = (elm);                                     \
 242 } while (/*CONSTCOND*/0)
 243
 244 #define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
 245         (elm)->field.stqe_next = NULL;                                  \
 246         *(head)->stqh_last = (elm);                                     \
 247         (head)->stqh_last = &(elm)->field.stqe_next;                    \
 248 } while (/*CONSTCOND*/0)
 249
 250 #define STAILQ_INSERT_AFTER(head, listelm, elm, field) do {             \
 251         if (((elm)->field.stqe_next = (listelm)->field.stqe_next) == NULL)\
 252                 (head)->stqh_last = &(elm)->field.stqe_next;            \
 253         (listelm)->field.stqe_next = (elm);                             \
 254 } while (/*CONSTCOND*/0)
 255
 256 #define STAILQ_REMOVE_HEAD(head, field) do {                            \
 257         if (((head)->stqh_first = (head)->stqh_first->field.stqe_next) == NULL) \
 258                 (head)->stqh_last = &(head)->stqh_first;                        \
 259 } while (/*CONSTCOND*/0)
 260
 261 #define STAILQ_REMOVE(head, elm, type, field) do {                      \
 262         if ((head)->stqh_first == (elm)) {                              \
 263                 STAILQ_REMOVE_HEAD((head), field);                      \
 264         } else {                                                        \
 265                 struct type *curelm = (head)->stqh_first;               \
 266                 while (curelm->field.stqe_next != (elm))                        \
 267                         curelm = curelm->field.stqe_next;               \
 268                 if ((curelm->field.stqe_next =                          \
 269                         curelm->field.stqe_next->field.stqe_next) == NULL) \
 270                             (head)->stqh_last = &(curelm)->field.stqe_next; \
 271         }                                                               \
 272 } while (/*CONSTCOND*/0)
 273
 274 #define STAILQ_FOREACH(var, head, field)                                \
 275         for ((var) = ((head)->stqh_first);                              \
 276                 (var);                                                  \
 277                 (var) = ((var)->field.stqe_next))
 278
 279 /*
 280  * Singly-linked Tail queue access methods.
 281  */
 282 #define STAILQ_EMPTY(head)      ((head)->stqh_first == NULL)
 283 #define STAILQ_FIRST(head)      ((head)->stqh_first)
 284 #define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
 285
 286
 287 /*
 288  * Simple queue definitions.
 289  */
 290 #define SIMPLEQ_HEAD(name, type)                                        \
 291 struct name {                                                           \
 292         struct type *sqh_first; /* first element */                     \
 293         struct type **sqh_last; /* addr of last next element */         \
 294 }
 295
 296 #define SIMPLEQ_HEAD_INITIALIZER(head)                                  \
 297         { NULL, &(head).sqh_first }
 298
 299 #define SIMPLEQ_ENTRY(type)                                             \
 300 struct {                                                                \
 301         struct type *sqe_next;  /* next element */                      \
 302 }
 303
 304 /*
 305  * Simple queue functions.
 306  */
 307 #define SIMPLEQ_INIT(head) do {                                         \
 308         (head)->sqh_first = NULL;                                       \
 309         (head)->sqh_last = &(head)->sqh_first;                          \
 310 } while (/*CONSTCOND*/0)
 311
 312 #define SIMPLEQ_INSERT_HEAD(head, elm, field) do {                      \
 313         if (((elm)->field.sqe_next = (head)->sqh_first) == NULL)        \
 314                 (head)->sqh_last = &(elm)->field.sqe_next;              \
 315         (head)->sqh_first = (elm);                                      \
 316 } while (/*CONSTCOND*/0)
 317
 318 #define SIMPLEQ_INSERT_TAIL(head, elm, field) do {                      \
 319         (elm)->field.sqe_next = NULL;                                   \
 320         *(head)->sqh_last = (elm);                                      \
 321         (head)->sqh_last = &(elm)->field.sqe_next;                      \
 322 } while (/*CONSTCOND*/0)
 323
 324 #define SIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do {            \
 325         if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL)\
 326                 (head)->sqh_last = &(elm)->field.sqe_next;              \
 327         (listelm)->field.sqe_next = (elm);                              \
 328 } while (/*CONSTCOND*/0)
 329
 330 #define SIMPLEQ_REMOVE_HEAD(head, field) do {                           \
 331         if (((head)->sqh_first = (head)->sqh_first->field.sqe_next) == NULL) \
 332                 (head)->sqh_last = &(head)->sqh_first;                  \
 333 } while (/*CONSTCOND*/0)
 334
 335 #define SIMPLEQ_REMOVE(head, elm, type, field) do {                     \
 336         if ((head)->sqh_first == (elm)) {                               \
 337                 SIMPLEQ_REMOVE_HEAD((head), field);                     \
 338         } else {                                                        \
 339                 struct type *curelm = (head)->sqh_first;                \
 340                 while (curelm->field.sqe_next != (elm))                 \
 341                         curelm = curelm->field.sqe_next;                \
 342                 if ((curelm->field.sqe_next =                           \
 343                         curelm->field.sqe_next->field.sqe_next) == NULL) \
 344                             (head)->sqh_last = &(curelm)->field.sqe_next; \
 345         }                                                               \
 346 } while (/*CONSTCOND*/0)
 347
 348 #define SIMPLEQ_FOREACH(var, head, field)                               \
 349         for ((var) = ((head)->sqh_first);                               \
 350                 (var);                                                  \
 351                 (var) = ((var)->field.sqe_next))
 352
 353 /*
 354  * Simple queue access methods.
 355  */
 356 #define SIMPLEQ_EMPTY(head)             ((head)->sqh_first == NULL)
 357 #define SIMPLEQ_FIRST(head)             ((head)->sqh_first)
 358 #define SIMPLEQ_NEXT(elm, field)        ((elm)->field.sqe_next)
 359
 360
 361 /*
 362  * Tail queue definitions.
 363  */
 364 #define _TAILQ_HEAD(name, type, qual)                                   \
 365 struct name {                                                           \
 366         qual type *tqh_first;           /* first element */             \
 367         qual type *qual *tqh_last;      /* addr of last next element */ \
 368 }
 369 #define TAILQ_HEAD(name, type)  _TAILQ_HEAD(name, struct type,)
 370
 371 #define TAILQ_HEAD_INITIALIZER(head)                                    \
 372         { NULL, &(head).tqh_first }
 373
 374 #define _TAILQ_ENTRY(type, qual)                                        \
 375 struct {                                                                \
 376         qual type *tqe_next;            /* next element */              \
 377         qual type *qual *tqe_prev;      /* address of previous next element */\
 378 }
 379 #define TAILQ_ENTRY(type)       _TAILQ_ENTRY(struct type,)
 380
 381 /*
 382  * Tail queue functions.
 383  */
 384 #define TAILQ_INIT(head) do {                                           \
 385         (head)->tqh_first = NULL;                                       \
 386         (head)->tqh_last = &(head)->tqh_first;                          \
 387 } while (/*CONSTCOND*/0)
 388
 389 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
 390         QUEUEDEBUG_TAILQ_INSERT_HEAD((head), (elm), field)              \
 391         if (((elm)->field.tqe_next = (head)->tqh_first) != NULL)        \
 392                 (head)->tqh_first->field.tqe_prev =                     \
 393                     &(elm)->field.tqe_next;                             \
 394         else                                                            \
 395                 (head)->tqh_last = &(elm)->field.tqe_next;              \
 396         (head)->tqh_first = (elm);                                      \
 397         (elm)->field.tqe_prev = &(head)->tqh_first;                     \
 398 } while (/*CONSTCOND*/0)
 399
 400 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
 401         QUEUEDEBUG_TAILQ_INSERT_TAIL((head), (elm), field)              \
 402         (elm)->field.tqe_next = NULL;                                   \
 403         (elm)->field.tqe_prev = (head)->tqh_last;                       \
 404         *(head)->tqh_last = (elm);                                      \
 405         (head)->tqh_last = &(elm)->field.tqe_next;                      \
 406 } while (/*CONSTCOND*/0)
 407
 408 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
 409         QUEUEDEBUG_TAILQ_OP((listelm), field)                           \
 410         if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)\
 411                 (elm)->field.tqe_next->field.tqe_prev =                 \
 412                     &(elm)->field.tqe_next;                             \
 413         else                                                            \
 414                 (head)->tqh_last = &(elm)->field.tqe_next;              \
 415         (listelm)->field.tqe_next = (elm);                              \
 416         (elm)->field.tqe_prev = &(listelm)->field.tqe_next;             \
 417 } while (/*CONSTCOND*/0)
 418
 419 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
 420         QUEUEDEBUG_TAILQ_OP((listelm), field)                           \
 421         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
 422         (elm)->field.tqe_next = (listelm);                              \
 423         *(listelm)->field.tqe_prev = (elm);                             \
 424         (listelm)->field.tqe_prev = &(elm)->field.tqe_next;             \
 425 } while (/*CONSTCOND*/0)
 426
 427 #define TAILQ_REMOVE(head, elm, field) do {                             \
 428         QUEUEDEBUG_TAILQ_PREREMOVE((head), (elm), field)                \
 429         QUEUEDEBUG_TAILQ_OP((elm), field)                               \
 430         if (((elm)->field.tqe_next) != NULL)                            \
 431                 (elm)->field.tqe_next->field.tqe_prev =                 \
 432                     (elm)->field.tqe_prev;                              \
 433         else                                                            \
 434                 (head)->tqh_last = (elm)->field.tqe_prev;               \
 435         *(elm)->field.tqe_prev = (elm)->field.tqe_next;                 \
 436         QUEUEDEBUG_TAILQ_POSTREMOVE((elm), field);                      \
 437 } while (/*CONSTCOND*/0)
 438
 439 #define TAILQ_FOREACH(var, head, field)                                 \
 440         for ((var) = ((head)->tqh_first);                               \
 441                 (var);                                                  \
 442                 (var) = ((var)->field.tqe_next))
 443
 444 #define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
 445         for ((var) = (*(((struct headname *)((head)->tqh_last))->tqh_last));    \
 446                 (var);                                                  \
 447                 (var) = (*(((struct headname *)((var)->field.tqe_prev))->tqh_last)))
 448
 449 /*
 450  * Tail queue access methods.
 451  */
 452 #define TAILQ_EMPTY(head)               ((head)->tqh_first == NULL)
 453 #define TAILQ_FIRST(head)               ((head)->tqh_first)
 454 #define TAILQ_NEXT(elm, field)          ((elm)->field.tqe_next)
 455
 456 #define TAILQ_LAST(head, headname) \
 457         (*(((struct headname *)((head)->tqh_last))->tqh_last))
 458 #define TAILQ_PREV(elm, headname, field) \
 459         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
 460
 461
 462 /*
 463  * Circular queue definitions.
 464  */
 465 #define CIRCLEQ_HEAD(name, type)                                        \
 466 struct name {                                                           \
 467         struct type *cqh_first;         /* first element */             \
 468         struct type *cqh_last;          /* last element */              \
 469 }
 470
 471 #define CIRCLEQ_HEAD_INITIALIZER(head)                                  \
 472         { (void *)&head, (void *)&head }
 473
 474 #define CIRCLEQ_ENTRY(type)                                             \
 475 struct {                                                                \
 476         struct type *cqe_next;          /* next element */              \
 477         struct type *cqe_prev;          /* previous element */          \
 478 }
 479
 480 /*
 481  * Circular queue functions.
 482  */
 483 #define CIRCLEQ_INIT(head) do {                                         \
 484         (head)->cqh_first = (void *)(head);                             \
 485         (head)->cqh_last = (void *)(head);                              \
 486 } while (/*CONSTCOND*/0)
 487
 488 #define CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {            \
 489         QUEUEDEBUG_CIRCLEQ_HEAD((head), field)                          \
 490         QUEUEDEBUG_CIRCLEQ_ELM((head), (listelm), field)                \
 491         (elm)->field.cqe_next = (listelm)->field.cqe_next;              \
 492         (elm)->field.cqe_prev = (listelm);                              \
 493         if ((listelm)->field.cqe_next == (void *)(head))                \
 494                 (head)->cqh_last = (elm);                               \
 495         else                                                            \
 496                 (listelm)->field.cqe_next->field.cqe_prev = (elm);      \
 497         (listelm)->field.cqe_next = (elm);                              \
 498 } while (/*CONSTCOND*/0)
 499
 500 #define CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do {           \
 501         QUEUEDEBUG_CIRCLEQ_HEAD((head), field)                          \
 502         QUEUEDEBUG_CIRCLEQ_ELM((head), (listelm), field)                \
 503         (elm)->field.cqe_next = (listelm);                              \
 504         (elm)->field.cqe_prev = (listelm)->field.cqe_prev;              \
 505         if ((listelm)->field.cqe_prev == (void *)(head))                \
 506                 (head)->cqh_first = (elm);                              \
 507         else                                                            \
 508                 (listelm)->field.cqe_prev->field.cqe_next = (elm);      \
 509         (listelm)->field.cqe_prev = (elm);                              \
 510 } while (/*CONSTCOND*/0)
 511
 512 #define CIRCLEQ_INSERT_HEAD(head, elm, field) do {                      \
 513         QUEUEDEBUG_CIRCLEQ_HEAD((head), field)                          \
 514         (elm)->field.cqe_next = (head)->cqh_first;                      \
 515         (elm)->field.cqe_prev = (void *)(head);                         \
 516         if ((head)->cqh_last == (void *)(head))                         \
 517                 (head)->cqh_last = (elm);                               \
 518         else                                                            \
 519                 (head)->cqh_first->field.cqe_prev = (elm);              \
 520         (head)->cqh_first = (elm);                                      \
 521 } while (/*CONSTCOND*/0)
 522
 523 #define CIRCLEQ_INSERT_TAIL(head, elm, field) do {                      \
 524         QUEUEDEBUG_CIRCLEQ_HEAD((head), field)                          \
 525         (elm)->field.cqe_next = (void *)(head);                         \
 526         (elm)->field.cqe_prev = (head)->cqh_last;                       \
 527         if ((head)->cqh_first == (void *)(head))                        \
 528                 (head)->cqh_first = (elm);                              \
 529         else                                                            \
 530                 (head)->cqh_last->field.cqe_next = (elm);               \
 531         (head)->cqh_last = (elm);                                       \
 532 } while (/*CONSTCOND*/0)
 533
 534 #define CIRCLEQ_REMOVE(head, elm, field) do {                           \
 535         QUEUEDEBUG_CIRCLEQ_HEAD((head), field)                          \
 536         QUEUEDEBUG_CIRCLEQ_ELM((head), (elm), field)                    \
 537         if ((elm)->field.cqe_next == (void *)(head))                    \
 538                 (head)->cqh_last = (elm)->field.cqe_prev;               \
 539         else                                                            \
 540                 (elm)->field.cqe_next->field.cqe_prev =                 \
 541                     (elm)->field.cqe_prev;                              \
 542         if ((elm)->field.cqe_prev == (void *)(head))                    \
 543                 (head)->cqh_first = (elm)->field.cqe_next;              \
 544         else                                                            \
 545                 (elm)->field.cqe_prev->field.cqe_next =                 \
 546                     (elm)->field.cqe_next;                              \
 547         QUEUEDEBUG_CIRCLEQ_POSTREMOVE((elm), field)                     \
 548 } while (/*CONSTCOND*/0)
 549
 550 #define CIRCLEQ_FOREACH(var, head, field)                               \
 551         for ((var) = ((head)->cqh_first);                               \
 552                 (var) != (const void *)(head);                          \
 553                 (var) = ((var)->field.cqe_next))
 554
 555 #define CIRCLEQ_FOREACH_REVERSE(var, head, field)                       \
 556         for ((var) = ((head)->cqh_last);                                \
 557                 (var) != (const void *)(head);                          \
 558                 (var) = ((var)->field.cqe_prev))
 559
 560 /*
 561  * Circular queue access methods.
 562  */
 563 #define CIRCLEQ_EMPTY(head)             ((head)->cqh_first == (void *)(head))
 564 #define CIRCLEQ_FIRST(head)             ((head)->cqh_first)
 565 #define CIRCLEQ_LAST(head)              ((head)->cqh_last)
 566 #define CIRCLEQ_NEXT(elm, field)        ((elm)->field.cqe_next)
 567 #define CIRCLEQ_PREV(elm, field)        ((elm)->field.cqe_prev)
 568
 569 #define CIRCLEQ_LOOP_NEXT(head, elm, field)                             \
 570         (((elm)->field.cqe_next == (void *)(head))                      \
 571             ? ((head)->cqh_first)                                       \
 572             : (elm->field.cqe_next))
 573 #define CIRCLEQ_LOOP_PREV(head, elm, field)                             \
 574         (((elm)->field.cqe_prev == (void *)(head))                      \
 575             ? ((head)->cqh_last)                                        \
 576             : (elm->field.cqe_prev))
 577
 578 #endif  /* sys/queue.h */