sys/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. All advertising materials mentioning features or use of this software
  14  *    must display the following acknowledgement:
  15  *      This product includes software developed by the University of
  16  *      California, Berkeley and its contributors.
  17  * 4. Neither the name of the University nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  *
  33  *      @(#)queue.h     8.5 (Berkeley) 8/20/94
  34  * $FreeBSD: src/sys/sys/queue.h,v 1.32.2.7 2002/04/17 14:21:02 des Exp $
  35  * $DragonFly: src/sys/sys/queue.h,v 1.8 2007/01/08 12:15:27 swildner Exp $
  36  */
  37
  38 #ifndef _SYS_QUEUE_H_
  39 #define _SYS_QUEUE_H_
  40
  41 #ifndef _MACHINE_STDINT_H_
  42 #include <machine/stdint.h>     /* for __offsetof */
  43 #endif
  44
  45 /*
  46  * This file defines five types of data structures: singly-linked lists,
  47  * singly-linked tail queues, lists, tail queues, and circular queues.
  48  *
  49  * A singly-linked list is headed by a single forward pointer. The elements
  50  * are singly linked for minimum space and pointer manipulation overhead at
  51  * the expense of O(n) removal for arbitrary elements. New elements can be
  52  * added to the list after an existing element or at the head of the list.
  53  * Elements being removed from the head of the list should use the explicit
  54  * macro for this purpose for optimum efficiency. A singly-linked list may
  55  * only be traversed in the forward direction.  Singly-linked lists are ideal
  56  * for applications with large datasets and few or no removals or for
  57  * implementing a LIFO queue.
  58  *
  59  * A singly-linked tail queue is headed by a pair of pointers, one to the
  60  * head of the list and the other to the tail of the list. The elements are
  61  * singly linked for minimum space and pointer manipulation overhead at the
  62  * expense of O(n) removal for arbitrary elements. New elements can be added
  63  * to the list after an existing element, at the head of the list, or at the
  64  * end of the list. Elements being removed from the head of the tail queue
  65  * should use the explicit macro for this purpose for optimum efficiency.
  66  * A singly-linked tail queue may only be traversed in the forward direction.
  67  * Singly-linked tail queues are ideal for applications with large datasets
  68  * and few or no removals or for implementing a FIFO queue.
  69  *
  70  * A list is headed by a single forward pointer (or an array of forward
  71  * pointers for a hash table header). The elements are doubly linked
  72  * 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
  74  * or after an existing element or at the head of the list. A list
  75  * may only be traversed in the forward direction.
  76  *
  77  * A tail queue is headed by a pair of pointers, one to the head of the
  78  * list and the other to the tail of the list. The elements are doubly
  79  * linked so that an arbitrary element can be removed without a need to
  80  * traverse the list. New elements can be added to the list before or
  81  * after an existing element, at the head of the list, or at the end of
  82  * the list. A tail queue may be traversed in either direction.
  83  *
  84  * A circle queue is headed by a pair of pointers, one to the head of the
  85  * list and the other to the tail of the list. The elements are doubly
  86  * linked so that an arbitrary element can be removed without a need to
  87  * traverse the list. New elements can be added to the list before or after
  88  * an existing element, at the head of the list, or at the end of the list.
  89  * A circle queue may be traversed in either direction, but has a more
  90  * complex end of list detection.
  91  *
  92  * For details on the use of these macros, see the queue(3) manual page.
  93  *
  94  *
  95  *                      SLIST   LIST    STAILQ  TAILQ   CIRCLEQ
  96  * _HEAD                +       +       +       +       +
  97  * _HEAD_INITIALIZER    +       +       +       +       +
  98  * _ENTRY               +       +       +       +       +
  99  * _INIT                +       +       +       +       +
 100  * _EMPTY               +       +       +       +       +
 101  * _FIRST               +       +       +       +       +
 102  * _NEXT                +       +       +       +       +
 103  * _PREV                -       -       -       +       +
 104  * _LAST                -       -       +       +       +
 105  * _FOREACH             +       +       +       +       +
 106  * _FOREACH_MUTABLE     -       +       -       +       -
 107  * _FOREACH_REVERSE     -       -       -       +       +
 108  * _INSERT_HEAD         +       +       +       +       +
 109  * _INSERT_BEFORE       -       +       -       +       +
 110  * _INSERT_AFTER        +       +       +       +       +
 111  * _INSERT_TAIL         -       -       +       +       +
 112  * _CONCAT              -       -       +       +       -
 113  * _REMOVE_HEAD         +       -       +       -       -
 114  * _REMOVE              +       +       +       +       +
 115  *
 116  */
 117
 118 /*
 119  * Singly-linked List declarations.
 120  */
 121 #define SLIST_HEAD(name, type)                                          \
 122 struct name {                                                           \
 123         struct type *slh_first; /* first element */                     \
 124 }
 125
 126 #define SLIST_HEAD_INITIALIZER(head)                                    \
 127         { NULL }
 128
 129 #define SLIST_ENTRY(type)                                               \
 130 struct {                                                                \
 131         struct type *sle_next;  /* next element */                      \
 132 }
 133
 134 #define SLIST_ENTRY_INITIALIZER { NULL }
 135
 136 /*
 137  * Singly-linked List functions.
 138  */
 139 #define SLIST_EMPTY(head)       ((head)->slh_first == NULL)
 140
 141 #define SLIST_FIRST(head)       ((head)->slh_first)
 142
 143 #define SLIST_FOREACH(var, head, field)                                 \
 144         for ((var) = SLIST_FIRST((head));                               \
 145             (var);                                                      \
 146             (var) = SLIST_NEXT((var), field))
 147
 148 #define SLIST_INIT(head) do {                                           \
 149         SLIST_FIRST((head)) = NULL;                                     \
 150 } while (0)
 151
 152 #define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
 153         SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);       \
 154         SLIST_NEXT((slistelm), field) = (elm);                          \
 155 } while (0)
 156
 157 #define SLIST_INSERT_HEAD(head, elm, field) do {                        \
 158         SLIST_NEXT((elm), field) = SLIST_FIRST((head));                 \
 159         SLIST_FIRST((head)) = (elm);                                    \
 160 } while (0)
 161
 162 #define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)
 163
 164 #define SLIST_REMOVE(head, elm, type, field) do {                       \
 165         if (SLIST_FIRST((head)) == (elm)) {                             \
 166                 SLIST_REMOVE_HEAD((head), field);                       \
 167         }                                                               \
 168         else {                                                          \
 169                 struct type *curelm = SLIST_FIRST((head));              \
 170                 while (SLIST_NEXT(curelm, field) != (elm))              \
 171                         curelm = SLIST_NEXT(curelm, field);             \
 172                 SLIST_NEXT(curelm, field) =                             \
 173                     SLIST_NEXT(SLIST_NEXT(curelm, field), field);       \
 174         }                                                               \
 175 } while (0)
 176
 177 #define SLIST_REMOVE_HEAD(head, field) do {                             \
 178         SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);   \
 179 } while (0)
 180
 181 /*
 182  * Singly-linked Tail queue declarations.
 183  */
 184 #define STAILQ_HEAD(name, type)                                         \
 185 struct name {                                                           \
 186         struct type *stqh_first;/* first element */                     \
 187         struct type **stqh_last;/* addr of last next element */         \
 188 }
 189
 190 #define STAILQ_HEAD_INITIALIZER(head)                                   \
 191         { NULL, &(head).stqh_first }
 192
 193 #define STAILQ_ENTRY(type)                                              \
 194 struct {                                                                \
 195         struct type *stqe_next; /* next element */                      \
 196 }
 197
 198 /*
 199  * Singly-linked Tail queue functions.
 200  */
 201 #define STAILQ_CONCAT(head1, head2) do {                                \
 202         if (!STAILQ_EMPTY((head2))) {                                   \
 203                 *(head1)->stqh_last = (head2)->stqh_first;              \
 204                 (head1)->stqh_last = (head2)->stqh_last;                \
 205                 STAILQ_INIT((head2));                                   \
 206         }                                                               \
 207 } while (0)
 208
 209 #define STAILQ_EMPTY(head)      ((head)->stqh_first == NULL)
 210
 211 #define STAILQ_FIRST(head)      ((head)->stqh_first)
 212
 213 #define STAILQ_FOREACH(var, head, field)                                \
 214         for((var) = STAILQ_FIRST((head));                               \
 215            (var);                                                       \
 216            (var) = STAILQ_NEXT((var), field))
 217
 218 #define STAILQ_INIT(head) do {                                          \
 219         STAILQ_FIRST((head)) = NULL;                                    \
 220         (head)->stqh_last = &STAILQ_FIRST((head));                      \
 221 } while (0)
 222
 223 #define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {               \
 224         if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
 225                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 226         STAILQ_NEXT((tqelm), field) = (elm);                            \
 227 } while (0)
 228
 229 #define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
 230         if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL) \
 231                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 232         STAILQ_FIRST((head)) = (elm);                                   \
 233 } while (0)
 234
 235 #define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
 236         STAILQ_NEXT((elm), field) = NULL;                               \
 237         *(head)->stqh_last = (elm);                                     \
 238         (head)->stqh_last = &STAILQ_NEXT((elm), field);                 \
 239 } while (0)
 240
 241 #define STAILQ_LAST(head, type, field)                                  \
 242         (STAILQ_EMPTY(head) ?                                           \
 243                 NULL :                                                  \
 244                 ((struct type *)                                        \
 245                 ((char *)((head)->stqh_last) - __offsetof(struct type, field))))
 246
 247 #define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
 248
 249 #define STAILQ_REMOVE(head, elm, type, field) do {                      \
 250         if (STAILQ_FIRST((head)) == (elm)) {                            \
 251                 STAILQ_REMOVE_HEAD(head, field);                        \
 252         }                                                               \
 253         else {                                                          \
 254                 struct type *curelm = STAILQ_FIRST((head));             \
 255                 while (STAILQ_NEXT(curelm, field) != (elm))             \
 256                         curelm = STAILQ_NEXT(curelm, field);            \
 257                 if ((STAILQ_NEXT(curelm, field) =                       \
 258                      STAILQ_NEXT(STAILQ_NEXT(curelm, field), field)) == NULL)\
 259                         (head)->stqh_last = &STAILQ_NEXT((curelm), field);\
 260         }                                                               \
 261 } while (0)
 262
 263 #define STAILQ_REMOVE_HEAD(head, field) do {                            \
 264         if ((STAILQ_FIRST((head)) =                                     \
 265              STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL)         \
 266                 (head)->stqh_last = &STAILQ_FIRST((head));              \
 267 } while (0)
 268
 269 #define STAILQ_REMOVE_HEAD_UNTIL(head, elm, field) do {                 \
 270         if ((STAILQ_FIRST((head)) = STAILQ_NEXT((elm), field)) == NULL) \
 271                 (head)->stqh_last = &STAILQ_FIRST((head));              \
 272 } while (0)
 273
 274 /*
 275  * List declarations.
 276  */
 277 #define LIST_HEAD(name, type)                                           \
 278 struct name {                                                           \
 279         struct type *lh_first;  /* first element */                     \
 280 }
 281
 282 #define LIST_HEAD_INITIALIZER(head)                                     \
 283         { NULL }
 284
 285 #define LIST_ENTRY(type)                                                \
 286 struct {                                                                \
 287         struct type *le_next;   /* next element */                      \
 288         struct type **le_prev;  /* address of previous next element */  \
 289 }
 290
 291 /*
 292  * List functions.
 293  */
 294
 295 #define LIST_EMPTY(head)        ((head)->lh_first == NULL)
 296
 297 #define LIST_FIRST(head)        ((head)->lh_first)
 298
 299 #define LIST_FOREACH(var, head, field)                                  \
 300         for ((var) = LIST_FIRST((head));                                \
 301             (var);                                                      \
 302             (var) = LIST_NEXT((var), field))
 303
 304 #define LIST_FOREACH_MUTABLE(var, head, field, nvar)                    \
 305         for ((var) = LIST_FIRST((head));                                \
 306              (var) && ((nvar) = LIST_NEXT((var), field), (var));        \
 307              (var) = (nvar))
 308
 309 #define LIST_INIT(head) do {                                            \
 310         LIST_FIRST((head)) = NULL;                                      \
 311 } while (0)
 312
 313 #define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
 314         if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
 315                 LIST_NEXT((listelm), field)->field.le_prev =            \
 316                     &LIST_NEXT((elm), field);                           \
 317         LIST_NEXT((listelm), field) = (elm);                            \
 318         (elm)->field.le_prev = &LIST_NEXT((listelm), field);            \
 319 } while (0)
 320
 321 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
 322         (elm)->field.le_prev = (listelm)->field.le_prev;                \
 323         LIST_NEXT((elm), field) = (listelm);                            \
 324         *(listelm)->field.le_prev = (elm);                              \
 325         (listelm)->field.le_prev = &LIST_NEXT((elm), field);            \
 326 } while (0)
 327
 328 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
 329         if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)     \
 330                 LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
 331         LIST_FIRST((head)) = (elm);                                     \
 332         (elm)->field.le_prev = &LIST_FIRST((head));                     \
 333 } while (0)
 334
 335 #define LIST_NEXT(elm, field)   ((elm)->field.le_next)
 336
 337 #define LIST_REMOVE(elm, field) do {                                    \
 338         if (LIST_NEXT((elm), field) != NULL)                            \
 339                 LIST_NEXT((elm), field)->field.le_prev =                \
 340                     (elm)->field.le_prev;                               \
 341         *(elm)->field.le_prev = LIST_NEXT((elm), field);                \
 342 } while (0)
 343
 344 /*
 345  * Tail queue declarations.
 346  */
 347 #define TAILQ_HEAD(name, type)                                          \
 348 struct name {                                                           \
 349         struct type *tqh_first; /* first element */                     \
 350         struct type **tqh_last; /* addr of last next element */         \
 351 }
 352
 353 #define TAILQ_HEAD_INITIALIZER(head)                                    \
 354         { NULL, &(head).tqh_first }
 355
 356 #define TAILQ_ENTRY(type)                                               \
 357 struct {                                                                \
 358         struct type *tqe_next;  /* next element */                      \
 359         struct type **tqe_prev; /* address of previous next element */  \
 360 }
 361
 362 /*
 363  * Tail queue functions.
 364  */
 365 #define TAILQ_CONCAT(head1, head2, field) do {                          \
 366         if (!TAILQ_EMPTY(head2)) {                                      \
 367                 *(head1)->tqh_last = (head2)->tqh_first;                \
 368                 (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last; \
 369                 (head1)->tqh_last = (head2)->tqh_last;                  \
 370                 TAILQ_INIT((head2));                                    \
 371         }                                                               \
 372 } while (0)
 373
 374 #define TAILQ_EMPTY(head)       ((head)->tqh_first == NULL)
 375
 376 #define TAILQ_FIRST(head)       ((head)->tqh_first)
 377
 378 #define TAILQ_FOREACH(var, head, field)                                 \
 379         for ((var) = TAILQ_FIRST((head));                               \
 380             (var);                                                      \
 381             (var) = TAILQ_NEXT((var), field))
 382
 383 #define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
 384         for ((var) = TAILQ_LAST((head), headname);                      \
 385             (var);                                                      \
 386             (var) = TAILQ_PREV((var), headname, field))
 387
 388 #define TAILQ_FOREACH_MUTABLE(var, head, field, nvar)                   \
 389         for ((var) = TAILQ_FIRST((head));                               \
 390              (var) && ((nvar) = TAILQ_NEXT((var), field), (var));       \
 391              (var) = (nvar))
 392
 393 #define TAILQ_INIT(head) do {                                           \
 394         TAILQ_FIRST((head)) = NULL;                                     \
 395         (head)->tqh_last = &TAILQ_FIRST((head));                        \
 396 } while (0)
 397
 398 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
 399         if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
 400                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
 401                     &TAILQ_NEXT((elm), field);                          \
 402         else                                                            \
 403                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
 404         TAILQ_NEXT((listelm), field) = (elm);                           \
 405         (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);          \
 406 } while (0)
 407
 408 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
 409         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
 410         TAILQ_NEXT((elm), field) = (listelm);                           \
 411         *(listelm)->field.tqe_prev = (elm);                             \
 412         (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);          \
 413 } while (0)
 414
 415 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
 416         if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)   \
 417                 TAILQ_FIRST((head))->field.tqe_prev =                   \
 418                     &TAILQ_NEXT((elm), field);                          \
 419         else                                                            \
 420                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
 421         TAILQ_FIRST((head)) = (elm);                                    \
 422         (elm)->field.tqe_prev = &TAILQ_FIRST((head));                   \
 423 } while (0)
 424
 425 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
 426         TAILQ_NEXT((elm), field) = NULL;                                \
 427         (elm)->field.tqe_prev = (head)->tqh_last;                       \
 428         *(head)->tqh_last = (elm);                                      \
 429         (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
 430 } while (0)
 431
 432 #define TAILQ_LAST(head, headname)                                      \
 433         (*(((struct headname *)((head)->tqh_last))->tqh_last))
 434
 435 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
 436
 437 #define TAILQ_PREV(elm, headname, field)                                \
 438         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
 439
 440 #define TAILQ_REMOVE(head, elm, field) do {                             \
 441         if ((TAILQ_NEXT((elm), field)) != NULL)                         \
 442                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
 443                     (elm)->field.tqe_prev;                              \
 444         else                                                            \
 445                 (head)->tqh_last = (elm)->field.tqe_prev;               \
 446         *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);              \
 447 } while (0)
 448
 449 /*
 450  * Circular queue declarations.
 451  */
 452 #define CIRCLEQ_HEAD(name, type)                                        \
 453 struct name {                                                           \
 454         struct type *cqh_first;         /* first element */             \
 455         struct type *cqh_last;          /* last element */              \
 456 }
 457
 458 #define CIRCLEQ_HEAD_INITIALIZER(head)                                  \
 459         { (void *)&(head), (void *)&(head) }
 460
 461 #define CIRCLEQ_ENTRY(type)                                             \
 462 struct {                                                                \
 463         struct type *cqe_next;          /* next element */              \
 464         struct type *cqe_prev;          /* previous element */          \
 465 }
 466
 467 /*
 468  * Circular queue functions.
 469  */
 470 #define CIRCLEQ_EMPTY(head)     ((head)->cqh_first == (void *)(head))
 471
 472 #define CIRCLEQ_FIRST(head)     ((head)->cqh_first)
 473
 474 #define CIRCLEQ_FOREACH(var, head, field)                               \
 475         for ((var) = CIRCLEQ_FIRST((head));                             \
 476             (var) != (void *)(head) || ((var) = NULL);                  \
 477             (var) = CIRCLEQ_NEXT((var), field))
 478
 479 #define CIRCLEQ_FOREACH_REVERSE(var, head, field)                       \
 480         for ((var) = CIRCLEQ_LAST((head));                              \
 481             (var) != (void *)(head) || ((var) = NULL);                  \
 482             (var) = CIRCLEQ_PREV((var), field))
 483
 484 #define CIRCLEQ_INIT(head) do {                                         \
 485         CIRCLEQ_FIRST((head)) = (void *)(head);                         \
 486         CIRCLEQ_LAST((head)) = (void *)(head);                          \
 487 } while (0)
 488
 489 #define CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {            \
 490         CIRCLEQ_NEXT((elm), field) = CIRCLEQ_NEXT((listelm), field);    \
 491         CIRCLEQ_PREV((elm), field) = (listelm);                         \
 492         if (CIRCLEQ_NEXT((listelm), field) == (void *)(head))           \
 493                 CIRCLEQ_LAST((head)) = (elm);                           \
 494         else                                                            \
 495                 CIRCLEQ_PREV(CIRCLEQ_NEXT((listelm), field), field) = (elm);\
 496         CIRCLEQ_NEXT((listelm), field) = (elm);                         \
 497 } while (0)
 498
 499 #define CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do {           \
 500         CIRCLEQ_NEXT((elm), field) = (listelm);                         \
 501         CIRCLEQ_PREV((elm), field) = CIRCLEQ_PREV((listelm), field);    \
 502         if (CIRCLEQ_PREV((listelm), field) == (void *)(head))           \
 503                 CIRCLEQ_FIRST((head)) = (elm);                          \
 504         else                                                            \
 505                 CIRCLEQ_NEXT(CIRCLEQ_PREV((listelm), field), field) = (elm);\
 506         CIRCLEQ_PREV((listelm), field) = (elm);                         \
 507 } while (0)
 508
 509 #define CIRCLEQ_INSERT_HEAD(head, elm, field) do {                      \
 510         CIRCLEQ_NEXT((elm), field) = CIRCLEQ_FIRST((head));             \
 511         CIRCLEQ_PREV((elm), field) = (void *)(head);                    \
 512         if (CIRCLEQ_LAST((head)) == (void *)(head))                     \
 513                 CIRCLEQ_LAST((head)) = (elm);                           \
 514         else                                                            \
 515                 CIRCLEQ_PREV(CIRCLEQ_FIRST((head)), field) = (elm);     \
 516         CIRCLEQ_FIRST((head)) = (elm);                                  \
 517 } while (0)
 518
 519 #define CIRCLEQ_INSERT_TAIL(head, elm, field) do {                      \
 520         CIRCLEQ_NEXT((elm), field) = (void *)(head);                    \
 521         CIRCLEQ_PREV((elm), field) = CIRCLEQ_LAST((head));              \
 522         if (CIRCLEQ_FIRST((head)) == (void *)(head))                    \
 523                 CIRCLEQ_FIRST((head)) = (elm);                          \
 524         else                                                            \
 525                 CIRCLEQ_NEXT(CIRCLEQ_LAST((head)), field) = (elm);      \
 526         CIRCLEQ_LAST((head)) = (elm);                                   \
 527 } while (0)
 528
 529 #define CIRCLEQ_LAST(head)      ((head)->cqh_last)
 530
 531 #define CIRCLEQ_NEXT(elm,field) ((elm)->field.cqe_next)
 532
 533 #define CIRCLEQ_PREV(elm,field) ((elm)->field.cqe_prev)
 534
 535 #define CIRCLEQ_REMOVE(head, elm, field) do {                           \
 536         if (CIRCLEQ_NEXT((elm), field) == (void *)(head))               \
 537                 CIRCLEQ_LAST((head)) = CIRCLEQ_PREV((elm), field);      \
 538         else                                                            \
 539                 CIRCLEQ_PREV(CIRCLEQ_NEXT((elm), field), field) =       \
 540                     CIRCLEQ_PREV((elm), field);                         \
 541         if (CIRCLEQ_PREV((elm), field) == (void *)(head))               \
 542                 CIRCLEQ_FIRST((head)) = CIRCLEQ_NEXT((elm), field);     \
 543         else                                                            \
 544                 CIRCLEQ_NEXT(CIRCLEQ_PREV((elm), field), field) =       \
 545                     CIRCLEQ_NEXT((elm), field);                         \
 546 } while (0)
 547
 548 #ifdef _KERNEL
 549
 550 /*
 551  * XXX insque() and remque() are an old way of handling certain queues.
 552  * They bogusly assumes that all queue heads look alike.
 553  */
 554
 555 struct quehead {
 556         struct quehead *qh_link;
 557         struct quehead *qh_rlink;
 558 };
 559
 560 #ifdef  __GNUC__
 561
 562 static __inline void
 563 insque(void *a, void *b)
 564 {
 565         struct quehead *element = (struct quehead *)a,
 566                  *head = (struct quehead *)b;
 567
 568         element->qh_link = head->qh_link;
 569         element->qh_rlink = head;
 570         head->qh_link = element;
 571         element->qh_link->qh_rlink = element;
 572 }
 573
 574 static __inline void
 575 remque(void *a)
 576 {
 577         struct quehead *element = (struct quehead *)a;
 578
 579         element->qh_link->qh_rlink = element->qh_rlink;
 580         element->qh_rlink->qh_link = element->qh_link;
 581         element->qh_rlink = 0;
 582 }
 583
 584 #else /* !__GNUC__ */
 585
 586 void    insque (void *a, void *b);
 587 void    remque (void *a);
 588
 589 #endif /* __GNUC__ */
 590
 591 #endif /* _KERNEL */
 592
 593 #endif /* !_SYS_QUEUE_H_ */