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 1.2 2003/06/17 04:28:58 dillon Exp $
  36  */
  37
  38 #ifndef _SYS_QUEUE_H_
  39 #define _SYS_QUEUE_H_
  40
  41 #include <machine/ansi.h>       /* for __offsetof */
  42
  43 /*
  44  * This file defines five types of data structures: singly-linked lists,
  45  * singly-linked tail queues, lists, tail queues, and circular queues.
  46  *
  47  * A singly-linked list is headed by a single forward pointer. The elements
  48  * are singly linked for minimum space and pointer manipulation overhead at
  49  * the expense of O(n) removal for arbitrary elements. New elements can be
  50  * added to the list after an existing element or at the head of the list.
  51  * Elements being removed from the head of the list should use the explicit
  52  * macro for this purpose for optimum efficiency. A singly-linked list may
  53  * only be traversed in the forward direction.  Singly-linked lists are ideal
  54  * for applications with large datasets and few or no removals or for
  55  * implementing a LIFO queue.
  56  *
  57  * A singly-linked tail queue is headed by a pair of pointers, one to the
  58  * head of the list and the other to the tail of the list. The elements are
  59  * singly linked for minimum space and pointer manipulation overhead at the
  60  * expense of O(n) removal for arbitrary elements. New elements can be added
  61  * to the list after an existing element, at the head of the list, or at the
  62  * end of the list. Elements being removed from the head of the tail queue
  63  * should use the explicit macro for this purpose for optimum efficiency.
  64  * A singly-linked tail queue may only be traversed in the forward direction.
  65  * Singly-linked tail queues are ideal for applications with large datasets
  66  * and few or no removals or for implementing a FIFO queue.
  67  *
  68  * A list is headed by a single forward pointer (or an array of forward
  69  * pointers for a hash table header). The elements are doubly linked
  70  * so that an arbitrary element can be removed without a need to
  71  * traverse the list. New elements can be added to the list before
  72  * or after an existing element or at the head of the list. A list
  73  * may only be traversed in the forward direction.
  74  *
  75  * A tail queue is headed by a pair of pointers, one to the head of the
  76  * list and the other to the tail of the list. The elements are doubly
  77  * linked so that an arbitrary element can be removed without a need to
  78  * traverse the list. New elements can be added to the list before or
  79  * after an existing element, at the head of the list, or at the end of
  80  * the list. A tail queue may be traversed in either direction.
  81  *
  82  * A circle queue is headed by a pair of pointers, one to the head of the
  83  * list and the other to the tail of the list. The elements are doubly
  84  * linked so that an arbitrary element can be removed without a need to
  85  * traverse the list. New elements can be added to the list before or after
  86  * an existing element, at the head of the list, or at the end of the list.
  87  * A circle queue may be traversed in either direction, but has a more
  88  * complex end of list detection.
  89  *
  90  * For details on the use of these macros, see the queue(3) manual page.
  91  *
  92  *
  93  *                      SLIST   LIST    STAILQ  TAILQ   CIRCLEQ
  94  * _HEAD                +       +       +       +       +
  95  * _HEAD_INITIALIZER    +       +       +       +       +
  96  * _ENTRY               +       +       +       +       +
  97  * _INIT                +       +       +       +       +
  98  * _EMPTY               +       +       +       +       +
  99  * _FIRST               +       +       +       +       +
 100  * _NEXT                +       +       +       +       +
 101  * _PREV                -       -       -       +       +
 102  * _LAST                -       -       +       +       +
 103  * _FOREACH             +       +       +       +       +
 104  * _FOREACH_REVERSE     -       -       -       +       +
 105  * _INSERT_HEAD         +       +       +       +       +
 106  * _INSERT_BEFORE       -       +       -       +       +
 107  * _INSERT_AFTER        +       +       +       +       +
 108  * _INSERT_TAIL         -       -       +       +       +
 109  * _REMOVE_HEAD         +       -       +       -       -
 110  * _REMOVE              +       +       +       +       +
 111  *
 112  */
 113
 114 /*
 115  * Singly-linked List declarations.
 116  */
 117 #define SLIST_HEAD(name, type)                                          \
 118 struct name {                                                           \
 119         struct type *slh_first; /* first element */                     \
 120 }
 121
 122 #define SLIST_HEAD_INITIALIZER(head)                                    \
 123         { NULL }
 124
 125 #define SLIST_ENTRY(type)                                               \
 126 struct {                                                                \
 127         struct type *sle_next;  /* next element */                      \
 128 }
 129
 130 /*
 131  * Singly-linked List functions.
 132  */
 133 #define SLIST_EMPTY(head)       ((head)->slh_first == NULL)
 134
 135 #define SLIST_FIRST(head)       ((head)->slh_first)
 136
 137 #define SLIST_FOREACH(var, head, field)                                 \
 138         for ((var) = SLIST_FIRST((head));                               \
 139             (var);                                                      \
 140             (var) = SLIST_NEXT((var), field))
 141
 142 #define SLIST_INIT(head) do {                                           \
 143         SLIST_FIRST((head)) = NULL;                                     \
 144 } while (0)
 145
 146 #define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
 147         SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);       \
 148         SLIST_NEXT((slistelm), field) = (elm);                          \
 149 } while (0)
 150
 151 #define SLIST_INSERT_HEAD(head, elm, field) do {                        \
 152         SLIST_NEXT((elm), field) = SLIST_FIRST((head));                 \
 153         SLIST_FIRST((head)) = (elm);                                    \
 154 } while (0)
 155
 156 #define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)
 157
 158 #define SLIST_REMOVE(head, elm, type, field) do {                       \
 159         if (SLIST_FIRST((head)) == (elm)) {                             \
 160                 SLIST_REMOVE_HEAD((head), field);                       \
 161         }                                                               \
 162         else {                                                          \
 163                 struct type *curelm = SLIST_FIRST((head));              \
 164                 while (SLIST_NEXT(curelm, field) != (elm))              \
 165                         curelm = SLIST_NEXT(curelm, field);             \
 166                 SLIST_NEXT(curelm, field) =                             \
 167                     SLIST_NEXT(SLIST_NEXT(curelm, field), field);       \
 168         }                                                               \
 169 } while (0)
 170
 171 #define SLIST_REMOVE_HEAD(head, field) do {                             \
 172         SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);   \
 173 } while (0)
 174
 175 /*
 176  * Singly-linked Tail queue declarations.
 177  */
 178 #define STAILQ_HEAD(name, type)                                         \
 179 struct name {                                                           \
 180         struct type *stqh_first;/* first element */                     \
 181         struct type **stqh_last;/* addr of last next element */         \
 182 }
 183
 184 #define STAILQ_HEAD_INITIALIZER(head)                                   \
 185         { NULL, &(head).stqh_first }
 186
 187 #define STAILQ_ENTRY(type)                                              \
 188 struct {                                                                \
 189         struct type *stqe_next; /* next element */                      \
 190 }
 191
 192 /*
 193  * Singly-linked Tail queue functions.
 194  */
 195 #define STAILQ_EMPTY(head)      ((head)->stqh_first == NULL)
 196
 197 #define STAILQ_FIRST(head)      ((head)->stqh_first)
 198
 199 #define STAILQ_FOREACH(var, head, field)                                \
 200         for((var) = STAILQ_FIRST((head));                               \
 201            (var);                                                       \
 202            (var) = STAILQ_NEXT((var), field))
 203
 204 #define STAILQ_INIT(head) do {                                          \
 205         STAILQ_FIRST((head)) = NULL;                                    \
 206         (head)->stqh_last = &STAILQ_FIRST((head));                      \
 207 } while (0)
 208
 209 #define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {               \
 210         if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
 211                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 212         STAILQ_NEXT((tqelm), field) = (elm);                            \
 213 } while (0)
 214
 215 #define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
 216         if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL) \
 217                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 218         STAILQ_FIRST((head)) = (elm);                                   \
 219 } while (0)
 220
 221 #define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
 222         STAILQ_NEXT((elm), field) = NULL;                               \
 223         *(head)->stqh_last = (elm);                                     \
 224         (head)->stqh_last = &STAILQ_NEXT((elm), field);                 \
 225 } while (0)
 226
 227 #define STAILQ_LAST(head, type, field)                                  \
 228         (STAILQ_EMPTY(head) ?                                           \
 229                 NULL :                                                  \
 230                 ((struct type *)                                        \
 231                 ((char *)((head)->stqh_last) - __offsetof(struct type, field))))
 232
 233 #define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
 234
 235 #define STAILQ_REMOVE(head, elm, type, field) do {                      \
 236         if (STAILQ_FIRST((head)) == (elm)) {                            \
 237                 STAILQ_REMOVE_HEAD(head, field);                        \
 238         }                                                               \
 239         else {                                                          \
 240                 struct type *curelm = STAILQ_FIRST((head));             \
 241                 while (STAILQ_NEXT(curelm, field) != (elm))             \
 242                         curelm = STAILQ_NEXT(curelm, field);            \
 243                 if ((STAILQ_NEXT(curelm, field) =                       \
 244                      STAILQ_NEXT(STAILQ_NEXT(curelm, field), field)) == NULL)\
 245                         (head)->stqh_last = &STAILQ_NEXT((curelm), field);\
 246         }                                                               \
 247 } while (0)
 248
 249 #define STAILQ_REMOVE_HEAD(head, field) do {                            \
 250         if ((STAILQ_FIRST((head)) =                                     \
 251              STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL)         \
 252                 (head)->stqh_last = &STAILQ_FIRST((head));              \
 253 } while (0)
 254
 255 #define STAILQ_REMOVE_HEAD_UNTIL(head, elm, field) do {                 \
 256         if ((STAILQ_FIRST((head)) = STAILQ_NEXT((elm), field)) == NULL) \
 257                 (head)->stqh_last = &STAILQ_FIRST((head));              \
 258 } while (0)
 259
 260 /*
 261  * List declarations.
 262  */
 263 #define LIST_HEAD(name, type)                                           \
 264 struct name {                                                           \
 265         struct type *lh_first;  /* first element */                     \
 266 }
 267
 268 #define LIST_HEAD_INITIALIZER(head)                                     \
 269         { NULL }
 270
 271 #define LIST_ENTRY(type)                                                \
 272 struct {                                                                \
 273         struct type *le_next;   /* next element */                      \
 274         struct type **le_prev;  /* address of previous next element */  \
 275 }
 276
 277 /*
 278  * List functions.
 279  */
 280
 281 #define LIST_EMPTY(head)        ((head)->lh_first == NULL)
 282
 283 #define LIST_FIRST(head)        ((head)->lh_first)
 284
 285 #define LIST_FOREACH(var, head, field)                                  \
 286         for ((var) = LIST_FIRST((head));                                \
 287             (var);                                                      \
 288             (var) = LIST_NEXT((var), field))
 289
 290 #define LIST_INIT(head) do {                                            \
 291         LIST_FIRST((head)) = NULL;                                      \
 292 } while (0)
 293
 294 #define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
 295         if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
 296                 LIST_NEXT((listelm), field)->field.le_prev =            \
 297                     &LIST_NEXT((elm), field);                           \
 298         LIST_NEXT((listelm), field) = (elm);                            \
 299         (elm)->field.le_prev = &LIST_NEXT((listelm), field);            \
 300 } while (0)
 301
 302 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
 303         (elm)->field.le_prev = (listelm)->field.le_prev;                \
 304         LIST_NEXT((elm), field) = (listelm);                            \
 305         *(listelm)->field.le_prev = (elm);                              \
 306         (listelm)->field.le_prev = &LIST_NEXT((elm), field);            \
 307 } while (0)
 308
 309 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
 310         if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)     \
 311                 LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
 312         LIST_FIRST((head)) = (elm);                                     \
 313         (elm)->field.le_prev = &LIST_FIRST((head));                     \
 314 } while (0)
 315
 316 #define LIST_NEXT(elm, field)   ((elm)->field.le_next)
 317
 318 #define LIST_REMOVE(elm, field) do {                                    \
 319         if (LIST_NEXT((elm), field) != NULL)                            \
 320                 LIST_NEXT((elm), field)->field.le_prev =                \
 321                     (elm)->field.le_prev;                               \
 322         *(elm)->field.le_prev = LIST_NEXT((elm), field);                \
 323 } while (0)
 324
 325 /*
 326  * Tail queue declarations.
 327  */
 328 #define TAILQ_HEAD(name, type)                                          \
 329 struct name {                                                           \
 330         struct type *tqh_first; /* first element */                     \
 331         struct type **tqh_last; /* addr of last next element */         \
 332 }
 333
 334 #define TAILQ_HEAD_INITIALIZER(head)                                    \
 335         { NULL, &(head).tqh_first }
 336
 337 #define TAILQ_ENTRY(type)                                               \
 338 struct {                                                                \
 339         struct type *tqe_next;  /* next element */                      \
 340         struct type **tqe_prev; /* address of previous next element */  \
 341 }
 342
 343 /*
 344  * Tail queue functions.
 345  */
 346 #define TAILQ_EMPTY(head)       ((head)->tqh_first == NULL)
 347
 348 #define TAILQ_FIRST(head)       ((head)->tqh_first)
 349
 350 #define TAILQ_FOREACH(var, head, field)                                 \
 351         for ((var) = TAILQ_FIRST((head));                               \
 352             (var);                                                      \
 353             (var) = TAILQ_NEXT((var), field))
 354
 355 #define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
 356         for ((var) = TAILQ_LAST((head), headname);                      \
 357             (var);                                                      \
 358             (var) = TAILQ_PREV((var), headname, field))
 359
 360 #define TAILQ_INIT(head) do {                                           \
 361         TAILQ_FIRST((head)) = NULL;                                     \
 362         (head)->tqh_last = &TAILQ_FIRST((head));                        \
 363 } while (0)
 364
 365 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
 366         if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
 367                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
 368                     &TAILQ_NEXT((elm), field);                          \
 369         else                                                            \
 370                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
 371         TAILQ_NEXT((listelm), field) = (elm);                           \
 372         (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);          \
 373 } while (0)
 374
 375 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
 376         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
 377         TAILQ_NEXT((elm), field) = (listelm);                           \
 378         *(listelm)->field.tqe_prev = (elm);                             \
 379         (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);          \
 380 } while (0)
 381
 382 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
 383         if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)   \
 384                 TAILQ_FIRST((head))->field.tqe_prev =                   \
 385                     &TAILQ_NEXT((elm), field);                          \
 386         else                                                            \
 387                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
 388         TAILQ_FIRST((head)) = (elm);                                    \
 389         (elm)->field.tqe_prev = &TAILQ_FIRST((head));                   \
 390 } while (0)
 391
 392 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
 393         TAILQ_NEXT((elm), field) = NULL;                                \
 394         (elm)->field.tqe_prev = (head)->tqh_last;                       \
 395         *(head)->tqh_last = (elm);                                      \
 396         (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
 397 } while (0)
 398
 399 #define TAILQ_LAST(head, headname)                                      \
 400         (*(((struct headname *)((head)->tqh_last))->tqh_last))
 401
 402 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
 403
 404 #define TAILQ_PREV(elm, headname, field)                                \
 405         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
 406
 407 #define TAILQ_REMOVE(head, elm, field) do {                             \
 408         if ((TAILQ_NEXT((elm), field)) != NULL)                         \
 409                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
 410                     (elm)->field.tqe_prev;                              \
 411         else                                                            \
 412                 (head)->tqh_last = (elm)->field.tqe_prev;               \
 413         *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);              \
 414 } while (0)
 415
 416 /*
 417  * Circular queue declarations.
 418  */
 419 #define CIRCLEQ_HEAD(name, type)                                        \
 420 struct name {                                                           \
 421         struct type *cqh_first;         /* first element */             \
 422         struct type *cqh_last;          /* last element */              \
 423 }
 424
 425 #define CIRCLEQ_HEAD_INITIALIZER(head)                                  \
 426         { (void *)&(head), (void *)&(head) }
 427
 428 #define CIRCLEQ_ENTRY(type)                                             \
 429 struct {                                                                \
 430         struct type *cqe_next;          /* next element */              \
 431         struct type *cqe_prev;          /* previous element */          \
 432 }
 433
 434 /*
 435  * Circular queue functions.
 436  */
 437 #define CIRCLEQ_EMPTY(head)     ((head)->cqh_first == (void *)(head))
 438
 439 #define CIRCLEQ_FIRST(head)     ((head)->cqh_first)
 440
 441 #define CIRCLEQ_FOREACH(var, head, field)                               \
 442         for ((var) = CIRCLEQ_FIRST((head));                             \
 443             (var) != (void *)(head) || ((var) = NULL);                  \
 444             (var) = CIRCLEQ_NEXT((var), field))
 445
 446 #define CIRCLEQ_FOREACH_REVERSE(var, head, field)                       \
 447         for ((var) = CIRCLEQ_LAST((head));                              \
 448             (var) != (void *)(head) || ((var) = NULL);                  \
 449             (var) = CIRCLEQ_PREV((var), field))
 450
 451 #define CIRCLEQ_INIT(head) do {                                         \
 452         CIRCLEQ_FIRST((head)) = (void *)(head);                         \
 453         CIRCLEQ_LAST((head)) = (void *)(head);                          \
 454 } while (0)
 455
 456 #define CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {            \
 457         CIRCLEQ_NEXT((elm), field) = CIRCLEQ_NEXT((listelm), field);    \
 458         CIRCLEQ_PREV((elm), field) = (listelm);                         \
 459         if (CIRCLEQ_NEXT((listelm), field) == (void *)(head))           \
 460                 CIRCLEQ_LAST((head)) = (elm);                           \
 461         else                                                            \
 462                 CIRCLEQ_PREV(CIRCLEQ_NEXT((listelm), field), field) = (elm);\
 463         CIRCLEQ_NEXT((listelm), field) = (elm);                         \
 464 } while (0)
 465
 466 #define CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do {           \
 467         CIRCLEQ_NEXT((elm), field) = (listelm);                         \
 468         CIRCLEQ_PREV((elm), field) = CIRCLEQ_PREV((listelm), field);    \
 469         if (CIRCLEQ_PREV((listelm), field) == (void *)(head))           \
 470                 CIRCLEQ_FIRST((head)) = (elm);                          \
 471         else                                                            \
 472                 CIRCLEQ_NEXT(CIRCLEQ_PREV((listelm), field), field) = (elm);\
 473         CIRCLEQ_PREV((listelm), field) = (elm);                         \
 474 } while (0)
 475
 476 #define CIRCLEQ_INSERT_HEAD(head, elm, field) do {                      \
 477         CIRCLEQ_NEXT((elm), field) = CIRCLEQ_FIRST((head));             \
 478         CIRCLEQ_PREV((elm), field) = (void *)(head);                    \
 479         if (CIRCLEQ_LAST((head)) == (void *)(head))                     \
 480                 CIRCLEQ_LAST((head)) = (elm);                           \
 481         else                                                            \
 482                 CIRCLEQ_PREV(CIRCLEQ_FIRST((head)), field) = (elm);     \
 483         CIRCLEQ_FIRST((head)) = (elm);                                  \
 484 } while (0)
 485
 486 #define CIRCLEQ_INSERT_TAIL(head, elm, field) do {                      \
 487         CIRCLEQ_NEXT((elm), field) = (void *)(head);                    \
 488         CIRCLEQ_PREV((elm), field) = CIRCLEQ_LAST((head));              \
 489         if (CIRCLEQ_FIRST((head)) == (void *)(head))                    \
 490                 CIRCLEQ_FIRST((head)) = (elm);                          \
 491         else                                                            \
 492                 CIRCLEQ_NEXT(CIRCLEQ_LAST((head)), field) = (elm);      \
 493         CIRCLEQ_LAST((head)) = (elm);                                   \
 494 } while (0)
 495
 496 #define CIRCLEQ_LAST(head)      ((head)->cqh_last)
 497
 498 #define CIRCLEQ_NEXT(elm,field) ((elm)->field.cqe_next)
 499
 500 #define CIRCLEQ_PREV(elm,field) ((elm)->field.cqe_prev)
 501
 502 #define CIRCLEQ_REMOVE(head, elm, field) do {                           \
 503         if (CIRCLEQ_NEXT((elm), field) == (void *)(head))               \
 504                 CIRCLEQ_LAST((head)) = CIRCLEQ_PREV((elm), field);      \
 505         else                                                            \
 506                 CIRCLEQ_PREV(CIRCLEQ_NEXT((elm), field), field) =       \
 507                     CIRCLEQ_PREV((elm), field);                         \
 508         if (CIRCLEQ_PREV((elm), field) == (void *)(head))               \
 509                 CIRCLEQ_FIRST((head)) = CIRCLEQ_NEXT((elm), field);     \
 510         else                                                            \
 511                 CIRCLEQ_NEXT(CIRCLEQ_PREV((elm), field), field) =       \
 512                     CIRCLEQ_NEXT((elm), field);                         \
 513 } while (0)
 514
 515 #ifdef _KERNEL
 516
 517 /*
 518  * XXX insque() and remque() are an old way of handling certain queues.
 519  * They bogusly assumes that all queue heads look alike.
 520  */
 521
 522 struct quehead {
 523         struct quehead *qh_link;
 524         struct quehead *qh_rlink;
 525 };
 526
 527 #ifdef  __GNUC__
 528
 529 static __inline void
 530 insque(void *a, void *b)
 531 {
 532         struct quehead *element = (struct quehead *)a,
 533                  *head = (struct quehead *)b;
 534
 535         element->qh_link = head->qh_link;
 536         element->qh_rlink = head;
 537         head->qh_link = element;
 538         element->qh_link->qh_rlink = element;
 539 }
 540
 541 static __inline void
 542 remque(void *a)
 543 {
 544         struct quehead *element = (struct quehead *)a;
 545
 546         element->qh_link->qh_rlink = element->qh_rlink;
 547         element->qh_rlink->qh_link = element->qh_link;
 548         element->qh_rlink = 0;
 549 }
 550
 551 #else /* !__GNUC__ */
 552
 553 void    insque __P((void *a, void *b));
 554 void    remque __P((void *a));
 555
 556 #endif /* __GNUC__ */
 557
 558 #endif /* _KERNEL */
 559
 560 #endif /* !_SYS_QUEUE_H_ */