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 1.7 2005/03/04 02:21:49 hsu 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_REVERSE     -       -       -       +       +
 107  * _INSERT_HEAD         +       +       +       +       +
 108  * _INSERT_BEFORE       -       +       -       +       +
 109  * _INSERT_AFTER        +       +       +       +       +
 110  * _INSERT_TAIL         -       -       +       +       +
 111  * _REMOVE_HEAD         +       -       +       -       -
 112  * _REMOVE              +       +       +       +       +
 113  *
 114  */
 115
 116 /*
 117  * Singly-linked List declarations.
 118  */
 119 #define SLIST_HEAD(name, type)                                          \
 120 struct name {                                                           \
 121         struct type *slh_first; /* first element */                     \
 122 }
 123
 124 #define SLIST_HEAD_INITIALIZER(head)                                    \
 125         { NULL }
 126
 127 #define SLIST_ENTRY(type)                                               \
 128 struct {                                                                \
 129         struct type *sle_next;  /* next element */                      \
 130 }
 131
 132 #define SLIST_ENTRY_INITIALIZER { NULL }
 133
 134 /*
 135  * Singly-linked List functions.
 136  */
 137 #define SLIST_EMPTY(head)       ((head)->slh_first == NULL)
 138
 139 #define SLIST_FIRST(head)       ((head)->slh_first)
 140
 141 #define SLIST_FOREACH(var, head, field)                                 \
 142         for ((var) = SLIST_FIRST((head));                               \
 143             (var);                                                      \
 144             (var) = SLIST_NEXT((var), field))
 145
 146 #define SLIST_INIT(head) do {                                           \
 147         SLIST_FIRST((head)) = NULL;                                     \
 148 } while (0)
 149
 150 #define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
 151         SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);       \
 152         SLIST_NEXT((slistelm), field) = (elm);                          \
 153 } while (0)
 154
 155 #define SLIST_INSERT_HEAD(head, elm, field) do {                        \
 156         SLIST_NEXT((elm), field) = SLIST_FIRST((head));                 \
 157         SLIST_FIRST((head)) = (elm);                                    \
 158 } while (0)
 159
 160 #define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)
 161
 162 #define SLIST_REMOVE(head, elm, type, field) do {                       \
 163         if (SLIST_FIRST((head)) == (elm)) {                             \
 164                 SLIST_REMOVE_HEAD((head), field);                       \
 165         }                                                               \
 166         else {                                                          \
 167                 struct type *curelm = SLIST_FIRST((head));              \
 168                 while (SLIST_NEXT(curelm, field) != (elm))              \
 169                         curelm = SLIST_NEXT(curelm, field);             \
 170                 SLIST_NEXT(curelm, field) =                             \
 171                     SLIST_NEXT(SLIST_NEXT(curelm, field), field);       \
 172         }                                                               \
 173 } while (0)
 174
 175 #define SLIST_REMOVE_HEAD(head, field) do {                             \
 176         SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);   \
 177 } while (0)
 178
 179 /*
 180  * Singly-linked Tail queue declarations.
 181  */
 182 #define STAILQ_HEAD(name, type)                                         \
 183 struct name {                                                           \
 184         struct type *stqh_first;/* first element */                     \
 185         struct type **stqh_last;/* addr of last next element */         \
 186 }
 187
 188 #define STAILQ_HEAD_INITIALIZER(head)                                   \
 189         { NULL, &(head).stqh_first }
 190
 191 #define STAILQ_ENTRY(type)                                              \
 192 struct {                                                                \
 193         struct type *stqe_next; /* next element */                      \
 194 }
 195
 196 /*
 197  * Singly-linked Tail queue functions.
 198  */
 199 #define STAILQ_EMPTY(head)      ((head)->stqh_first == NULL)
 200
 201 #define STAILQ_FIRST(head)      ((head)->stqh_first)
 202
 203 #define STAILQ_FOREACH(var, head, field)                                \
 204         for((var) = STAILQ_FIRST((head));                               \
 205            (var);                                                       \
 206            (var) = STAILQ_NEXT((var), field))
 207
 208 #define STAILQ_INIT(head) do {                                          \
 209         STAILQ_FIRST((head)) = NULL;                                    \
 210         (head)->stqh_last = &STAILQ_FIRST((head));                      \
 211 } while (0)
 212
 213 #define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {               \
 214         if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
 215                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 216         STAILQ_NEXT((tqelm), field) = (elm);                            \
 217 } while (0)
 218
 219 #define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
 220         if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL) \
 221                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 222         STAILQ_FIRST((head)) = (elm);                                   \
 223 } while (0)
 224
 225 #define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
 226         STAILQ_NEXT((elm), field) = NULL;                               \
 227         *(head)->stqh_last = (elm);                                     \
 228         (head)->stqh_last = &STAILQ_NEXT((elm), field);                 \
 229 } while (0)
 230
 231 #define STAILQ_LAST(head, type, field)                                  \
 232         (STAILQ_EMPTY(head) ?                                           \
 233                 NULL :                                                  \
 234                 ((struct type *)                                        \
 235                 ((char *)((head)->stqh_last) - __offsetof(struct type, field))))
 236
 237 #define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
 238
 239 #define STAILQ_REMOVE(head, elm, type, field) do {                      \
 240         if (STAILQ_FIRST((head)) == (elm)) {                            \
 241                 STAILQ_REMOVE_HEAD(head, field);                        \
 242         }                                                               \
 243         else {                                                          \
 244                 struct type *curelm = STAILQ_FIRST((head));             \
 245                 while (STAILQ_NEXT(curelm, field) != (elm))             \
 246                         curelm = STAILQ_NEXT(curelm, field);            \
 247                 if ((STAILQ_NEXT(curelm, field) =                       \
 248                      STAILQ_NEXT(STAILQ_NEXT(curelm, field), field)) == NULL)\
 249                         (head)->stqh_last = &STAILQ_NEXT((curelm), field);\
 250         }                                                               \
 251 } while (0)
 252
 253 #define STAILQ_REMOVE_HEAD(head, field) do {                            \
 254         if ((STAILQ_FIRST((head)) =                                     \
 255              STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL)         \
 256                 (head)->stqh_last = &STAILQ_FIRST((head));              \
 257 } while (0)
 258
 259 #define STAILQ_REMOVE_HEAD_UNTIL(head, elm, field) do {                 \
 260         if ((STAILQ_FIRST((head)) = STAILQ_NEXT((elm), field)) == NULL) \
 261                 (head)->stqh_last = &STAILQ_FIRST((head));              \
 262 } while (0)
 263
 264 /*
 265  * List declarations.
 266  */
 267 #define LIST_HEAD(name, type)                                           \
 268 struct name {                                                           \
 269         struct type *lh_first;  /* first element */                     \
 270 }
 271
 272 #define LIST_HEAD_INITIALIZER(head)                                     \
 273         { NULL }
 274
 275 #define LIST_ENTRY(type)                                                \
 276 struct {                                                                \
 277         struct type *le_next;   /* next element */                      \
 278         struct type **le_prev;  /* address of previous next element */  \
 279 }
 280
 281 /*
 282  * List functions.
 283  */
 284
 285 #define LIST_EMPTY(head)        ((head)->lh_first == NULL)
 286
 287 #define LIST_FIRST(head)        ((head)->lh_first)
 288
 289 #define LIST_FOREACH(var, head, field)                                  \
 290         for ((var) = LIST_FIRST((head));                                \
 291             (var);                                                      \
 292             (var) = LIST_NEXT((var), field))
 293
 294 #define LIST_FOREACH_MUTABLE(var, head, field, nvar)                    \
 295         for ((var) = LIST_FIRST((head));                                \
 296              (var) && ((nvar) = LIST_NEXT((var), field), (var));        \
 297              (var) = (nvar))
 298
 299 #define LIST_INIT(head) do {                                            \
 300         LIST_FIRST((head)) = NULL;                                      \
 301 } while (0)
 302
 303 #define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
 304         if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
 305                 LIST_NEXT((listelm), field)->field.le_prev =            \
 306                     &LIST_NEXT((elm), field);                           \
 307         LIST_NEXT((listelm), field) = (elm);                            \
 308         (elm)->field.le_prev = &LIST_NEXT((listelm), field);            \
 309 } while (0)
 310
 311 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
 312         (elm)->field.le_prev = (listelm)->field.le_prev;                \
 313         LIST_NEXT((elm), field) = (listelm);                            \
 314         *(listelm)->field.le_prev = (elm);                              \
 315         (listelm)->field.le_prev = &LIST_NEXT((elm), field);            \
 316 } while (0)
 317
 318 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
 319         if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)     \
 320                 LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
 321         LIST_FIRST((head)) = (elm);                                     \
 322         (elm)->field.le_prev = &LIST_FIRST((head));                     \
 323 } while (0)
 324
 325 #define LIST_NEXT(elm, field)   ((elm)->field.le_next)
 326
 327 #define LIST_REMOVE(elm, field) do {                                    \
 328         if (LIST_NEXT((elm), field) != NULL)                            \
 329                 LIST_NEXT((elm), field)->field.le_prev =                \
 330                     (elm)->field.le_prev;                               \
 331         *(elm)->field.le_prev = LIST_NEXT((elm), field);                \
 332 } while (0)
 333
 334 /*
 335  * Tail queue declarations.
 336  */
 337 #define TAILQ_HEAD(name, type)                                          \
 338 struct name {                                                           \
 339         struct type *tqh_first; /* first element */                     \
 340         struct type **tqh_last; /* addr of last next element */         \
 341 }
 342
 343 #define TAILQ_HEAD_INITIALIZER(head)                                    \
 344         { NULL, &(head).tqh_first }
 345
 346 #define TAILQ_ENTRY(type)                                               \
 347 struct {                                                                \
 348         struct type *tqe_next;  /* next element */                      \
 349         struct type **tqe_prev; /* address of previous next element */  \
 350 }
 351
 352 /*
 353  * Tail queue functions.
 354  */
 355 #define TAILQ_EMPTY(head)       ((head)->tqh_first == NULL)
 356
 357 #define TAILQ_FIRST(head)       ((head)->tqh_first)
 358
 359 #define TAILQ_FOREACH(var, head, field)                                 \
 360         for ((var) = TAILQ_FIRST((head));                               \
 361             (var);                                                      \
 362             (var) = TAILQ_NEXT((var), field))
 363
 364 #define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
 365         for ((var) = TAILQ_LAST((head), headname);                      \
 366             (var);                                                      \
 367             (var) = TAILQ_PREV((var), headname, field))
 368
 369 #define TAILQ_FOREACH_MUTABLE(var, head, field, nvar)                   \
 370         for ((var) = TAILQ_FIRST((head));                               \
 371              (var) && ((nvar) = TAILQ_NEXT((var), field), (var));       \
 372              (var) = (nvar))
 373
 374 #define TAILQ_INIT(head) do {                                           \
 375         TAILQ_FIRST((head)) = NULL;                                     \
 376         (head)->tqh_last = &TAILQ_FIRST((head));                        \
 377 } while (0)
 378
 379 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
 380         if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
 381                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
 382                     &TAILQ_NEXT((elm), field);                          \
 383         else                                                            \
 384                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
 385         TAILQ_NEXT((listelm), field) = (elm);                           \
 386         (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);          \
 387 } while (0)
 388
 389 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
 390         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
 391         TAILQ_NEXT((elm), field) = (listelm);                           \
 392         *(listelm)->field.tqe_prev = (elm);                             \
 393         (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);          \
 394 } while (0)
 395
 396 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
 397         if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)   \
 398                 TAILQ_FIRST((head))->field.tqe_prev =                   \
 399                     &TAILQ_NEXT((elm), field);                          \
 400         else                                                            \
 401                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
 402         TAILQ_FIRST((head)) = (elm);                                    \
 403         (elm)->field.tqe_prev = &TAILQ_FIRST((head));                   \
 404 } while (0)
 405
 406 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
 407         TAILQ_NEXT((elm), field) = NULL;                                \
 408         (elm)->field.tqe_prev = (head)->tqh_last;                       \
 409         *(head)->tqh_last = (elm);                                      \
 410         (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
 411 } while (0)
 412
 413 #define TAILQ_LAST(head, headname)                                      \
 414         (*(((struct headname *)((head)->tqh_last))->tqh_last))
 415
 416 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
 417
 418 #define TAILQ_PREV(elm, headname, field)                                \
 419         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
 420
 421 #define TAILQ_REMOVE(head, elm, field) do {                             \
 422         if ((TAILQ_NEXT((elm), field)) != NULL)                         \
 423                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
 424                     (elm)->field.tqe_prev;                              \
 425         else                                                            \
 426                 (head)->tqh_last = (elm)->field.tqe_prev;               \
 427         *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);              \
 428 } while (0)
 429
 430 /*
 431  * Circular queue declarations.
 432  */
 433 #define CIRCLEQ_HEAD(name, type)                                        \
 434 struct name {                                                           \
 435         struct type *cqh_first;         /* first element */             \
 436         struct type *cqh_last;          /* last element */              \
 437 }
 438
 439 #define CIRCLEQ_HEAD_INITIALIZER(head)                                  \
 440         { (void *)&(head), (void *)&(head) }
 441
 442 #define CIRCLEQ_ENTRY(type)                                             \
 443 struct {                                                                \
 444         struct type *cqe_next;          /* next element */              \
 445         struct type *cqe_prev;          /* previous element */          \
 446 }
 447
 448 /*
 449  * Circular queue functions.
 450  */
 451 #define CIRCLEQ_EMPTY(head)     ((head)->cqh_first == (void *)(head))
 452
 453 #define CIRCLEQ_FIRST(head)     ((head)->cqh_first)
 454
 455 #define CIRCLEQ_FOREACH(var, head, field)                               \
 456         for ((var) = CIRCLEQ_FIRST((head));                             \
 457             (var) != (void *)(head) || ((var) = NULL);                  \
 458             (var) = CIRCLEQ_NEXT((var), field))
 459
 460 #define CIRCLEQ_FOREACH_REVERSE(var, head, field)                       \
 461         for ((var) = CIRCLEQ_LAST((head));                              \
 462             (var) != (void *)(head) || ((var) = NULL);                  \
 463             (var) = CIRCLEQ_PREV((var), field))
 464
 465 #define CIRCLEQ_INIT(head) do {                                         \
 466         CIRCLEQ_FIRST((head)) = (void *)(head);                         \
 467         CIRCLEQ_LAST((head)) = (void *)(head);                          \
 468 } while (0)
 469
 470 #define CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {            \
 471         CIRCLEQ_NEXT((elm), field) = CIRCLEQ_NEXT((listelm), field);    \
 472         CIRCLEQ_PREV((elm), field) = (listelm);                         \
 473         if (CIRCLEQ_NEXT((listelm), field) == (void *)(head))           \
 474                 CIRCLEQ_LAST((head)) = (elm);                           \
 475         else                                                            \
 476                 CIRCLEQ_PREV(CIRCLEQ_NEXT((listelm), field), field) = (elm);\
 477         CIRCLEQ_NEXT((listelm), field) = (elm);                         \
 478 } while (0)
 479
 480 #define CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do {           \
 481         CIRCLEQ_NEXT((elm), field) = (listelm);                         \
 482         CIRCLEQ_PREV((elm), field) = CIRCLEQ_PREV((listelm), field);    \
 483         if (CIRCLEQ_PREV((listelm), field) == (void *)(head))           \
 484                 CIRCLEQ_FIRST((head)) = (elm);                          \
 485         else                                                            \
 486                 CIRCLEQ_NEXT(CIRCLEQ_PREV((listelm), field), field) = (elm);\
 487         CIRCLEQ_PREV((listelm), field) = (elm);                         \
 488 } while (0)
 489
 490 #define CIRCLEQ_INSERT_HEAD(head, elm, field) do {                      \
 491         CIRCLEQ_NEXT((elm), field) = CIRCLEQ_FIRST((head));             \
 492         CIRCLEQ_PREV((elm), field) = (void *)(head);                    \
 493         if (CIRCLEQ_LAST((head)) == (void *)(head))                     \
 494                 CIRCLEQ_LAST((head)) = (elm);                           \
 495         else                                                            \
 496                 CIRCLEQ_PREV(CIRCLEQ_FIRST((head)), field) = (elm);     \
 497         CIRCLEQ_FIRST((head)) = (elm);                                  \
 498 } while (0)
 499
 500 #define CIRCLEQ_INSERT_TAIL(head, elm, field) do {                      \
 501         CIRCLEQ_NEXT((elm), field) = (void *)(head);                    \
 502         CIRCLEQ_PREV((elm), field) = CIRCLEQ_LAST((head));              \
 503         if (CIRCLEQ_FIRST((head)) == (void *)(head))                    \
 504                 CIRCLEQ_FIRST((head)) = (elm);                          \
 505         else                                                            \
 506                 CIRCLEQ_NEXT(CIRCLEQ_LAST((head)), field) = (elm);      \
 507         CIRCLEQ_LAST((head)) = (elm);                                   \
 508 } while (0)
 509
 510 #define CIRCLEQ_LAST(head)      ((head)->cqh_last)
 511
 512 #define CIRCLEQ_NEXT(elm,field) ((elm)->field.cqe_next)
 513
 514 #define CIRCLEQ_PREV(elm,field) ((elm)->field.cqe_prev)
 515
 516 #define CIRCLEQ_REMOVE(head, elm, field) do {                           \
 517         if (CIRCLEQ_NEXT((elm), field) == (void *)(head))               \
 518                 CIRCLEQ_LAST((head)) = CIRCLEQ_PREV((elm), field);      \
 519         else                                                            \
 520                 CIRCLEQ_PREV(CIRCLEQ_NEXT((elm), field), field) =       \
 521                     CIRCLEQ_PREV((elm), field);                         \
 522         if (CIRCLEQ_PREV((elm), field) == (void *)(head))               \
 523                 CIRCLEQ_FIRST((head)) = CIRCLEQ_NEXT((elm), field);     \
 524         else                                                            \
 525                 CIRCLEQ_NEXT(CIRCLEQ_PREV((elm), field), field) =       \
 526                     CIRCLEQ_NEXT((elm), field);                         \
 527 } while (0)
 528
 529 #ifdef _KERNEL
 530
 531 /*
 532  * XXX insque() and remque() are an old way of handling certain queues.
 533  * They bogusly assumes that all queue heads look alike.
 534  */
 535
 536 struct quehead {
 537         struct quehead *qh_link;
 538         struct quehead *qh_rlink;
 539 };
 540
 541 #ifdef  __GNUC__
 542
 543 static __inline void
 544 insque(void *a, void *b)
 545 {
 546         struct quehead *element = (struct quehead *)a,
 547                  *head = (struct quehead *)b;
 548
 549         element->qh_link = head->qh_link;
 550         element->qh_rlink = head;
 551         head->qh_link = element;
 552         element->qh_link->qh_rlink = element;
 553 }
 554
 555 static __inline void
 556 remque(void *a)
 557 {
 558         struct quehead *element = (struct quehead *)a;
 559
 560         element->qh_link->qh_rlink = element->qh_rlink;
 561         element->qh_rlink->qh_link = element->qh_link;
 562         element->qh_rlink = 0;
 563 }
 564
 565 #else /* !__GNUC__ */
 566
 567 void    insque (void *a, void *b);
 568 void    remque (void *a);
 569
 570 #endif /* __GNUC__ */
 571
 572 #endif /* _KERNEL */
 573
 574 #endif /* !_SYS_QUEUE_H_ */