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         if (((elm)->field.le_next = (listelm)->field.le_next) != NULL)  \
 107                 (listelm)->field.le_next->field.le_prev =               \
 108                     &(elm)->field.le_next;                              \
 109         (listelm)->field.le_next = (elm);                               \
 110         (elm)->field.le_prev = &(listelm)->field.le_next;               \
 111 } while (/*CONSTCOND*/0)
 112
 113 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
 114         (elm)->field.le_prev = (listelm)->field.le_prev;                \
 115         (elm)->field.le_next = (listelm);                               \
 116         *(listelm)->field.le_prev = (elm);                              \
 117         (listelm)->field.le_prev = &(elm)->field.le_next;               \
 118 } while (/*CONSTCOND*/0)
 119
 120 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
 121         if (((elm)->field.le_next = (head)->lh_first) != NULL)          \
 122                 (head)->lh_first->field.le_prev = &(elm)->field.le_next;\
 123         (head)->lh_first = (elm);                                       \
 124         (elm)->field.le_prev = &(head)->lh_first;                       \
 125 } while (/*CONSTCOND*/0)
 126
 127 #define LIST_REMOVE(elm, field) do {                                    \
 128         if ((elm)->field.le_next != NULL)                               \
 129                 (elm)->field.le_next->field.le_prev =                   \
 130                     (elm)->field.le_prev;                               \
 131         *(elm)->field.le_prev = (elm)->field.le_next;                   \
 132 } while (/*CONSTCOND*/0)
 133
 134 #define LIST_FOREACH(var, head, field)                                  \
 135         for ((var) = ((head)->lh_first);                                \
 136                 (var);                                                  \
 137                 (var) = ((var)->field.le_next))
 138
 139 /*
 140  * List access methods.
 141  */
 142 #define LIST_EMPTY(head)                ((head)->lh_first == NULL)
 143 #define LIST_FIRST(head)                ((head)->lh_first)
 144 #define LIST_NEXT(elm, field)           ((elm)->field.le_next)
 145
 146
 147 /*
 148  * Singly-linked List definitions.
 149  */
 150 #define SLIST_HEAD(name, type)                                          \
 151 struct name {                                                           \
 152         struct type *slh_first; /* first element */                     \
 153 }
 154
 155 #define SLIST_HEAD_INITIALIZER(head)                                    \
 156         { NULL }
 157
 158 #define SLIST_ENTRY(type)                                               \
 159 struct {                                                                \
 160         struct type *sle_next;  /* next element */                      \
 161 }
 162
 163 /*
 164  * Singly-linked List functions.
 165  */
 166 #define SLIST_INIT(head) do {                                           \
 167         (head)->slh_first = NULL;                                       \
 168 } while (/*CONSTCOND*/0)
 169
 170 #define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
 171         (elm)->field.sle_next = (slistelm)->field.sle_next;             \
 172         (slistelm)->field.sle_next = (elm);                             \
 173 } while (/*CONSTCOND*/0)
 174
 175 #define SLIST_INSERT_HEAD(head, elm, field) do {                        \
 176         (elm)->field.sle_next = (head)->slh_first;                      \
 177         (head)->slh_first = (elm);                                      \
 178 } while (/*CONSTCOND*/0)
 179
 180 #define SLIST_REMOVE_HEAD(head, field) do {                             \
 181         (head)->slh_first = (head)->slh_first->field.sle_next;          \
 182 } while (/*CONSTCOND*/0)
 183
 184 #define SLIST_REMOVE(head, elm, type, field) do {                       \
 185         if ((head)->slh_first == (elm)) {                               \
 186                 SLIST_REMOVE_HEAD((head), field);                       \
 187         }                                                               \
 188         else {                                                          \
 189                 struct type *curelm = (head)->slh_first;                \
 190                 while(curelm->field.sle_next != (elm))                  \
 191                         curelm = curelm->field.sle_next;                \
 192                 curelm->field.sle_next =                                \
 193                     curelm->field.sle_next->field.sle_next;             \
 194         }                                                               \
 195 } while (/*CONSTCOND*/0)
 196
 197 #define SLIST_FOREACH(var, head, field)                                 \
 198         for((var) = (head)->slh_first; (var); (var) = (var)->field.sle_next)
 199
 200 /*
 201  * Singly-linked List access methods.
 202  */
 203 #define SLIST_EMPTY(head)       ((head)->slh_first == NULL)
 204 #define SLIST_FIRST(head)       ((head)->slh_first)
 205 #define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)
 206
 207
 208 /*
 209  * Singly-linked Tail queue declarations.
 210  */
 211 #define STAILQ_HEAD(name, type)                                 \
 212 struct name {                                                           \
 213         struct type *stqh_first;        /* first element */                     \
 214         struct type **stqh_last;        /* addr of last next element */         \
 215 }
 216
 217 #define STAILQ_HEAD_INITIALIZER(head)                                   \
 218         { NULL, &(head).stqh_first }
 219
 220 #define STAILQ_ENTRY(type)                                              \
 221 struct {                                                                \
 222         struct type *stqe_next; /* next element */                      \
 223 }
 224
 225 /*
 226  * Singly-linked Tail queue functions.
 227  */
 228 #define STAILQ_INIT(head) do {                                          \
 229         (head)->stqh_first = NULL;                                      \
 230         (head)->stqh_last = &(head)->stqh_first;                                \
 231 } while (/*CONSTCOND*/0)
 232
 233 #define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
 234         if (((elm)->field.stqe_next = (head)->stqh_first) == NULL)      \
 235                 (head)->stqh_last = &(elm)->field.stqe_next;            \
 236         (head)->stqh_first = (elm);                                     \
 237 } while (/*CONSTCOND*/0)
 238
 239 #define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
 240         (elm)->field.stqe_next = NULL;                                  \
 241         *(head)->stqh_last = (elm);                                     \
 242         (head)->stqh_last = &(elm)->field.stqe_next;                    \
 243 } while (/*CONSTCOND*/0)
 244
 245 #define STAILQ_INSERT_AFTER(head, listelm, elm, field) do {             \
 246         if (((elm)->field.stqe_next = (listelm)->field.stqe_next) == NULL)\
 247                 (head)->stqh_last = &(elm)->field.stqe_next;            \
 248         (listelm)->field.stqe_next = (elm);                             \
 249 } while (/*CONSTCOND*/0)
 250
 251 #define STAILQ_REMOVE_HEAD(head, field) do {                            \
 252         if (((head)->stqh_first = (head)->stqh_first->field.stqe_next) == NULL) \
 253                 (head)->stqh_last = &(head)->stqh_first;                        \
 254 } while (/*CONSTCOND*/0)
 255
 256 #define STAILQ_REMOVE(head, elm, type, field) do {                      \
 257         if ((head)->stqh_first == (elm)) {                              \
 258                 STAILQ_REMOVE_HEAD((head), field);                      \
 259         } else {                                                        \
 260                 struct type *curelm = (head)->stqh_first;               \
 261                 while (curelm->field.stqe_next != (elm))                        \
 262                         curelm = curelm->field.stqe_next;               \
 263                 if ((curelm->field.stqe_next =                          \
 264                         curelm->field.stqe_next->field.stqe_next) == NULL) \
 265                             (head)->stqh_last = &(curelm)->field.stqe_next; \
 266         }                                                               \
 267 } while (/*CONSTCOND*/0)
 268
 269 #define STAILQ_FOREACH(var, head, field)                                \
 270         for ((var) = ((head)->stqh_first);                              \
 271                 (var);                                                  \
 272                 (var) = ((var)->field.stqe_next))
 273
 274 #define STAILQ_CONCAT(head1, head2) do {                                \
 275         if (!STAILQ_EMPTY((head2))) {                                   \
 276                 *(head1)->stqh_last = (head2)->stqh_first;              \
 277                 (head1)->stqh_last = (head2)->stqh_last;                \
 278                 STAILQ_INIT((head2));                                   \
 279         }                                                               \
 280 } while (/*CONSTCOND*/0)
 281
 282 /*
 283  * Singly-linked Tail queue access methods.
 284  */
 285 #define STAILQ_EMPTY(head)      ((head)->stqh_first == NULL)
 286 #define STAILQ_FIRST(head)      ((head)->stqh_first)
 287 #define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
 288
 289
 290 /*
 291  * Simple queue definitions.
 292  */
 293 #define SIMPLEQ_HEAD(name, type)                                        \
 294 struct name {                                                           \
 295         struct type *sqh_first; /* first element */                     \
 296         struct type **sqh_last; /* addr of last next element */         \
 297 }
 298
 299 #define SIMPLEQ_HEAD_INITIALIZER(head)                                  \
 300         { NULL, &(head).sqh_first }
 301
 302 #define SIMPLEQ_ENTRY(type)                                             \
 303 struct {                                                                \
 304         struct type *sqe_next;  /* next element */                      \
 305 }
 306
 307 /*
 308  * Simple queue functions.
 309  */
 310 #define SIMPLEQ_INIT(head) do {                                         \
 311         (head)->sqh_first = NULL;                                       \
 312         (head)->sqh_last = &(head)->sqh_first;                          \
 313 } while (/*CONSTCOND*/0)
 314
 315 #define SIMPLEQ_INSERT_HEAD(head, elm, field) do {                      \
 316         if (((elm)->field.sqe_next = (head)->sqh_first) == NULL)        \
 317                 (head)->sqh_last = &(elm)->field.sqe_next;              \
 318         (head)->sqh_first = (elm);                                      \
 319 } while (/*CONSTCOND*/0)
 320
 321 #define SIMPLEQ_INSERT_TAIL(head, elm, field) do {                      \
 322         (elm)->field.sqe_next = NULL;                                   \
 323         *(head)->sqh_last = (elm);                                      \
 324         (head)->sqh_last = &(elm)->field.sqe_next;                      \
 325 } while (/*CONSTCOND*/0)
 326
 327 #define SIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do {            \
 328         if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL)\
 329                 (head)->sqh_last = &(elm)->field.sqe_next;              \
 330         (listelm)->field.sqe_next = (elm);                              \
 331 } while (/*CONSTCOND*/0)
 332
 333 #define SIMPLEQ_REMOVE_HEAD(head, field) do {                           \
 334         if (((head)->sqh_first = (head)->sqh_first->field.sqe_next) == NULL) \
 335                 (head)->sqh_last = &(head)->sqh_first;                  \
 336 } while (/*CONSTCOND*/0)
 337
 338 #define SIMPLEQ_REMOVE(head, elm, type, field) do {                     \
 339         if ((head)->sqh_first == (elm)) {                               \
 340                 SIMPLEQ_REMOVE_HEAD((head), field);                     \
 341         } else {                                                        \
 342                 struct type *curelm = (head)->sqh_first;                \
 343                 while (curelm->field.sqe_next != (elm))                 \
 344                         curelm = curelm->field.sqe_next;                \
 345                 if ((curelm->field.sqe_next =                           \
 346                         curelm->field.sqe_next->field.sqe_next) == NULL) \
 347                             (head)->sqh_last = &(curelm)->field.sqe_next; \
 348         }                                                               \
 349 } while (/*CONSTCOND*/0)
 350
 351 #define SIMPLEQ_FOREACH(var, head, field)                               \
 352         for ((var) = ((head)->sqh_first);                               \
 353                 (var);                                                  \
 354                 (var) = ((var)->field.sqe_next))
 355
 356 /*
 357  * Simple queue access methods.
 358  */
 359 #define SIMPLEQ_EMPTY(head)             ((head)->sqh_first == NULL)
 360 #define SIMPLEQ_FIRST(head)             ((head)->sqh_first)
 361 #define SIMPLEQ_NEXT(elm, field)        ((elm)->field.sqe_next)
 362
 363
 364 /*
 365  * Tail queue definitions.
 366  */
 367 #define _TAILQ_HEAD(name, type, qual)                                   \
 368 struct name {                                                           \
 369         qual type *tqh_first;           /* first element */             \
 370         qual type *qual *tqh_last;      /* addr of last next element */ \
 371 }
 372 #define TAILQ_HEAD(name, type)  _TAILQ_HEAD(name, struct type,)
 373
 374 #define TAILQ_HEAD_INITIALIZER(head)                                    \
 375         { NULL, &(head).tqh_first }
 376
 377 #define _TAILQ_ENTRY(type, qual)                                        \
 378 struct {                                                                \
 379         qual type *tqe_next;            /* next element */              \
 380         qual type *qual *tqe_prev;      /* address of previous next element */\
 381 }
 382 #define TAILQ_ENTRY(type)       _TAILQ_ENTRY(struct type,)
 383
 384 /*
 385  * Tail queue functions.
 386  */
 387 #define TAILQ_INIT(head) do {                                           \
 388         (head)->tqh_first = NULL;                                       \
 389         (head)->tqh_last = &(head)->tqh_first;                          \
 390 } while (/*CONSTCOND*/0)
 391
 392 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
 393         if (((elm)->field.tqe_next = (head)->tqh_first) != NULL)        \
 394                 (head)->tqh_first->field.tqe_prev =                     \
 395                     &(elm)->field.tqe_next;                             \
 396         else                                                            \
 397                 (head)->tqh_last = &(elm)->field.tqe_next;              \
 398         (head)->tqh_first = (elm);                                      \
 399         (elm)->field.tqe_prev = &(head)->tqh_first;                     \
 400 } while (/*CONSTCOND*/0)
 401
 402 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
 403         (elm)->field.tqe_next = NULL;                                   \
 404         (elm)->field.tqe_prev = (head)->tqh_last;                       \
 405         *(head)->tqh_last = (elm);                                      \
 406         (head)->tqh_last = &(elm)->field.tqe_next;                      \
 407 } while (/*CONSTCOND*/0)
 408
 409 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
 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         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
 421         (elm)->field.tqe_next = (listelm);                              \
 422         *(listelm)->field.tqe_prev = (elm);                             \
 423         (listelm)->field.tqe_prev = &(elm)->field.tqe_next;             \
 424 } while (/*CONSTCOND*/0)
 425
 426 #define TAILQ_REMOVE(head, elm, field) do {                             \
 427         if (((elm)->field.tqe_next) != NULL)                            \
 428                 (elm)->field.tqe_next->field.tqe_prev =                 \
 429                     (elm)->field.tqe_prev;                              \
 430         else                                                            \
 431                 (head)->tqh_last = (elm)->field.tqe_prev;               \
 432         *(elm)->field.tqe_prev = (elm)->field.tqe_next;                 \
 433 } while (/*CONSTCOND*/0)
 434
 435 #define TAILQ_FOREACH(var, head, field)                                 \
 436         for ((var) = ((head)->tqh_first);                               \
 437                 (var);                                                  \
 438                 (var) = ((var)->field.tqe_next))
 439
 440 #define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
 441         for ((var) = (*(((struct headname *)((head)->tqh_last))->tqh_last));    \
 442                 (var);                                                  \
 443                 (var) = (*(((struct headname *)((var)->field.tqe_prev))->tqh_last)))
 444
 445 #define TAILQ_CONCAT(head1, head2, field) do {                          \
 446         if (!TAILQ_EMPTY(head2)) {                                      \
 447                 *(head1)->tqh_last = (head2)->tqh_first;                \
 448                 (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last; \
 449                 (head1)->tqh_last = (head2)->tqh_last;                  \
 450                 TAILQ_INIT((head2));                                    \
 451         }                                                               \
 452 } while (/*CONSTCOND*/0)
 453
 454 /*
 455  * Tail queue access methods.
 456  */
 457 #define TAILQ_EMPTY(head)               ((head)->tqh_first == NULL)
 458 #define TAILQ_FIRST(head)               ((head)->tqh_first)
 459 #define TAILQ_NEXT(elm, field)          ((elm)->field.tqe_next)
 460
 461 #define TAILQ_LAST(head, headname) \
 462         (*(((struct headname *)((head)->tqh_last))->tqh_last))
 463 #define TAILQ_PREV(elm, headname, field) \
 464         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
 465
 466
 467 /*
 468  * Circular queue definitions.
 469  */
 470 #define CIRCLEQ_HEAD(name, type)                                        \
 471 struct name {                                                           \
 472         struct type *cqh_first;         /* first element */             \
 473         struct type *cqh_last;          /* last element */              \
 474 }
 475
 476 #define CIRCLEQ_HEAD_INITIALIZER(head)                                  \
 477         { (void *)&head, (void *)&head }
 478
 479 #define CIRCLEQ_ENTRY(type)                                             \
 480 struct {                                                                \
 481         struct type *cqe_next;          /* next element */              \
 482         struct type *cqe_prev;          /* previous element */          \
 483 }
 484
 485 /*
 486  * Circular queue functions.
 487  */
 488 #define CIRCLEQ_INIT(head) do {                                         \
 489         (head)->cqh_first = (void *)(head);                             \
 490         (head)->cqh_last = (void *)(head);                              \
 491 } while (/*CONSTCOND*/0)
 492
 493 #define CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {            \
 494         (elm)->field.cqe_next = (listelm)->field.cqe_next;              \
 495         (elm)->field.cqe_prev = (listelm);                              \
 496         if ((listelm)->field.cqe_next == (void *)(head))                \
 497                 (head)->cqh_last = (elm);                               \
 498         else                                                            \
 499                 (listelm)->field.cqe_next->field.cqe_prev = (elm);      \
 500         (listelm)->field.cqe_next = (elm);                              \
 501 } while (/*CONSTCOND*/0)
 502
 503 #define CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do {           \
 504         (elm)->field.cqe_next = (listelm);                              \
 505         (elm)->field.cqe_prev = (listelm)->field.cqe_prev;              \
 506         if ((listelm)->field.cqe_prev == (void *)(head))                \
 507                 (head)->cqh_first = (elm);                              \
 508         else                                                            \
 509                 (listelm)->field.cqe_prev->field.cqe_next = (elm);      \
 510         (listelm)->field.cqe_prev = (elm);                              \
 511 } while (/*CONSTCOND*/0)
 512
 513 #define CIRCLEQ_INSERT_HEAD(head, elm, field) do {                      \
 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         (elm)->field.cqe_next = (void *)(head);                         \
 525         (elm)->field.cqe_prev = (head)->cqh_last;                       \
 526         if ((head)->cqh_first == (void *)(head))                        \
 527                 (head)->cqh_first = (elm);                              \
 528         else                                                            \
 529                 (head)->cqh_last->field.cqe_next = (elm);               \
 530         (head)->cqh_last = (elm);                                       \
 531 } while (/*CONSTCOND*/0)
 532
 533 #define CIRCLEQ_REMOVE(head, elm, field) do {                           \
 534         if ((elm)->field.cqe_next == (void *)(head))                    \
 535                 (head)->cqh_last = (elm)->field.cqe_prev;               \
 536         else                                                            \
 537                 (elm)->field.cqe_next->field.cqe_prev =                 \
 538                     (elm)->field.cqe_prev;                              \
 539         if ((elm)->field.cqe_prev == (void *)(head))                    \
 540                 (head)->cqh_first = (elm)->field.cqe_next;              \
 541         else                                                            \
 542                 (elm)->field.cqe_prev->field.cqe_next =                 \
 543                     (elm)->field.cqe_next;                              \
 544 } while (/*CONSTCOND*/0)
 545
 546 #define CIRCLEQ_FOREACH(var, head, field)                               \
 547         for ((var) = ((head)->cqh_first);                               \
 548                 (var) != (const void *)(head);                          \
 549                 (var) = ((var)->field.cqe_next))
 550
 551 #define CIRCLEQ_FOREACH_REVERSE(var, head, field)                       \
 552         for ((var) = ((head)->cqh_last);                                \
 553                 (var) != (const void *)(head);                          \
 554                 (var) = ((var)->field.cqe_prev))
 555
 556 /*
 557  * Circular queue access methods.
 558  */
 559 #define CIRCLEQ_EMPTY(head)             ((head)->cqh_first == (void *)(head))
 560 #define CIRCLEQ_FIRST(head)             ((head)->cqh_first)
 561 #define CIRCLEQ_LAST(head)              ((head)->cqh_last)
 562 #define CIRCLEQ_NEXT(elm, field)        ((elm)->field.cqe_next)
 563 #define CIRCLEQ_PREV(elm, field)        ((elm)->field.cqe_prev)
 564
 565 #define CIRCLEQ_LOOP_NEXT(head, elm, field)                             \
 566         (((elm)->field.cqe_next == (void *)(head))                      \
 567             ? ((head)->cqh_first)                                       \
 568             : (elm->field.cqe_next))
 569 #define CIRCLEQ_LOOP_PREV(head, elm, field)                             \
 570         (((elm)->field.cqe_prev == (void *)(head))                      \
 571             ? ((head)->cqh_last)                                        \
 572             : (elm->field.cqe_prev))
 573
 574 #endif  /* sys/queue.h */