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   1 /*      $OpenBSD: queue.h,v 1.1 2007/10/26 03:14:08 niallo Exp $        */
   2 /*      $NetBSD: queue.h,v 1.11 1996/05/16 05:17:14 mycroft Exp $       */
   3
   4 /*
   5  * Copyright (c) 1991, 1993
   6  *      The Regents of the University of California.  All rights reserved.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  * 3. Neither the name of the University nor the names of its contributors
  17  *    may be used to endorse or promote products derived from this software
  18  *    without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  *
  32  *      @(#)queue.h     8.5 (Berkeley) 8/20/94
  33  */
  34
  35 #ifndef _SYS_QUEUE_H_
  36 #define _SYS_QUEUE_H_
  37
  38 /*
  39  * This file defines five types of data structures: singly-linked lists,
  40  * lists, simple queues, tail queues, and circular queues.
  41  *
  42  *
  43  * A singly-linked list is headed by a single forward pointer. The elements
  44  * are singly linked for minimum space and pointer manipulation overhead at
  45  * the expense of O(n) removal for arbitrary elements. New elements can be
  46  * added to the list after an existing element or at the head of the list.
  47  * Elements being removed from the head of the list should use the explicit
  48  * macro for this purpose for optimum efficiency. A singly-linked list may
  49  * only be traversed in the forward direction.  Singly-linked lists are ideal
  50  * for applications with large datasets and few or no removals or for
  51  * implementing a LIFO queue.
  52  *
  53  * A list is headed by a single forward pointer (or an array of forward
  54  * pointers for a hash table header). The elements are doubly linked
  55  * so that an arbitrary element can be removed without a need to
  56  * traverse the list. New elements can be added to the list before
  57  * or after an existing element or at the head of the list. A list
  58  * may only be traversed in the forward direction.
  59  *
  60  * A simple queue is headed by a pair of pointers, one the head of the
  61  * list and the other to the tail of the list. The elements are singly
  62  * linked to save space, so elements can only be removed from the
  63  * head of the list. New elements can be added to the list before or after
  64  * an existing element, at the head of the list, or at the end of the
  65  * list. A simple queue may only be traversed in the forward direction.
  66  *
  67  * A tail queue is headed by a pair of pointers, one to the head of the
  68  * list and the other to the tail of the list. The elements are doubly
  69  * linked so that an arbitrary element can be removed without a need to
  70  * traverse the list. New elements can be added to the list before or
  71  * after an existing element, at the head of the list, or at the end of
  72  * the list. A tail queue may be traversed in either direction.
  73  *
  74  * A circle queue is headed by a pair of pointers, one to the head of the
  75  * list and the other to the tail of the list. The elements are doubly
  76  * linked so that an arbitrary element can be removed without a need to
  77  * traverse the list. New elements can be added to the list before or after
  78  * an existing element, at the head of the list, or at the end of the list.
  79  * A circle queue may be traversed in either direction, but has a more
  80  * complex end of list detection.
  81  *
  82  * For details on the use of these macros, see the queue(3) manual page.
  83  */
  84
  85 #if defined(QUEUE_MACRO_DEBUG) || (defined(_KERNEL) && defined(DIAGNOSTIC))
  86 #define _Q_INVALIDATE(a) (a) = ((void *)-1)
  87 #else
  88 #define _Q_INVALIDATE(a)
  89 #endif
  90
  91 /*
  92  * Singly-linked List definitions.
  93  */
  94 #define SLIST_HEAD(name, type)                      \
  95     struct name {                                   \
  96         struct type *slh_first; /* first element */ \
  97     }
  98
  99 #define SLIST_HEAD_INITIALIZER(head) \
 100     { NULL }
 101
 102 #define SLIST_ENTRY(type)                         \
 103     struct {                                      \
 104         struct type *sle_next; /* next element */ \
 105     }
 106
 107 /*
 108  * Singly-linked List access methods.
 109  */
 110 #define SLIST_FIRST(head) ((head)->slh_first)
 111 #define SLIST_END(head) NULL
 112 #define SLIST_EMPTY(head) (SLIST_FIRST(head) == SLIST_END(head))
 113 #define SLIST_NEXT(elm, field) ((elm)->field.sle_next)
 114
 115 #define SLIST_FOREACH(var, head, field) \
 116     for ((var) = SLIST_FIRST(head);     \
 117          (var) != SLIST_END(head);      \
 118          (var) = SLIST_NEXT(var, field))
 119
 120 #define SLIST_FOREACH_PREVPTR(var, varp, head, field) \
 121     for ((varp) = &SLIST_FIRST((head));               \
 122          ((var) = *(varp)) != SLIST_END(head);        \
 123          (varp) = &SLIST_NEXT((var), field))
 124
 125 /*
 126  * Singly-linked List functions.
 127  */
 128 #define SLIST_INIT(head)                     \
 129     {                                        \
 130         SLIST_FIRST(head) = SLIST_END(head); \
 131     }
 132
 133 #define SLIST_INSERT_AFTER(slistelm, elm, field)            \
 134     do {                                                    \
 135         (elm)->field.sle_next = (slistelm)->field.sle_next; \
 136         (slistelm)->field.sle_next = (elm);                 \
 137     } while (0)
 138
 139 #define SLIST_INSERT_HEAD(head, elm, field)        \
 140     do {                                           \
 141         (elm)->field.sle_next = (head)->slh_first; \
 142         (head)->slh_first = (elm);                 \
 143     } while (0)
 144
 145 #define SLIST_REMOVE_NEXT(head, elm, field)                            \
 146     do {                                                               \
 147         (elm)->field.sle_next = (elm)->field.sle_next->field.sle_next; \
 148     } while (0)
 149
 150 #define SLIST_REMOVE_HEAD(head, field)                         \
 151     do {                                                       \
 152         (head)->slh_first = (head)->slh_first->field.sle_next; \
 153     } while (0)
 154
 155 #define SLIST_REMOVE(head, elm, type, field)                                 \
 156     do {                                                                     \
 157         if ((head)->slh_first == (elm)) {                                    \
 158             SLIST_REMOVE_HEAD((head), field);                                \
 159         } else {                                                             \
 160             struct type *curelm = (head)->slh_first;                         \
 161                                                                              \
 162             while (curelm->field.sle_next != (elm))                          \
 163                 curelm = curelm->field.sle_next;                             \
 164             curelm->field.sle_next = curelm->field.sle_next->field.sle_next; \
 165             _Q_INVALIDATE((elm)->field.sle_next);                            \
 166         }                                                                    \
 167     } while (0)
 168
 169 /*
 170  * List definitions.
 171  */
 172 #define LIST_HEAD(name, type)                      \
 173     struct name {                                  \
 174         struct type *lh_first; /* first element */ \
 175     }
 176
 177 #define LIST_HEAD_INITIALIZER(head) \
 178     { NULL }
 179
 180 #define LIST_ENTRY(type)                                              \
 181     struct {                                                          \
 182         struct type *le_next;  /* next element */                     \
 183         struct type **le_prev; /* address of previous next element */ \
 184     }
 185
 186 /*
 187  * List access methods
 188  */
 189 #define LIST_FIRST(head) ((head)->lh_first)
 190 #define LIST_END(head) NULL
 191 #define LIST_EMPTY(head) (LIST_FIRST(head) == LIST_END(head))
 192 #define LIST_NEXT(elm, field) ((elm)->field.le_next)
 193
 194 #define LIST_FOREACH(var, head, field) \
 195     for ((var) = LIST_FIRST(head);     \
 196          (var) != LIST_END(head);      \
 197          (var) = LIST_NEXT(var, field))
 198
 199 /*
 200  * List functions.
 201  */
 202 #define LIST_INIT(head)                    \
 203     do {                                   \
 204         LIST_FIRST(head) = LIST_END(head); \
 205     } while (0)
 206
 207 #define LIST_INSERT_AFTER(listelm, elm, field)                               \
 208     do {                                                                     \
 209         if (((elm)->field.le_next = (listelm)->field.le_next) != NULL)       \
 210             (listelm)->field.le_next->field.le_prev = &(elm)->field.le_next; \
 211         (listelm)->field.le_next = (elm);                                    \
 212         (elm)->field.le_prev = &(listelm)->field.le_next;                    \
 213     } while (0)
 214
 215 #define LIST_INSERT_BEFORE(listelm, elm, field)           \
 216     do {                                                  \
 217         (elm)->field.le_prev = (listelm)->field.le_prev;  \
 218         (elm)->field.le_next = (listelm);                 \
 219         *(listelm)->field.le_prev = (elm);                \
 220         (listelm)->field.le_prev = &(elm)->field.le_next; \
 221     } while (0)
 222
 223 #define LIST_INSERT_HEAD(head, elm, field)                           \
 224     do {                                                             \
 225         if (((elm)->field.le_next = (head)->lh_first) != NULL)       \
 226             (head)->lh_first->field.le_prev = &(elm)->field.le_next; \
 227         (head)->lh_first = (elm);                                    \
 228         (elm)->field.le_prev = &(head)->lh_first;                    \
 229     } while (0)
 230
 231 #define LIST_REMOVE(elm, field)                                         \
 232     do {                                                                \
 233         if ((elm)->field.le_next != NULL)                               \
 234             (elm)->field.le_next->field.le_prev = (elm)->field.le_prev; \
 235         *(elm)->field.le_prev = (elm)->field.le_next;                   \
 236         _Q_INVALIDATE((elm)->field.le_prev);                            \
 237         _Q_INVALIDATE((elm)->field.le_next);                            \
 238     } while (0)
 239
 240 #define LIST_REPLACE(elm, elm2, field)                                     \
 241     do {                                                                   \
 242         if (((elm2)->field.le_next = (elm)->field.le_next) != NULL)        \
 243             (elm2)->field.le_next->field.le_prev = &(elm2)->field.le_next; \
 244         (elm2)->field.le_prev = (elm)->field.le_prev;                      \
 245         *(elm2)->field.le_prev = (elm2);                                   \
 246         _Q_INVALIDATE((elm)->field.le_prev);                               \
 247         _Q_INVALIDATE((elm)->field.le_next);                               \
 248     } while (0)
 249
 250 /*
 251  * Simple queue definitions.
 252  */
 253 #define SIMPLEQ_HEAD(name, type)                                \
 254     struct name {                                               \
 255         struct type *sqh_first; /* first element */             \
 256         struct type **sqh_last; /* addr of last next element */ \
 257     }
 258
 259 #define SIMPLEQ_HEAD_INITIALIZER(head) \
 260     { NULL, &(head).sqh_first }
 261
 262 #define SIMPLEQ_ENTRY(type)                       \
 263     struct {                                      \
 264         struct type *sqe_next; /* next element */ \
 265     }
 266
 267 /*
 268  * Simple queue access methods.
 269  */
 270 #define SIMPLEQ_FIRST(head) ((head)->sqh_first)
 271 #define SIMPLEQ_END(head) NULL
 272 #define SIMPLEQ_EMPTY(head) (SIMPLEQ_FIRST(head) == SIMPLEQ_END(head))
 273 #define SIMPLEQ_NEXT(elm, field) ((elm)->field.sqe_next)
 274
 275 #define SIMPLEQ_FOREACH(var, head, field) \
 276     for ((var) = SIMPLEQ_FIRST(head);     \
 277          (var) != SIMPLEQ_END(head);      \
 278          (var) = SIMPLEQ_NEXT(var, field))
 279
 280 /*
 281  * Simple queue functions.
 282  */
 283 #define SIMPLEQ_INIT(head)                     \
 284     do {                                       \
 285         (head)->sqh_first = NULL;              \
 286         (head)->sqh_last = &(head)->sqh_first; \
 287     } while (0)
 288
 289 #define SIMPLEQ_INSERT_HEAD(head, elm, field)                    \
 290     do {                                                         \
 291         if (((elm)->field.sqe_next = (head)->sqh_first) == NULL) \
 292             (head)->sqh_last = &(elm)->field.sqe_next;           \
 293         (head)->sqh_first = (elm);                               \
 294     } while (0)
 295
 296 #define SIMPLEQ_INSERT_TAIL(head, elm, field)      \
 297     do {                                           \
 298         (elm)->field.sqe_next = NULL;              \
 299         *(head)->sqh_last = (elm);                 \
 300         (head)->sqh_last = &(elm)->field.sqe_next; \
 301     } while (0)
 302
 303 #define SIMPLEQ_INSERT_AFTER(head, listelm, elm, field)                  \
 304     do {                                                                 \
 305         if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL) \
 306             (head)->sqh_last = &(elm)->field.sqe_next;                   \
 307         (listelm)->field.sqe_next = (elm);                               \
 308     } while (0)
 309
 310 #define SIMPLEQ_REMOVE_HEAD(head, field)                                     \
 311     do {                                                                     \
 312         if (((head)->sqh_first = (head)->sqh_first->field.sqe_next) == NULL) \
 313             (head)->sqh_last = &(head)->sqh_first;                           \
 314     } while (0)
 315
 316 /*
 317  * Tail queue definitions.
 318  */
 319 #define TAILQ_HEAD(name, type)                                  \
 320     struct name {                                               \
 321         struct type *tqh_first; /* first element */             \
 322         struct type **tqh_last; /* addr of last next element */ \
 323     }
 324
 325 #define TAILQ_HEAD_INITIALIZER(head) \
 326     { NULL, &(head).tqh_first }
 327
 328 #define TAILQ_ENTRY(type)                                              \
 329     struct {                                                           \
 330         struct type *tqe_next;  /* next element */                     \
 331         struct type **tqe_prev; /* address of previous next element */ \
 332     }
 333
 334 /*
 335  * tail queue access methods
 336  */
 337 #define TAILQ_FIRST(head) ((head)->tqh_first)
 338 #define TAILQ_END(head) NULL
 339 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
 340 #define TAILQ_LAST(head, headname) \
 341     (*(((struct headname *)((head)->tqh_last))->tqh_last))
 342 /* XXX */
 343 #define TAILQ_PREV(elm, headname, field) \
 344     (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
 345 #define TAILQ_EMPTY(head) \
 346     (TAILQ_FIRST(head) == TAILQ_END(head))
 347
 348 #define TAILQ_FOREACH(var, head, field) \
 349     for ((var) = TAILQ_FIRST(head);     \
 350          (var) != TAILQ_END(head);      \
 351          (var) = TAILQ_NEXT(var, field))
 352
 353 #define TAILQ_FOREACH_REVERSE(var, head, headname, field) \
 354     for ((var) = TAILQ_LAST(head, headname);              \
 355          (var) != TAILQ_END(head);                        \
 356          (var) = TAILQ_PREV(var, headname, field))
 357
 358 /*
 359  * Tail queue functions.
 360  */
 361 #define TAILQ_INIT(head)                       \
 362     do {                                       \
 363         (head)->tqh_first = NULL;              \
 364         (head)->tqh_last = &(head)->tqh_first; \
 365     } while (0)
 366
 367 #define TAILQ_INSERT_HEAD(head, elm, field)                             \
 368     do {                                                                \
 369         if (((elm)->field.tqe_next = (head)->tqh_first) != NULL)        \
 370             (head)->tqh_first->field.tqe_prev = &(elm)->field.tqe_next; \
 371         else                                                            \
 372             (head)->tqh_last = &(elm)->field.tqe_next;                  \
 373         (head)->tqh_first = (elm);                                      \
 374         (elm)->field.tqe_prev = &(head)->tqh_first;                     \
 375     } while (0)
 376
 377 #define TAILQ_INSERT_TAIL(head, elm, field)        \
 378     do {                                           \
 379         (elm)->field.tqe_next = NULL;              \
 380         (elm)->field.tqe_prev = (head)->tqh_last;  \
 381         *(head)->tqh_last = (elm);                 \
 382         (head)->tqh_last = &(elm)->field.tqe_next; \
 383     } while (0)
 384
 385 #define TAILQ_INSERT_AFTER(head, listelm, elm, field)                       \
 386     do {                                                                    \
 387         if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)    \
 388             (elm)->field.tqe_next->field.tqe_prev = &(elm)->field.tqe_next; \
 389         else                                                                \
 390             (head)->tqh_last = &(elm)->field.tqe_next;                      \
 391         (listelm)->field.tqe_next = (elm);                                  \
 392         (elm)->field.tqe_prev = &(listelm)->field.tqe_next;                 \
 393     } while (0)
 394
 395 #define TAILQ_INSERT_BEFORE(listelm, elm, field)            \
 396     do {                                                    \
 397         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;  \
 398         (elm)->field.tqe_next = (listelm);                  \
 399         *(listelm)->field.tqe_prev = (elm);                 \
 400         (listelm)->field.tqe_prev = &(elm)->field.tqe_next; \
 401     } while (0)
 402
 403 #define TAILQ_REMOVE(head, elm, field)                                     \
 404     do {                                                                   \
 405         if (((elm)->field.tqe_next) != NULL)                               \
 406             (elm)->field.tqe_next->field.tqe_prev = (elm)->field.tqe_prev; \
 407         else                                                               \
 408             (head)->tqh_last = (elm)->field.tqe_prev;                      \
 409         *(elm)->field.tqe_prev = (elm)->field.tqe_next;                    \
 410         _Q_INVALIDATE((elm)->field.tqe_prev);                              \
 411         _Q_INVALIDATE((elm)->field.tqe_next);                              \
 412     } while (0)
 413
 414 #define TAILQ_REPLACE(head, elm, elm2, field)                                 \
 415     do {                                                                      \
 416         if (((elm2)->field.tqe_next = (elm)->field.tqe_next) != NULL)         \
 417             (elm2)->field.tqe_next->field.tqe_prev = &(elm2)->field.tqe_next; \
 418         else                                                                  \
 419             (head)->tqh_last = &(elm2)->field.tqe_next;                       \
 420         (elm2)->field.tqe_prev = (elm)->field.tqe_prev;                       \
 421         *(elm2)->field.tqe_prev = (elm2);                                     \
 422         _Q_INVALIDATE((elm)->field.tqe_prev);                                 \
 423         _Q_INVALIDATE((elm)->field.tqe_next);                                 \
 424     } while (0)
 425
 426 /*
 427  * Circular queue definitions.
 428  */
 429 #define CIRCLEQ_HEAD(name, type)                    \
 430     struct name {                                   \
 431         struct type *cqh_first; /* first element */ \
 432         struct type *cqh_last;  /* last element */  \
 433     }
 434
 435 #define CIRCLEQ_HEAD_INITIALIZER(head) \
 436     {                                  \
 437         CIRCLEQ_END(&head)             \
 438         , CIRCLEQ_END(&head)           \
 439     }
 440
 441 #define CIRCLEQ_ENTRY(type)                           \
 442     struct {                                          \
 443         struct type *cqe_next; /* next element */     \
 444         struct type *cqe_prev; /* previous element */ \
 445     }
 446
 447 /*
 448  * Circular queue access methods
 449  */
 450 #define CIRCLEQ_FIRST(head) ((head)->cqh_first)
 451 #define CIRCLEQ_LAST(head) ((head)->cqh_last)
 452 #define CIRCLEQ_END(head) ((void *)(head))
 453 #define CIRCLEQ_NEXT(elm, field) ((elm)->field.cqe_next)
 454 #define CIRCLEQ_PREV(elm, field) ((elm)->field.cqe_prev)
 455 #define CIRCLEQ_EMPTY(head) \
 456     (CIRCLEQ_FIRST(head) == CIRCLEQ_END(head))
 457
 458 #define CIRCLEQ_FOREACH(var, head, field) \
 459     for ((var) = CIRCLEQ_FIRST(head);     \
 460          (var) != CIRCLEQ_END(head);      \
 461          (var) = CIRCLEQ_NEXT(var, field))
 462
 463 #define CIRCLEQ_FOREACH_REVERSE(var, head, field) \
 464     for ((var) = CIRCLEQ_LAST(head);              \
 465          (var) != CIRCLEQ_END(head);              \
 466          (var) = CIRCLEQ_PREV(var, field))
 467
 468 /*
 469  * Circular queue functions.
 470  */
 471 #define CIRCLEQ_INIT(head)                     \
 472     do {                                       \
 473         (head)->cqh_first = CIRCLEQ_END(head); \
 474         (head)->cqh_last = CIRCLEQ_END(head);  \
 475     } while (0)
 476
 477 #define CIRCLEQ_INSERT_AFTER(head, listelm, elm, field)        \
 478     do {                                                       \
 479         (elm)->field.cqe_next = (listelm)->field.cqe_next;     \
 480         (elm)->field.cqe_prev = (listelm);                     \
 481         if ((listelm)->field.cqe_next == CIRCLEQ_END(head))    \
 482             (head)->cqh_last = (elm);                          \
 483         else                                                   \
 484             (listelm)->field.cqe_next->field.cqe_prev = (elm); \
 485         (listelm)->field.cqe_next = (elm);                     \
 486     } while (0)
 487
 488 #define CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field)       \
 489     do {                                                       \
 490         (elm)->field.cqe_next = (listelm);                     \
 491         (elm)->field.cqe_prev = (listelm)->field.cqe_prev;     \
 492         if ((listelm)->field.cqe_prev == CIRCLEQ_END(head))    \
 493             (head)->cqh_first = (elm);                         \
 494         else                                                   \
 495             (listelm)->field.cqe_prev->field.cqe_next = (elm); \
 496         (listelm)->field.cqe_prev = (elm);                     \
 497     } while (0)
 498
 499 #define CIRCLEQ_INSERT_HEAD(head, elm, field)          \
 500     do {                                               \
 501         (elm)->field.cqe_next = (head)->cqh_first;     \
 502         (elm)->field.cqe_prev = CIRCLEQ_END(head);     \
 503         if ((head)->cqh_last == CIRCLEQ_END(head))     \
 504             (head)->cqh_last = (elm);                  \
 505         else                                           \
 506             (head)->cqh_first->field.cqe_prev = (elm); \
 507         (head)->cqh_first = (elm);                     \
 508     } while (0)
 509
 510 #define CIRCLEQ_INSERT_TAIL(head, elm, field)         \
 511     do {                                              \
 512         (elm)->field.cqe_next = CIRCLEQ_END(head);    \
 513         (elm)->field.cqe_prev = (head)->cqh_last;     \
 514         if ((head)->cqh_first == CIRCLEQ_END(head))   \
 515             (head)->cqh_first = (elm);                \
 516         else                                          \
 517             (head)->cqh_last->field.cqe_next = (elm); \
 518         (head)->cqh_last = (elm);                     \
 519     } while (0)
 520
 521 #define CIRCLEQ_REMOVE(head, elm, field)                                   \
 522     do {                                                                   \
 523         if ((elm)->field.cqe_next == CIRCLEQ_END(head))                    \
 524             (head)->cqh_last = (elm)->field.cqe_prev;                      \
 525         else                                                               \
 526             (elm)->field.cqe_next->field.cqe_prev = (elm)->field.cqe_prev; \
 527         if ((elm)->field.cqe_prev == CIRCLEQ_END(head))                    \
 528             (head)->cqh_first = (elm)->field.cqe_next;                     \
 529         else                                                               \
 530             (elm)->field.cqe_prev->field.cqe_next = (elm)->field.cqe_next; \
 531         _Q_INVALIDATE((elm)->field.cqe_prev);                              \
 532         _Q_INVALIDATE((elm)->field.cqe_next);                              \
 533     } while (0)
 534
 535 #define CIRCLEQ_REPLACE(head, elm, elm2, field)                                    \
 536     do {                                                                           \
 537         if (((elm2)->field.cqe_next = (elm)->field.cqe_next) == CIRCLEQ_END(head)) \
 538             (head)->cqh_last = (elm2);                                             \
 539         else                                                                       \
 540             (elm2)->field.cqe_next->field.cqe_prev = (elm2);                       \
 541         if (((elm2)->field.cqe_prev = (elm)->field.cqe_prev) == CIRCLEQ_END(head)) \
 542             (head)->cqh_first = (elm2);                                            \
 543         else                                                                       \
 544             (elm2)->field.cqe_prev->field.cqe_next = (elm2);                       \
 545         _Q_INVALIDATE((elm)->field.cqe_prev);                                      \
 546         _Q_INVALIDATE((elm)->field.cqe_next);                                      \
 547     } while (0)
 548
 549 #endif /* !_SYS_QUEUE_H_ */