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   1 /*      $OpenBSD: queue.h,v 1.22 2001/06/23 04:39:35 angelos Exp $      */
   2 /*      $NetBSD: queue.h,v 1.11 1996/05/16 05:17:14 mycroft Exp $       */
   3
   4 /*
   5  *      University of California, Berkeley "advertising clause" removed as per
   6  *      authorisation given by William Hoskins, Director, Office of Technology
   7  *      Licensing, University of California, Berkeley, on the 22nd day of July
   8  *      1999.
   9  */
  10
  11 /*
  12  * Copyright (c) 1991, 1993
  13  *      The Regents of the University of California.  All rights reserved.
  14  *
  15  * Redistribution and use in source and binary forms, with or without
  16  * modification, are permitted provided that the following conditions
  17  * are met:
  18  * 1. Redistributions of source code must retain the above copyright
  19  *    notice, this list of conditions and the following disclaimer.
  20  * 2. Redistributions in binary form must reproduce the above copyright
  21  *    notice, this list of conditions and the following disclaimer in the
  22  *    documentation and/or other materials provided with the distribution.
  23  * 3. Neither the name of the University nor the names of its contributors
  24  *    may be used to endorse or promote products derived from this software
  25  *    without specific prior written permission.
  26  *
  27  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  28  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  29  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  30  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  31  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  32  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  33  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  34  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  35  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  36  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  37  * SUCH DAMAGE.
  38  *
  39  *      @(#)queue.h     8.5 (Berkeley) 8/20/94
  40  */
  41
  42 #ifndef _LOCAL_SYS_QUEUE_H_
  43 #define _LOCAL_SYS_QUEUE_H_
  44
  45 /*
  46  * This file defines five types of data structures: singly-linked lists,
  47  * lists, simple queues, tail queues, and circular queues.
  48  *
  49  *
  50  * A singly-linked list is headed by a single forward pointer. The elements
  51  * are singly linked for minimum space and pointer manipulation overhead at
  52  * the expense of O(n) removal for arbitrary elements. New elements can be
  53  * added to the list after an existing element or at the head of the list.
  54  * Elements being removed from the head of the list should use the explicit
  55  * macro for this purpose for optimum efficiency. A singly-linked list may
  56  * only be traversed in the forward direction.  Singly-linked lists are ideal
  57  * for applications with large datasets and few or no removals or for
  58  * implementing a LIFO queue.
  59  *
  60  * A list is headed by a single forward pointer (or an array of forward
  61  * pointers for a hash table header). The elements are doubly linked
  62  * so that an arbitrary element can be removed without a need to
  63  * traverse the list. New elements can be added to the list before
  64  * or after an existing element or at the head of the list. A list
  65  * may only be traversed in the forward direction.
  66  *
  67  * A simple queue is headed by a pair of pointers, one the head of the
  68  * list and the other to the tail of the list. The elements are singly
  69  * linked to save space, so elements can only be removed from the
  70  * head of the list. New elements can be added to the list before or after
  71  * an existing element, at the head of the list, or at the end of the
  72  * list. A simple queue may only be traversed in the forward direction.
  73  *
  74  * A tail 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
  78  * after an existing element, at the head of the list, or at the end of
  79  * the list. A tail queue may be traversed in either direction.
  80  *
  81  * A circle queue is headed by a pair of pointers, one to the head of the
  82  * list and the other to the tail of the list. The elements are doubly
  83  * linked so that an arbitrary element can be removed without a need to
  84  * traverse the list. New elements can be added to the list before or after
  85  * an existing element, at the head of the list, or at the end of the list.
  86  * A circle queue may be traversed in either direction, but has a more
  87  * complex end of list detection.
  88  *
  89  * For details on the use of these macros, see the queue(3) manual page.
  90  */
  91
  92 /*
  93  * Singly-linked List definitions.
  94  */
  95 #define SLIST_HEAD(name, type)                                          \
  96 struct name {                                                           \
  97         struct type *slh_first; /* first element */                     \
  98 }
  99
 100 #define SLIST_HEAD_INITIALIZER(head)                                    \
 101         { NULL }
 102
 103 /* Conflicts with winnt.h */
 104 #define bSLIST_ENTRY(type)                                               \
 105 struct {                                                                \
 106         struct type *sle_next;  /* next element */                      \
 107 }
 108
 109 /*
 110  * Singly-linked List access methods.
 111  */
 112 #define SLIST_FIRST(head)       ((head)->slh_first)
 113 #define SLIST_END(head)         NULL
 114 #define SLIST_EMPTY(head)       (SLIST_FIRST(head) == SLIST_END(head))
 115 #define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)
 116
 117 #define SLIST_FOREACH(var, head, field)                                 \
 118         for((var) = SLIST_FIRST(head);                                  \
 119             (var) != SLIST_END(head);                                   \
 120             (var) = SLIST_NEXT(var, field))
 121
 122 #define SLIST_FOREACH_SAFE(var, head, field, tvar)                      \
 123         for((var) = SLIST_FIRST(head);                                  \
 124             (var) != SLIST_END(head) &&                                 \
 125             ((tvar) = SLIST_NEXT(var, field), 1);                       \
 126             (var) = (tvar))
 127
 128 /*
 129  * Singly-linked List functions.
 130  */
 131 #define SLIST_INIT(head) {                                              \
 132         SLIST_FIRST(head) = SLIST_END(head);                            \
 133 }
 134
 135 #define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
 136         (elm)->field.sle_next = (slistelm)->field.sle_next;             \
 137         (slistelm)->field.sle_next = (elm);                             \
 138 } while (0)
 139
 140 #define SLIST_INSERT_HEAD(head, elm, field) do {                        \
 141         (elm)->field.sle_next = (head)->slh_first;                      \
 142         (head)->slh_first = (elm);                                      \
 143 } while (0)
 144
 145 #define SLIST_REMOVE_HEAD(head, field) do {                             \
 146         (head)->slh_first = (head)->slh_first->field.sle_next;          \
 147 } while (0)
 148
 149 #define SLIST_REMOVE(head, elm, type, field) do {                       \
 150         if ((head)->slh_first == (elm)) {                               \
 151                 SLIST_REMOVE_HEAD((head), field);                       \
 152         }                                                               \
 153         else {                                                          \
 154                 struct type *curelm = (head)->slh_first;                \
 155                 while( curelm->field.sle_next != (elm) )                \
 156                         curelm = curelm->field.sle_next;                \
 157                 curelm->field.sle_next =                                \
 158                     curelm->field.sle_next->field.sle_next;             \
 159         }                                                               \
 160 } while (0)
 161
 162 /*
 163  * List definitions.
 164  */
 165 #define LIST_HEAD(name, type)                                           \
 166 struct name {                                                           \
 167         struct type *lh_first;  /* first element */                     \
 168 }
 169
 170 #define LIST_HEAD_INITIALIZER(head)                                     \
 171         { NULL }
 172
 173 #define LIST_ENTRY(type)                                                \
 174 struct {                                                                \
 175         struct type *le_next;   /* next element */                      \
 176         struct type **le_prev;  /* address of previous next element */  \
 177 }
 178
 179 /*
 180  * List access methods
 181  */
 182 #define LIST_FIRST(head)                ((head)->lh_first)
 183 #define LIST_END(head)                  NULL
 184 #define LIST_EMPTY(head)                (LIST_FIRST(head) == LIST_END(head))
 185 #define LIST_NEXT(elm, field)           ((elm)->field.le_next)
 186
 187 #define LIST_FOREACH(var, head, field)                                  \
 188         for((var) = LIST_FIRST(head);                                   \
 189             (var)!= LIST_END(head);                                     \
 190             (var) = LIST_NEXT(var, field))
 191
 192 #define LIST_FOREACH_SAFE(var, head, field, tvar)                       \
 193         for((var) = LIST_FIRST(head);                                   \
 194             (var)!= LIST_END(head) &&                                   \
 195             ((tvar) = LIST_NEXT(var, field), 1);                        \
 196             (var) = (tvar))
 197
 198
 199 /*
 200  * List functions.
 201  */
 202 #define LIST_INIT(head) do {                                            \
 203         LIST_FIRST(head) = LIST_END(head);                              \
 204 } while (0)
 205
 206 #define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
 207         if (((elm)->field.le_next = (listelm)->field.le_next) != NULL)  \
 208                 (listelm)->field.le_next->field.le_prev =               \
 209                     &(elm)->field.le_next;                              \
 210         (listelm)->field.le_next = (elm);                               \
 211         (elm)->field.le_prev = &(listelm)->field.le_next;               \
 212 } while (0)
 213
 214 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
 215         (elm)->field.le_prev = (listelm)->field.le_prev;                \
 216         (elm)->field.le_next = (listelm);                               \
 217         *(listelm)->field.le_prev = (elm);                              \
 218         (listelm)->field.le_prev = &(elm)->field.le_next;               \
 219 } while (0)
 220
 221 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
 222         if (((elm)->field.le_next = (head)->lh_first) != NULL)          \
 223                 (head)->lh_first->field.le_prev = &(elm)->field.le_next;\
 224         (head)->lh_first = (elm);                                       \
 225         (elm)->field.le_prev = &(head)->lh_first;                       \
 226 } while (0)
 227
 228 #define LIST_REMOVE(elm, field) do {                                    \
 229         if ((elm)->field.le_next != NULL)                               \
 230                 (elm)->field.le_next->field.le_prev =                   \
 231                     (elm)->field.le_prev;                               \
 232         *(elm)->field.le_prev = (elm)->field.le_next;                   \
 233 } while (0)
 234
 235 #define LIST_REPLACE(elm, elm2, field) do {                             \
 236         if (((elm2)->field.le_next = (elm)->field.le_next) != NULL)     \
 237                 (elm2)->field.le_next->field.le_prev =                  \
 238                     &(elm2)->field.le_next;                             \
 239         (elm2)->field.le_prev = (elm)->field.le_prev;                   \
 240         *(elm2)->field.le_prev = (elm2);                                \
 241 } while (0)
 242
 243 /*
 244  * Simple queue definitions.
 245  */
 246 #define SIMPLEQ_HEAD(name, type)                                        \
 247 struct name {                                                           \
 248         struct type *sqh_first; /* first element */                     \
 249         struct type **sqh_last; /* addr of last next element */         \
 250 }
 251
 252 #define SIMPLEQ_HEAD_INITIALIZER(head)                                  \
 253         { NULL, &(head).sqh_first }
 254
 255 #define SIMPLEQ_ENTRY(type)                                             \
 256 struct {                                                                \
 257         struct type *sqe_next;  /* next element */                      \
 258 }
 259
 260 /*
 261  * Simple queue access methods.
 262  */
 263 #define SIMPLEQ_FIRST(head)         ((head)->sqh_first)
 264 #define SIMPLEQ_END(head)           NULL
 265 #define SIMPLEQ_EMPTY(head)         (SIMPLEQ_FIRST(head) == SIMPLEQ_END(head))
 266 #define SIMPLEQ_NEXT(elm, field)    ((elm)->field.sqe_next)
 267
 268 #define SIMPLEQ_FOREACH(var, head, field)                               \
 269         for((var) = SIMPLEQ_FIRST(head);                                \
 270             (var) != SIMPLEQ_END(head);                                 \
 271             (var) = SIMPLEQ_NEXT(var, field))
 272
 273 #define SIMPLEQ_FOREACH_SAFE(var, head, field, tvar)                    \
 274         for((var) = SIMPLEQ_FIRST(head);                                \
 275             (var) != SIMPLEQ_END(head) &&                               \
 276             ((tvar) = SIMPLEQ_NEXT(var, field), 1);                     \
 277             (var) = (tvar))
 278
 279 /*
 280  * Simple queue functions.
 281  */
 282 #define SIMPLEQ_INIT(head) do {                                         \
 283         (head)->sqh_first = NULL;                                       \
 284         (head)->sqh_last = &(head)->sqh_first;                          \
 285 } while (0)
 286
 287 #define SIMPLEQ_INSERT_HEAD(head, elm, field) do {                      \
 288         if (((elm)->field.sqe_next = (head)->sqh_first) == NULL)        \
 289                 (head)->sqh_last = &(elm)->field.sqe_next;              \
 290         (head)->sqh_first = (elm);                                      \
 291 } while (0)
 292
 293 #define SIMPLEQ_INSERT_TAIL(head, elm, field) do {                      \
 294         (elm)->field.sqe_next = NULL;                                   \
 295         *(head)->sqh_last = (elm);                                      \
 296         (head)->sqh_last = &(elm)->field.sqe_next;                      \
 297 } while (0)
 298
 299 #define SIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do {            \
 300         if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL)\
 301                 (head)->sqh_last = &(elm)->field.sqe_next;              \
 302         (listelm)->field.sqe_next = (elm);                              \
 303 } while (0)
 304
 305 #define SIMPLEQ_REMOVE_HEAD(head, elm, field) do {                      \
 306         if (((head)->sqh_first = (elm)->field.sqe_next) == NULL)        \
 307                 (head)->sqh_last = &(head)->sqh_first;                  \
 308 } while (0)
 309
 310 /*
 311  * Tail queue definitions.
 312  */
 313 #define TAILQ_HEAD(name, type)                                          \
 314 struct name {                                                           \
 315         struct type *tqh_first; /* first element */                     \
 316         struct type **tqh_last; /* addr of last next element */         \
 317 }
 318
 319 #define TAILQ_HEAD_INITIALIZER(head)                                    \
 320         { NULL, &(head).tqh_first }
 321
 322 #define TAILQ_ENTRY(type)                                               \
 323 struct {                                                                \
 324         struct type *tqe_next;  /* next element */                      \
 325         struct type **tqe_prev; /* address of previous next element */  \
 326 }
 327
 328 /*
 329  * tail queue access methods
 330  */
 331 #define TAILQ_FIRST(head)               ((head)->tqh_first)
 332 #define TAILQ_END(head)                 NULL
 333 #define TAILQ_NEXT(elm, field)          ((elm)->field.tqe_next)
 334 #define TAILQ_LAST(head, headname)                                      \
 335         (*(((struct headname *)((head)->tqh_last))->tqh_last))
 336 /* XXX */
 337 #define TAILQ_PREV(elm, headname, field)                                \
 338         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
 339 #define TAILQ_EMPTY(head)                                               \
 340         (TAILQ_FIRST(head) == TAILQ_END(head))
 341
 342 #define TAILQ_FOREACH(var, head, field)                                 \
 343         for((var) = TAILQ_FIRST(head);                                  \
 344             (var) != TAILQ_END(head);                                   \
 345             (var) = TAILQ_NEXT(var, field))
 346
 347 #define TAILQ_FOREACH_SAFE(var, head, field, tvar)                      \
 348         for((var) = TAILQ_FIRST(head);                                  \
 349             (var) != TAILQ_END(head) &&                                 \
 350             ((tvar) = TAILQ_NEXT(var, field), 1);                       \
 351             (var) = (tvar))
 352
 353 #define TAILQ_FOREACH_REVERSE(var, head, field, headname)               \
 354         for((var) = TAILQ_LAST(head, headname);                         \
 355             (var) != TAILQ_END(head);                                   \
 356             (var) = TAILQ_PREV(var, headname, field))
 357
 358 #define TAILQ_FOREACH_REVERSE_SAFE(var, head, field, headname, tvar)    \
 359         for((var) = TAILQ_LAST(head, headname);                         \
 360             (var) != TAILQ_END(head) &&                                 \
 361             ((tvar) = TAILQ_PREV(var, headname, field), 1);             \
 362             (var) = (tvar))
 363
 364 /*
 365  * Tail queue functions.
 366  */
 367 #define TAILQ_INIT(head) do {                                           \
 368         (head)->tqh_first = NULL;                                       \
 369         (head)->tqh_last = &(head)->tqh_first;                          \
 370 } while (0)
 371
 372 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
 373         if (((elm)->field.tqe_next = (head)->tqh_first) != NULL)        \
 374                 (head)->tqh_first->field.tqe_prev =                     \
 375                     &(elm)->field.tqe_next;                             \
 376         else                                                            \
 377                 (head)->tqh_last = &(elm)->field.tqe_next;              \
 378         (head)->tqh_first = (elm);                                      \
 379         (elm)->field.tqe_prev = &(head)->tqh_first;                     \
 380 } while (0)
 381
 382 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
 383         (elm)->field.tqe_next = NULL;                                   \
 384         (elm)->field.tqe_prev = (head)->tqh_last;                       \
 385         *(head)->tqh_last = (elm);                                      \
 386         (head)->tqh_last = &(elm)->field.tqe_next;                      \
 387 } while (0)
 388
 389 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
 390         if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)\
 391                 (elm)->field.tqe_next->field.tqe_prev =                 \
 392                     &(elm)->field.tqe_next;                             \
 393         else                                                            \
 394                 (head)->tqh_last = &(elm)->field.tqe_next;              \
 395         (listelm)->field.tqe_next = (elm);                              \
 396         (elm)->field.tqe_prev = &(listelm)->field.tqe_next;             \
 397 } while (0)
 398
 399 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
 400         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
 401         (elm)->field.tqe_next = (listelm);                              \
 402         *(listelm)->field.tqe_prev = (elm);                             \
 403         (listelm)->field.tqe_prev = &(elm)->field.tqe_next;             \
 404 } while (0)
 405
 406 #define TAILQ_REMOVE(head, elm, field) do {                             \
 407         if (((elm)->field.tqe_next) != NULL)                            \
 408                 (elm)->field.tqe_next->field.tqe_prev =                 \
 409                     (elm)->field.tqe_prev;                              \
 410         else                                                            \
 411                 (head)->tqh_last = (elm)->field.tqe_prev;               \
 412         *(elm)->field.tqe_prev = (elm)->field.tqe_next;                 \
 413 } while (0)
 414
 415 #define TAILQ_REPLACE(head, elm, elm2, field) do {                      \
 416         if (((elm2)->field.tqe_next = (elm)->field.tqe_next) != NULL)   \
 417                 (elm2)->field.tqe_next->field.tqe_prev =                \
 418                     &(elm2)->field.tqe_next;                            \
 419         else                                                            \
 420                 (head)->tqh_last = &(elm2)->field.tqe_next;             \
 421         (elm2)->field.tqe_prev = (elm)->field.tqe_prev;                 \
 422         *(elm2)->field.tqe_prev = (elm2);                               \
 423 } while (0)
 424
 425 /*
 426  * Circular queue definitions.
 427  */
 428 #define CIRCLEQ_HEAD(name, type)                                        \
 429 struct name {                                                           \
 430         struct type *cqh_first;         /* first element */             \
 431         struct type *cqh_last;          /* last element */              \
 432 }
 433
 434 #define CIRCLEQ_HEAD_INITIALIZER(head)                                  \
 435         { CIRCLEQ_END(&head), CIRCLEQ_END(&head) }
 436
 437 #define CIRCLEQ_ENTRY(type)                                             \
 438 struct {                                                                \
 439         struct type *cqe_next;          /* next element */              \
 440         struct type *cqe_prev;          /* previous element */          \
 441 }
 442
 443 /*
 444  * Circular queue access methods
 445  */
 446 #define CIRCLEQ_FIRST(head)             ((head)->cqh_first)
 447 #define CIRCLEQ_LAST(head)              ((head)->cqh_last)
 448 #define CIRCLEQ_END(head)               ((void *)(head))
 449 #define CIRCLEQ_NEXT(elm, field)        ((elm)->field.cqe_next)
 450 #define CIRCLEQ_PREV(elm, field)        ((elm)->field.cqe_prev)
 451 #define CIRCLEQ_EMPTY(head)                                             \
 452         (CIRCLEQ_FIRST(head) == CIRCLEQ_END(head))
 453
 454 #define CIRCLEQ_FOREACH(var, head, field)                               \
 455         for((var) = CIRCLEQ_FIRST(head);                                \
 456             (var) != CIRCLEQ_END(head);                                 \
 457             (var) = CIRCLEQ_NEXT(var, field))
 458
 459 #define CIRCLEQ_FOREACH_SAFE(var, head, field, tvar)                    \
 460         for((var) = CIRCLEQ_FIRST(head);                                \
 461             (var) != CIRCLEQ_END(head) &&                               \
 462             ((tvar) = CIRCLEQ_NEXT(var, field), 1);                     \
 463             (var) = (tvar))
 464
 465 #define CIRCLEQ_FOREACH_REVERSE(var, head, field)                       \
 466         for((var) = CIRCLEQ_LAST(head);                                 \
 467             (var) != CIRCLEQ_END(head);                                 \
 468             (var) = CIRCLEQ_PREV(var, field))
 469
 470 #define CIRCLEQ_FOREACH_REVERSE_SAFE(var, head, field, tvar)            \
 471         for((var) = CIRCLEQ_LAST(head);                                 \
 472             (var) != CIRCLEQ_END(head) &&                               \
 473             ((tvar) = CIRCLEQ_PREV(var, field), 1);                     \
 474             (var) = (tvar))
 475
 476 /*
 477  * Circular queue functions.
 478  */
 479 #define CIRCLEQ_INIT(head) do {                                         \
 480         (head)->cqh_first = CIRCLEQ_END(head);                          \
 481         (head)->cqh_last = CIRCLEQ_END(head);                           \
 482 } while (0)
 483
 484 #define CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {            \
 485         (elm)->field.cqe_next = (listelm)->field.cqe_next;              \
 486         (elm)->field.cqe_prev = (listelm);                              \
 487         if ((listelm)->field.cqe_next == CIRCLEQ_END(head))             \
 488                 (head)->cqh_last = (elm);                               \
 489         else                                                            \
 490                 (listelm)->field.cqe_next->field.cqe_prev = (elm);      \
 491         (listelm)->field.cqe_next = (elm);                              \
 492 } while (0)
 493
 494 #define CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do {           \
 495         (elm)->field.cqe_next = (listelm);                              \
 496         (elm)->field.cqe_prev = (listelm)->field.cqe_prev;              \
 497         if ((listelm)->field.cqe_prev == CIRCLEQ_END(head))             \
 498                 (head)->cqh_first = (elm);                              \
 499         else                                                            \
 500                 (listelm)->field.cqe_prev->field.cqe_next = (elm);      \
 501         (listelm)->field.cqe_prev = (elm);                              \
 502 } while (0)
 503
 504 #define CIRCLEQ_INSERT_HEAD(head, elm, field) do {                      \
 505         (elm)->field.cqe_next = (head)->cqh_first;                      \
 506         (elm)->field.cqe_prev = CIRCLEQ_END(head);                      \
 507         if ((head)->cqh_last == CIRCLEQ_END(head))                      \
 508                 (head)->cqh_last = (elm);                               \
 509         else                                                            \
 510                 (head)->cqh_first->field.cqe_prev = (elm);              \
 511         (head)->cqh_first = (elm);                                      \
 512 } while (0)
 513
 514 #define CIRCLEQ_INSERT_TAIL(head, elm, field) do {                      \
 515         (elm)->field.cqe_next = CIRCLEQ_END(head);                      \
 516         (elm)->field.cqe_prev = (head)->cqh_last;                       \
 517         if ((head)->cqh_first == CIRCLEQ_END(head))                     \
 518                 (head)->cqh_first = (elm);                              \
 519         else                                                            \
 520                 (head)->cqh_last->field.cqe_next = (elm);               \
 521         (head)->cqh_last = (elm);                                       \
 522 } while (0)
 523
 524 #define CIRCLEQ_REMOVE(head, elm, field) do {                           \
 525         if ((elm)->field.cqe_next == CIRCLEQ_END(head))                 \
 526                 (head)->cqh_last = (elm)->field.cqe_prev;               \
 527         else                                                            \
 528                 (elm)->field.cqe_next->field.cqe_prev =                 \
 529                     (elm)->field.cqe_prev;                              \
 530         if ((elm)->field.cqe_prev == CIRCLEQ_END(head))                 \
 531                 (head)->cqh_first = (elm)->field.cqe_next;              \
 532         else                                                            \
 533                 (elm)->field.cqe_prev->field.cqe_next =                 \
 534                     (elm)->field.cqe_next;                              \
 535 } while (0)
 536
 537 #define CIRCLEQ_REPLACE(head, elm, elm2, field) do {                    \
 538         if (((elm2)->field.cqe_next = (elm)->field.cqe_next) ==         \
 539             CIRCLEQ_END(head))                                          \
 540                 (head).cqh_last = (elm2);                               \
 541         else                                                            \
 542                 (elm2)->field.cqe_next->field.cqe_prev = (elm2);        \
 543         if (((elm2)->field.cqe_prev = (elm)->field.cqe_prev) ==         \
 544             CIRCLEQ_END(head))                                          \
 545                 (head).cqh_first = (elm2);                              \
 546         else                                                            \
 547                 (elm2)->field.cqe_prev->field.cqe_next = (elm2);        \
 548 } while (0)
 549
 550 #endif  /* !_LOCAL_SYS_QUEUE_H_ */