qemu-queue.h

   1 /*      $NetBSD: queue.h,v 1.52 2009/04/20 09:56:08 mschuett Exp $ */
   2
   3 /*
   4  * Qemu version: Copy from netbsd, removed debug code, removed some of
   5  * the implementations.  Left in singly-linked lists, lists, simple
   6  * queues, tail queues and circular queues.
   7  */
   8
   9 /*
  10  * Copyright (c) 1991, 1993
  11  *      The Regents of the University of California.  All rights reserved.
  12  *
  13  * Redistribution and use in source and binary forms, with or without
  14  * modification, are permitted provided that the following conditions
  15  * are met:
  16  * 1. Redistributions of source code must retain the above copyright
  17  *    notice, this list of conditions and the following disclaimer.
  18  * 2. Redistributions in binary form must reproduce the above copyright
  19  *    notice, this list of conditions and the following disclaimer in the
  20  *    documentation and/or other materials provided with the distribution.
  21  * 3. Neither the name of the University nor the names of its contributors
  22  *    may be used to endorse or promote products derived from this software
  23  *    without specific prior written permission.
  24  *
  25  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  26  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  27  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  28  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  29  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  30  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  31  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  32  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  33  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  34  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  35  * SUCH DAMAGE.
  36  *
  37  *      @(#)queue.h     8.5 (Berkeley) 8/20/94
  38  */
  39
  40 #ifndef QEMU_SYS_QUEUE_H_
  41 #define QEMU_SYS_QUEUE_H_
  42
  43 /*
  44  * This file defines five types of data structures: singly-linked lists,
  45  * lists, simple queues, tail queues, and circular queues.
  46  *
  47  * A singly-linked list is headed by a single forward pointer. The
  48  * elements are singly linked for minimum space and pointer manipulation
  49  * overhead at the expense of O(n) removal for arbitrary elements. New
  50  * elements can be added to the list after an existing element or at the
  51  * head of the list.  Elements being removed from the head of the list
  52  * should use the explicit macro for this purpose for optimum
  53  * efficiency. A singly-linked list may only be traversed in the forward
  54  * direction.  Singly-linked lists are ideal for applications with large
  55  * datasets and few or no removals or for implementing a LIFO queue.
  56  *
  57  * A list is headed by a single forward pointer (or an array of forward
  58  * pointers for a hash table header). The elements are doubly linked
  59  * so that an arbitrary element can be removed without a need to
  60  * traverse the list. New elements can be added to the list before
  61  * or after an existing element or at the head of the list. A list
  62  * may only be traversed in the forward direction.
  63  *
  64  * A simple queue is headed by a pair of pointers, one the head of the
  65  * list and the other to the tail of the list. The elements are singly
  66  * linked to save space, so elements can only be removed from the
  67  * head of the list. New elements can be added to the list after
  68  * an existing element, at the head of the list, or at the end of the
  69  * list. A simple queue may only be traversed in the forward direction.
  70  *
  71  * A tail queue is headed by a pair of pointers, one to the head of the
  72  * list and the other to the tail of the list. The elements are doubly
  73  * linked so that an arbitrary element can be removed without a need to
  74  * traverse the list. New elements can be added to the list before or
  75  * after an existing element, at the head of the list, or at the end of
  76  * the list. A tail queue may be traversed in either direction.
  77  *
  78  * A circle queue is headed by a pair of pointers, one to the head of the
  79  * list and the other to the tail of the list. The elements are doubly
  80  * linked so that an arbitrary element can be removed without a need to
  81  * traverse the list. New elements can be added to the list before or after
  82  * an existing element, at the head of the list, or at the end of the list.
  83  * A circle queue may be traversed in either direction, but has a more
  84  * complex end of list detection.
  85  *
  86  * For details on the use of these macros, see the queue(3) manual page.
  87  */
  88
  89 #include "qemu-barrier.h" /* for smp_wmb() */
  90
  91 /*
  92  * List definitions.
  93  */
  94 #define QLIST_HEAD(name, type)                                          \
  95 struct name {                                                           \
  96         struct type *lh_first;  /* first element */                     \
  97 }
  98
  99 #define QLIST_HEAD_INITIALIZER(head)                                    \
 100         { NULL }
 101
 102 #define QLIST_ENTRY(type)                                               \
 103 struct {                                                                \
 104         struct type *le_next;   /* next element */                      \
 105         struct type **le_prev;  /* address of previous next element */  \
 106 }
 107
 108 /*
 109  * List functions.
 110  */
 111 #define QLIST_INIT(head) do {                                           \
 112         (head)->lh_first = NULL;                                        \
 113 } while (/*CONSTCOND*/0)
 114
 115 #define QLIST_INSERT_AFTER(listelm, elm, field) do {                    \
 116         if (((elm)->field.le_next = (listelm)->field.le_next) != NULL)  \
 117                 (listelm)->field.le_next->field.le_prev =               \
 118                     &(elm)->field.le_next;                              \
 119         (listelm)->field.le_next = (elm);                               \
 120         (elm)->field.le_prev = &(listelm)->field.le_next;               \
 121 } while (/*CONSTCOND*/0)
 122
 123 #define QLIST_INSERT_BEFORE(listelm, elm, field) do {                   \
 124         (elm)->field.le_prev = (listelm)->field.le_prev;                \
 125         (elm)->field.le_next = (listelm);                               \
 126         *(listelm)->field.le_prev = (elm);                              \
 127         (listelm)->field.le_prev = &(elm)->field.le_next;               \
 128 } while (/*CONSTCOND*/0)
 129
 130 #define QLIST_INSERT_HEAD(head, elm, field) do {                        \
 131         if (((elm)->field.le_next = (head)->lh_first) != NULL)          \
 132                 (head)->lh_first->field.le_prev = &(elm)->field.le_next;\
 133         (head)->lh_first = (elm);                                       \
 134         (elm)->field.le_prev = &(head)->lh_first;                       \
 135 } while (/*CONSTCOND*/0)
 136
 137 #define QLIST_INSERT_HEAD_RCU(head, elm, field) do {                    \
 138         (elm)->field.le_prev = &(head)->lh_first;                       \
 139         (elm)->field.le_next = (head)->lh_first;                        \
 140         smp_wmb(); /* fill elm before linking it */                     \
 141         if ((head)->lh_first != NULL)  {                                \
 142             (head)->lh_first->field.le_prev = &(elm)->field.le_next;    \
 143         }                                                               \
 144         (head)->lh_first = (elm);                                       \
 145         smp_wmb();                                                      \
 146 } while (/* CONSTCOND*/0)
 147
 148 #define QLIST_REMOVE(elm, field) do {                                   \
 149         if ((elm)->field.le_next != NULL)                               \
 150                 (elm)->field.le_next->field.le_prev =                   \
 151                     (elm)->field.le_prev;                               \
 152         *(elm)->field.le_prev = (elm)->field.le_next;                   \
 153 } while (/*CONSTCOND*/0)
 154
 155 #define QLIST_FOREACH(var, head, field)                                 \
 156         for ((var) = ((head)->lh_first);                                \
 157                 (var);                                                  \
 158                 (var) = ((var)->field.le_next))
 159
 160 #define QLIST_FOREACH_SAFE(var, head, field, next_var)                  \
 161         for ((var) = ((head)->lh_first);                                \
 162                 (var) && ((next_var) = ((var)->field.le_next), 1);      \
 163                 (var) = (next_var))
 164
 165 /*
 166  * List access methods.
 167  */
 168 #define QLIST_EMPTY(head)                ((head)->lh_first == NULL)
 169 #define QLIST_FIRST(head)                ((head)->lh_first)
 170 #define QLIST_NEXT(elm, field)           ((elm)->field.le_next)
 171
 172
 173 /*
 174  * Singly-linked List definitions.
 175  */
 176 #define QSLIST_HEAD(name, type)                                          \
 177 struct name {                                                           \
 178         struct type *slh_first; /* first element */                     \
 179 }
 180
 181 #define QSLIST_HEAD_INITIALIZER(head)                                    \
 182         { NULL }
 183
 184 #define QSLIST_ENTRY(type)                                               \
 185 struct {                                                                \
 186         struct type *sle_next;  /* next element */                      \
 187 }
 188
 189 /*
 190  * Singly-linked List functions.
 191  */
 192 #define QSLIST_INIT(head) do {                                           \
 193         (head)->slh_first = NULL;                                       \
 194 } while (/*CONSTCOND*/0)
 195
 196 #define QSLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
 197         (elm)->field.sle_next = (slistelm)->field.sle_next;             \
 198         (slistelm)->field.sle_next = (elm);                             \
 199 } while (/*CONSTCOND*/0)
 200
 201 #define QSLIST_INSERT_HEAD(head, elm, field) do {                        \
 202         (elm)->field.sle_next = (head)->slh_first;                      \
 203         (head)->slh_first = (elm);                                      \
 204 } while (/*CONSTCOND*/0)
 205
 206 #define QSLIST_REMOVE_HEAD(head, field) do {                             \
 207         (head)->slh_first = (head)->slh_first->field.sle_next;          \
 208 } while (/*CONSTCOND*/0)
 209
 210 #define QSLIST_REMOVE_AFTER(slistelm, field) do {                        \
 211         (slistelm)->field.sle_next =                                    \
 212             QSLIST_NEXT(QSLIST_NEXT((slistelm), field), field);           \
 213 } while (/*CONSTCOND*/0)
 214
 215 #define QSLIST_FOREACH(var, head, field)                                 \
 216         for((var) = (head)->slh_first; (var); (var) = (var)->field.sle_next)
 217
 218 #define QSLIST_FOREACH_SAFE(var, head, field, tvar)                      \
 219         for ((var) = QSLIST_FIRST((head));                               \
 220             (var) && ((tvar) = QSLIST_NEXT((var), field), 1);            \
 221             (var) = (tvar))
 222
 223 /*
 224  * Singly-linked List access methods.
 225  */
 226 #define QSLIST_EMPTY(head)       ((head)->slh_first == NULL)
 227 #define QSLIST_FIRST(head)       ((head)->slh_first)
 228 #define QSLIST_NEXT(elm, field)  ((elm)->field.sle_next)
 229
 230
 231 /*
 232  * Simple queue definitions.
 233  */
 234 #define QSIMPLEQ_HEAD(name, type)                                       \
 235 struct name {                                                           \
 236     struct type *sqh_first;    /* first element */                      \
 237     struct type **sqh_last;    /* addr of last next element */          \
 238 }
 239
 240 #define QSIMPLEQ_HEAD_INITIALIZER(head)                                 \
 241     { NULL, &(head).sqh_first }
 242
 243 #define QSIMPLEQ_ENTRY(type)                                            \
 244 struct {                                                                \
 245     struct type *sqe_next;    /* next element */                        \
 246 }
 247
 248 /*
 249  * Simple queue functions.
 250  */
 251 #define QSIMPLEQ_INIT(head) do {                                        \
 252     (head)->sqh_first = NULL;                                           \
 253     (head)->sqh_last = &(head)->sqh_first;                              \
 254 } while (/*CONSTCOND*/0)
 255
 256 #define QSIMPLEQ_INSERT_HEAD(head, elm, field) do {                     \
 257     if (((elm)->field.sqe_next = (head)->sqh_first) == NULL)            \
 258         (head)->sqh_last = &(elm)->field.sqe_next;                      \
 259     (head)->sqh_first = (elm);                                          \
 260 } while (/*CONSTCOND*/0)
 261
 262 #define QSIMPLEQ_INSERT_TAIL(head, elm, field) do {                     \
 263     (elm)->field.sqe_next = NULL;                                       \
 264     *(head)->sqh_last = (elm);                                          \
 265     (head)->sqh_last = &(elm)->field.sqe_next;                          \
 266 } while (/*CONSTCOND*/0)
 267
 268 #define QSIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do {           \
 269     if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL)    \
 270         (head)->sqh_last = &(elm)->field.sqe_next;                      \
 271     (listelm)->field.sqe_next = (elm);                                  \
 272 } while (/*CONSTCOND*/0)
 273
 274 #define QSIMPLEQ_REMOVE_HEAD(head, field) do {                          \
 275     if (((head)->sqh_first = (head)->sqh_first->field.sqe_next) == NULL)\
 276         (head)->sqh_last = &(head)->sqh_first;                          \
 277 } while (/*CONSTCOND*/0)
 278
 279 #define QSIMPLEQ_REMOVE(head, elm, type, field) do {                    \
 280     if ((head)->sqh_first == (elm)) {                                   \
 281         QSIMPLEQ_REMOVE_HEAD((head), field);                            \
 282     } else {                                                            \
 283         struct type *curelm = (head)->sqh_first;                        \
 284         while (curelm->field.sqe_next != (elm))                         \
 285             curelm = curelm->field.sqe_next;                            \
 286         if ((curelm->field.sqe_next =                                   \
 287             curelm->field.sqe_next->field.sqe_next) == NULL)            \
 288                 (head)->sqh_last = &(curelm)->field.sqe_next;           \
 289     }                                                                   \
 290 } while (/*CONSTCOND*/0)
 291
 292 #define QSIMPLEQ_FOREACH(var, head, field)                              \
 293     for ((var) = ((head)->sqh_first);                                   \
 294         (var);                                                          \
 295         (var) = ((var)->field.sqe_next))
 296
 297 #define QSIMPLEQ_FOREACH_SAFE(var, head, field, next)                   \
 298     for ((var) = ((head)->sqh_first);                                   \
 299         (var) && ((next = ((var)->field.sqe_next)), 1);                 \
 300         (var) = (next))
 301
 302 #define QSIMPLEQ_CONCAT(head1, head2) do {                              \
 303     if (!QSIMPLEQ_EMPTY((head2))) {                                     \
 304         *(head1)->sqh_last = (head2)->sqh_first;                        \
 305         (head1)->sqh_last = (head2)->sqh_last;                          \
 306         QSIMPLEQ_INIT((head2));                                         \
 307     }                                                                   \
 308 } while (/*CONSTCOND*/0)
 309
 310 #define QSIMPLEQ_LAST(head, type, field)                                \
 311     (QSIMPLEQ_EMPTY((head)) ?                                           \
 312         NULL :                                                          \
 313             ((struct type *)(void *)                                    \
 314         ((char *)((head)->sqh_last) - offsetof(struct type, field))))
 315
 316 /*
 317  * Simple queue access methods.
 318  */
 319 #define QSIMPLEQ_EMPTY(head)        ((head)->sqh_first == NULL)
 320 #define QSIMPLEQ_FIRST(head)        ((head)->sqh_first)
 321 #define QSIMPLEQ_NEXT(elm, field)   ((elm)->field.sqe_next)
 322
 323
 324 /*
 325  * Tail queue definitions.
 326  */
 327 #define Q_TAILQ_HEAD(name, type, qual)                                  \
 328 struct name {                                                           \
 329         qual type *tqh_first;           /* first element */             \
 330         qual type *qual *tqh_last;      /* addr of last next element */ \
 331 }
 332 #define QTAILQ_HEAD(name, type)  Q_TAILQ_HEAD(name, struct type,)
 333
 334 #define QTAILQ_HEAD_INITIALIZER(head)                                   \
 335         { NULL, &(head).tqh_first }
 336
 337 #define Q_TAILQ_ENTRY(type, qual)                                       \
 338 struct {                                                                \
 339         qual type *tqe_next;            /* next element */              \
 340         qual type *qual *tqe_prev;      /* address of previous next element */\
 341 }
 342 #define QTAILQ_ENTRY(type)       Q_TAILQ_ENTRY(struct type,)
 343
 344 /*
 345  * Tail queue functions.
 346  */
 347 #define QTAILQ_INIT(head) do {                                          \
 348         (head)->tqh_first = NULL;                                       \
 349         (head)->tqh_last = &(head)->tqh_first;                          \
 350 } while (/*CONSTCOND*/0)
 351
 352 #define QTAILQ_INSERT_HEAD(head, elm, field) do {                       \
 353         if (((elm)->field.tqe_next = (head)->tqh_first) != NULL)        \
 354                 (head)->tqh_first->field.tqe_prev =                     \
 355                     &(elm)->field.tqe_next;                             \
 356         else                                                            \
 357                 (head)->tqh_last = &(elm)->field.tqe_next;              \
 358         (head)->tqh_first = (elm);                                      \
 359         (elm)->field.tqe_prev = &(head)->tqh_first;                     \
 360 } while (/*CONSTCOND*/0)
 361
 362 #define QTAILQ_INSERT_TAIL(head, elm, field) do {                       \
 363         (elm)->field.tqe_next = NULL;                                   \
 364         (elm)->field.tqe_prev = (head)->tqh_last;                       \
 365         *(head)->tqh_last = (elm);                                      \
 366         (head)->tqh_last = &(elm)->field.tqe_next;                      \
 367 } while (/*CONSTCOND*/0)
 368
 369 #define QTAILQ_INSERT_AFTER(head, listelm, elm, field) do {             \
 370         if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)\
 371                 (elm)->field.tqe_next->field.tqe_prev =                 \
 372                     &(elm)->field.tqe_next;                             \
 373         else                                                            \
 374                 (head)->tqh_last = &(elm)->field.tqe_next;              \
 375         (listelm)->field.tqe_next = (elm);                              \
 376         (elm)->field.tqe_prev = &(listelm)->field.tqe_next;             \
 377 } while (/*CONSTCOND*/0)
 378
 379 #define QTAILQ_INSERT_BEFORE(listelm, elm, field) do {                  \
 380         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
 381         (elm)->field.tqe_next = (listelm);                              \
 382         *(listelm)->field.tqe_prev = (elm);                             \
 383         (listelm)->field.tqe_prev = &(elm)->field.tqe_next;             \
 384 } while (/*CONSTCOND*/0)
 385
 386 #define QTAILQ_REMOVE(head, elm, field) do {                            \
 387         if (((elm)->field.tqe_next) != NULL)                            \
 388                 (elm)->field.tqe_next->field.tqe_prev =                 \
 389                     (elm)->field.tqe_prev;                              \
 390         else                                                            \
 391                 (head)->tqh_last = (elm)->field.tqe_prev;               \
 392         *(elm)->field.tqe_prev = (elm)->field.tqe_next;                 \
 393 } while (/*CONSTCOND*/0)
 394
 395 #define QTAILQ_FOREACH(var, head, field)                                \
 396         for ((var) = ((head)->tqh_first);                               \
 397                 (var);                                                  \
 398                 (var) = ((var)->field.tqe_next))
 399
 400 #define QTAILQ_FOREACH_SAFE(var, head, field, next_var)                 \
 401         for ((var) = ((head)->tqh_first);                               \
 402                 (var) && ((next_var) = ((var)->field.tqe_next), 1);     \
 403                 (var) = (next_var))
 404
 405 #define QTAILQ_FOREACH_REVERSE(var, head, headname, field)              \
 406         for ((var) = (*(((struct headname *)((head)->tqh_last))->tqh_last));    \
 407                 (var);                                                  \
 408                 (var) = (*(((struct headname *)((var)->field.tqe_prev))->tqh_last)))
 409
 410 /*
 411  * Tail queue access methods.
 412  */
 413 #define QTAILQ_EMPTY(head)               ((head)->tqh_first == NULL)
 414 #define QTAILQ_FIRST(head)               ((head)->tqh_first)
 415 #define QTAILQ_NEXT(elm, field)          ((elm)->field.tqe_next)
 416
 417 #define QTAILQ_LAST(head, headname) \
 418         (*(((struct headname *)((head)->tqh_last))->tqh_last))
 419 #define QTAILQ_PREV(elm, headname, field) \
 420         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
 421
 422
 423 /*
 424  * Circular queue definitions.
 425  */
 426 #define QCIRCLEQ_HEAD(name, type)                                       \
 427 struct name {                                                           \
 428         struct type *cqh_first;         /* first element */             \
 429         struct type *cqh_last;          /* last element */              \
 430 }
 431
 432 #define QCIRCLEQ_HEAD_INITIALIZER(head)                                 \
 433         { (void *)&head, (void *)&head }
 434
 435 #define QCIRCLEQ_ENTRY(type)                                            \
 436 struct {                                                                \
 437         struct type *cqe_next;          /* next element */              \
 438         struct type *cqe_prev;          /* previous element */          \
 439 }
 440
 441 /*
 442  * Circular queue functions.
 443  */
 444 #define QCIRCLEQ_INIT(head) do {                                        \
 445         (head)->cqh_first = (void *)(head);                             \
 446         (head)->cqh_last = (void *)(head);                              \
 447 } while (/*CONSTCOND*/0)
 448
 449 #define QCIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {           \
 450         (elm)->field.cqe_next = (listelm)->field.cqe_next;              \
 451         (elm)->field.cqe_prev = (listelm);                              \
 452         if ((listelm)->field.cqe_next == (void *)(head))                \
 453                 (head)->cqh_last = (elm);                               \
 454         else                                                            \
 455                 (listelm)->field.cqe_next->field.cqe_prev = (elm);      \
 456         (listelm)->field.cqe_next = (elm);                              \
 457 } while (/*CONSTCOND*/0)
 458
 459 #define QCIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do {          \
 460         (elm)->field.cqe_next = (listelm);                              \
 461         (elm)->field.cqe_prev = (listelm)->field.cqe_prev;              \
 462         if ((listelm)->field.cqe_prev == (void *)(head))                \
 463                 (head)->cqh_first = (elm);                              \
 464         else                                                            \
 465                 (listelm)->field.cqe_prev->field.cqe_next = (elm);      \
 466         (listelm)->field.cqe_prev = (elm);                              \
 467 } while (/*CONSTCOND*/0)
 468
 469 #define QCIRCLEQ_INSERT_HEAD(head, elm, field) do {                     \
 470         (elm)->field.cqe_next = (head)->cqh_first;                      \
 471         (elm)->field.cqe_prev = (void *)(head);                         \
 472         if ((head)->cqh_last == (void *)(head))                         \
 473                 (head)->cqh_last = (elm);                               \
 474         else                                                            \
 475                 (head)->cqh_first->field.cqe_prev = (elm);              \
 476         (head)->cqh_first = (elm);                                      \
 477 } while (/*CONSTCOND*/0)
 478
 479 #define QCIRCLEQ_INSERT_TAIL(head, elm, field) do {                     \
 480         (elm)->field.cqe_next = (void *)(head);                         \
 481         (elm)->field.cqe_prev = (head)->cqh_last;                       \
 482         if ((head)->cqh_first == (void *)(head))                        \
 483                 (head)->cqh_first = (elm);                              \
 484         else                                                            \
 485                 (head)->cqh_last->field.cqe_next = (elm);               \
 486         (head)->cqh_last = (elm);                                       \
 487 } while (/*CONSTCOND*/0)
 488
 489 #define QCIRCLEQ_REMOVE(head, elm, field) do {                          \
 490         if ((elm)->field.cqe_next == (void *)(head))                    \
 491                 (head)->cqh_last = (elm)->field.cqe_prev;               \
 492         else                                                            \
 493                 (elm)->field.cqe_next->field.cqe_prev =                 \
 494                     (elm)->field.cqe_prev;                              \
 495         if ((elm)->field.cqe_prev == (void *)(head))                    \
 496                 (head)->cqh_first = (elm)->field.cqe_next;              \
 497         else                                                            \
 498                 (elm)->field.cqe_prev->field.cqe_next =                 \
 499                     (elm)->field.cqe_next;                              \
 500 } while (/*CONSTCOND*/0)
 501
 502 #define QCIRCLEQ_FOREACH(var, head, field)                              \
 503         for ((var) = ((head)->cqh_first);                               \
 504                 (var) != (const void *)(head);                          \
 505                 (var) = ((var)->field.cqe_next))
 506
 507 #define QCIRCLEQ_FOREACH_REVERSE(var, head, field)                      \
 508         for ((var) = ((head)->cqh_last);                                \
 509                 (var) != (const void *)(head);                          \
 510                 (var) = ((var)->field.cqe_prev))
 511
 512 /*
 513  * Circular queue access methods.
 514  */
 515 #define QCIRCLEQ_EMPTY(head)             ((head)->cqh_first == (void *)(head))
 516 #define QCIRCLEQ_FIRST(head)             ((head)->cqh_first)
 517 #define QCIRCLEQ_LAST(head)              ((head)->cqh_last)
 518 #define QCIRCLEQ_NEXT(elm, field)        ((elm)->field.cqe_next)
 519 #define QCIRCLEQ_PREV(elm, field)        ((elm)->field.cqe_prev)
 520
 521 #define QCIRCLEQ_LOOP_NEXT(head, elm, field)                            \
 522         (((elm)->field.cqe_next == (void *)(head))                      \
 523             ? ((head)->cqh_first)                                       \
 524             : (elm->field.cqe_next))
 525 #define QCIRCLEQ_LOOP_PREV(head, elm, field)                            \
 526         (((elm)->field.cqe_prev == (void *)(head))                      \
 527             ? ((head)->cqh_last)                                        \
 528             : (elm->field.cqe_prev))
 529
 530 #endif  /* !QEMU_SYS_QUEUE_H_ */