include/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, and tail 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 four types of data structures: singly-linked lists,
  45  * lists, simple queues, and tail 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  * For details on the use of these macros, see the queue(3) manual page.
  79  */
  80
  81 /*
  82  * List definitions.
  83  */
  84 #define QLIST_HEAD(name, type)                                          \
  85 struct name {                                                           \
  86         struct type *lh_first;  /* first element */                     \
  87 }
  88
  89 #define QLIST_HEAD_INITIALIZER(head)                                    \
  90         { NULL }
  91
  92 #define QLIST_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 QLIST_INIT(head) do {                                           \
 102         (head)->lh_first = NULL;                                        \
 103 } while (/*CONSTCOND*/0)
 104
 105 #define QLIST_SWAP(dstlist, srclist, field) do {                        \
 106         void *tmplist;                                                  \
 107         tmplist = (srclist)->lh_first;                                  \
 108         (srclist)->lh_first = (dstlist)->lh_first;                      \
 109         if ((srclist)->lh_first != NULL) {                              \
 110             (srclist)->lh_first->field.le_prev = &(srclist)->lh_first;  \
 111         }                                                               \
 112         (dstlist)->lh_first = tmplist;                                  \
 113         if ((dstlist)->lh_first != NULL) {                              \
 114             (dstlist)->lh_first->field.le_prev = &(dstlist)->lh_first;  \
 115         }                                                               \
 116 } while (/*CONSTCOND*/0)
 117
 118 #define QLIST_INSERT_AFTER(listelm, elm, field) do {                    \
 119         if (((elm)->field.le_next = (listelm)->field.le_next) != NULL)  \
 120                 (listelm)->field.le_next->field.le_prev =               \
 121                     &(elm)->field.le_next;                              \
 122         (listelm)->field.le_next = (elm);                               \
 123         (elm)->field.le_prev = &(listelm)->field.le_next;               \
 124 } while (/*CONSTCOND*/0)
 125
 126 #define QLIST_INSERT_BEFORE(listelm, elm, field) do {                   \
 127         (elm)->field.le_prev = (listelm)->field.le_prev;                \
 128         (elm)->field.le_next = (listelm);                               \
 129         *(listelm)->field.le_prev = (elm);                              \
 130         (listelm)->field.le_prev = &(elm)->field.le_next;               \
 131 } while (/*CONSTCOND*/0)
 132
 133 #define QLIST_INSERT_HEAD(head, elm, field) do {                        \
 134         if (((elm)->field.le_next = (head)->lh_first) != NULL)          \
 135                 (head)->lh_first->field.le_prev = &(elm)->field.le_next;\
 136         (head)->lh_first = (elm);                                       \
 137         (elm)->field.le_prev = &(head)->lh_first;                       \
 138 } while (/*CONSTCOND*/0)
 139
 140 #define QLIST_REMOVE(elm, field) do {                                   \
 141         if ((elm)->field.le_next != NULL)                               \
 142                 (elm)->field.le_next->field.le_prev =                   \
 143                     (elm)->field.le_prev;                               \
 144         *(elm)->field.le_prev = (elm)->field.le_next;                   \
 145         (elm)->field.le_next = NULL;                                    \
 146         (elm)->field.le_prev = NULL;                                    \
 147 } while (/*CONSTCOND*/0)
 148
 149 /*
 150  * Like QLIST_REMOVE() but safe to call when elm is not in a list
 151  */
 152 #define QLIST_SAFE_REMOVE(elm, field) do {                              \
 153         if ((elm)->field.le_prev != NULL) {                             \
 154                 if ((elm)->field.le_next != NULL)                       \
 155                         (elm)->field.le_next->field.le_prev =           \
 156                             (elm)->field.le_prev;                       \
 157                 *(elm)->field.le_prev = (elm)->field.le_next;           \
 158                 (elm)->field.le_next = NULL;                            \
 159                 (elm)->field.le_prev = NULL;                            \
 160         }                                                               \
 161 } while (/*CONSTCOND*/0)
 162
 163 /* Is elm in a list? */
 164 #define QLIST_IS_INSERTED(elm, field) ((elm)->field.le_prev != NULL)
 165
 166 #define QLIST_FOREACH(var, head, field)                                 \
 167         for ((var) = ((head)->lh_first);                                \
 168                 (var);                                                  \
 169                 (var) = ((var)->field.le_next))
 170
 171 #define QLIST_FOREACH_SAFE(var, head, field, next_var)                  \
 172         for ((var) = ((head)->lh_first);                                \
 173                 (var) && ((next_var) = ((var)->field.le_next), 1);      \
 174                 (var) = (next_var))
 175
 176 /*
 177  * List access methods.
 178  */
 179 #define QLIST_EMPTY(head)                ((head)->lh_first == NULL)
 180 #define QLIST_FIRST(head)                ((head)->lh_first)
 181 #define QLIST_NEXT(elm, field)           ((elm)->field.le_next)
 182
 183
 184 /*
 185  * Singly-linked List definitions.
 186  */
 187 #define QSLIST_HEAD(name, type)                                          \
 188 struct name {                                                           \
 189         struct type *slh_first; /* first element */                     \
 190 }
 191
 192 #define QSLIST_HEAD_INITIALIZER(head)                                    \
 193         { NULL }
 194
 195 #define QSLIST_ENTRY(type)                                               \
 196 struct {                                                                \
 197         struct type *sle_next;  /* next element */                      \
 198 }
 199
 200 /*
 201  * Singly-linked List functions.
 202  */
 203 #define QSLIST_INIT(head) do {                                           \
 204         (head)->slh_first = NULL;                                       \
 205 } while (/*CONSTCOND*/0)
 206
 207 #define QSLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
 208         (elm)->field.sle_next = (slistelm)->field.sle_next;             \
 209         (slistelm)->field.sle_next = (elm);                             \
 210 } while (/*CONSTCOND*/0)
 211
 212 #define QSLIST_INSERT_HEAD(head, elm, field) do {                        \
 213         (elm)->field.sle_next = (head)->slh_first;                       \
 214         (head)->slh_first = (elm);                                       \
 215 } while (/*CONSTCOND*/0)
 216
 217 #define QSLIST_INSERT_HEAD_ATOMIC(head, elm, field) do {                     \
 218         typeof(elm) save_sle_next;                                           \
 219         do {                                                                 \
 220             save_sle_next = (elm)->field.sle_next = (head)->slh_first;       \
 221         } while (qatomic_cmpxchg(&(head)->slh_first, save_sle_next, (elm)) !=\
 222                  save_sle_next);                                             \
 223 } while (/*CONSTCOND*/0)
 224
 225 #define QSLIST_MOVE_ATOMIC(dest, src) do {                               \
 226         (dest)->slh_first = qatomic_xchg(&(src)->slh_first, NULL);       \
 227 } while (/*CONSTCOND*/0)
 228
 229 #define QSLIST_REMOVE_HEAD(head, field) do {                             \
 230         typeof((head)->slh_first) elm = (head)->slh_first;               \
 231         (head)->slh_first = elm->field.sle_next;                         \
 232         elm->field.sle_next = NULL;                                      \
 233 } while (/*CONSTCOND*/0)
 234
 235 #define QSLIST_REMOVE_AFTER(slistelm, field) do {                       \
 236         typeof(slistelm) next = (slistelm)->field.sle_next;             \
 237         (slistelm)->field.sle_next = next->field.sle_next;              \
 238         next->field.sle_next = NULL;                                    \
 239 } while (/*CONSTCOND*/0)
 240
 241 #define QSLIST_REMOVE(head, elm, type, field) do {                      \
 242     if ((head)->slh_first == (elm)) {                                   \
 243         QSLIST_REMOVE_HEAD((head), field);                              \
 244     } else {                                                            \
 245         struct type *curelm = (head)->slh_first;                        \
 246         while (curelm->field.sle_next != (elm))                         \
 247             curelm = curelm->field.sle_next;                            \
 248         curelm->field.sle_next = curelm->field.sle_next->field.sle_next; \
 249         (elm)->field.sle_next = NULL;                                   \
 250     }                                                                   \
 251 } while (/*CONSTCOND*/0)
 252
 253 #define QSLIST_FOREACH(var, head, field)                                 \
 254         for((var) = (head)->slh_first; (var); (var) = (var)->field.sle_next)
 255
 256 #define QSLIST_FOREACH_SAFE(var, head, field, tvar)                      \
 257         for ((var) = QSLIST_FIRST((head));                               \
 258             (var) && ((tvar) = QSLIST_NEXT((var), field), 1);            \
 259             (var) = (tvar))
 260
 261 /*
 262  * Singly-linked List access methods.
 263  */
 264 #define QSLIST_EMPTY(head)       ((head)->slh_first == NULL)
 265 #define QSLIST_FIRST(head)       ((head)->slh_first)
 266 #define QSLIST_NEXT(elm, field)  ((elm)->field.sle_next)
 267
 268
 269 /*
 270  * Simple queue definitions.
 271  */
 272 #define QSIMPLEQ_HEAD(name, type)                                       \
 273 struct name {                                                           \
 274     struct type *sqh_first;    /* first element */                      \
 275     struct type **sqh_last;    /* addr of last next element */          \
 276 }
 277
 278 #define QSIMPLEQ_HEAD_INITIALIZER(head)                                 \
 279     { NULL, &(head).sqh_first }
 280
 281 #define QSIMPLEQ_ENTRY(type)                                            \
 282 struct {                                                                \
 283     struct type *sqe_next;    /* next element */                        \
 284 }
 285
 286 /*
 287  * Simple queue functions.
 288  */
 289 #define QSIMPLEQ_INIT(head) do {                                        \
 290     (head)->sqh_first = NULL;                                           \
 291     (head)->sqh_last = &(head)->sqh_first;                              \
 292 } while (/*CONSTCOND*/0)
 293
 294 #define QSIMPLEQ_INSERT_HEAD(head, elm, field) do {                     \
 295     if (((elm)->field.sqe_next = (head)->sqh_first) == NULL)            \
 296         (head)->sqh_last = &(elm)->field.sqe_next;                      \
 297     (head)->sqh_first = (elm);                                          \
 298 } while (/*CONSTCOND*/0)
 299
 300 #define QSIMPLEQ_INSERT_TAIL(head, elm, field) do {                     \
 301     (elm)->field.sqe_next = NULL;                                       \
 302     *(head)->sqh_last = (elm);                                          \
 303     (head)->sqh_last = &(elm)->field.sqe_next;                          \
 304 } while (/*CONSTCOND*/0)
 305
 306 #define QSIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do {           \
 307     if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL)    \
 308         (head)->sqh_last = &(elm)->field.sqe_next;                      \
 309     (listelm)->field.sqe_next = (elm);                                  \
 310 } while (/*CONSTCOND*/0)
 311
 312 #define QSIMPLEQ_REMOVE_HEAD(head, field) do {                          \
 313     typeof((head)->sqh_first) elm = (head)->sqh_first;                  \
 314     if (((head)->sqh_first = elm->field.sqe_next) == NULL)              \
 315         (head)->sqh_last = &(head)->sqh_first;                          \
 316     elm->field.sqe_next = NULL;                                         \
 317 } while (/*CONSTCOND*/0)
 318
 319 #define QSIMPLEQ_SPLIT_AFTER(head, elm, field, removed) do {            \
 320     QSIMPLEQ_INIT(removed);                                             \
 321     if (((removed)->sqh_first = (head)->sqh_first) != NULL) {           \
 322         if (((head)->sqh_first = (elm)->field.sqe_next) == NULL) {      \
 323             (head)->sqh_last = &(head)->sqh_first;                      \
 324         }                                                               \
 325         (removed)->sqh_last = &(elm)->field.sqe_next;                   \
 326         (elm)->field.sqe_next = NULL;                                   \
 327     }                                                                   \
 328 } while (/*CONSTCOND*/0)
 329
 330 #define QSIMPLEQ_REMOVE(head, elm, type, field) do {                    \
 331     if ((head)->sqh_first == (elm)) {                                   \
 332         QSIMPLEQ_REMOVE_HEAD((head), field);                            \
 333     } else {                                                            \
 334         struct type *curelm = (head)->sqh_first;                        \
 335         while (curelm->field.sqe_next != (elm))                         \
 336             curelm = curelm->field.sqe_next;                            \
 337         if ((curelm->field.sqe_next =                                   \
 338             curelm->field.sqe_next->field.sqe_next) == NULL)            \
 339                 (head)->sqh_last = &(curelm)->field.sqe_next;           \
 340         (elm)->field.sqe_next = NULL;                                   \
 341     }                                                                   \
 342 } while (/*CONSTCOND*/0)
 343
 344 #define QSIMPLEQ_FOREACH(var, head, field)                              \
 345     for ((var) = ((head)->sqh_first);                                   \
 346         (var);                                                          \
 347         (var) = ((var)->field.sqe_next))
 348
 349 #define QSIMPLEQ_FOREACH_SAFE(var, head, field, next)                   \
 350     for ((var) = ((head)->sqh_first);                                   \
 351         (var) && ((next = ((var)->field.sqe_next)), 1);                 \
 352         (var) = (next))
 353
 354 #define QSIMPLEQ_CONCAT(head1, head2) do {                              \
 355     if (!QSIMPLEQ_EMPTY((head2))) {                                     \
 356         *(head1)->sqh_last = (head2)->sqh_first;                        \
 357         (head1)->sqh_last = (head2)->sqh_last;                          \
 358         QSIMPLEQ_INIT((head2));                                         \
 359     }                                                                   \
 360 } while (/*CONSTCOND*/0)
 361
 362 #define QSIMPLEQ_PREPEND(head1, head2) do {                             \
 363     if (!QSIMPLEQ_EMPTY((head2))) {                                     \
 364         *(head2)->sqh_last = (head1)->sqh_first;                        \
 365         (head1)->sqh_first = (head2)->sqh_first;                          \
 366         QSIMPLEQ_INIT((head2));                                         \
 367     }                                                                   \
 368 } while (/*CONSTCOND*/0)
 369
 370 #define QSIMPLEQ_LAST(head, type, field)                                \
 371     (QSIMPLEQ_EMPTY((head)) ?                                           \
 372         NULL :                                                          \
 373             ((struct type *)(void *)                                    \
 374         ((char *)((head)->sqh_last) - offsetof(struct type, field))))
 375
 376 /*
 377  * Simple queue access methods.
 378  */
 379 #define QSIMPLEQ_EMPTY_ATOMIC(head) \
 380     (qatomic_read(&((head)->sqh_first)) == NULL)
 381 #define QSIMPLEQ_EMPTY(head)        ((head)->sqh_first == NULL)
 382 #define QSIMPLEQ_FIRST(head)        ((head)->sqh_first)
 383 #define QSIMPLEQ_NEXT(elm, field)   ((elm)->field.sqe_next)
 384
 385 typedef struct QTailQLink {
 386     void *tql_next;
 387     struct QTailQLink *tql_prev;
 388 } QTailQLink;
 389
 390 /*
 391  * Tail queue definitions.  The union acts as a poor man template, as if
 392  * it were QTailQLink<type>.
 393  */
 394 #define QTAILQ_HEAD(name, type)                                         \
 395 union name {                                                            \
 396         struct type *tqh_first;       /* first element */               \
 397         QTailQLink tqh_circ;          /* link for circular backwards list */ \
 398 }
 399
 400 #define QTAILQ_HEAD_INITIALIZER(head)                                   \
 401         { .tqh_circ = { NULL, &(head).tqh_circ } }
 402
 403 #define QTAILQ_ENTRY(type)                                              \
 404 union {                                                                 \
 405         struct type *tqe_next;        /* next element */                \
 406         QTailQLink tqe_circ;          /* link for circular backwards list */ \
 407 }
 408
 409 /*
 410  * Tail queue functions.
 411  */
 412 #define QTAILQ_INIT(head) do {                                          \
 413         (head)->tqh_first = NULL;                                       \
 414         (head)->tqh_circ.tql_prev = &(head)->tqh_circ;                  \
 415 } while (/*CONSTCOND*/0)
 416
 417 #define QTAILQ_INSERT_HEAD(head, elm, field) do {                       \
 418         if (((elm)->field.tqe_next = (head)->tqh_first) != NULL)        \
 419             (head)->tqh_first->field.tqe_circ.tql_prev =                \
 420                 &(elm)->field.tqe_circ;                                 \
 421         else                                                            \
 422             (head)->tqh_circ.tql_prev = &(elm)->field.tqe_circ;         \
 423         (head)->tqh_first = (elm);                                      \
 424         (elm)->field.tqe_circ.tql_prev = &(head)->tqh_circ;             \
 425 } while (/*CONSTCOND*/0)
 426
 427 #define QTAILQ_INSERT_TAIL(head, elm, field) do {                       \
 428         (elm)->field.tqe_next = NULL;                                   \
 429         (elm)->field.tqe_circ.tql_prev = (head)->tqh_circ.tql_prev;     \
 430         (head)->tqh_circ.tql_prev->tql_next = (elm);                    \
 431         (head)->tqh_circ.tql_prev = &(elm)->field.tqe_circ;             \
 432 } while (/*CONSTCOND*/0)
 433
 434 #define QTAILQ_INSERT_AFTER(head, listelm, elm, field) do {             \
 435         if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)\
 436             (elm)->field.tqe_next->field.tqe_circ.tql_prev =            \
 437                 &(elm)->field.tqe_circ;                                 \
 438         else                                                            \
 439             (head)->tqh_circ.tql_prev = &(elm)->field.tqe_circ;         \
 440         (listelm)->field.tqe_next = (elm);                              \
 441         (elm)->field.tqe_circ.tql_prev = &(listelm)->field.tqe_circ;    \
 442 } while (/*CONSTCOND*/0)
 443
 444 #define QTAILQ_INSERT_BEFORE(listelm, elm, field) do {                       \
 445         (elm)->field.tqe_circ.tql_prev = (listelm)->field.tqe_circ.tql_prev; \
 446         (elm)->field.tqe_next = (listelm);                                   \
 447         (listelm)->field.tqe_circ.tql_prev->tql_next = (elm);                \
 448         (listelm)->field.tqe_circ.tql_prev = &(elm)->field.tqe_circ;         \
 449 } while (/*CONSTCOND*/0)
 450
 451 #define QTAILQ_REMOVE(head, elm, field) do {                            \
 452         if (((elm)->field.tqe_next) != NULL)                            \
 453             (elm)->field.tqe_next->field.tqe_circ.tql_prev =            \
 454                 (elm)->field.tqe_circ.tql_prev;                         \
 455         else                                                            \
 456             (head)->tqh_circ.tql_prev = (elm)->field.tqe_circ.tql_prev; \
 457         (elm)->field.tqe_circ.tql_prev->tql_next = (elm)->field.tqe_next; \
 458         (elm)->field.tqe_circ.tql_prev = NULL;                          \
 459         (elm)->field.tqe_circ.tql_next = NULL;                          \
 460         (elm)->field.tqe_next = NULL;                                   \
 461 } while (/*CONSTCOND*/0)
 462
 463 /* remove @left, @right and all elements in between from @head */
 464 #define QTAILQ_REMOVE_SEVERAL(head, left, right, field) do {            \
 465         if (((right)->field.tqe_next) != NULL)                          \
 466             (right)->field.tqe_next->field.tqe_circ.tql_prev =          \
 467                 (left)->field.tqe_circ.tql_prev;                        \
 468         else                                                            \
 469             (head)->tqh_circ.tql_prev = (left)->field.tqe_circ.tql_prev; \
 470         (left)->field.tqe_circ.tql_prev->tql_next = (right)->field.tqe_next; \
 471     } while (/*CONSTCOND*/0)
 472
 473 #define QTAILQ_FOREACH(var, head, field)                                \
 474         for ((var) = ((head)->tqh_first);                               \
 475                 (var);                                                  \
 476                 (var) = ((var)->field.tqe_next))
 477
 478 #define QTAILQ_FOREACH_SAFE(var, head, field, next_var)                 \
 479         for ((var) = ((head)->tqh_first);                               \
 480                 (var) && ((next_var) = ((var)->field.tqe_next), 1);     \
 481                 (var) = (next_var))
 482
 483 #define QTAILQ_FOREACH_REVERSE(var, head, field)                        \
 484         for ((var) = QTAILQ_LAST(head);                                 \
 485                 (var);                                                  \
 486                 (var) = QTAILQ_PREV(var, field))
 487
 488 #define QTAILQ_FOREACH_REVERSE_SAFE(var, head, field, prev_var)         \
 489         for ((var) = QTAILQ_LAST(head);                                 \
 490              (var) && ((prev_var) = QTAILQ_PREV(var, field), 1);        \
 491              (var) = (prev_var))
 492
 493 /*
 494  * Tail queue access methods.
 495  */
 496 #define QTAILQ_EMPTY(head)               ((head)->tqh_first == NULL)
 497 #define QTAILQ_FIRST(head)               ((head)->tqh_first)
 498 #define QTAILQ_NEXT(elm, field)          ((elm)->field.tqe_next)
 499 #define QTAILQ_IN_USE(elm, field)        ((elm)->field.tqe_circ.tql_prev != NULL)
 500
 501 #define QTAILQ_LINK_PREV(link)                                          \
 502         ((link).tql_prev->tql_prev->tql_next)
 503 #define QTAILQ_LAST(head)                                               \
 504         ((typeof((head)->tqh_first)) QTAILQ_LINK_PREV((head)->tqh_circ))
 505 #define QTAILQ_PREV(elm, field)                                         \
 506         ((typeof((elm)->field.tqe_next)) QTAILQ_LINK_PREV((elm)->field.tqe_circ))
 507
 508 #define field_at_offset(base, offset, type)                                    \
 509         ((type *) (((char *) (base)) + (offset)))
 510
 511 /*
 512  * Raw access of elements of a tail queue head.  Offsets are all zero
 513  * because it's a union.
 514  */
 515 #define QTAILQ_RAW_FIRST(head)                                                 \
 516         field_at_offset(head, 0, void *)
 517 #define QTAILQ_RAW_TQH_CIRC(head)                                              \
 518         field_at_offset(head, 0, QTailQLink)
 519
 520 /*
 521  * Raw access of elements of a tail entry
 522  */
 523 #define QTAILQ_RAW_NEXT(elm, entry)                                            \
 524         field_at_offset(elm, entry, void *)
 525 #define QTAILQ_RAW_TQE_CIRC(elm, entry)                                        \
 526         field_at_offset(elm, entry, QTailQLink)
 527 /*
 528  * Tail queue traversal using pointer arithmetic.
 529  */
 530 #define QTAILQ_RAW_FOREACH(elm, head, entry)                                   \
 531         for ((elm) = *QTAILQ_RAW_FIRST(head);                                  \
 532              (elm);                                                            \
 533              (elm) = *QTAILQ_RAW_NEXT(elm, entry))
 534 /*
 535  * Tail queue insertion using pointer arithmetic.
 536  */
 537 #define QTAILQ_RAW_INSERT_TAIL(head, elm, entry) do {                           \
 538         *QTAILQ_RAW_NEXT(elm, entry) = NULL;                                    \
 539         QTAILQ_RAW_TQE_CIRC(elm, entry)->tql_prev = QTAILQ_RAW_TQH_CIRC(head)->tql_prev; \
 540         QTAILQ_RAW_TQH_CIRC(head)->tql_prev->tql_next = (elm);                  \
 541         QTAILQ_RAW_TQH_CIRC(head)->tql_prev = QTAILQ_RAW_TQE_CIRC(elm, entry);  \
 542 } while (/*CONSTCOND*/0)
 543
 544 #define QLIST_RAW_FIRST(head)                                                  \
 545         field_at_offset(head, 0, void *)
 546
 547 #define QLIST_RAW_NEXT(elm, entry)                                             \
 548         field_at_offset(elm, entry, void *)
 549
 550 #define QLIST_RAW_PREVIOUS(elm, entry)                                         \
 551         field_at_offset(elm, entry + sizeof(void *), void *)
 552
 553 #define QLIST_RAW_FOREACH(elm, head, entry)                                    \
 554         for ((elm) = *QLIST_RAW_FIRST(head);                                   \
 555              (elm);                                                            \
 556              (elm) = *QLIST_RAW_NEXT(elm, entry))
 557
 558 #define QLIST_RAW_INSERT_AFTER(head, prev, elem, entry) do {                   \
 559         *QLIST_RAW_NEXT(prev, entry) = elem;                                   \
 560         *QLIST_RAW_PREVIOUS(elem, entry) = QLIST_RAW_NEXT(prev, entry);        \
 561         *QLIST_RAW_NEXT(elem, entry) = NULL;                                   \
 562 } while (0)
 563
 564 #define QLIST_RAW_INSERT_HEAD(head, elm, entry) do {                           \
 565         void *first = *QLIST_RAW_FIRST(head);                                  \
 566         *QLIST_RAW_FIRST(head) = elm;                                          \
 567         *QLIST_RAW_PREVIOUS(elm, entry) = QLIST_RAW_FIRST(head);               \
 568         if (first) {                                                           \
 569             *QLIST_RAW_NEXT(elm, entry) = first;                               \
 570             *QLIST_RAW_PREVIOUS(first, entry) = QLIST_RAW_NEXT(elm, entry);    \
 571         } else {                                                               \
 572             *QLIST_RAW_NEXT(elm, entry) = NULL;                                \
 573         }                                                                      \
 574 } while (0)
 575
 576 #endif /* QEMU_SYS_QUEUE_H */