kernel/drivers/scsi/aic7xxx/queue.h

   1 /*
   2  * Copyright (c) 1991, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  24  * SUCH DAMAGE.
  25  *
  26  *      @(#)queue.h     8.5 (Berkeley) 8/20/94
  27  * $FreeBSD: src/sys/sys/queue.h,v 1.38 2000/05/26 02:06:56 jake Exp $
  28  */
  29
  30 #ifndef _SYS_QUEUE_H_
  31 #define _SYS_QUEUE_H_
  32
  33 /*
  34  * This file defines five types of data structures: singly-linked lists,
  35  * singly-linked tail queues, lists, tail queues, and circular queues.
  36  *
  37  * A singly-linked list is headed by a single forward pointer. The elements
  38  * are singly linked for minimum space and pointer manipulation overhead at
  39  * the expense of O(n) removal for arbitrary elements. New elements can be
  40  * added to the list after an existing element or at the head of the list.
  41  * Elements being removed from the head of the list should use the explicit
  42  * macro for this purpose for optimum efficiency. A singly-linked list may
  43  * only be traversed in the forward direction.  Singly-linked lists are ideal
  44  * for applications with large datasets and few or no removals or for
  45  * implementing a LIFO queue.
  46  *
  47  * A singly-linked tail queue is headed by a pair of pointers, one to the
  48  * head of the list and the other to the tail of the list. The elements are
  49  * singly linked for minimum space and pointer manipulation overhead at the
  50  * expense of O(n) removal for arbitrary elements. New elements can be added
  51  * to the list after an existing element, at the head of the list, or at the
  52  * end of the list. Elements being removed from the head of the tail queue
  53  * should use the explicit macro for this purpose for optimum efficiency.
  54  * A singly-linked tail queue may only be traversed in the forward direction.
  55  * Singly-linked tail queues are ideal for applications with large datasets
  56  * and few or no removals or for implementing a FIFO queue.
  57  *
  58  * A list is headed by a single forward pointer (or an array of forward
  59  * pointers for a hash table header). The elements are doubly linked
  60  * so that an arbitrary element can be removed without a need to
  61  * traverse the list. New elements can be added to the list before
  62  * or after an existing element or at the head of the list. A list
  63  * may only be traversed in the forward direction.
  64  *
  65  * A tail queue is headed by a pair of pointers, one to the head of the
  66  * list and the other to the tail of the list. The elements are doubly
  67  * linked so that an arbitrary element can be removed without a need to
  68  * traverse the list. New elements can be added to the list before or
  69  * after an existing element, at the head of the list, or at the end of
  70  * the list. A tail queue may be traversed in either direction.
  71  *
  72  * A circle queue is headed by a pair of pointers, one to the head of the
  73  * list and the other to the tail of the list. The elements are doubly
  74  * linked so that an arbitrary element can be removed without a need to
  75  * traverse the list. New elements can be added to the list before or after
  76  * an existing element, at the head of the list, or at the end of the list.
  77  * A circle queue may be traversed in either direction, but has a more
  78  * complex end of list detection.
  79  *
  80  * For details on the use of these macros, see the queue(3) manual page.
  81  *
  82  *
  83  *                      SLIST   LIST    STAILQ  TAILQ   CIRCLEQ
  84  * _HEAD                +       +       +       +       +
  85  * _HEAD_INITIALIZER    +       +       +       +       +
  86  * _ENTRY               +       +       +       +       +
  87  * _INIT                +       +       +       +       +
  88  * _EMPTY               +       +       +       +       +
  89  * _FIRST               +       +       +       +       +
  90  * _NEXT                +       +       +       +       +
  91  * _PREV                -       -       -       +       +
  92  * _LAST                -       -       +       +       +
  93  * _FOREACH             +       +       +       +       +
  94  * _FOREACH_REVERSE     -       -       -       +       +
  95  * _INSERT_HEAD         +       +       +       +       +
  96  * _INSERT_BEFORE       -       +       -       +       +
  97  * _INSERT_AFTER        +       +       +       +       +
  98  * _INSERT_TAIL         -       -       +       +       +
  99  * _REMOVE_HEAD         +       -       +       -       -
 100  * _REMOVE              +       +       +       +       +
 101  *
 102  */
 103
 104 /*
 105  * Singly-linked List declarations.
 106  */
 107 #define SLIST_HEAD(name, type)                                          \
 108 struct name {                                                           \
 109         struct type *slh_first; /* first element */                     \
 110 }
 111
 112 #define SLIST_HEAD_INITIALIZER(head)                                    \
 113         { NULL }
 114
 115 #define SLIST_ENTRY(type)                                               \
 116 struct {                                                                \
 117         struct type *sle_next;  /* next element */                      \
 118 }
 119
 120 /*
 121  * Singly-linked List functions.
 122  */
 123 #define SLIST_EMPTY(head)       ((head)->slh_first == NULL)
 124
 125 #define SLIST_FIRST(head)       ((head)->slh_first)
 126
 127 #define SLIST_FOREACH(var, head, field)                                 \
 128         for ((var) = SLIST_FIRST((head));                               \
 129             (var);                                                      \
 130             (var) = SLIST_NEXT((var), field))
 131
 132 #define SLIST_INIT(head) do {                                           \
 133         SLIST_FIRST((head)) = NULL;                                     \
 134 } while (0)
 135
 136 #define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
 137         SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);       \
 138         SLIST_NEXT((slistelm), field) = (elm);                          \
 139 } while (0)
 140
 141 #define SLIST_INSERT_HEAD(head, elm, field) do {                        \
 142         SLIST_NEXT((elm), field) = SLIST_FIRST((head));                 \
 143         SLIST_FIRST((head)) = (elm);                                    \
 144 } while (0)
 145
 146 #define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)
 147
 148 #define SLIST_REMOVE(head, elm, type, field) do {                       \
 149         if (SLIST_FIRST((head)) == (elm)) {                             \
 150                 SLIST_REMOVE_HEAD((head), field);                       \
 151         }                                                               \
 152         else {                                                          \
 153                 struct type *curelm = SLIST_FIRST((head));              \
 154                 while (SLIST_NEXT(curelm, field) != (elm))              \
 155                         curelm = SLIST_NEXT(curelm, field);             \
 156                 SLIST_NEXT(curelm, field) =                             \
 157                     SLIST_NEXT(SLIST_NEXT(curelm, field), field);       \
 158         }                                                               \
 159 } while (0)
 160
 161 #define SLIST_REMOVE_HEAD(head, field) do {                             \
 162         SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);   \
 163 } while (0)
 164
 165 /*
 166  * Singly-linked Tail queue declarations.
 167  */
 168 #define STAILQ_HEAD(name, type)                                         \
 169 struct name {                                                           \
 170         struct type *stqh_first;/* first element */                     \
 171         struct type **stqh_last;/* addr of last next element */         \
 172 }
 173
 174 #define STAILQ_HEAD_INITIALIZER(head)                                   \
 175         { NULL, &(head).stqh_first }
 176
 177 #define STAILQ_ENTRY(type)                                              \
 178 struct {                                                                \
 179         struct type *stqe_next; /* next element */                      \
 180 }
 181
 182 /*
 183  * Singly-linked Tail queue functions.
 184  */
 185 #define STAILQ_EMPTY(head)      ((head)->stqh_first == NULL)
 186
 187 #define STAILQ_FIRST(head)      ((head)->stqh_first)
 188
 189 #define STAILQ_FOREACH(var, head, field)                                \
 190         for((var) = STAILQ_FIRST((head));                               \
 191            (var);                                                       \
 192            (var) = STAILQ_NEXT((var), field))
 193
 194 #define STAILQ_INIT(head) do {                                          \
 195         STAILQ_FIRST((head)) = NULL;                                    \
 196         (head)->stqh_last = &STAILQ_FIRST((head));                      \
 197 } while (0)
 198
 199 #define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {               \
 200         if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
 201                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 202         STAILQ_NEXT((tqelm), field) = (elm);                            \
 203 } while (0)
 204
 205 #define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
 206         if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL) \
 207                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 208         STAILQ_FIRST((head)) = (elm);                                   \
 209 } while (0)
 210
 211 #define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
 212         STAILQ_NEXT((elm), field) = NULL;                               \
 213         STAILQ_LAST((head)) = (elm);                                    \
 214         (head)->stqh_last = &STAILQ_NEXT((elm), field);                 \
 215 } while (0)
 216
 217 #define STAILQ_LAST(head)       (*(head)->stqh_last)
 218
 219 #define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
 220
 221 #define STAILQ_REMOVE(head, elm, type, field) do {                      \
 222         if (STAILQ_FIRST((head)) == (elm)) {                            \
 223                 STAILQ_REMOVE_HEAD(head, field);                        \
 224         }                                                               \
 225         else {                                                          \
 226                 struct type *curelm = STAILQ_FIRST((head));             \
 227                 while (STAILQ_NEXT(curelm, field) != (elm))             \
 228                         curelm = STAILQ_NEXT(curelm, field);            \
 229                 if ((STAILQ_NEXT(curelm, field) =                       \
 230                      STAILQ_NEXT(STAILQ_NEXT(curelm, field), field)) == NULL)\
 231                         (head)->stqh_last = &STAILQ_NEXT((curelm), field);\
 232         }                                                               \
 233 } while (0)
 234
 235 #define STAILQ_REMOVE_HEAD(head, field) do {                            \
 236         if ((STAILQ_FIRST((head)) =                                     \
 237              STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL)         \
 238                 (head)->stqh_last = &STAILQ_FIRST((head));              \
 239 } while (0)
 240
 241 #define STAILQ_REMOVE_HEAD_UNTIL(head, elm, field) do {                 \
 242         if ((STAILQ_FIRST((head)) = STAILQ_NEXT((elm), field)) == NULL) \
 243                 (head)->stqh_last = &STAILQ_FIRST((head));              \
 244 } while (0)
 245
 246 /*
 247  * List declarations.
 248  */
 249 #define LIST_HEAD(name, type)                                           \
 250 struct name {                                                           \
 251         struct type *lh_first;  /* first element */                     \
 252 }
 253
 254 #define LIST_HEAD_INITIALIZER(head)                                     \
 255         { NULL }
 256
 257 #define LIST_ENTRY(type)                                                \
 258 struct {                                                                \
 259         struct type *le_next;   /* next element */                      \
 260         struct type **le_prev;  /* address of previous next element */  \
 261 }
 262
 263 /*
 264  * List functions.
 265  */
 266
 267 #define LIST_EMPTY(head)        ((head)->lh_first == NULL)
 268
 269 #define LIST_FIRST(head)        ((head)->lh_first)
 270
 271 #define LIST_FOREACH(var, head, field)                                  \
 272         for ((var) = LIST_FIRST((head));                                \
 273             (var);                                                      \
 274             (var) = LIST_NEXT((var), field))
 275
 276 #define LIST_INIT(head) do {                                            \
 277         LIST_FIRST((head)) = NULL;                                      \
 278 } while (0)
 279
 280 #define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
 281         if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
 282                 LIST_NEXT((listelm), field)->field.le_prev =            \
 283                     &LIST_NEXT((elm), field);                           \
 284         LIST_NEXT((listelm), field) = (elm);                            \
 285         (elm)->field.le_prev = &LIST_NEXT((listelm), field);            \
 286 } while (0)
 287
 288 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
 289         (elm)->field.le_prev = (listelm)->field.le_prev;                \
 290         LIST_NEXT((elm), field) = (listelm);                            \
 291         *(listelm)->field.le_prev = (elm);                              \
 292         (listelm)->field.le_prev = &LIST_NEXT((elm), field);            \
 293 } while (0)
 294
 295 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
 296         if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)     \
 297                 LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
 298         LIST_FIRST((head)) = (elm);                                     \
 299         (elm)->field.le_prev = &LIST_FIRST((head));                     \
 300 } while (0)
 301
 302 #define LIST_NEXT(elm, field)   ((elm)->field.le_next)
 303
 304 #define LIST_REMOVE(elm, field) do {                                    \
 305         if (LIST_NEXT((elm), field) != NULL)                            \
 306                 LIST_NEXT((elm), field)->field.le_prev =                \
 307                     (elm)->field.le_prev;                               \
 308         *(elm)->field.le_prev = LIST_NEXT((elm), field);                \
 309 } while (0)
 310
 311 /*
 312  * Tail queue declarations.
 313  */
 314 #define TAILQ_HEAD(name, type)                                          \
 315 struct name {                                                           \
 316         struct type *tqh_first; /* first element */                     \
 317         struct type **tqh_last; /* addr of last next element */         \
 318 }
 319
 320 #define TAILQ_HEAD_INITIALIZER(head)                                    \
 321         { NULL, &(head).tqh_first }
 322
 323 #define TAILQ_ENTRY(type)                                               \
 324 struct {                                                                \
 325         struct type *tqe_next;  /* next element */                      \
 326         struct type **tqe_prev; /* address of previous next element */  \
 327 }
 328
 329 /*
 330  * Tail queue functions.
 331  */
 332 #define TAILQ_EMPTY(head)       ((head)->tqh_first == NULL)
 333
 334 #define TAILQ_FIRST(head)       ((head)->tqh_first)
 335
 336 #define TAILQ_FOREACH(var, head, field)                                 \
 337         for ((var) = TAILQ_FIRST((head));                               \
 338             (var);                                                      \
 339             (var) = TAILQ_NEXT((var), field))
 340
 341 #define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
 342         for ((var) = TAILQ_LAST((head), headname);                      \
 343             (var);                                                      \
 344             (var) = TAILQ_PREV((var), headname, field))
 345
 346 #define TAILQ_INIT(head) do {                                           \
 347         TAILQ_FIRST((head)) = NULL;                                     \
 348         (head)->tqh_last = &TAILQ_FIRST((head));                        \
 349 } while (0)
 350
 351 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
 352         if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
 353                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
 354                     &TAILQ_NEXT((elm), field);                          \
 355         else                                                            \
 356                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
 357         TAILQ_NEXT((listelm), field) = (elm);                           \
 358         (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);          \
 359 } while (0)
 360
 361 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
 362         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
 363         TAILQ_NEXT((elm), field) = (listelm);                           \
 364         *(listelm)->field.tqe_prev = (elm);                             \
 365         (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);          \
 366 } while (0)
 367
 368 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
 369         if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)   \
 370                 TAILQ_FIRST((head))->field.tqe_prev =                   \
 371                     &TAILQ_NEXT((elm), field);                          \
 372         else                                                            \
 373                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
 374         TAILQ_FIRST((head)) = (elm);                                    \
 375         (elm)->field.tqe_prev = &TAILQ_FIRST((head));                   \
 376 } while (0)
 377
 378 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
 379         TAILQ_NEXT((elm), field) = NULL;                                \
 380         (elm)->field.tqe_prev = (head)->tqh_last;                       \
 381         *(head)->tqh_last = (elm);                                      \
 382         (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
 383 } while (0)
 384
 385 #define TAILQ_LAST(head, headname)                                      \
 386         (*(((struct headname *)((head)->tqh_last))->tqh_last))
 387
 388 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
 389
 390 #define TAILQ_PREV(elm, headname, field)                                \
 391         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
 392
 393 #define TAILQ_REMOVE(head, elm, field) do {                             \
 394         if ((TAILQ_NEXT((elm), field)) != NULL)                         \
 395                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
 396                     (elm)->field.tqe_prev;                              \
 397         else                                                            \
 398                 (head)->tqh_last = (elm)->field.tqe_prev;               \
 399         *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);              \
 400 } while (0)
 401
 402 /*
 403  * Circular queue declarations.
 404  */
 405 #define CIRCLEQ_HEAD(name, type)                                        \
 406 struct name {                                                           \
 407         struct type *cqh_first;         /* first element */             \
 408         struct type *cqh_last;          /* last element */              \
 409 }
 410
 411 #define CIRCLEQ_HEAD_INITIALIZER(head)                                  \
 412         { (void *)&(head), (void *)&(head) }
 413
 414 #define CIRCLEQ_ENTRY(type)                                             \
 415 struct {                                                                \
 416         struct type *cqe_next;          /* next element */              \
 417         struct type *cqe_prev;          /* previous element */          \
 418 }
 419
 420 /*
 421  * Circular queue functions.
 422  */
 423 #define CIRCLEQ_EMPTY(head)     ((head)->cqh_first == (void *)(head))
 424
 425 #define CIRCLEQ_FIRST(head)     ((head)->cqh_first)
 426
 427 #define CIRCLEQ_FOREACH(var, head, field)                               \
 428         for ((var) = CIRCLEQ_FIRST((head));                             \
 429             (var) != (void *)(head);                                    \
 430             (var) = CIRCLEQ_NEXT((var), field))
 431
 432 #define CIRCLEQ_FOREACH_REVERSE(var, head, field)                       \
 433         for ((var) = CIRCLEQ_LAST((head));                              \
 434             (var) != (void *)(head);                                    \
 435             (var) = CIRCLEQ_PREV((var), field))
 436
 437 #define CIRCLEQ_INIT(head) do {                                         \
 438         CIRCLEQ_FIRST((head)) = (void *)(head);                         \
 439         CIRCLEQ_LAST((head)) = (void *)(head);                          \
 440 } while (0)
 441
 442 #define CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {            \
 443         CIRCLEQ_NEXT((elm), field) = CIRCLEQ_NEXT((listelm), field);    \
 444         CIRCLEQ_PREV((elm), field) = (listelm);                         \
 445         if (CIRCLEQ_NEXT((listelm), field) == (void *)(head))           \
 446                 CIRCLEQ_LAST((head)) = (elm);                           \
 447         else                                                            \
 448                 CIRCLEQ_PREV(CIRCLEQ_NEXT((listelm), field), field) = (elm);\
 449         CIRCLEQ_NEXT((listelm), field) = (elm);                         \
 450 } while (0)
 451
 452 #define CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do {           \
 453         CIRCLEQ_NEXT((elm), field) = (listelm);                         \
 454         CIRCLEQ_PREV((elm), field) = CIRCLEQ_PREV((listelm), field);    \
 455         if (CIRCLEQ_PREV((listelm), field) == (void *)(head))           \
 456                 CIRCLEQ_FIRST((head)) = (elm);                          \
 457         else                                                            \
 458                 CIRCLEQ_NEXT(CIRCLEQ_PREV((listelm), field), field) = (elm);\
 459         CIRCLEQ_PREV((listelm), field) = (elm);                         \
 460 } while (0)
 461
 462 #define CIRCLEQ_INSERT_HEAD(head, elm, field) do {                      \
 463         CIRCLEQ_NEXT((elm), field) = CIRCLEQ_FIRST((head));             \
 464         CIRCLEQ_PREV((elm), field) = (void *)(head);                    \
 465         if (CIRCLEQ_LAST((head)) == (void *)(head))                     \
 466                 CIRCLEQ_LAST((head)) = (elm);                           \
 467         else                                                            \
 468                 CIRCLEQ_PREV(CIRCLEQ_FIRST((head)), field) = (elm);     \
 469         CIRCLEQ_FIRST((head)) = (elm);                                  \
 470 } while (0)
 471
 472 #define CIRCLEQ_INSERT_TAIL(head, elm, field) do {                      \
 473         CIRCLEQ_NEXT((elm), field) = (void *)(head);                    \
 474         CIRCLEQ_PREV((elm), field) = CIRCLEQ_LAST((head));              \
 475         if (CIRCLEQ_FIRST((head)) == (void *)(head))                    \
 476                 CIRCLEQ_FIRST((head)) = (elm);                          \
 477         else                                                            \
 478                 CIRCLEQ_NEXT(CIRCLEQ_LAST((head)), field) = (elm);      \
 479         CIRCLEQ_LAST((head)) = (elm);                                   \
 480 } while (0)
 481
 482 #define CIRCLEQ_LAST(head)      ((head)->cqh_last)
 483
 484 #define CIRCLEQ_NEXT(elm,field) ((elm)->field.cqe_next)
 485
 486 #define CIRCLEQ_PREV(elm,field) ((elm)->field.cqe_prev)
 487
 488 #define CIRCLEQ_REMOVE(head, elm, field) do {                           \
 489         if (CIRCLEQ_NEXT((elm), field) == (void *)(head))               \
 490                 CIRCLEQ_LAST((head)) = CIRCLEQ_PREV((elm), field);      \
 491         else                                                            \
 492                 CIRCLEQ_PREV(CIRCLEQ_NEXT((elm), field), field) =       \
 493                     CIRCLEQ_PREV((elm), field);                         \
 494         if (CIRCLEQ_PREV((elm), field) == (void *)(head))               \
 495                 CIRCLEQ_FIRST((head)) = CIRCLEQ_NEXT((elm), field);     \
 496         else                                                            \
 497                 CIRCLEQ_NEXT(CIRCLEQ_PREV((elm), field), field) =       \
 498                     CIRCLEQ_NEXT((elm), field);                         \
 499 } while (0)
 500
 501 #endif /* !_SYS_QUEUE_H_ */