sys/sys/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  * 3. All advertising materials mentioning features or use of this software
  14  *    must display the following acknowledgement:
  15  *      This product includes software developed by the University of
  16  *      California, Berkeley and its contributors.
  17  * 4. Neither the name of the University nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  *
  33  *      @(#)queue.h     8.5 (Berkeley) 8/20/94
  34  * $FreeBSD$
  35  */
  36
  37 #ifndef _SYS_QUEUE_H_
  38 #define _SYS_QUEUE_H_
  39
  40 #include <sys/cdefs.h>
  41
  42 /*
  43  * This file defines four types of data structures: singly-linked lists,
  44  * singly-linked tail queues, lists and tail queues.
  45  *
  46  * A singly-linked list is headed by a single forward pointer. The elements
  47  * are singly linked for minimum space and pointer manipulation overhead at
  48  * the expense of O(n) removal for arbitrary elements. New elements can be
  49  * added to the list after an existing element or at the head of the list.
  50  * Elements being removed from the head of the list should use the explicit
  51  * macro for this purpose for optimum efficiency. A singly-linked list may
  52  * only be traversed in the forward direction.  Singly-linked lists are ideal
  53  * for applications with large datasets and few or no removals or for
  54  * implementing a LIFO queue.
  55  *
  56  * A singly-linked tail queue is headed by a pair of pointers, one to the
  57  * head of the list and the other to the tail of the list. The elements are
  58  * singly linked for minimum space and pointer manipulation overhead at the
  59  * expense of O(n) removal for arbitrary elements. New elements can be added
  60  * to the list after an existing element, at the head of the list, or at the
  61  * end of the list. Elements being removed from the head of the tail queue
  62  * should use the explicit macro for this purpose for optimum efficiency.
  63  * A singly-linked tail queue may only be traversed in the forward direction.
  64  * Singly-linked tail queues are ideal for applications with large datasets
  65  * and few or no removals or for implementing a FIFO queue.
  66  *
  67  * A list is headed by a single forward pointer (or an array of forward
  68  * pointers for a hash table header). The elements are doubly linked
  69  * so that an arbitrary element can be removed without a need to
  70  * traverse the list. New elements can be added to the list before
  71  * or after an existing element or at the head of the list. A list
  72  * 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  * For details on the use of these macros, see the queue(3) manual page.
  82  *
  83  *
  84  *                              SLIST   LIST    STAILQ  TAILQ
  85  * _HEAD                        +       +       +       +
  86  * _HEAD_INITIALIZER            +       +       +       +
  87  * _ENTRY                       +       +       +       +
  88  * _INIT                        +       +       +       +
  89  * _EMPTY                       +       +       +       +
  90  * _FIRST                       +       +       +       +
  91  * _NEXT                        +       +       +       +
  92  * _PREV                        -       -       -       +
  93  * _LAST                        -       -       +       +
  94  * _FOREACH                     +       +       +       +
  95  * _FOREACH_SAFE                +       +       +       +
  96  * _FOREACH_REVERSE             -       -       -       +
  97  * _FOREACH_REVERSE_SAFE        -       -       -       +
  98  * _INSERT_HEAD                 +       +       +       +
  99  * _INSERT_BEFORE               -       +       -       +
 100  * _INSERT_AFTER                +       +       +       +
 101  * _INSERT_TAIL                 -       -       +       +
 102  * _CONCAT                      -       -       +       +
 103  * _REMOVE_HEAD                 +       -       +       -
 104  * _REMOVE                      +       +       +       +
 105  *
 106  */
 107 #define QUEUE_MACRO_DEBUG 0
 108 #if QUEUE_MACRO_DEBUG
 109 /* Store the last 2 places the queue element or head was altered */
 110 struct qm_trace {
 111         char * lastfile;
 112         int lastline;
 113         char * prevfile;
 114         int prevline;
 115 };
 116
 117 #define TRACEBUF        struct qm_trace trace;
 118 #define TRASHIT(x)      do {(x) = (void *)-1;} while (0)
 119
 120 #define QMD_TRACE_HEAD(head) do {                                       \
 121         (head)->trace.prevline = (head)->trace.lastline;                \
 122         (head)->trace.prevfile = (head)->trace.lastfile;                \
 123         (head)->trace.lastline = __LINE__;                              \
 124         (head)->trace.lastfile = __FILE__;                              \
 125 } while (0)
 126
 127 #define QMD_TRACE_ELEM(elem) do {                                       \
 128         (elem)->trace.prevline = (elem)->trace.lastline;                \
 129         (elem)->trace.prevfile = (elem)->trace.lastfile;                \
 130         (elem)->trace.lastline = __LINE__;                              \
 131         (elem)->trace.lastfile = __FILE__;                              \
 132 } while (0)
 133
 134 #else
 135 #define QMD_TRACE_ELEM(elem)
 136 #define QMD_TRACE_HEAD(head)
 137 #define TRACEBUF
 138 #define TRASHIT(x)
 139 #endif  /* QUEUE_MACRO_DEBUG */
 140
 141 /*
 142  * Singly-linked List declarations.
 143  */
 144 #define SLIST_HEAD(name, type)                                          \
 145 struct name {                                                           \
 146         struct type *slh_first; /* first element */                     \
 147 }
 148
 149 #define SLIST_HEAD_INITIALIZER(head)                                    \
 150         { NULL }
 151
 152 #define SLIST_ENTRY(type)                                               \
 153 struct {                                                                \
 154         struct type *sle_next;  /* next element */                      \
 155 }
 156
 157 /*
 158  * Singly-linked List functions.
 159  */
 160 #define SLIST_EMPTY(head)       ((head)->slh_first == NULL)
 161
 162 #define SLIST_FIRST(head)       ((head)->slh_first)
 163
 164 #define SLIST_FOREACH(var, head, field)                                 \
 165         for ((var) = SLIST_FIRST((head));                               \
 166             (var);                                                      \
 167             (var) = SLIST_NEXT((var), field))
 168
 169 #define SLIST_FOREACH_SAFE(var, head, field, tvar)                      \
 170         for ((var) = SLIST_FIRST((head));                               \
 171             (var) && ((tvar) = SLIST_NEXT((var), field), 1);            \
 172             (var) = (tvar))
 173
 174 #define SLIST_FOREACH_PREVPTR(var, varp, head, field)                   \
 175         for ((varp) = &SLIST_FIRST((head));                             \
 176             ((var) = *(varp)) != NULL;                                  \
 177             (varp) = &SLIST_NEXT((var), field))
 178
 179 #define SLIST_INIT(head) do {                                           \
 180         SLIST_FIRST((head)) = NULL;                                     \
 181 } while (0)
 182
 183 #define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
 184         SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);       \
 185         SLIST_NEXT((slistelm), field) = (elm);                          \
 186 } while (0)
 187
 188 #define SLIST_INSERT_HEAD(head, elm, field) do {                        \
 189         SLIST_NEXT((elm), field) = SLIST_FIRST((head));                 \
 190         SLIST_FIRST((head)) = (elm);                                    \
 191 } while (0)
 192
 193 #define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)
 194
 195 #define SLIST_REMOVE(head, elm, type, field) do {                       \
 196         if (SLIST_FIRST((head)) == (elm)) {                             \
 197                 SLIST_REMOVE_HEAD((head), field);                       \
 198         }                                                               \
 199         else {                                                          \
 200                 struct type *curelm = SLIST_FIRST((head));              \
 201                 while (SLIST_NEXT(curelm, field) != (elm))              \
 202                         curelm = SLIST_NEXT(curelm, field);             \
 203                 SLIST_NEXT(curelm, field) =                             \
 204                     SLIST_NEXT(SLIST_NEXT(curelm, field), field);       \
 205         }                                                               \
 206 } while (0)
 207
 208 #define SLIST_REMOVE_HEAD(head, field) do {                             \
 209         SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);   \
 210 } while (0)
 211
 212 /*
 213  * Singly-linked Tail queue declarations.
 214  */
 215 #define STAILQ_HEAD(name, type)                                         \
 216 struct name {                                                           \
 217         struct type *stqh_first;/* first element */                     \
 218         struct type **stqh_last;/* addr of last next element */         \
 219 }
 220
 221 #define STAILQ_HEAD_INITIALIZER(head)                                   \
 222         { NULL, &(head).stqh_first }
 223
 224 #define STAILQ_ENTRY(type)                                              \
 225 struct {                                                                \
 226         struct type *stqe_next; /* next element */                      \
 227 }
 228
 229 /*
 230  * Singly-linked Tail queue functions.
 231  */
 232 #define STAILQ_CONCAT(head1, head2) do {                                \
 233         if (!STAILQ_EMPTY((head2))) {                                   \
 234                 *(head1)->stqh_last = (head2)->stqh_first;              \
 235                 (head1)->stqh_last = (head2)->stqh_last;                \
 236                 STAILQ_INIT((head2));                                   \
 237         }                                                               \
 238 } while (0)
 239
 240 #define STAILQ_EMPTY(head)      ((head)->stqh_first == NULL)
 241
 242 #define STAILQ_FIRST(head)      ((head)->stqh_first)
 243
 244 #define STAILQ_FOREACH(var, head, field)                                \
 245         for((var) = STAILQ_FIRST((head));                               \
 246            (var);                                                       \
 247            (var) = STAILQ_NEXT((var), field))
 248
 249
 250 #define STAILQ_FOREACH_SAFE(var, head, field, tvar)                     \
 251         for ((var) = STAILQ_FIRST((head));                              \
 252             (var) && ((tvar) = STAILQ_NEXT((var), field), 1);           \
 253             (var) = (tvar))
 254
 255 #define STAILQ_INIT(head) do {                                          \
 256         STAILQ_FIRST((head)) = NULL;                                    \
 257         (head)->stqh_last = &STAILQ_FIRST((head));                      \
 258 } while (0)
 259
 260 #define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {               \
 261         if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
 262                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 263         STAILQ_NEXT((tqelm), field) = (elm);                            \
 264 } while (0)
 265
 266 #define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
 267         if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL) \
 268                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 269         STAILQ_FIRST((head)) = (elm);                                   \
 270 } while (0)
 271
 272 #define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
 273         STAILQ_NEXT((elm), field) = NULL;                               \
 274         *(head)->stqh_last = (elm);                                     \
 275         (head)->stqh_last = &STAILQ_NEXT((elm), field);                 \
 276 } while (0)
 277
 278 #define STAILQ_LAST(head, type, field)                                  \
 279         (STAILQ_EMPTY((head)) ?                                         \
 280                 NULL :                                                  \
 281                 ((struct type *)                                        \
 282                 ((char *)((head)->stqh_last) - __offsetof(struct type, field))))
 283
 284 #define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
 285
 286 #define STAILQ_REMOVE(head, elm, type, field) do {                      \
 287         if (STAILQ_FIRST((head)) == (elm)) {                            \
 288                 STAILQ_REMOVE_HEAD((head), field);                      \
 289         }                                                               \
 290         else {                                                          \
 291                 struct type *curelm = STAILQ_FIRST((head));             \
 292                 while (STAILQ_NEXT(curelm, field) != (elm))             \
 293                         curelm = STAILQ_NEXT(curelm, field);            \
 294                 if ((STAILQ_NEXT(curelm, field) =                       \
 295                      STAILQ_NEXT(STAILQ_NEXT(curelm, field), field)) == NULL)\
 296                         (head)->stqh_last = &STAILQ_NEXT((curelm), field);\
 297         }                                                               \
 298 } while (0)
 299
 300 #define STAILQ_REMOVE_HEAD(head, field) do {                            \
 301         if ((STAILQ_FIRST((head)) =                                     \
 302              STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL)         \
 303                 (head)->stqh_last = &STAILQ_FIRST((head));              \
 304 } while (0)
 305
 306 #define STAILQ_REMOVE_HEAD_UNTIL(head, elm, field) do {                 \
 307         if ((STAILQ_FIRST((head)) = STAILQ_NEXT((elm), field)) == NULL) \
 308                 (head)->stqh_last = &STAILQ_FIRST((head));              \
 309 } while (0)
 310
 311 /*
 312  * List declarations.
 313  */
 314 #define LIST_HEAD(name, type)                                           \
 315 struct name {                                                           \
 316         struct type *lh_first;  /* first element */                     \
 317 }
 318
 319 #define LIST_HEAD_INITIALIZER(head)                                     \
 320         { NULL }
 321
 322 #define LIST_ENTRY(type)                                                \
 323 struct {                                                                \
 324         struct type *le_next;   /* next element */                      \
 325         struct type **le_prev;  /* address of previous next element */  \
 326 }
 327
 328 /*
 329  * List functions.
 330  */
 331
 332 #define LIST_EMPTY(head)        ((head)->lh_first == NULL)
 333
 334 #define LIST_FIRST(head)        ((head)->lh_first)
 335
 336 #define LIST_FOREACH(var, head, field)                                  \
 337         for ((var) = LIST_FIRST((head));                                \
 338             (var);                                                      \
 339             (var) = LIST_NEXT((var), field))
 340
 341 #define LIST_FOREACH_SAFE(var, head, field, tvar)                       \
 342         for ((var) = LIST_FIRST((head));                                \
 343             (var) && ((tvar) = LIST_NEXT((var), field), 1);             \
 344             (var) = (tvar))
 345
 346 #define LIST_INIT(head) do {                                            \
 347         LIST_FIRST((head)) = NULL;                                      \
 348 } while (0)
 349
 350 #define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
 351         if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
 352                 LIST_NEXT((listelm), field)->field.le_prev =            \
 353                     &LIST_NEXT((elm), field);                           \
 354         LIST_NEXT((listelm), field) = (elm);                            \
 355         (elm)->field.le_prev = &LIST_NEXT((listelm), field);            \
 356 } while (0)
 357
 358 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
 359         (elm)->field.le_prev = (listelm)->field.le_prev;                \
 360         LIST_NEXT((elm), field) = (listelm);                            \
 361         *(listelm)->field.le_prev = (elm);                              \
 362         (listelm)->field.le_prev = &LIST_NEXT((elm), field);            \
 363 } while (0)
 364
 365 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
 366         if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)     \
 367                 LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
 368         LIST_FIRST((head)) = (elm);                                     \
 369         (elm)->field.le_prev = &LIST_FIRST((head));                     \
 370 } while (0)
 371
 372 #define LIST_NEXT(elm, field)   ((elm)->field.le_next)
 373
 374 #define LIST_REMOVE(elm, field) do {                                    \
 375         if (LIST_NEXT((elm), field) != NULL)                            \
 376                 LIST_NEXT((elm), field)->field.le_prev =                \
 377                     (elm)->field.le_prev;                               \
 378         *(elm)->field.le_prev = LIST_NEXT((elm), field);                \
 379 } while (0)
 380
 381 /*
 382  * Tail queue declarations.
 383  */
 384 #define TAILQ_HEAD(name, type)                                          \
 385 struct name {                                                           \
 386         struct type *tqh_first; /* first element */                     \
 387         struct type **tqh_last; /* addr of last next element */         \
 388         TRACEBUF                                                        \
 389 }
 390
 391 #define TAILQ_HEAD_INITIALIZER(head)                                    \
 392         { NULL, &(head).tqh_first }
 393
 394 #define TAILQ_ENTRY(type)                                               \
 395 struct {                                                                \
 396         struct type *tqe_next;  /* next element */                      \
 397         struct type **tqe_prev; /* address of previous next element */  \
 398         TRACEBUF                                                        \
 399 }
 400
 401 /*
 402  * Tail queue functions.
 403  */
 404 #define TAILQ_CONCAT(head1, head2, field) do {                          \
 405         if (!TAILQ_EMPTY(head2)) {                                      \
 406                 *(head1)->tqh_last = (head2)->tqh_first;                \
 407                 (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last; \
 408                 (head1)->tqh_last = (head2)->tqh_last;                  \
 409                 TAILQ_INIT((head2));                                    \
 410                 QMD_TRACE_HEAD(head);                                   \
 411                 QMD_TRACE_HEAD(head2);                                  \
 412         }                                                               \
 413 } while (0)
 414
 415 #define TAILQ_EMPTY(head)       ((head)->tqh_first == NULL)
 416
 417 #define TAILQ_FIRST(head)       ((head)->tqh_first)
 418
 419 #define TAILQ_FOREACH(var, head, field)                                 \
 420         for ((var) = TAILQ_FIRST((head));                               \
 421             (var);                                                      \
 422             (var) = TAILQ_NEXT((var), field))
 423
 424 #define TAILQ_FOREACH_SAFE(var, head, field, tvar)                      \
 425         for ((var) = TAILQ_FIRST((head));                               \
 426             (var) && ((tvar) = TAILQ_NEXT((var), field), 1);            \
 427             (var) = (tvar))
 428
 429 #define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
 430         for ((var) = TAILQ_LAST((head), headname);                      \
 431             (var);                                                      \
 432             (var) = TAILQ_PREV((var), headname, field))
 433
 434 #define TAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar)    \
 435         for ((var) = TAILQ_LAST((head), headname);                      \
 436             (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);  \
 437             (var) = (tvar))
 438
 439 #define TAILQ_INIT(head) do {                                           \
 440         TAILQ_FIRST((head)) = NULL;                                     \
 441         (head)->tqh_last = &TAILQ_FIRST((head));                        \
 442         QMD_TRACE_HEAD(head);                                           \
 443 } while (0)
 444
 445 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
 446         if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
 447                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
 448                     &TAILQ_NEXT((elm), field);                          \
 449         else {                                                          \
 450                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
 451                 QMD_TRACE_HEAD(head);                                   \
 452         }                                                               \
 453         TAILQ_NEXT((listelm), field) = (elm);                           \
 454         (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);          \
 455         QMD_TRACE_ELEM(&(elm)->field);                                  \
 456         QMD_TRACE_ELEM(&listelm->field);                                \
 457 } while (0)
 458
 459 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
 460         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
 461         TAILQ_NEXT((elm), field) = (listelm);                           \
 462         *(listelm)->field.tqe_prev = (elm);                             \
 463         (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);          \
 464         QMD_TRACE_ELEM(&(elm)->field);                                  \
 465         QMD_TRACE_ELEM(&listelm->field);                                \
 466 } while (0)
 467
 468 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
 469         if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)   \
 470                 TAILQ_FIRST((head))->field.tqe_prev =                   \
 471                     &TAILQ_NEXT((elm), field);                          \
 472         else                                                            \
 473                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
 474         TAILQ_FIRST((head)) = (elm);                                    \
 475         (elm)->field.tqe_prev = &TAILQ_FIRST((head));                   \
 476         QMD_TRACE_HEAD(head);                                           \
 477         QMD_TRACE_ELEM(&(elm)->field);                                  \
 478 } while (0)
 479
 480 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
 481         TAILQ_NEXT((elm), field) = NULL;                                \
 482         (elm)->field.tqe_prev = (head)->tqh_last;                       \
 483         *(head)->tqh_last = (elm);                                      \
 484         (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
 485         QMD_TRACE_HEAD(head);                                           \
 486         QMD_TRACE_ELEM(&(elm)->field);                                  \
 487 } while (0)
 488
 489 #define TAILQ_LAST(head, headname)                                      \
 490         (*(((struct headname *)((head)->tqh_last))->tqh_last))
 491
 492 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
 493
 494 #define TAILQ_PREV(elm, headname, field)                                \
 495         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
 496
 497 #define TAILQ_REMOVE(head, elm, field) do {                             \
 498         if ((TAILQ_NEXT((elm), field)) != NULL)                         \
 499                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
 500                     (elm)->field.tqe_prev;                              \
 501         else {                                                          \
 502                 (head)->tqh_last = (elm)->field.tqe_prev;               \
 503                 QMD_TRACE_HEAD(head);                                   \
 504         }                                                               \
 505         *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);              \
 506         TRASHIT((elm)->field.tqe_next);                                 \
 507         TRASHIT((elm)->field.tqe_prev);                                 \
 508         QMD_TRACE_ELEM(&(elm)->field);                                  \
 509 } while (0)
 510
 511
 512 #ifdef _KERNEL
 513
 514 /*
 515  * XXX insque() and remque() are an old way of handling certain queues.
 516  * They bogusly assumes that all queue heads look alike.
 517  */
 518
 519 struct quehead {
 520         struct quehead *qh_link;
 521         struct quehead *qh_rlink;
 522 };
 523
 524 #ifdef  __GNUC__
 525
 526 static __inline void
 527 insque(void *a, void *b)
 528 {
 529         struct quehead *element = (struct quehead *)a,
 530                  *head = (struct quehead *)b;
 531
 532         element->qh_link = head->qh_link;
 533         element->qh_rlink = head;
 534         head->qh_link = element;
 535         element->qh_link->qh_rlink = element;
 536 }
 537
 538 static __inline void
 539 remque(void *a)
 540 {
 541         struct quehead *element = (struct quehead *)a;
 542
 543         element->qh_link->qh_rlink = element->qh_rlink;
 544         element->qh_rlink->qh_link = element->qh_link;
 545         element->qh_rlink = 0;
 546 }
 547
 548 #else /* !__GNUC__ */
 549
 550 void    insque(void *a, void *b);
 551 void    remque(void *a);
 552
 553 #endif /* __GNUC__ */
 554
 555 #endif /* _KERNEL */
 556
 557 #endif /* !_SYS_QUEUE_H_ */