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  * 4. Neither the name of the University nor the names of its contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  *
  29  *      @(#)queue.h     8.5 (Berkeley) 8/20/94
  30  * $FreeBSD: src/sys/sys/queue.h,v 1.69 2008/05/22 14:40:03 ed Exp $
  31  * $DragonFly: src/sys/sys/queue.h,v 1.11 2008/08/28 08:42:29 hasso Exp $
  32  */
  33
  34 #ifndef _SYS_QUEUE_H_
  35 #define _SYS_QUEUE_H_
  36
  37 #include <sys/cdefs.h>
  38
  39 /*
  40  * This file defines four types of data structures: singly-linked lists,
  41  * singly-linked tail queues, lists and tail queues.
  42  *
  43  * A singly-linked list is headed by a single forward pointer. The elements
  44  * are singly linked for minimum space and pointer manipulation overhead at
  45  * the expense of O(n) removal for arbitrary elements. New elements can be
  46  * added to the list after an existing element or at the head of the list.
  47  * Elements being removed from the head of the list should use the explicit
  48  * macro for this purpose for optimum efficiency. A singly-linked list may
  49  * only be traversed in the forward direction.  Singly-linked lists are ideal
  50  * for applications with large datasets and few or no removals or for
  51  * implementing a LIFO queue.
  52  *
  53  * A singly-linked tail queue is headed by a pair of pointers, one to the
  54  * head of the list and the other to the tail of the list. The elements are
  55  * singly linked for minimum space and pointer manipulation overhead at the
  56  * expense of O(n) removal for arbitrary elements. New elements can be added
  57  * to the list after an existing element, at the head of the list, or at the
  58  * end of the list. Elements being removed from the head of the tail queue
  59  * should use the explicit macro for this purpose for optimum efficiency.
  60  * A singly-linked tail queue may only be traversed in the forward direction.
  61  * Singly-linked tail queues are ideal for applications with large datasets
  62  * and few or no removals or for implementing a FIFO queue.
  63  *
  64  * A list is headed by a single forward pointer (or an array of forward
  65  * pointers for a hash table header). The elements are doubly linked
  66  * so that an arbitrary element can be removed without a need to
  67  * traverse the list. New elements can be added to the list before
  68  * or after an existing element or at the head of the list. A list
  69  * 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  *                              SLIST   LIST    STAILQ  TAILQ
  82  * _HEAD                        +       +       +       +
  83  * _HEAD_INITIALIZER            +       +       +       +
  84  * _ENTRY                       +       +       +       +
  85  * _INIT                        +       +       +       +
  86  * _EMPTY                       +       +       +       +
  87  * _FIRST                       +       +       +       +
  88  * _NEXT                        +       +       +       +
  89  * _PREV                        -       -       -       +
  90  * _LAST                        -       -       +       +
  91  * _FOREACH                     +       +       +       +
  92  * _FOREACH_MUTABLE             +       +       +       +
  93  * _FOREACH_REVERSE             -       -       -       +
  94  * _FOREACH_REVERSE_MUTABLE     -       -       -       +
  95  * _INSERT_HEAD                 +       +       +       +
  96  * _INSERT_BEFORE               -       +       -       +
  97  * _INSERT_AFTER                +       +       +       +
  98  * _INSERT_TAIL                 -       -       +       +
  99  * _CONCAT                      -       -       +       +
 100  * _REMOVE_HEAD                 +       -       +       -
 101  * _REMOVE_NEXT                 +       -       +       -
 102  * _REMOVE                      +       +       +       +
 103  *
 104  */
 105 #ifdef QUEUE_MACRO_DEBUG
 106 /* Store the last 2 places the queue element or head was altered */
 107 struct qm_trace {
 108         char    *lastfile;
 109         int      lastline;
 110         char    *prevfile;
 111         int      prevline;
 112 };
 113
 114 #define TRACEBUF        struct qm_trace trace;
 115 #define TRASHIT(x)      do {(x) = (void *)-1;} while (0)
 116
 117 #define QMD_TRACE_HEAD(head) do {                                       \
 118         (head)->trace.prevline = (head)->trace.lastline;                \
 119         (head)->trace.prevfile = (head)->trace.lastfile;                \
 120         (head)->trace.lastline = __LINE__;                              \
 121         (head)->trace.lastfile = __FILE__;                              \
 122 } while (0)
 123
 124 #define QMD_TRACE_ELEM(elem) do {                                       \
 125         (elem)->trace.prevline = (elem)->trace.lastline;                \
 126         (elem)->trace.prevfile = (elem)->trace.lastfile;                \
 127         (elem)->trace.lastline = __LINE__;                              \
 128         (elem)->trace.lastfile = __FILE__;                              \
 129 } while (0)
 130
 131 #else
 132 #define QMD_TRACE_ELEM(elem)
 133 #define QMD_TRACE_HEAD(head)
 134 #define TRACEBUF
 135 #define TRASHIT(x)
 136 #endif  /* QUEUE_MACRO_DEBUG */
 137
 138 /*
 139  * Singly-linked List declarations.
 140  */
 141 #define SLIST_HEAD(name, type)                                          \
 142 struct name {                                                           \
 143         struct type *slh_first; /* first element */                     \
 144 }
 145
 146 #define SLIST_HEAD_INITIALIZER(head)                                    \
 147         { NULL }
 148
 149 #define SLIST_ENTRY(type)                                               \
 150 struct {                                                                \
 151         struct type *sle_next;  /* next element */                      \
 152 }
 153
 154 #define SLIST_ENTRY_INITIALIZER { NULL }
 155
 156 /*
 157  * Singly-linked List functions.
 158  */
 159 #define SLIST_EMPTY(head)       ((head)->slh_first == NULL)
 160
 161 #define SLIST_FIRST(head)       ((head)->slh_first)
 162
 163 #define SLIST_FOREACH(var, head, field)                                 \
 164         for ((var) = SLIST_FIRST((head));                               \
 165             (var);                                                      \
 166             (var) = SLIST_NEXT((var), field))
 167
 168 #define SLIST_FOREACH_MUTABLE(var, head, field, tvar)                   \
 169         for ((var) = SLIST_FIRST((head));                               \
 170             (var) && ((tvar) = SLIST_NEXT((var), field), 1);            \
 171             (var) = (tvar))
 172
 173 #define SLIST_FOREACH_PREVPTR(var, varp, head, field)                   \
 174         for ((varp) = &SLIST_FIRST((head));                             \
 175             ((var) = *(varp)) != NULL;                                  \
 176             (varp) = &SLIST_NEXT((var), field))
 177
 178 #define SLIST_INIT(head) do {                                           \
 179         SLIST_FIRST((head)) = NULL;                                     \
 180 } while (0)
 181
 182 #define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
 183         SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);       \
 184         SLIST_NEXT((slistelm), field) = (elm);                          \
 185 } while (0)
 186
 187 #define SLIST_INSERT_HEAD(head, elm, field) do {                        \
 188         SLIST_NEXT((elm), field) = SLIST_FIRST((head));                 \
 189         SLIST_FIRST((head)) = (elm);                                    \
 190 } while (0)
 191
 192 #define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)
 193
 194 #define SLIST_REMOVE(head, elm, type, field) do {                       \
 195         if (SLIST_FIRST((head)) == (elm)) {                             \
 196                 SLIST_REMOVE_HEAD((head), field);                       \
 197         }                                                               \
 198         else {                                                          \
 199                 struct type *curelm = SLIST_FIRST((head));              \
 200                 while (SLIST_NEXT(curelm, field) != (elm))              \
 201                         curelm = SLIST_NEXT(curelm, field);             \
 202                 SLIST_REMOVE_NEXT(head, curelm, field);                 \
 203         }                                                               \
 204         TRASHIT((elm)->field.sle_next);                                 \
 205 } while (0)
 206
 207 #define SLIST_REMOVE_NEXT(head, elm, field) do {                                \
 208         SLIST_NEXT(elm, field) =                                        \
 209             SLIST_NEXT(SLIST_NEXT(elm, field), field);                  \
 210 } while (0)
 211
 212 #define SLIST_REMOVE_HEAD(head, field) do {                             \
 213         SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);   \
 214 } while (0)
 215
 216 /*
 217  * Singly-linked Tail queue declarations.
 218  */
 219 #define STAILQ_HEAD(name, type)                                         \
 220 struct name {                                                           \
 221         struct type *stqh_first;/* first element */                     \
 222         struct type **stqh_last;/* addr of last next element */         \
 223 }
 224
 225 #define STAILQ_HEAD_INITIALIZER(head)                                   \
 226         { NULL, &(head).stqh_first }
 227
 228 #define STAILQ_ENTRY(type)                                              \
 229 struct {                                                                \
 230         struct type *stqe_next; /* next element */                      \
 231 }
 232
 233 /*
 234  * Singly-linked Tail queue functions.
 235  */
 236 #define STAILQ_CONCAT(head1, head2) do {                                \
 237         if (!STAILQ_EMPTY((head2))) {                                   \
 238                 *(head1)->stqh_last = (head2)->stqh_first;              \
 239                 (head1)->stqh_last = (head2)->stqh_last;                \
 240                 STAILQ_INIT((head2));                                   \
 241         }                                                               \
 242 } while (0)
 243
 244 #define STAILQ_EMPTY(head)      ((head)->stqh_first == NULL)
 245
 246 #define STAILQ_FIRST(head)      ((head)->stqh_first)
 247
 248 #define STAILQ_FOREACH(var, head, field)                                \
 249         for((var) = STAILQ_FIRST((head));                               \
 250            (var);                                                       \
 251            (var) = STAILQ_NEXT((var), field))
 252
 253
 254 #define STAILQ_FOREACH_MUTABLE(var, head, field, tvar)                  \
 255         for ((var) = STAILQ_FIRST((head));                              \
 256             (var) && ((tvar) = STAILQ_NEXT((var), field), 1);           \
 257             (var) = (tvar))
 258
 259 #define STAILQ_INIT(head) do {                                          \
 260         STAILQ_FIRST((head)) = NULL;                                    \
 261         (head)->stqh_last = &STAILQ_FIRST((head));                      \
 262 } while (0)
 263
 264 #define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {               \
 265         if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
 266                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 267         STAILQ_NEXT((tqelm), field) = (elm);                            \
 268 } while (0)
 269
 270 #define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
 271         if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL) \
 272                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 273         STAILQ_FIRST((head)) = (elm);                                   \
 274 } while (0)
 275
 276 #define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
 277         STAILQ_NEXT((elm), field) = NULL;                               \
 278         *(head)->stqh_last = (elm);                                     \
 279         (head)->stqh_last = &STAILQ_NEXT((elm), field);                 \
 280 } while (0)
 281
 282 #define STAILQ_LAST(head, type, field)                                  \
 283         (STAILQ_EMPTY((head)) ?                                         \
 284                 NULL :                                                  \
 285                 ((struct type *)(void *)                                \
 286                 ((char *)((head)->stqh_last) - __offsetof(struct type, field))))
 287
 288 #define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
 289
 290 #define STAILQ_REMOVE(head, elm, type, field) do {                      \
 291         if (STAILQ_FIRST((head)) == (elm)) {                            \
 292                 STAILQ_REMOVE_HEAD((head), field);                      \
 293         }                                                               \
 294         else {                                                          \
 295                 struct type *curelm = STAILQ_FIRST((head));             \
 296                 while (STAILQ_NEXT(curelm, field) != (elm))             \
 297                         curelm = STAILQ_NEXT(curelm, field);            \
 298                 STAILQ_REMOVE_NEXT(head, curelm, field);                \
 299         }                                                               \
 300         TRASHIT((elm)->field.stqe_next);                                \
 301 } while (0)
 302
 303 #define STAILQ_REMOVE_HEAD(head, field) do {                            \
 304         if ((STAILQ_FIRST((head)) =                                     \
 305              STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL)         \
 306                 (head)->stqh_last = &STAILQ_FIRST((head));              \
 307 } while (0)
 308
 309 #define STAILQ_REMOVE_NEXT(head, elm, field) do {                       \
 310         if ((STAILQ_NEXT(elm, field) =                                  \
 311              STAILQ_NEXT(STAILQ_NEXT(elm, field), field)) == NULL)      \
 312                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 313 } while (0)
 314
 315 /*
 316  * List declarations.
 317  */
 318 #define LIST_HEAD(name, type)                                           \
 319 struct name {                                                           \
 320         struct type *lh_first;  /* first element */                     \
 321 }
 322
 323 #define LIST_HEAD_INITIALIZER(head)                                     \
 324         { NULL }
 325
 326 #define LIST_ENTRY(type)                                                \
 327 struct {                                                                \
 328         struct type *le_next;   /* next element */                      \
 329         struct type **le_prev;  /* address of previous next element */  \
 330 }
 331
 332 /*
 333  * List functions.
 334  */
 335
 336 #if (defined(_KERNEL) && defined(INVARIANTS))
 337 #define QMD_LIST_CHECK_HEAD(head, field) do {                           \
 338         if (LIST_FIRST((head)) != NULL &&                               \
 339             LIST_FIRST((head))->field.le_prev !=                        \
 340              &LIST_FIRST((head)))                                       \
 341                 panic("Bad list head %p first->prev != head", (head));  \
 342 } while (0)
 343
 344 #define QMD_LIST_CHECK_NEXT(elm, field) do {                            \
 345         if (LIST_NEXT((elm), field) != NULL &&                          \
 346             LIST_NEXT((elm), field)->field.le_prev !=                   \
 347              &((elm)->field.le_next))                                   \
 348                 panic("Bad link elm %p next->prev != elm", (elm));      \
 349 } while (0)
 350
 351 #define QMD_LIST_CHECK_PREV(elm, field) do {                            \
 352         if (*(elm)->field.le_prev != (elm))                             \
 353                 panic("Bad link elm %p prev->next != elm", (elm));      \
 354 } while (0)
 355 #else
 356 #define QMD_LIST_CHECK_HEAD(head, field)
 357 #define QMD_LIST_CHECK_NEXT(elm, field)
 358 #define QMD_LIST_CHECK_PREV(elm, field)
 359 #endif /* (_KERNEL && INVARIANTS) */
 360
 361 #define LIST_EMPTY(head)        ((head)->lh_first == NULL)
 362
 363 #define LIST_FIRST(head)        ((head)->lh_first)
 364
 365 #define LIST_FOREACH(var, head, field)                                  \
 366         for ((var) = LIST_FIRST((head));                                \
 367             (var);                                                      \
 368             (var) = LIST_NEXT((var), field))
 369
 370 #define LIST_FOREACH_MUTABLE(var, head, field, tvar)                    \
 371         for ((var) = LIST_FIRST((head));                                \
 372             (var) && ((tvar) = LIST_NEXT((var), field), 1);             \
 373             (var) = (tvar))
 374
 375 #define LIST_INIT(head) do {                                            \
 376         LIST_FIRST((head)) = NULL;                                      \
 377 } while (0)
 378
 379 #define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
 380         QMD_LIST_CHECK_NEXT(listelm, field);                            \
 381         if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
 382                 LIST_NEXT((listelm), field)->field.le_prev =            \
 383                     &LIST_NEXT((elm), field);                           \
 384         LIST_NEXT((listelm), field) = (elm);                            \
 385         (elm)->field.le_prev = &LIST_NEXT((listelm), field);            \
 386 } while (0)
 387
 388 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
 389         QMD_LIST_CHECK_PREV(listelm, field);                            \
 390         (elm)->field.le_prev = (listelm)->field.le_prev;                \
 391         LIST_NEXT((elm), field) = (listelm);                            \
 392         *(listelm)->field.le_prev = (elm);                              \
 393         (listelm)->field.le_prev = &LIST_NEXT((elm), field);            \
 394 } while (0)
 395
 396 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
 397         QMD_LIST_CHECK_HEAD((head), field);                             \
 398         if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)     \
 399                 LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
 400         LIST_FIRST((head)) = (elm);                                     \
 401         (elm)->field.le_prev = &LIST_FIRST((head));                     \
 402 } while (0)
 403
 404 #define LIST_NEXT(elm, field)   ((elm)->field.le_next)
 405
 406 #define LIST_REMOVE(elm, field) do {                                    \
 407         QMD_LIST_CHECK_NEXT(elm, field);                                \
 408         QMD_LIST_CHECK_PREV(elm, field);                                \
 409         if (LIST_NEXT((elm), field) != NULL)                            \
 410                 LIST_NEXT((elm), field)->field.le_prev =                \
 411                     (elm)->field.le_prev;                               \
 412         *(elm)->field.le_prev = LIST_NEXT((elm), field);                \
 413         TRASHIT((elm)->field.le_next);                                  \
 414         TRASHIT((elm)->field.le_prev);                                  \
 415 } while (0)
 416
 417 /*
 418  * Tail queue declarations.
 419  */
 420 #define TAILQ_HEAD(name, type)                                          \
 421 struct name {                                                           \
 422         struct type *tqh_first; /* first element */                     \
 423         struct type **tqh_last; /* addr of last next element */         \
 424         TRACEBUF                                                        \
 425 }
 426
 427 #define TAILQ_HEAD_INITIALIZER(head)                                    \
 428         { NULL, &(head).tqh_first }
 429
 430 #define TAILQ_ENTRY(type)                                               \
 431 struct {                                                                \
 432         struct type *tqe_next;  /* next element */                      \
 433         struct type **tqe_prev; /* address of previous next element */  \
 434         TRACEBUF                                                        \
 435 }
 436
 437 /*
 438  * Tail queue functions.
 439  */
 440 #if (defined(_KERNEL) && defined(INVARIANTS))
 441 #define QMD_TAILQ_CHECK_HEAD(head, field) do {                          \
 442         if (!TAILQ_EMPTY(head) &&                                       \
 443             TAILQ_FIRST((head))->field.tqe_prev !=                      \
 444              &TAILQ_FIRST((head)))                                      \
 445                 panic("Bad tailq head %p first->prev != head", (head)); \
 446 } while (0)
 447
 448 #define QMD_TAILQ_CHECK_TAIL(head, field) do {                          \
 449         if (*(head)->tqh_last != NULL)                                  \
 450                 panic("Bad tailq NEXT(%p->tqh_last) != NULL", (head));  \
 451 } while (0)
 452
 453 #define QMD_TAILQ_CHECK_NEXT(elm, field) do {                           \
 454         if (TAILQ_NEXT((elm), field) != NULL &&                         \
 455             TAILQ_NEXT((elm), field)->field.tqe_prev !=                 \
 456              &((elm)->field.tqe_next))                                  \
 457                 panic("Bad link elm %p next->prev != elm", (elm));      \
 458 } while (0)
 459
 460 #define QMD_TAILQ_CHECK_PREV(elm, field) do {                           \
 461         if (*(elm)->field.tqe_prev != (elm))                            \
 462                 panic("Bad link elm %p prev->next != elm", (elm));      \
 463 } while (0)
 464 #else
 465 #define QMD_TAILQ_CHECK_HEAD(head, field)
 466 #define QMD_TAILQ_CHECK_TAIL(head, headname)
 467 #define QMD_TAILQ_CHECK_NEXT(elm, field)
 468 #define QMD_TAILQ_CHECK_PREV(elm, field)
 469 #endif /* (_KERNEL && INVARIANTS) */
 470
 471 #define TAILQ_CONCAT(head1, head2, field) do {                          \
 472         if (!TAILQ_EMPTY(head2)) {                                      \
 473                 *(head1)->tqh_last = (head2)->tqh_first;                \
 474                 (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last; \
 475                 (head1)->tqh_last = (head2)->tqh_last;                  \
 476                 TAILQ_INIT((head2));                                    \
 477                 QMD_TRACE_HEAD(head1);                                  \
 478                 QMD_TRACE_HEAD(head2);                                  \
 479         }                                                               \
 480 } while (0)
 481
 482 #define TAILQ_EMPTY(head)       ((head)->tqh_first == NULL)
 483
 484 #define TAILQ_FIRST(head)       ((head)->tqh_first)
 485
 486 #define TAILQ_FOREACH(var, head, field)                                 \
 487         for ((var) = TAILQ_FIRST((head));                               \
 488             (var);                                                      \
 489             (var) = TAILQ_NEXT((var), field))
 490
 491 #define TAILQ_FOREACH_MUTABLE(var, head, field, tvar)                   \
 492         for ((var) = TAILQ_FIRST((head));                               \
 493             (var) && ((tvar) = TAILQ_NEXT((var), field), 1);            \
 494             (var) = (tvar))
 495
 496 #define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
 497         for ((var) = TAILQ_LAST((head), headname);                      \
 498             (var);                                                      \
 499             (var) = TAILQ_PREV((var), headname, field))
 500
 501 #define TAILQ_FOREACH_REVERSE_MUTABLE(var, head, headname, field, tvar) \
 502         for ((var) = TAILQ_LAST((head), headname);                      \
 503             (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);  \
 504             (var) = (tvar))
 505
 506 #define TAILQ_INIT(head) do {                                           \
 507         TAILQ_FIRST((head)) = NULL;                                     \
 508         (head)->tqh_last = &TAILQ_FIRST((head));                        \
 509         QMD_TRACE_HEAD(head);                                           \
 510 } while (0)
 511
 512 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
 513         QMD_TAILQ_CHECK_NEXT(listelm, field);                           \
 514         if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
 515                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
 516                     &TAILQ_NEXT((elm), field);                          \
 517         else {                                                          \
 518                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
 519                 QMD_TRACE_HEAD(head);                                   \
 520         }                                                               \
 521         TAILQ_NEXT((listelm), field) = (elm);                           \
 522         (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);          \
 523         QMD_TRACE_ELEM(&(elm)->field);                                  \
 524         QMD_TRACE_ELEM(&listelm->field);                                \
 525 } while (0)
 526
 527 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
 528         QMD_TAILQ_CHECK_PREV(listelm, field);                           \
 529         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
 530         TAILQ_NEXT((elm), field) = (listelm);                           \
 531         *(listelm)->field.tqe_prev = (elm);                             \
 532         (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);          \
 533         QMD_TRACE_ELEM(&(elm)->field);                                  \
 534         QMD_TRACE_ELEM(&listelm->field);                                \
 535 } while (0)
 536
 537 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
 538         QMD_TAILQ_CHECK_HEAD(head, field);                              \
 539         if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)   \
 540                 TAILQ_FIRST((head))->field.tqe_prev =                   \
 541                     &TAILQ_NEXT((elm), field);                          \
 542         else                                                            \
 543                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
 544         TAILQ_FIRST((head)) = (elm);                                    \
 545         (elm)->field.tqe_prev = &TAILQ_FIRST((head));                   \
 546         QMD_TRACE_HEAD(head);                                           \
 547         QMD_TRACE_ELEM(&(elm)->field);                                  \
 548 } while (0)
 549
 550 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
 551         QMD_TAILQ_CHECK_TAIL(head, field);                              \
 552         TAILQ_NEXT((elm), field) = NULL;                                \
 553         (elm)->field.tqe_prev = (head)->tqh_last;                       \
 554         *(head)->tqh_last = (elm);                                      \
 555         (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
 556         QMD_TRACE_HEAD(head);                                           \
 557         QMD_TRACE_ELEM(&(elm)->field);                                  \
 558 } while (0)
 559
 560 #define TAILQ_LAST(head, headname)                                      \
 561         (*(((struct headname *)((head)->tqh_last))->tqh_last))
 562
 563 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
 564
 565 #define TAILQ_PREV(elm, headname, field)                                \
 566         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
 567
 568 #define TAILQ_REMOVE(head, elm, field) do {                             \
 569         QMD_TAILQ_CHECK_NEXT(elm, field);                               \
 570         QMD_TAILQ_CHECK_PREV(elm, field);                               \
 571         if ((TAILQ_NEXT((elm), field)) != NULL)                         \
 572                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
 573                     (elm)->field.tqe_prev;                              \
 574         else {                                                          \
 575                 (head)->tqh_last = (elm)->field.tqe_prev;               \
 576                 QMD_TRACE_HEAD(head);                                   \
 577         }                                                               \
 578         *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);              \
 579         TRASHIT((elm)->field.tqe_next);                                 \
 580         TRASHIT((elm)->field.tqe_prev);                                 \
 581         QMD_TRACE_ELEM(&(elm)->field);                                  \
 582 } while (0)
 583
 584
 585 #ifdef _KERNEL
 586
 587 /*
 588  * XXX insque() and remque() are an old way of handling certain queues.
 589  * They bogusly assumes that all queue heads look alike.
 590  */
 591
 592 struct quehead {
 593         struct quehead *qh_link;
 594         struct quehead *qh_rlink;
 595 };
 596
 597 #ifdef __GNUC__
 598
 599 static __inline void
 600 insque(void *a, void *b)
 601 {
 602         struct quehead *element = (struct quehead *)a,
 603                  *head = (struct quehead *)b;
 604
 605         element->qh_link = head->qh_link;
 606         element->qh_rlink = head;
 607         head->qh_link = element;
 608         element->qh_link->qh_rlink = element;
 609 }
 610
 611 static __inline void
 612 remque(void *a)
 613 {
 614         struct quehead *element = (struct quehead *)a;
 615
 616         element->qh_link->qh_rlink = element->qh_rlink;
 617         element->qh_rlink->qh_link = element->qh_link;
 618         element->qh_rlink = 0;
 619 }
 620
 621 #else /* !__GNUC__ */
 622
 623 void    insque(void *a, void *b);
 624 void    remque(void *a);
 625
 626 #endif /* __GNUC__ */
 627
 628 #endif /* _KERNEL */
 629
 630 #endif /* !_SYS_QUEUE_H_ */