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. 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 1.74 2010/12/03 16:07:50 kib Exp $
  31  */
  32
  33 #ifndef _SYS_QUEUE_H_
  34 #define _SYS_QUEUE_H_
  35
  36 #include <sys/cdefs.h>
  37
  38 /*
  39  * This file defines four types of data structures: singly-linked lists,
  40  * singly-linked tail queues, lists and tail queues.
  41  *
  42  * A singly-linked list is headed by a single forward pointer. The elements
  43  * are singly linked for minimum space and pointer manipulation overhead at
  44  * the expense of O(n) removal for arbitrary elements. New elements can be
  45  * added to the list after an existing element or at the head of the list.
  46  * Elements being removed from the head of the list should use the explicit
  47  * macro for this purpose for optimum efficiency. A singly-linked list may
  48  * only be traversed in the forward direction.  Singly-linked lists are ideal
  49  * for applications with large datasets and few or no removals or for
  50  * implementing a LIFO queue.
  51  *
  52  * A singly-linked tail queue is headed by a pair of pointers, one to the
  53  * head of the list and the other to the tail of the list. The elements are
  54  * singly linked for minimum space and pointer manipulation overhead at the
  55  * expense of O(n) removal for arbitrary elements. New elements can be added
  56  * to the list after an existing element, at the head of the list, or at the
  57  * end of the list. Elements being removed from the head of the tail queue
  58  * should use the explicit macro for this purpose for optimum efficiency.
  59  * A singly-linked tail queue may only be traversed in the forward direction.
  60  * Singly-linked tail queues are ideal for applications with large datasets
  61  * and few or no removals or for implementing a FIFO queue.
  62  *
  63  * A list is headed by a single forward pointer (or an array of forward
  64  * pointers for a hash table header). The elements are doubly linked
  65  * so that an arbitrary element can be removed without a need to
  66  * traverse the list. New elements can be added to the list before
  67  * or after an existing element or at the head of the list. A list
  68  * may only be traversed in the forward direction.
  69  *
  70  * A tail queue is headed by a pair of pointers, one to the head of the
  71  * list and the other to the tail of the list. The elements are doubly
  72  * linked so that an arbitrary element can be removed without a need to
  73  * traverse the list. New elements can be added to the list before or
  74  * after an existing element, at the head of the list, or at the end of
  75  * the list. A tail queue may be traversed in either direction.
  76  *
  77  * For details on the use of these macros, see the queue(3) manual page.
  78  *
  79  *
  80  *                              SLIST   LIST    STAILQ  TAILQ
  81  * _HEAD                        +       +       +       +
  82  * _HEAD_INITIALIZER            +       +       +       +
  83  * _ENTRY                       +       +       +       +
  84  * _INIT                        +       +       +       +
  85  * _EMPTY                       +       +       +       +
  86  * _FIRST                       +       +       +       +
  87  * _NEXT                        +       +       +       +
  88  * _PREV                        -       -       -       +
  89  * _LAST                        -       -       +       +
  90  * _FOREACH                     +       +       +       +
  91  * _FOREACH_MUTABLE             +       +       +       +
  92  * _FOREACH_REVERSE             -       -       -       +
  93  * _FOREACH_REVERSE_MUTABLE     -       -       -       +
  94  * _INSERT_HEAD                 +       +       +       +
  95  * _INSERT_BEFORE               -       +       -       +
  96  * _INSERT_AFTER                +       +       +       +
  97  * _INSERT_TAIL                 -       -       +       +
  98  * _CONCAT                      -       -       +       +
  99  * _REMOVE_AFTER                +       -       +       -
 100  * _REMOVE_HEAD                 +       -       +       -
 101  * _REMOVE                      +       +       +       +
 102  * _SWAP                        +       +       +       +
 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 #define QMD_SAVELINK(name, link)        void **name = (void *)&(link)
 117
 118 #define QMD_TRACE_HEAD(head) do {                                       \
 119         (head)->trace.prevline = (head)->trace.lastline;                \
 120         (head)->trace.prevfile = (head)->trace.lastfile;                \
 121         (head)->trace.lastline = __LINE__;                              \
 122         (head)->trace.lastfile = __FILE__;                              \
 123 } while (0)
 124
 125 #define QMD_TRACE_ELEM(elem) do {                                       \
 126         (elem)->trace.prevline = (elem)->trace.lastline;                \
 127         (elem)->trace.prevfile = (elem)->trace.lastfile;                \
 128         (elem)->trace.lastline = __LINE__;                              \
 129         (elem)->trace.lastfile = __FILE__;                              \
 130 } while (0)
 131
 132 #else
 133 #define QMD_TRACE_ELEM(elem)
 134 #define QMD_TRACE_HEAD(head)
 135 #define QMD_SAVELINK(name, link)
 136 #define TRACEBUF
 137 #define TRASHIT(x)
 138 #endif  /* QUEUE_MACRO_DEBUG */
 139
 140 /*
 141  * Singly-linked List declarations.
 142  */
 143 #define SLIST_HEAD(name, type)                                          \
 144 struct name {                                                           \
 145         struct type *slh_first; /* first element */                     \
 146 }
 147
 148 #define SLIST_HEAD_INITIALIZER(head)                                    \
 149         { NULL }
 150
 151 #define SLIST_ENTRY(type)                                               \
 152 struct {                                                                \
 153         struct type *sle_next;  /* next element */                      \
 154 }
 155
 156 #define SLIST_ENTRY_INITIALIZER { NULL }
 157
 158 /*
 159  * Singly-linked List functions.
 160  */
 161 #define SLIST_EMPTY(head)       ((head)->slh_first == NULL)
 162
 163 #define SLIST_FIRST(head)       ((head)->slh_first)
 164
 165 #define SLIST_FOREACH(var, head, field)                                 \
 166         for ((var) = SLIST_FIRST((head));                               \
 167             (var);                                                      \
 168             (var) = SLIST_NEXT((var), field))
 169
 170 #define SLIST_FOREACH_MUTABLE(var, head, field, tvar)                   \
 171         for ((var) = SLIST_FIRST((head));                               \
 172             (var) && ((tvar) = SLIST_NEXT((var), field), 1);            \
 173             (var) = (tvar))
 174
 175 #define SLIST_FOREACH_PREVPTR(var, varp, head, field)                   \
 176         for ((varp) = &SLIST_FIRST((head));                             \
 177             ((var) = *(varp)) != NULL;                                  \
 178             (varp) = &SLIST_NEXT((var), field))
 179
 180 #define SLIST_INIT(head) do {                                           \
 181         SLIST_FIRST((head)) = NULL;                                     \
 182 } while (0)
 183
 184 #define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
 185         SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);       \
 186         SLIST_NEXT((slistelm), field) = (elm);                          \
 187 } while (0)
 188
 189 #define SLIST_INSERT_HEAD(head, elm, field) do {                        \
 190         SLIST_NEXT((elm), field) = SLIST_FIRST((head));                 \
 191         SLIST_FIRST((head)) = (elm);                                    \
 192 } while (0)
 193
 194 #define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)
 195
 196 #define SLIST_REMOVE(head, elm, type, field) do {                       \
 197         QMD_SAVELINK(oldnext, (elm)->field.sle_next);                   \
 198         if (SLIST_FIRST((head)) == (elm)) {                             \
 199                 SLIST_REMOVE_HEAD((head), field);                       \
 200         }                                                               \
 201         else {                                                          \
 202                 struct type *curelm = SLIST_FIRST((head));              \
 203                 while (SLIST_NEXT(curelm, field) != (elm))              \
 204                         curelm = SLIST_NEXT(curelm, field);             \
 205                 SLIST_REMOVE_AFTER(curelm, field);                      \
 206         }                                                               \
 207         TRASHIT(*oldnext);                                              \
 208 } while (0)
 209
 210 #define SLIST_REMOVE_AFTER(elm, field) do {                             \
 211         SLIST_NEXT(elm, field) =                                        \
 212             SLIST_NEXT(SLIST_NEXT(elm, field), field);                  \
 213 } while (0)
 214
 215 #define SLIST_REMOVE_HEAD(head, field) do {                             \
 216         SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);   \
 217 } while (0)
 218
 219 #define SLIST_SWAP(head1, head2, type) do {                             \
 220         struct type *swap_first = SLIST_FIRST(head1);                   \
 221         SLIST_FIRST(head1) = SLIST_FIRST(head2);                        \
 222         SLIST_FIRST(head2) = swap_first;                                \
 223 } while (0)
 224
 225 /*
 226  * Singly-linked Tail queue declarations.
 227  */
 228 #define STAILQ_HEAD(name, type)                                         \
 229 struct name {                                                           \
 230         struct type *stqh_first;/* first element */                     \
 231         struct type **stqh_last;/* addr of last next element */         \
 232 }
 233
 234 #define STAILQ_HEAD_INITIALIZER(head)                                   \
 235         { NULL, &(head).stqh_first }
 236
 237 #define STAILQ_ENTRY(type)                                              \
 238 struct {                                                                \
 239         struct type *stqe_next; /* next element */                      \
 240 }
 241
 242 /*
 243  * Singly-linked Tail queue functions.
 244  */
 245 #define STAILQ_CONCAT(head1, head2) do {                                \
 246         if (!STAILQ_EMPTY((head2))) {                                   \
 247                 *(head1)->stqh_last = (head2)->stqh_first;              \
 248                 (head1)->stqh_last = (head2)->stqh_last;                \
 249                 STAILQ_INIT((head2));                                   \
 250         }                                                               \
 251 } while (0)
 252
 253 #define STAILQ_EMPTY(head)      ((head)->stqh_first == NULL)
 254
 255 #define STAILQ_FIRST(head)      ((head)->stqh_first)
 256
 257 #define STAILQ_FOREACH(var, head, field)                                \
 258         for((var) = STAILQ_FIRST((head));                               \
 259            (var);                                                       \
 260            (var) = STAILQ_NEXT((var), field))
 261
 262
 263 #define STAILQ_FOREACH_MUTABLE(var, head, field, tvar)                  \
 264         for ((var) = STAILQ_FIRST((head));                              \
 265             (var) && ((tvar) = STAILQ_NEXT((var), field), 1);           \
 266             (var) = (tvar))
 267
 268 #define STAILQ_INIT(head) do {                                          \
 269         STAILQ_FIRST((head)) = NULL;                                    \
 270         (head)->stqh_last = &STAILQ_FIRST((head));                      \
 271 } while (0)
 272
 273 #define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {               \
 274         if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
 275                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 276         STAILQ_NEXT((tqelm), field) = (elm);                            \
 277 } while (0)
 278
 279 #define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
 280         if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL) \
 281                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 282         STAILQ_FIRST((head)) = (elm);                                   \
 283 } while (0)
 284
 285 #define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
 286         STAILQ_NEXT((elm), field) = NULL;                               \
 287         *(head)->stqh_last = (elm);                                     \
 288         (head)->stqh_last = &STAILQ_NEXT((elm), field);                 \
 289 } while (0)
 290
 291 #define STAILQ_LAST(head, type, field)                                  \
 292         (STAILQ_EMPTY((head)) ?                                         \
 293                 NULL :                                                  \
 294                 ((struct type *)(void *)                                \
 295                 ((char *)((head)->stqh_last) - __offsetof(struct type, field))))
 296
 297 #define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
 298
 299 #define STAILQ_REMOVE(head, elm, type, field) do {                      \
 300         QMD_SAVELINK(oldnext, (elm)->field.stqe_next);                  \
 301         if (STAILQ_FIRST((head)) == (elm)) {                            \
 302                 STAILQ_REMOVE_HEAD((head), field);                      \
 303         }                                                               \
 304         else {                                                          \
 305                 struct type *curelm = STAILQ_FIRST((head));             \
 306                 while (STAILQ_NEXT(curelm, field) != (elm))             \
 307                         curelm = STAILQ_NEXT(curelm, field);            \
 308                 STAILQ_REMOVE_AFTER(head, curelm, field);               \
 309         }                                                               \
 310         TRASHIT(*oldnext);                                              \
 311 } while (0)
 312
 313 #define STAILQ_REMOVE_HEAD(head, field) do {                            \
 314         if ((STAILQ_FIRST((head)) =                                     \
 315              STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL)         \
 316                 (head)->stqh_last = &STAILQ_FIRST((head));              \
 317 } while (0)
 318
 319 #define STAILQ_REMOVE_AFTER(head, elm, field) do {                      \
 320         if ((STAILQ_NEXT(elm, field) =                                  \
 321              STAILQ_NEXT(STAILQ_NEXT(elm, field), field)) == NULL)      \
 322                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 323 } while (0)
 324
 325 #define STAILQ_SWAP(head1, head2, type) do {                            \
 326         struct type *swap_first = STAILQ_FIRST(head1);                  \
 327         struct type **swap_last = (head1)->stqh_last;                   \
 328         STAILQ_FIRST(head1) = STAILQ_FIRST(head2);                      \
 329         (head1)->stqh_last = (head2)->stqh_last;                        \
 330         STAILQ_FIRST(head2) = swap_first;                               \
 331         (head2)->stqh_last = swap_last;                                 \
 332         if (STAILQ_EMPTY(head1))                                        \
 333                 (head1)->stqh_last = &STAILQ_FIRST(head1);              \
 334         if (STAILQ_EMPTY(head2))                                        \
 335                 (head2)->stqh_last = &STAILQ_FIRST(head2);              \
 336 } while (0)
 337
 338
 339 /*
 340  * List declarations.
 341  */
 342 #define LIST_HEAD(name, type)                                           \
 343 struct name {                                                           \
 344         struct type *lh_first;  /* first element */                     \
 345 }
 346
 347 #define LIST_HEAD_INITIALIZER(head)                                     \
 348         { NULL }
 349
 350 #define LIST_ENTRY(type)                                                \
 351 struct {                                                                \
 352         struct type *le_next;   /* next element */                      \
 353         struct type **le_prev;  /* address of previous next element */  \
 354 }
 355
 356 /*
 357  * List functions.
 358  */
 359
 360 #if (defined(_KERNEL) && defined(INVARIANTS))
 361 #define QMD_LIST_CHECK_HEAD(head, field) do {                           \
 362         if (LIST_FIRST((head)) != NULL &&                               \
 363             LIST_FIRST((head))->field.le_prev !=                        \
 364              &LIST_FIRST((head)))                                       \
 365                 panic("Bad list head %p first->prev != head", (head));  \
 366 } while (0)
 367
 368 #define QMD_LIST_CHECK_NEXT(elm, field) do {                            \
 369         if (LIST_NEXT((elm), field) != NULL &&                          \
 370             LIST_NEXT((elm), field)->field.le_prev !=                   \
 371              &((elm)->field.le_next))                                   \
 372                 panic("Bad link elm %p next->prev != elm", (elm));      \
 373 } while (0)
 374
 375 #define QMD_LIST_CHECK_PREV(elm, field) do {                            \
 376         if (*(elm)->field.le_prev != (elm))                             \
 377                 panic("Bad link elm %p prev->next != elm", (elm));      \
 378 } while (0)
 379 #else
 380 #define QMD_LIST_CHECK_HEAD(head, field)
 381 #define QMD_LIST_CHECK_NEXT(elm, field)
 382 #define QMD_LIST_CHECK_PREV(elm, field)
 383 #endif /* (_KERNEL && INVARIANTS) */
 384
 385 #define LIST_EMPTY(head)        ((head)->lh_first == NULL)
 386
 387 #define LIST_FIRST(head)        ((head)->lh_first)
 388
 389 #define LIST_FOREACH(var, head, field)                                  \
 390         for ((var) = LIST_FIRST((head));                                \
 391             (var);                                                      \
 392             (var) = LIST_NEXT((var), field))
 393
 394 #define LIST_FOREACH_MUTABLE(var, head, field, tvar)                    \
 395         for ((var) = LIST_FIRST((head));                                \
 396             (var) && ((tvar) = LIST_NEXT((var), field), 1);             \
 397             (var) = (tvar))
 398
 399 #define LIST_INIT(head) do {                                            \
 400         LIST_FIRST((head)) = NULL;                                      \
 401 } while (0)
 402
 403 #define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
 404         QMD_LIST_CHECK_NEXT(listelm, field);                            \
 405         if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
 406                 LIST_NEXT((listelm), field)->field.le_prev =            \
 407                     &LIST_NEXT((elm), field);                           \
 408         LIST_NEXT((listelm), field) = (elm);                            \
 409         (elm)->field.le_prev = &LIST_NEXT((listelm), field);            \
 410 } while (0)
 411
 412 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
 413         QMD_LIST_CHECK_PREV(listelm, field);                            \
 414         (elm)->field.le_prev = (listelm)->field.le_prev;                \
 415         LIST_NEXT((elm), field) = (listelm);                            \
 416         *(listelm)->field.le_prev = (elm);                              \
 417         (listelm)->field.le_prev = &LIST_NEXT((elm), field);            \
 418 } while (0)
 419
 420 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
 421         QMD_LIST_CHECK_HEAD((head), field);                             \
 422         if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)     \
 423                 LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
 424         LIST_FIRST((head)) = (elm);                                     \
 425         (elm)->field.le_prev = &LIST_FIRST((head));                     \
 426 } while (0)
 427
 428 #define LIST_NEXT(elm, field)   ((elm)->field.le_next)
 429
 430 #define LIST_REMOVE(elm, field) do {                                    \
 431         QMD_SAVELINK(oldnext, (elm)->field.le_next);                    \
 432         QMD_SAVELINK(oldprev, (elm)->field.le_prev);                    \
 433         QMD_LIST_CHECK_NEXT(elm, field);                                \
 434         QMD_LIST_CHECK_PREV(elm, field);                                \
 435         if (LIST_NEXT((elm), field) != NULL)                            \
 436                 LIST_NEXT((elm), field)->field.le_prev =                \
 437                     (elm)->field.le_prev;                               \
 438         *(elm)->field.le_prev = LIST_NEXT((elm), field);                \
 439         TRASHIT(*oldnext);                                              \
 440         TRASHIT(*oldprev);                                              \
 441 } while (0)
 442
 443 #define LIST_SWAP(head1, head2, type, field) do {                       \
 444         struct type *swap_tmp = LIST_FIRST((head1));                    \
 445         LIST_FIRST((head1)) = LIST_FIRST((head2));                      \
 446         LIST_FIRST((head2)) = swap_tmp;                                 \
 447         if ((swap_tmp = LIST_FIRST((head1))) != NULL)                   \
 448                 swap_tmp->field.le_prev = &LIST_FIRST((head1));         \
 449         if ((swap_tmp = LIST_FIRST((head2))) != NULL)                   \
 450                 swap_tmp->field.le_prev = &LIST_FIRST((head2));         \
 451 } while (0)
 452
 453 /*
 454  * Tail queue declarations.
 455  */
 456 #define TAILQ_HEAD(name, type)                                          \
 457 struct name {                                                           \
 458         struct type *tqh_first; /* first element */                     \
 459         struct type **tqh_last; /* addr of last next element */         \
 460         TRACEBUF                                                        \
 461 }
 462
 463 #define TAILQ_HEAD_INITIALIZER(head)                                    \
 464         { NULL, &(head).tqh_first }
 465
 466 #define TAILQ_ENTRY(type)                                               \
 467 struct {                                                                \
 468         struct type *tqe_next;  /* next element */                      \
 469         struct type **tqe_prev; /* address of previous next element */  \
 470         TRACEBUF                                                        \
 471 }
 472
 473 /*
 474  * Tail queue functions.
 475  */
 476 #if (defined(_KERNEL) && defined(INVARIANTS))
 477 #define QMD_TAILQ_CHECK_HEAD(head, field) do {                          \
 478         if (!TAILQ_EMPTY(head) &&                                       \
 479             TAILQ_FIRST((head))->field.tqe_prev !=                      \
 480              &TAILQ_FIRST((head)))                                      \
 481                 panic("Bad tailq head %p first->prev != head", (head)); \
 482 } while (0)
 483
 484 #define QMD_TAILQ_CHECK_TAIL(head, field) do {                          \
 485         if (*(head)->tqh_last != NULL) {                                \
 486                 panic("Bad tailq NEXT(%p->tqh_last) != NULL, last %p",  \
 487                     (head), *(head)->tqh_last);                         \
 488         }                                                               \
 489 } while (0)
 490
 491 #define QMD_TAILQ_CHECK_NEXT(elm, field) do {                           \
 492         if (TAILQ_NEXT((elm), field) != NULL &&                         \
 493             TAILQ_NEXT((elm), field)->field.tqe_prev !=                 \
 494              &((elm)->field.tqe_next))                                  \
 495                 panic("Bad link elm %p next->prev != elm", (elm));      \
 496 } while (0)
 497
 498 #define QMD_TAILQ_CHECK_PREV(elm, field) do {                           \
 499         if (*(elm)->field.tqe_prev != (elm))                            \
 500                 panic("Bad link elm %p prev->next != elm", (elm));      \
 501 } while (0)
 502 #else
 503 #define QMD_TAILQ_CHECK_HEAD(head, field)
 504 #define QMD_TAILQ_CHECK_TAIL(head, headname)
 505 #define QMD_TAILQ_CHECK_NEXT(elm, field)
 506 #define QMD_TAILQ_CHECK_PREV(elm, field)
 507 #endif /* (_KERNEL && INVARIANTS) */
 508
 509 #define TAILQ_CONCAT(head1, head2, field) do {                          \
 510         if (!TAILQ_EMPTY(head2)) {                                      \
 511                 *(head1)->tqh_last = (head2)->tqh_first;                \
 512                 (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last; \
 513                 (head1)->tqh_last = (head2)->tqh_last;                  \
 514                 TAILQ_INIT((head2));                                    \
 515                 QMD_TRACE_HEAD(head1);                                  \
 516                 QMD_TRACE_HEAD(head2);                                  \
 517         }                                                               \
 518 } while (0)
 519
 520 #define TAILQ_EMPTY(head)       ((head)->tqh_first == NULL)
 521
 522 #define TAILQ_FIRST(head)       ((head)->tqh_first)
 523
 524 #define TAILQ_FOREACH(var, head, field)                                 \
 525         for ((var) = TAILQ_FIRST((head));                               \
 526             (var);                                                      \
 527             (var) = TAILQ_NEXT((var), field))
 528
 529 #define TAILQ_FOREACH_MUTABLE(var, head, field, tvar)                   \
 530         for ((var) = TAILQ_FIRST((head));                               \
 531             (var) && ((tvar) = TAILQ_NEXT((var), field), 1);            \
 532             (var) = (tvar))
 533
 534 #define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
 535         for ((var) = TAILQ_LAST((head), headname);                      \
 536             (var);                                                      \
 537             (var) = TAILQ_PREV((var), headname, field))
 538
 539 #define TAILQ_FOREACH_REVERSE_MUTABLE(var, head, headname, field, tvar) \
 540         for ((var) = TAILQ_LAST((head), headname);                      \
 541             (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);  \
 542             (var) = (tvar))
 543
 544 #define TAILQ_INIT(head) do {                                           \
 545         TAILQ_FIRST((head)) = NULL;                                     \
 546         (head)->tqh_last = &TAILQ_FIRST((head));                        \
 547         QMD_TRACE_HEAD(head);                                           \
 548 } while (0)
 549
 550 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
 551         QMD_TAILQ_CHECK_NEXT(listelm, field);                           \
 552         if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
 553                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
 554                     &TAILQ_NEXT((elm), field);                          \
 555         else {                                                          \
 556                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
 557                 QMD_TRACE_HEAD(head);                                   \
 558         }                                                               \
 559         TAILQ_NEXT((listelm), field) = (elm);                           \
 560         (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);          \
 561         QMD_TRACE_ELEM(&(elm)->field);                                  \
 562         QMD_TRACE_ELEM(&listelm->field);                                \
 563 } while (0)
 564
 565 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
 566         QMD_TAILQ_CHECK_PREV(listelm, field);                           \
 567         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
 568         TAILQ_NEXT((elm), field) = (listelm);                           \
 569         *(listelm)->field.tqe_prev = (elm);                             \
 570         (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);          \
 571         QMD_TRACE_ELEM(&(elm)->field);                                  \
 572         QMD_TRACE_ELEM(&listelm->field);                                \
 573 } while (0)
 574
 575 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
 576         QMD_TAILQ_CHECK_HEAD(head, field);                              \
 577         if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)   \
 578                 TAILQ_FIRST((head))->field.tqe_prev =                   \
 579                     &TAILQ_NEXT((elm), field);                          \
 580         else                                                            \
 581                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
 582         TAILQ_FIRST((head)) = (elm);                                    \
 583         (elm)->field.tqe_prev = &TAILQ_FIRST((head));                   \
 584         QMD_TRACE_HEAD(head);                                           \
 585         QMD_TRACE_ELEM(&(elm)->field);                                  \
 586 } while (0)
 587
 588 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
 589         QMD_TAILQ_CHECK_TAIL(head, field);                              \
 590         TAILQ_NEXT((elm), field) = NULL;                                \
 591         (elm)->field.tqe_prev = (head)->tqh_last;                       \
 592         *(head)->tqh_last = (elm);                                      \
 593         (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
 594         QMD_TRACE_HEAD(head);                                           \
 595         QMD_TRACE_ELEM(&(elm)->field);                                  \
 596 } while (0)
 597
 598 #define TAILQ_LAST(head, headname)                                      \
 599         (*(((struct headname *)((head)->tqh_last))->tqh_last))
 600
 601 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
 602
 603 #define TAILQ_PREV(elm, headname, field)                                \
 604         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
 605
 606 #define TAILQ_REMOVE(head, elm, field) do {                             \
 607         QMD_SAVELINK(oldnext, (elm)->field.tqe_next);                   \
 608         QMD_SAVELINK(oldprev, (elm)->field.tqe_prev);                   \
 609         QMD_TAILQ_CHECK_NEXT(elm, field);                               \
 610         QMD_TAILQ_CHECK_PREV(elm, field);                               \
 611         if ((TAILQ_NEXT((elm), field)) != NULL)                         \
 612                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
 613                     (elm)->field.tqe_prev;                              \
 614         else {                                                          \
 615                 (head)->tqh_last = (elm)->field.tqe_prev;               \
 616                 QMD_TRACE_HEAD(head);                                   \
 617         }                                                               \
 618         *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);              \
 619         TRASHIT(*oldnext);                                              \
 620         TRASHIT(*oldprev);                                              \
 621         QMD_TRACE_ELEM(&(elm)->field);                                  \
 622 } while (0)
 623
 624 #define TAILQ_SWAP(head1, head2, type, field) do {                      \
 625         struct type *swap_first = (head1)->tqh_first;                   \
 626         struct type **swap_last = (head1)->tqh_last;                    \
 627         (head1)->tqh_first = (head2)->tqh_first;                        \
 628         (head1)->tqh_last = (head2)->tqh_last;                          \
 629         (head2)->tqh_first = swap_first;                                \
 630         (head2)->tqh_last = swap_last;                                  \
 631         if ((swap_first = (head1)->tqh_first) != NULL)                  \
 632                 swap_first->field.tqe_prev = &(head1)->tqh_first;       \
 633         else                                                            \
 634                 (head1)->tqh_last = &(head1)->tqh_first;                \
 635         if ((swap_first = (head2)->tqh_first) != NULL)                  \
 636                 swap_first->field.tqe_prev = &(head2)->tqh_first;       \
 637         else                                                            \
 638                 (head2)->tqh_last = &(head2)->tqh_first;                \
 639 } while (0)
 640
 641 #endif /* !_SYS_QUEUE_H_ */