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_FROM                +       +       +       +
  92  * _FOREACH_MUTABLE             +       +       +       +
  93  * _FOREACH_FROM_MUTABLE        +       +       +       +
  94  * _FOREACH_REVERSE             -       -       -       +
  95  * _FOREACH_REVERSE_MUTABLE     -       -       -       +
  96  * _INSERT_HEAD                 +       +       +       +
  97  * _INSERT_BEFORE               -       +       -       +
  98  * _INSERT_AFTER                +       +       +       +
  99  * _INSERT_TAIL                 -       -       +       +
 100  * _CONCAT                      -       -       +       +
 101  * _REMOVE_AFTER                +       -       +       -
 102  * _REMOVE_HEAD                 +       -       +       -
 103  * _REMOVE                      +       +       +       +
 104  * _SWAP                        +       +       +       +
 105  *
 106  */
 107 #ifdef QUEUE_MACRO_DEBUG
 108 /* Store the last 2 places the queue element or head was altered */
 109 struct qm_trace {
 110         char    *lastfile;
 111         int      lastline;
 112         char    *prevfile;
 113         int      prevline;
 114 };
 115
 116 #define TRACEBUF        struct qm_trace trace;
 117 #define TRASHIT(x)      do {(x) = (void *)-1;} while (0)
 118 #define QMD_SAVELINK(name, link)        void **name = (void *)&(link)
 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 QMD_SAVELINK(name, link)
 138 #define TRACEBUF
 139 #define TRASHIT(x)
 140 #endif  /* QUEUE_MACRO_DEBUG */
 141
 142 /*
 143  * Singly-linked List declarations.
 144  */
 145 #define SLIST_HEAD(name, type)                                          \
 146 struct name {                                                           \
 147         struct type *slh_first; /* first element */                     \
 148 }
 149
 150 #define SLIST_HEAD_INITIALIZER(head)                                    \
 151         { NULL }
 152
 153 #define SLIST_ENTRY(type)                                               \
 154 struct {                                                                \
 155         struct type *sle_next;  /* next element */                      \
 156 }
 157
 158 #define SLIST_ENTRY_INITIALIZER { NULL }
 159
 160 /*
 161  * Singly-linked List functions.
 162  */
 163 #define SLIST_EMPTY(head)       ((head)->slh_first == NULL)
 164
 165 #define SLIST_FIRST(head)       ((head)->slh_first)
 166
 167 #define SLIST_FOREACH(var, head, field)                                 \
 168         for ((var) = SLIST_FIRST((head));                               \
 169             (var);                                                      \
 170             (var) = SLIST_NEXT((var), field))
 171
 172 #define SLIST_FOREACH_FROM(var, head, field)                            \
 173         for ((var) = ((var) ? (var) : SLIST_FIRST((head)));             \
 174             (var);                                                      \
 175             (var) = SLIST_NEXT((var), field))
 176
 177 #define SLIST_FOREACH_MUTABLE(var, head, field, tvar)                   \
 178         for ((var) = SLIST_FIRST((head));                               \
 179             (var) && ((tvar) = SLIST_NEXT((var), field), 1);            \
 180             (var) = (tvar))
 181
 182 #define SLIST_FOREACH_FROM_MUTABLE(var, head, field, tvar)              \
 183         for ((var) = ((var) ? (var) : SLIST_FIRST((head)));             \
 184             (var) && ((tvar) = SLIST_NEXT((var), field), 1);            \
 185             (var) = (tvar))
 186
 187 #define SLIST_FOREACH_PREVPTR(var, varp, head, field)                   \
 188         for ((varp) = &SLIST_FIRST((head));                             \
 189             ((var) = *(varp)) != NULL;                                  \
 190             (varp) = &SLIST_NEXT((var), field))
 191
 192 #define SLIST_INIT(head) do {                                           \
 193         SLIST_FIRST((head)) = NULL;                                     \
 194 } while (0)
 195
 196 #define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
 197         SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);       \
 198         SLIST_NEXT((slistelm), field) = (elm);                          \
 199 } while (0)
 200
 201 #define SLIST_INSERT_HEAD(head, elm, field) do {                        \
 202         SLIST_NEXT((elm), field) = SLIST_FIRST((head));                 \
 203         SLIST_FIRST((head)) = (elm);                                    \
 204 } while (0)
 205
 206 #define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)
 207
 208 #define SLIST_REMOVE(head, elm, type, field) do {                       \
 209         QMD_SAVELINK(oldnext, (elm)->field.sle_next);                   \
 210         if (SLIST_FIRST((head)) == (elm)) {                             \
 211                 SLIST_REMOVE_HEAD((head), field);                       \
 212         }                                                               \
 213         else {                                                          \
 214                 struct type *curelm = SLIST_FIRST((head));              \
 215                 while (SLIST_NEXT(curelm, field) != (elm))              \
 216                         curelm = SLIST_NEXT(curelm, field);             \
 217                 SLIST_REMOVE_AFTER(curelm, field);                      \
 218         }                                                               \
 219         TRASHIT(*oldnext);                                              \
 220 } while (0)
 221
 222 #define SLIST_REMOVE_AFTER(elm, field) do {                             \
 223         SLIST_NEXT(elm, field) =                                        \
 224             SLIST_NEXT(SLIST_NEXT(elm, field), field);                  \
 225 } while (0)
 226
 227 #define SLIST_REMOVE_HEAD(head, field) do {                             \
 228         SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);   \
 229 } while (0)
 230
 231 #define SLIST_SWAP(head1, head2, type) do {                             \
 232         struct type *swap_first = SLIST_FIRST(head1);                   \
 233         SLIST_FIRST(head1) = SLIST_FIRST(head2);                        \
 234         SLIST_FIRST(head2) = swap_first;                                \
 235 } while (0)
 236
 237 /*
 238  * Singly-linked Tail queue declarations.
 239  */
 240 #define STAILQ_HEAD(name, type)                                         \
 241 struct name {                                                           \
 242         struct type *stqh_first;/* first element */                     \
 243         struct type **stqh_last;/* addr of last next element */         \
 244 }
 245
 246 #define STAILQ_HEAD_INITIALIZER(head)                                   \
 247         { NULL, &(head).stqh_first }
 248
 249 #define STAILQ_ENTRY(type)                                              \
 250 struct {                                                                \
 251         struct type *stqe_next; /* next element */                      \
 252 }
 253
 254 /*
 255  * Singly-linked Tail queue functions.
 256  */
 257 #define STAILQ_CONCAT(head1, head2) do {                                \
 258         if (!STAILQ_EMPTY((head2))) {                                   \
 259                 *(head1)->stqh_last = (head2)->stqh_first;              \
 260                 (head1)->stqh_last = (head2)->stqh_last;                \
 261                 STAILQ_INIT((head2));                                   \
 262         }                                                               \
 263 } while (0)
 264
 265 #define STAILQ_EMPTY(head)      ((head)->stqh_first == NULL)
 266
 267 #define STAILQ_FIRST(head)      ((head)->stqh_first)
 268
 269 #define STAILQ_FOREACH(var, head, field)                                \
 270         for((var) = STAILQ_FIRST((head));                               \
 271            (var);                                                       \
 272            (var) = STAILQ_NEXT((var), field))
 273
 274 #define STAILQ_FOREACH_FROM(var, head, field)                           \
 275         for ((var) = ((var) ? (var) : STAILQ_FIRST((head)));            \
 276            (var);                                                       \
 277            (var) = STAILQ_NEXT((var), field))
 278
 279 #define STAILQ_FOREACH_MUTABLE(var, head, field, tvar)                  \
 280         for ((var) = STAILQ_FIRST((head));                              \
 281             (var) && ((tvar) = STAILQ_NEXT((var), field), 1);           \
 282             (var) = (tvar))
 283
 284 #define STAILQ_FOREACH_FROM_MUTABLE(var, head, field, tvar)             \
 285         for ((var) = ((var) ? (var) : STAILQ_FIRST((head)));            \
 286             (var) && ((tvar) = STAILQ_NEXT((var), field), 1);           \
 287             (var) = (tvar))
 288
 289 #define STAILQ_INIT(head) do {                                          \
 290         STAILQ_FIRST((head)) = NULL;                                    \
 291         (head)->stqh_last = &STAILQ_FIRST((head));                      \
 292 } while (0)
 293
 294 #define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {               \
 295         if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
 296                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 297         STAILQ_NEXT((tqelm), field) = (elm);                            \
 298 } while (0)
 299
 300 #define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
 301         if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL) \
 302                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 303         STAILQ_FIRST((head)) = (elm);                                   \
 304 } while (0)
 305
 306 #define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
 307         STAILQ_NEXT((elm), field) = NULL;                               \
 308         *(head)->stqh_last = (elm);                                     \
 309         (head)->stqh_last = &STAILQ_NEXT((elm), field);                 \
 310 } while (0)
 311
 312 #define STAILQ_LAST(head, type, field)                                  \
 313         (STAILQ_EMPTY((head)) ?                                         \
 314                 NULL :                                                  \
 315                 __containerof((head)->stqh_last, struct type, field.stqe_next))
 316
 317 #define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
 318
 319 #define STAILQ_REMOVE(head, elm, type, field) do {                      \
 320         QMD_SAVELINK(oldnext, (elm)->field.stqe_next);                  \
 321         if (STAILQ_FIRST((head)) == (elm)) {                            \
 322                 STAILQ_REMOVE_HEAD((head), field);                      \
 323         }                                                               \
 324         else {                                                          \
 325                 struct type *curelm = STAILQ_FIRST((head));             \
 326                 while (STAILQ_NEXT(curelm, field) != (elm))             \
 327                         curelm = STAILQ_NEXT(curelm, field);            \
 328                 STAILQ_REMOVE_AFTER(head, curelm, field);               \
 329         }                                                               \
 330         TRASHIT(*oldnext);                                              \
 331 } while (0)
 332
 333 #define STAILQ_REMOVE_HEAD(head, field) do {                            \
 334         if ((STAILQ_FIRST((head)) =                                     \
 335              STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL)         \
 336                 (head)->stqh_last = &STAILQ_FIRST((head));              \
 337 } while (0)
 338
 339 #define STAILQ_REMOVE_AFTER(head, elm, field) do {                      \
 340         if ((STAILQ_NEXT(elm, field) =                                  \
 341              STAILQ_NEXT(STAILQ_NEXT(elm, field), field)) == NULL)      \
 342                 (head)->stqh_last = &STAILQ_NEXT((elm), field);         \
 343 } while (0)
 344
 345 #define STAILQ_SWAP(head1, head2, type) do {                            \
 346         struct type *swap_first = STAILQ_FIRST(head1);                  \
 347         struct type **swap_last = (head1)->stqh_last;                   \
 348         STAILQ_FIRST(head1) = STAILQ_FIRST(head2);                      \
 349         (head1)->stqh_last = (head2)->stqh_last;                        \
 350         STAILQ_FIRST(head2) = swap_first;                               \
 351         (head2)->stqh_last = swap_last;                                 \
 352         if (STAILQ_EMPTY(head1))                                        \
 353                 (head1)->stqh_last = &STAILQ_FIRST(head1);              \
 354         if (STAILQ_EMPTY(head2))                                        \
 355                 (head2)->stqh_last = &STAILQ_FIRST(head2);              \
 356 } while (0)
 357
 358
 359 /*
 360  * List declarations.
 361  */
 362 #define LIST_HEAD(name, type)                                           \
 363 struct name {                                                           \
 364         struct type *lh_first;  /* first element */                     \
 365 }
 366
 367 #define LIST_HEAD_INITIALIZER(head)                                     \
 368         { NULL }
 369
 370 #define LIST_ENTRY(type)                                                \
 371 struct {                                                                \
 372         struct type *le_next;   /* next element */                      \
 373         struct type **le_prev;  /* address of previous next element */  \
 374 }
 375
 376 /*
 377  * List functions.
 378  */
 379
 380 #if (defined(_KERNEL) && defined(INVARIANTS))
 381 #define QMD_LIST_CHECK_HEAD(head, field) do {                           \
 382         if (LIST_FIRST((head)) != NULL &&                               \
 383             LIST_FIRST((head))->field.le_prev !=                        \
 384              &LIST_FIRST((head)))                                       \
 385                 panic("Bad list head %p first->prev != head", (head));  \
 386 } while (0)
 387
 388 #define QMD_LIST_CHECK_NEXT(elm, field) do {                            \
 389         if (LIST_NEXT((elm), field) != NULL &&                          \
 390             LIST_NEXT((elm), field)->field.le_prev !=                   \
 391              &((elm)->field.le_next))                                   \
 392                 panic("Bad link elm %p next->prev != elm", (elm));      \
 393 } while (0)
 394
 395 #define QMD_LIST_CHECK_PREV(elm, field) do {                            \
 396         if (*(elm)->field.le_prev != (elm))                             \
 397                 panic("Bad link elm %p prev->next != elm", (elm));      \
 398 } while (0)
 399 #else
 400 #define QMD_LIST_CHECK_HEAD(head, field)
 401 #define QMD_LIST_CHECK_NEXT(elm, field)
 402 #define QMD_LIST_CHECK_PREV(elm, field)
 403 #endif /* (_KERNEL && INVARIANTS) */
 404
 405 #define LIST_EMPTY(head)        ((head)->lh_first == NULL)
 406
 407 #define LIST_FIRST(head)        ((head)->lh_first)
 408
 409 #define LIST_FOREACH(var, head, field)                                  \
 410         for ((var) = LIST_FIRST((head));                                \
 411             (var);                                                      \
 412             (var) = LIST_NEXT((var), field))
 413
 414 #define LIST_FOREACH_FROM(var, head, field)                             \
 415         for ((var) = ((var) ? (var) : LIST_FIRST((head)));              \
 416             (var);                                                      \
 417             (var) = LIST_NEXT((var), field))
 418
 419 #define LIST_FOREACH_MUTABLE(var, head, field, tvar)                    \
 420         for ((var) = LIST_FIRST((head));                                \
 421             (var) && ((tvar) = LIST_NEXT((var), field), 1);             \
 422             (var) = (tvar))
 423
 424 #define LIST_FOREACH_FROM_MUTABLE(var, head, field, tvar)               \
 425         for ((var) = ((var) ? (var) : LIST_FIRST((head)));              \
 426             (var) && ((tvar) = LIST_NEXT((var), field), 1);             \
 427             (var) = (tvar))
 428
 429 #define LIST_INIT(head) do {                                            \
 430         LIST_FIRST((head)) = NULL;                                      \
 431 } while (0)
 432
 433 #define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
 434         QMD_LIST_CHECK_NEXT(listelm, field);                            \
 435         if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
 436                 LIST_NEXT((listelm), field)->field.le_prev =            \
 437                     &LIST_NEXT((elm), field);                           \
 438         LIST_NEXT((listelm), field) = (elm);                            \
 439         (elm)->field.le_prev = &LIST_NEXT((listelm), field);            \
 440 } while (0)
 441
 442 #define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
 443         QMD_LIST_CHECK_PREV(listelm, field);                            \
 444         (elm)->field.le_prev = (listelm)->field.le_prev;                \
 445         LIST_NEXT((elm), field) = (listelm);                            \
 446         *(listelm)->field.le_prev = (elm);                              \
 447         (listelm)->field.le_prev = &LIST_NEXT((elm), field);            \
 448 } while (0)
 449
 450 #define LIST_INSERT_HEAD(head, elm, field) do {                         \
 451         QMD_LIST_CHECK_HEAD((head), field);                             \
 452         if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)     \
 453                 LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
 454         LIST_FIRST((head)) = (elm);                                     \
 455         (elm)->field.le_prev = &LIST_FIRST((head));                     \
 456 } while (0)
 457
 458 #define LIST_NEXT(elm, field)   ((elm)->field.le_next)
 459
 460 #define LIST_REMOVE(elm, field) do {                                    \
 461         QMD_SAVELINK(oldnext, (elm)->field.le_next);                    \
 462         QMD_SAVELINK(oldprev, (elm)->field.le_prev);                    \
 463         QMD_LIST_CHECK_NEXT(elm, field);                                \
 464         QMD_LIST_CHECK_PREV(elm, field);                                \
 465         if (LIST_NEXT((elm), field) != NULL)                            \
 466                 LIST_NEXT((elm), field)->field.le_prev =                \
 467                     (elm)->field.le_prev;                               \
 468         *(elm)->field.le_prev = LIST_NEXT((elm), field);                \
 469         TRASHIT(*oldnext);                                              \
 470         TRASHIT(*oldprev);                                              \
 471 } while (0)
 472
 473 #define LIST_SWAP(head1, head2, type, field) do {                       \
 474         struct type *swap_tmp = LIST_FIRST((head1));                    \
 475         LIST_FIRST((head1)) = LIST_FIRST((head2));                      \
 476         LIST_FIRST((head2)) = swap_tmp;                                 \
 477         if ((swap_tmp = LIST_FIRST((head1))) != NULL)                   \
 478                 swap_tmp->field.le_prev = &LIST_FIRST((head1));         \
 479         if ((swap_tmp = LIST_FIRST((head2))) != NULL)                   \
 480                 swap_tmp->field.le_prev = &LIST_FIRST((head2));         \
 481 } while (0)
 482
 483 /*
 484  * Tail queue declarations.
 485  */
 486 #define TAILQ_HEAD(name, type)                                          \
 487 struct name {                                                           \
 488         struct type *tqh_first; /* first element */                     \
 489         struct type **tqh_last; /* addr of last next element */         \
 490         TRACEBUF                                                        \
 491 }
 492
 493 #define TAILQ_HEAD_INITIALIZER(head)                                    \
 494         { NULL, &(head).tqh_first }
 495
 496 #define TAILQ_ENTRY(type)                                               \
 497 struct {                                                                \
 498         struct type *tqe_next;  /* next element */                      \
 499         struct type **tqe_prev; /* address of previous next element */  \
 500         TRACEBUF                                                        \
 501 }
 502
 503 /*
 504  * Tail queue functions.
 505  */
 506 #if (defined(_KERNEL) && defined(INVARIANTS))
 507 #define QMD_TAILQ_CHECK_HEAD(head, field) do {                          \
 508         if (!TAILQ_EMPTY(head) &&                                       \
 509             TAILQ_FIRST((head))->field.tqe_prev !=                      \
 510              &TAILQ_FIRST((head)))                                      \
 511                 panic("Bad tailq head %p first->prev != head", (head)); \
 512 } while (0)
 513
 514 #define QMD_TAILQ_CHECK_TAIL(head, field) do {                          \
 515         if (*(head)->tqh_last != NULL) {                                \
 516                 panic("Bad tailq NEXT(%p->tqh_last) != NULL, last %p",  \
 517                     (head), *(head)->tqh_last);                         \
 518         }                                                               \
 519 } while (0)
 520
 521 #define QMD_TAILQ_CHECK_NEXT(elm, field) do {                           \
 522         if (TAILQ_NEXT((elm), field) != NULL &&                         \
 523             TAILQ_NEXT((elm), field)->field.tqe_prev !=                 \
 524              &((elm)->field.tqe_next))                                  \
 525                 panic("Bad link elm %p next->prev != elm", (elm));      \
 526 } while (0)
 527
 528 #define QMD_TAILQ_CHECK_PREV(elm, field) do {                           \
 529         if (*(elm)->field.tqe_prev != (elm))                            \
 530                 panic("Bad link elm %p prev->next != elm", (elm));      \
 531 } while (0)
 532 #else
 533 #define QMD_TAILQ_CHECK_HEAD(head, field)
 534 #define QMD_TAILQ_CHECK_TAIL(head, headname)
 535 #define QMD_TAILQ_CHECK_NEXT(elm, field)
 536 #define QMD_TAILQ_CHECK_PREV(elm, field)
 537 #endif /* (_KERNEL && INVARIANTS) */
 538
 539 #define TAILQ_CONCAT(head1, head2, field) do {                          \
 540         if (!TAILQ_EMPTY(head2)) {                                      \
 541                 *(head1)->tqh_last = (head2)->tqh_first;                \
 542                 (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last; \
 543                 (head1)->tqh_last = (head2)->tqh_last;                  \
 544                 TAILQ_INIT((head2));                                    \
 545                 QMD_TRACE_HEAD(head1);                                  \
 546                 QMD_TRACE_HEAD(head2);                                  \
 547         }                                                               \
 548 } while (0)
 549
 550 #define TAILQ_EMPTY(head)       ((head)->tqh_first == NULL)
 551
 552 #define TAILQ_FIRST(head)       ((head)->tqh_first)
 553
 554 #define TAILQ_FOREACH(var, head, field)                                 \
 555         for ((var) = TAILQ_FIRST((head));                               \
 556             (var);                                                      \
 557             (var) = TAILQ_NEXT((var), field))
 558
 559 #define TAILQ_FOREACH_FROM(var, head, field)                            \
 560         for ((var) = ((var) ? (var) : TAILQ_FIRST((head)));             \
 561             (var);                                                      \
 562             (var) = TAILQ_NEXT((var), field))
 563
 564 #define TAILQ_FOREACH_MUTABLE(var, head, field, tvar)                   \
 565         for ((var) = TAILQ_FIRST((head));                               \
 566             (var) && ((tvar) = TAILQ_NEXT((var), field), 1);            \
 567             (var) = (tvar))
 568
 569 #define TAILQ_FOREACH_FROM_MUTABLE(var, head, field, tvar)              \
 570         for ((var) = ((var) ? (var) : TAILQ_FIRST((head)));             \
 571             (var) && ((tvar) = TAILQ_NEXT((var), field), 1);            \
 572             (var) = (tvar))
 573
 574 #define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
 575         for ((var) = TAILQ_LAST((head), headname);                      \
 576             (var);                                                      \
 577             (var) = TAILQ_PREV((var), headname, field))
 578
 579 #define TAILQ_FOREACH_REVERSE_MUTABLE(var, head, headname, field, tvar) \
 580         for ((var) = TAILQ_LAST((head), headname);                      \
 581             (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);  \
 582             (var) = (tvar))
 583
 584 #define TAILQ_INIT(head) do {                                           \
 585         TAILQ_FIRST((head)) = NULL;                                     \
 586         (head)->tqh_last = &TAILQ_FIRST((head));                        \
 587         QMD_TRACE_HEAD(head);                                           \
 588 } while (0)
 589
 590 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
 591         QMD_TAILQ_CHECK_NEXT(listelm, field);                           \
 592         if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
 593                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
 594                     &TAILQ_NEXT((elm), field);                          \
 595         else {                                                          \
 596                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
 597                 QMD_TRACE_HEAD(head);                                   \
 598         }                                                               \
 599         TAILQ_NEXT((listelm), field) = (elm);                           \
 600         (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);          \
 601         QMD_TRACE_ELEM(&(elm)->field);                                  \
 602         QMD_TRACE_ELEM(&listelm->field);                                \
 603 } while (0)
 604
 605 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
 606         QMD_TAILQ_CHECK_PREV(listelm, field);                           \
 607         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
 608         TAILQ_NEXT((elm), field) = (listelm);                           \
 609         *(listelm)->field.tqe_prev = (elm);                             \
 610         (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);          \
 611         QMD_TRACE_ELEM(&(elm)->field);                                  \
 612         QMD_TRACE_ELEM(&listelm->field);                                \
 613 } while (0)
 614
 615 #define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
 616         QMD_TAILQ_CHECK_HEAD(head, field);                              \
 617         if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)   \
 618                 TAILQ_FIRST((head))->field.tqe_prev =                   \
 619                     &TAILQ_NEXT((elm), field);                          \
 620         else                                                            \
 621                 (head)->tqh_last = &TAILQ_NEXT((elm), field);           \
 622         TAILQ_FIRST((head)) = (elm);                                    \
 623         (elm)->field.tqe_prev = &TAILQ_FIRST((head));                   \
 624         QMD_TRACE_HEAD(head);                                           \
 625         QMD_TRACE_ELEM(&(elm)->field);                                  \
 626 } while (0)
 627
 628 #define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
 629         QMD_TAILQ_CHECK_TAIL(head, field);                              \
 630         TAILQ_NEXT((elm), field) = NULL;                                \
 631         (elm)->field.tqe_prev = (head)->tqh_last;                       \
 632         *(head)->tqh_last = (elm);                                      \
 633         (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
 634         QMD_TRACE_HEAD(head);                                           \
 635         QMD_TRACE_ELEM(&(elm)->field);                                  \
 636 } while (0)
 637
 638 #define TAILQ_LAST(head, headname)                                      \
 639         (*(((struct headname *)((head)->tqh_last))->tqh_last))
 640
 641 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
 642
 643 #define TAILQ_PREV(elm, headname, field)                                \
 644         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
 645
 646 #define TAILQ_REMOVE(head, elm, field) do {                             \
 647         QMD_SAVELINK(oldnext, (elm)->field.tqe_next);                   \
 648         QMD_SAVELINK(oldprev, (elm)->field.tqe_prev);                   \
 649         QMD_TAILQ_CHECK_NEXT(elm, field);                               \
 650         QMD_TAILQ_CHECK_PREV(elm, field);                               \
 651         if ((TAILQ_NEXT((elm), field)) != NULL)                         \
 652                 TAILQ_NEXT((elm), field)->field.tqe_prev =              \
 653                     (elm)->field.tqe_prev;                              \
 654         else {                                                          \
 655                 (head)->tqh_last = (elm)->field.tqe_prev;               \
 656                 QMD_TRACE_HEAD(head);                                   \
 657         }                                                               \
 658         *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);              \
 659         TRASHIT(*oldnext);                                              \
 660         TRASHIT(*oldprev);                                              \
 661         QMD_TRACE_ELEM(&(elm)->field);                                  \
 662 } while (0)
 663
 664 #define TAILQ_SWAP(head1, head2, type, field) do {                      \
 665         struct type *swap_first = (head1)->tqh_first;                   \
 666         struct type **swap_last = (head1)->tqh_last;                    \
 667         (head1)->tqh_first = (head2)->tqh_first;                        \
 668         (head1)->tqh_last = (head2)->tqh_last;                          \
 669         (head2)->tqh_first = swap_first;                                \
 670         (head2)->tqh_last = swap_last;                                  \
 671         if ((swap_first = (head1)->tqh_first) != NULL)                  \
 672                 swap_first->field.tqe_prev = &(head1)->tqh_first;       \
 673         else                                                            \
 674                 (head1)->tqh_last = &(head1)->tqh_first;                \
 675         if ((swap_first = (head2)->tqh_first) != NULL)                  \
 676                 swap_first->field.tqe_prev = &(head2)->tqh_first;       \
 677         else                                                            \
 678                 (head2)->tqh_last = &(head2)->tqh_first;                \
 679 } while (0)
 680
 681 #endif /* !_SYS_QUEUE_H_ */