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sys-queue.h
1 /* $OpenBSD: queue.h,v 1.45 2018/07/12 14:22:54 sashan Exp $ */
2 /* $NetBSD: queue.h,v 1.11 1996/05/16 05:17:14 mycroft Exp $ */
3 
4 /*
5  * Copyright (c) 1991, 1993
6  * The Regents of the University of California. All rights reserved.
7  *
8  * Redistribution and use in source and binary forms, with or without
9  * modification, are permitted provided that the following conditions
10  * are met:
11  * 1. Redistributions of source code must retain the above copyright
12  * notice, this list of conditions and the following disclaimer.
13  * 2. Redistributions in binary form must reproduce the above copyright
14  * notice, this list of conditions and the following disclaimer in the
15  * documentation and/or other materials provided with the distribution.
16  * 3. Neither the name of the University nor the names of its contributors
17  * may be used to endorse or promote products derived from this software
18  * without specific prior written permission.
19  *
20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23  * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30  * SUCH DAMAGE.
31  *
32  * @(#)queue.h 8.5 (Berkeley) 8/20/94
33  */
34 
35 /* OPENBSD ORIGINAL: sys/sys/queue.h */
36 
37 #ifndef _FAKE_QUEUE_H_
38 #define _FAKE_QUEUE_H_
39 
40 /*
41  * Require for OS/X and other platforms that have old/broken/incomplete
42  * <sys/queue.h>.
43  */
44 #undef CIRCLEQ_EMPTY
45 #undef CIRCLEQ_END
46 #undef CIRCLEQ_ENTRY
47 #undef CIRCLEQ_FIRST
48 #undef CIRCLEQ_FOREACH
49 #undef CIRCLEQ_FOREACH_REVERSE
50 #undef CIRCLEQ_HEAD
51 #undef CIRCLEQ_HEAD_INITIALIZER
52 #undef CIRCLEQ_INIT
53 #undef CIRCLEQ_INSERT_AFTER
54 #undef CIRCLEQ_INSERT_BEFORE
55 #undef CIRCLEQ_INSERT_HEAD
56 #undef CIRCLEQ_INSERT_TAIL
57 #undef CIRCLEQ_LAST
58 #undef CIRCLEQ_NEXT
59 #undef CIRCLEQ_PREV
60 #undef CIRCLEQ_REMOVE
61 #undef CIRCLEQ_REPLACE
62 #undef LIST_EMPTY
63 #undef LIST_END
64 #undef LIST_ENTRY
65 #undef LIST_FIRST
66 #undef LIST_FOREACH
67 #undef LIST_FOREACH_SAFE
68 #undef LIST_HEAD
69 #undef LIST_HEAD_INITIALIZER
70 #undef LIST_INIT
71 #undef LIST_INSERT_AFTER
72 #undef LIST_INSERT_BEFORE
73 #undef LIST_INSERT_HEAD
74 #undef LIST_NEXT
75 #undef LIST_REMOVE
76 #undef LIST_REPLACE
77 #undef SIMPLEQ_CONCAT
78 #undef SIMPLEQ_EMPTY
79 #undef SIMPLEQ_END
80 #undef SIMPLEQ_ENTRY
81 #undef SIMPLEQ_FIRST
82 #undef SIMPLEQ_FOREACH
83 #undef SIMPLEQ_FOREACH_SAFE
84 #undef SIMPLEQ_HEAD
85 #undef SIMPLEQ_HEAD_INITIALIZER
86 #undef SIMPLEQ_INIT
87 #undef SIMPLEQ_INSERT_AFTER
88 #undef SIMPLEQ_INSERT_HEAD
89 #undef SIMPLEQ_INSERT_TAIL
90 #undef SIMPLEQ_NEXT
91 #undef SIMPLEQ_REMOVE_AFTER
92 #undef SIMPLEQ_REMOVE_HEAD
93 #undef SLIST_EMPTY
94 #undef SLIST_END
95 #undef SLIST_ENTRY
96 #undef SLIST_FIRST
97 #undef SLIST_FOREACH
98 #undef SLIST_FOREACH_PREVPTR
99 #undef SLIST_FOREACH_SAFE
100 #undef SLIST_HEAD
101 #undef SLIST_HEAD_INITIALIZER
102 #undef SLIST_INIT
103 #undef SLIST_INSERT_AFTER
104 #undef SLIST_INSERT_HEAD
105 #undef SLIST_NEXT
106 #undef SLIST_REMOVE
107 #undef SLIST_REMOVE_AFTER
108 #undef SLIST_REMOVE_HEAD
109 #undef SLIST_REMOVE_NEXT
110 #undef TAILQ_CONCAT
111 #undef TAILQ_EMPTY
112 #undef TAILQ_END
113 #undef TAILQ_ENTRY
114 #undef TAILQ_FIRST
115 #undef TAILQ_FOREACH
116 #undef TAILQ_FOREACH_REVERSE
117 #undef TAILQ_FOREACH_REVERSE_SAFE
118 #undef TAILQ_FOREACH_SAFE
119 #undef TAILQ_HEAD
120 #undef TAILQ_HEAD_INITIALIZER
121 #undef TAILQ_INIT
122 #undef TAILQ_INSERT_AFTER
123 #undef TAILQ_INSERT_BEFORE
124 #undef TAILQ_INSERT_HEAD
125 #undef TAILQ_INSERT_TAIL
126 #undef TAILQ_LAST
127 #undef TAILQ_NEXT
128 #undef TAILQ_PREV
129 #undef TAILQ_REMOVE
130 #undef TAILQ_REPLACE
131 
132 /*
133  * This file defines five types of data structures: singly-linked lists,
134  * lists, simple queues, tail queues and XOR simple queues.
135  *
136  *
137  * A singly-linked list is headed by a single forward pointer. The elements
138  * are singly linked for minimum space and pointer manipulation overhead at
139  * the expense of O(n) removal for arbitrary elements. New elements can be
140  * added to the list after an existing element or at the head of the list.
141  * Elements being removed from the head of the list should use the explicit
142  * macro for this purpose for optimum efficiency. A singly-linked list may
143  * only be traversed in the forward direction. Singly-linked lists are ideal
144  * for applications with large datasets and few or no removals or for
145  * implementing a LIFO queue.
146  *
147  * A list is headed by a single forward pointer (or an array of forward
148  * pointers for a hash table header). The elements are doubly linked
149  * so that an arbitrary element can be removed without a need to
150  * traverse the list. New elements can be added to the list before
151  * or after an existing element or at the head of the list. A list
152  * may only be traversed in the forward direction.
153  *
154  * A simple queue is headed by a pair of pointers, one to the head of the
155  * list and the other to the tail of the list. The elements are singly
156  * linked to save space, so elements can only be removed from the
157  * head of the list. New elements can be added to the list before or after
158  * an existing element, at the head of the list, or at the end of the
159  * list. A simple queue may only be traversed in the forward direction.
160  *
161  * A tail queue is headed by a pair of pointers, one to the head of the
162  * list and the other to the tail of the list. The elements are doubly
163  * linked so that an arbitrary element can be removed without a need to
164  * traverse the list. New elements can be added to the list before or
165  * after an existing element, at the head of the list, or at the end of
166  * the list. A tail queue may be traversed in either direction.
167  *
168  * An XOR simple queue is used in the same way as a regular simple queue.
169  * The difference is that the head structure also includes a "cookie" that
170  * is XOR'd with the queue pointer (first, last or next) to generate the
171  * real pointer value.
172  *
173  * For details on the use of these macros, see the queue(3) manual page.
174  */
175 
176 #if defined(QUEUE_MACRO_DEBUG) || (defined(_KERNEL) && defined(DIAGNOSTIC))
177 #define _Q_INVALID ((void *)-1)
178 #define _Q_INVALIDATE(a) (a) = _Q_INVALID
179 #else
180 #define _Q_INVALIDATE(a)
181 #endif
182 
183 /*
184  * Singly-linked List definitions.
185  */
186 #define SLIST_HEAD(name, type) \
187 struct name { \
188  struct type *slh_first; /* first element */ \
189 }
190 
191 #define SLIST_HEAD_INITIALIZER(head) \
192  { NULL }
193 
194 #define SLIST_ENTRY(type) \
195 struct { \
196  struct type *sle_next; /* next element */ \
197 }
198 
199 /*
200  * Singly-linked List access methods.
201  */
202 #define SLIST_FIRST(head) ((head)->slh_first)
203 #define SLIST_END(head) NULL
204 #define SLIST_EMPTY(head) (SLIST_FIRST(head) == SLIST_END(head))
205 #define SLIST_NEXT(elm, field) ((elm)->field.sle_next)
206 
207 #define SLIST_FOREACH(var, head, field) \
208  for((var) = SLIST_FIRST(head); \
209  (var) != SLIST_END(head); \
210  (var) = SLIST_NEXT(var, field))
211 
212 #define SLIST_FOREACH_SAFE(var, head, field, tvar) \
213  for ((var) = SLIST_FIRST(head); \
214  (var) && ((tvar) = SLIST_NEXT(var, field), 1); \
215  (var) = (tvar))
216 
217 /*
218  * Singly-linked List functions.
219  */
220 #define SLIST_INIT(head) { \
221  SLIST_FIRST(head) = SLIST_END(head); \
222 }
223 
224 #define SLIST_INSERT_AFTER(slistelm, elm, field) do { \
225  (elm)->field.sle_next = (slistelm)->field.sle_next; \
226  (slistelm)->field.sle_next = (elm); \
227 } while (0)
228 
229 #define SLIST_INSERT_HEAD(head, elm, field) do { \
230  (elm)->field.sle_next = (head)->slh_first; \
231  (head)->slh_first = (elm); \
232 } while (0)
233 
234 #define SLIST_REMOVE_AFTER(elm, field) do { \
235  (elm)->field.sle_next = (elm)->field.sle_next->field.sle_next; \
236 } while (0)
237 
238 #define SLIST_REMOVE_HEAD(head, field) do { \
239  (head)->slh_first = (head)->slh_first->field.sle_next; \
240 } while (0)
241 
242 #define SLIST_REMOVE(head, elm, type, field) do { \
243  if ((head)->slh_first == (elm)) { \
244  SLIST_REMOVE_HEAD((head), field); \
245  } else { \
246  struct type *curelm = (head)->slh_first; \
247  \
248  while (curelm->field.sle_next != (elm)) \
249  curelm = curelm->field.sle_next; \
250  curelm->field.sle_next = \
251  curelm->field.sle_next->field.sle_next; \
252  } \
253  _Q_INVALIDATE((elm)->field.sle_next); \
254 } while (0)
255 
256 /*
257  * List definitions.
258  */
259 #define LIST_HEAD(name, type) \
260 struct name { \
261  struct type *lh_first; /* first element */ \
262 }
263 
264 #define LIST_HEAD_INITIALIZER(head) \
265  { NULL }
266 
267 #define LIST_ENTRY(type) \
268 struct { \
269  struct type *le_next; /* next element */ \
270  struct type **le_prev; /* address of previous next element */ \
271 }
272 
273 /*
274  * List access methods.
275  */
276 #define LIST_FIRST(head) ((head)->lh_first)
277 #define LIST_END(head) NULL
278 #define LIST_EMPTY(head) (LIST_FIRST(head) == LIST_END(head))
279 #define LIST_NEXT(elm, field) ((elm)->field.le_next)
280 
281 #define LIST_FOREACH(var, head, field) \
282  for((var) = LIST_FIRST(head); \
283  (var)!= LIST_END(head); \
284  (var) = LIST_NEXT(var, field))
285 
286 #define LIST_FOREACH_SAFE(var, head, field, tvar) \
287  for ((var) = LIST_FIRST(head); \
288  (var) && ((tvar) = LIST_NEXT(var, field), 1); \
289  (var) = (tvar))
290 
291 /*
292  * List functions.
293  */
294 #define LIST_INIT(head) do { \
295  LIST_FIRST(head) = LIST_END(head); \
296 } while (0)
297 
298 #define LIST_INSERT_AFTER(listelm, elm, field) do { \
299  if (((elm)->field.le_next = (listelm)->field.le_next) != NULL) \
300  (listelm)->field.le_next->field.le_prev = \
301  &(elm)->field.le_next; \
302  (listelm)->field.le_next = (elm); \
303  (elm)->field.le_prev = &(listelm)->field.le_next; \
304 } while (0)
305 
306 #define LIST_INSERT_BEFORE(listelm, elm, field) do { \
307  (elm)->field.le_prev = (listelm)->field.le_prev; \
308  (elm)->field.le_next = (listelm); \
309  *(listelm)->field.le_prev = (elm); \
310  (listelm)->field.le_prev = &(elm)->field.le_next; \
311 } while (0)
312 
313 #define LIST_INSERT_HEAD(head, elm, field) do { \
314  if (((elm)->field.le_next = (head)->lh_first) != NULL) \
315  (head)->lh_first->field.le_prev = &(elm)->field.le_next;\
316  (head)->lh_first = (elm); \
317  (elm)->field.le_prev = &(head)->lh_first; \
318 } while (0)
319 
320 #define LIST_REMOVE(elm, field) do { \
321  if ((elm)->field.le_next != NULL) \
322  (elm)->field.le_next->field.le_prev = \
323  (elm)->field.le_prev; \
324  *(elm)->field.le_prev = (elm)->field.le_next; \
325  _Q_INVALIDATE((elm)->field.le_prev); \
326  _Q_INVALIDATE((elm)->field.le_next); \
327 } while (0)
328 
329 #define LIST_REPLACE(elm, elm2, field) do { \
330  if (((elm2)->field.le_next = (elm)->field.le_next) != NULL) \
331  (elm2)->field.le_next->field.le_prev = \
332  &(elm2)->field.le_next; \
333  (elm2)->field.le_prev = (elm)->field.le_prev; \
334  *(elm2)->field.le_prev = (elm2); \
335  _Q_INVALIDATE((elm)->field.le_prev); \
336  _Q_INVALIDATE((elm)->field.le_next); \
337 } while (0)
338 
339 /*
340  * Simple queue definitions.
341  */
342 #define SIMPLEQ_HEAD(name, type) \
343 struct name { \
344  struct type *sqh_first; /* first element */ \
345  struct type **sqh_last; /* addr of last next element */ \
346 }
347 
348 #define SIMPLEQ_HEAD_INITIALIZER(head) \
349  { NULL, &(head).sqh_first }
350 
351 #define SIMPLEQ_ENTRY(type) \
352 struct { \
353  struct type *sqe_next; /* next element */ \
354 }
355 
356 /*
357  * Simple queue access methods.
358  */
359 #define SIMPLEQ_FIRST(head) ((head)->sqh_first)
360 #define SIMPLEQ_END(head) NULL
361 #define SIMPLEQ_EMPTY(head) (SIMPLEQ_FIRST(head) == SIMPLEQ_END(head))
362 #define SIMPLEQ_NEXT(elm, field) ((elm)->field.sqe_next)
363 
364 #define SIMPLEQ_FOREACH(var, head, field) \
365  for((var) = SIMPLEQ_FIRST(head); \
366  (var) != SIMPLEQ_END(head); \
367  (var) = SIMPLEQ_NEXT(var, field))
368 
369 #define SIMPLEQ_FOREACH_SAFE(var, head, field, tvar) \
370  for ((var) = SIMPLEQ_FIRST(head); \
371  (var) && ((tvar) = SIMPLEQ_NEXT(var, field), 1); \
372  (var) = (tvar))
373 
374 /*
375  * Simple queue functions.
376  */
377 #define SIMPLEQ_INIT(head) do { \
378  (head)->sqh_first = NULL; \
379  (head)->sqh_last = &(head)->sqh_first; \
380 } while (0)
381 
382 #define SIMPLEQ_INSERT_HEAD(head, elm, field) do { \
383  if (((elm)->field.sqe_next = (head)->sqh_first) == NULL) \
384  (head)->sqh_last = &(elm)->field.sqe_next; \
385  (head)->sqh_first = (elm); \
386 } while (0)
387 
388 #define SIMPLEQ_INSERT_TAIL(head, elm, field) do { \
389  (elm)->field.sqe_next = NULL; \
390  *(head)->sqh_last = (elm); \
391  (head)->sqh_last = &(elm)->field.sqe_next; \
392 } while (0)
393 
394 #define SIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do { \
395  if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL)\
396  (head)->sqh_last = &(elm)->field.sqe_next; \
397  (listelm)->field.sqe_next = (elm); \
398 } while (0)
399 
400 #define SIMPLEQ_REMOVE_HEAD(head, field) do { \
401  if (((head)->sqh_first = (head)->sqh_first->field.sqe_next) == NULL) \
402  (head)->sqh_last = &(head)->sqh_first; \
403 } while (0)
404 
405 #define SIMPLEQ_REMOVE_AFTER(head, elm, field) do { \
406  if (((elm)->field.sqe_next = (elm)->field.sqe_next->field.sqe_next) \
407  == NULL) \
408  (head)->sqh_last = &(elm)->field.sqe_next; \
409 } while (0)
410 
411 #define SIMPLEQ_CONCAT(head1, head2) do { \
412  if (!SIMPLEQ_EMPTY((head2))) { \
413  *(head1)->sqh_last = (head2)->sqh_first; \
414  (head1)->sqh_last = (head2)->sqh_last; \
415  SIMPLEQ_INIT((head2)); \
416  } \
417 } while (0)
418 
419 /*
420  * XOR Simple queue definitions.
421  */
422 #define XSIMPLEQ_HEAD(name, type) \
423 struct name { \
424  struct type *sqx_first; /* first element */ \
425  struct type **sqx_last; /* addr of last next element */ \
426  unsigned long sqx_cookie; \
427 }
428 
429 #define XSIMPLEQ_ENTRY(type) \
430 struct { \
431  struct type *sqx_next; /* next element */ \
432 }
433 
434 /*
435  * XOR Simple queue access methods.
436  */
437 #define XSIMPLEQ_XOR(head, ptr) ((__typeof(ptr))((head)->sqx_cookie ^ \
438  (unsigned long)(ptr)))
439 #define XSIMPLEQ_FIRST(head) XSIMPLEQ_XOR(head, ((head)->sqx_first))
440 #define XSIMPLEQ_END(head) NULL
441 #define XSIMPLEQ_EMPTY(head) (XSIMPLEQ_FIRST(head) == XSIMPLEQ_END(head))
442 #define XSIMPLEQ_NEXT(head, elm, field) XSIMPLEQ_XOR(head, ((elm)->field.sqx_next))
443 
444 
445 #define XSIMPLEQ_FOREACH(var, head, field) \
446  for ((var) = XSIMPLEQ_FIRST(head); \
447  (var) != XSIMPLEQ_END(head); \
448  (var) = XSIMPLEQ_NEXT(head, var, field))
449 
450 #define XSIMPLEQ_FOREACH_SAFE(var, head, field, tvar) \
451  for ((var) = XSIMPLEQ_FIRST(head); \
452  (var) && ((tvar) = XSIMPLEQ_NEXT(head, var, field), 1); \
453  (var) = (tvar))
454 
455 /*
456  * XOR Simple queue functions.
457  */
458 #define XSIMPLEQ_INIT(head) do { \
459  arc4random_buf(&(head)->sqx_cookie, sizeof((head)->sqx_cookie)); \
460  (head)->sqx_first = XSIMPLEQ_XOR(head, NULL); \
461  (head)->sqx_last = XSIMPLEQ_XOR(head, &(head)->sqx_first); \
462 } while (0)
463 
464 #define XSIMPLEQ_INSERT_HEAD(head, elm, field) do { \
465  if (((elm)->field.sqx_next = (head)->sqx_first) == \
466  XSIMPLEQ_XOR(head, NULL)) \
467  (head)->sqx_last = XSIMPLEQ_XOR(head, &(elm)->field.sqx_next); \
468  (head)->sqx_first = XSIMPLEQ_XOR(head, (elm)); \
469 } while (0)
470 
471 #define XSIMPLEQ_INSERT_TAIL(head, elm, field) do { \
472  (elm)->field.sqx_next = XSIMPLEQ_XOR(head, NULL); \
473  *(XSIMPLEQ_XOR(head, (head)->sqx_last)) = XSIMPLEQ_XOR(head, (elm)); \
474  (head)->sqx_last = XSIMPLEQ_XOR(head, &(elm)->field.sqx_next); \
475 } while (0)
476 
477 #define XSIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do { \
478  if (((elm)->field.sqx_next = (listelm)->field.sqx_next) == \
479  XSIMPLEQ_XOR(head, NULL)) \
480  (head)->sqx_last = XSIMPLEQ_XOR(head, &(elm)->field.sqx_next); \
481  (listelm)->field.sqx_next = XSIMPLEQ_XOR(head, (elm)); \
482 } while (0)
483 
484 #define XSIMPLEQ_REMOVE_HEAD(head, field) do { \
485  if (((head)->sqx_first = XSIMPLEQ_XOR(head, \
486  (head)->sqx_first)->field.sqx_next) == XSIMPLEQ_XOR(head, NULL)) \
487  (head)->sqx_last = XSIMPLEQ_XOR(head, &(head)->sqx_first); \
488 } while (0)
489 
490 #define XSIMPLEQ_REMOVE_AFTER(head, elm, field) do { \
491  if (((elm)->field.sqx_next = XSIMPLEQ_XOR(head, \
492  (elm)->field.sqx_next)->field.sqx_next) \
493  == XSIMPLEQ_XOR(head, NULL)) \
494  (head)->sqx_last = \
495  XSIMPLEQ_XOR(head, &(elm)->field.sqx_next); \
496 } while (0)
497 
498 
499 /*
500  * Tail queue definitions.
501  */
502 #define TAILQ_HEAD(name, type) \
503 struct name { \
504  struct type *tqh_first; /* first element */ \
505  struct type **tqh_last; /* addr of last next element */ \
506 }
507 
508 #define TAILQ_HEAD_INITIALIZER(head) \
509  { NULL, &(head).tqh_first }
510 
511 #define TAILQ_ENTRY(type) \
512 struct { \
513  struct type *tqe_next; /* next element */ \
514  struct type **tqe_prev; /* address of previous next element */ \
515 }
516 
517 /*
518  * Tail queue access methods.
519  */
520 #define TAILQ_FIRST(head) ((head)->tqh_first)
521 #define TAILQ_END(head) NULL
522 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
523 #define TAILQ_LAST(head, headname) \
524  (*(((struct headname *)((head)->tqh_last))->tqh_last))
525 /* XXX */
526 #define TAILQ_PREV(elm, headname, field) \
527  (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
528 #define TAILQ_EMPTY(head) \
529  (TAILQ_FIRST(head) == TAILQ_END(head))
530 
531 #define TAILQ_FOREACH(var, head, field) \
532  for((var) = TAILQ_FIRST(head); \
533  (var) != TAILQ_END(head); \
534  (var) = TAILQ_NEXT(var, field))
535 
536 #define TAILQ_FOREACH_SAFE(var, head, field, tvar) \
537  for ((var) = TAILQ_FIRST(head); \
538  (var) != TAILQ_END(head) && \
539  ((tvar) = TAILQ_NEXT(var, field), 1); \
540  (var) = (tvar))
541 
542 
543 #define TAILQ_FOREACH_REVERSE(var, head, headname, field) \
544  for((var) = TAILQ_LAST(head, headname); \
545  (var) != TAILQ_END(head); \
546  (var) = TAILQ_PREV(var, headname, field))
547 
548 #define TAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar) \
549  for ((var) = TAILQ_LAST(head, headname); \
550  (var) != TAILQ_END(head) && \
551  ((tvar) = TAILQ_PREV(var, headname, field), 1); \
552  (var) = (tvar))
553 
554 /*
555  * Tail queue functions.
556  */
557 #define TAILQ_INIT(head) do { \
558  (head)->tqh_first = NULL; \
559  (head)->tqh_last = &(head)->tqh_first; \
560 } while (0)
561 
562 #define TAILQ_INSERT_HEAD(head, elm, field) do { \
563  if (((elm)->field.tqe_next = (head)->tqh_first) != NULL) \
564  (head)->tqh_first->field.tqe_prev = \
565  &(elm)->field.tqe_next; \
566  else \
567  (head)->tqh_last = &(elm)->field.tqe_next; \
568  (head)->tqh_first = (elm); \
569  (elm)->field.tqe_prev = &(head)->tqh_first; \
570 } while (0)
571 
572 #define TAILQ_INSERT_TAIL(head, elm, field) do { \
573  (elm)->field.tqe_next = NULL; \
574  (elm)->field.tqe_prev = (head)->tqh_last; \
575  *(head)->tqh_last = (elm); \
576  (head)->tqh_last = &(elm)->field.tqe_next; \
577 } while (0)
578 
579 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do { \
580  if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)\
581  (elm)->field.tqe_next->field.tqe_prev = \
582  &(elm)->field.tqe_next; \
583  else \
584  (head)->tqh_last = &(elm)->field.tqe_next; \
585  (listelm)->field.tqe_next = (elm); \
586  (elm)->field.tqe_prev = &(listelm)->field.tqe_next; \
587 } while (0)
588 
589 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do { \
590  (elm)->field.tqe_prev = (listelm)->field.tqe_prev; \
591  (elm)->field.tqe_next = (listelm); \
592  *(listelm)->field.tqe_prev = (elm); \
593  (listelm)->field.tqe_prev = &(elm)->field.tqe_next; \
594 } while (0)
595 
596 #define TAILQ_REMOVE(head, elm, field) do { \
597  if (((elm)->field.tqe_next) != NULL) \
598  (elm)->field.tqe_next->field.tqe_prev = \
599  (elm)->field.tqe_prev; \
600  else \
601  (head)->tqh_last = (elm)->field.tqe_prev; \
602  *(elm)->field.tqe_prev = (elm)->field.tqe_next; \
603  _Q_INVALIDATE((elm)->field.tqe_prev); \
604  _Q_INVALIDATE((elm)->field.tqe_next); \
605 } while (0)
606 
607 #define TAILQ_REPLACE(head, elm, elm2, field) do { \
608  if (((elm2)->field.tqe_next = (elm)->field.tqe_next) != NULL) \
609  (elm2)->field.tqe_next->field.tqe_prev = \
610  &(elm2)->field.tqe_next; \
611  else \
612  (head)->tqh_last = &(elm2)->field.tqe_next; \
613  (elm2)->field.tqe_prev = (elm)->field.tqe_prev; \
614  *(elm2)->field.tqe_prev = (elm2); \
615  _Q_INVALIDATE((elm)->field.tqe_prev); \
616  _Q_INVALIDATE((elm)->field.tqe_next); \
617 } while (0)
618 
619 #define TAILQ_CONCAT(head1, head2, field) do { \
620  if (!TAILQ_EMPTY(head2)) { \
621  *(head1)->tqh_last = (head2)->tqh_first; \
622  (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last; \
623  (head1)->tqh_last = (head2)->tqh_last; \
624  TAILQ_INIT((head2)); \
625  } \
626 } while (0)
627 
628 #endif /* !_SYS_QUEUE_H_ */