xref: /dragonfly/sys/sys/queue.h (revision 984263bc)
1 /*
2  * Copyright (c) 1991, 1993
3  *	The Regents of the University of California.  All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in the
12  *    documentation and/or other materials provided with the distribution.
13  * 3. All advertising materials mentioning features or use of this software
14  *    must display the following acknowledgement:
15  *	This product includes software developed by the University of
16  *	California, Berkeley and its contributors.
17  * 4. Neither the name of the University nor the names of its contributors
18  *    may be used to endorse or promote products derived from this software
19  *    without specific prior written permission.
20  *
21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31  * SUCH DAMAGE.
32  *
33  *	@(#)queue.h	8.5 (Berkeley) 8/20/94
34  * $FreeBSD: src/sys/sys/queue.h,v 1.32.2.7 2002/04/17 14:21:02 des Exp $
35  */
36 
37 #ifndef _SYS_QUEUE_H_
38 #define	_SYS_QUEUE_H_
39 
40 #include <machine/ansi.h>	/* for __offsetof */
41 
42 /*
43  * This file defines five types of data structures: singly-linked lists,
44  * singly-linked tail queues, lists, tail queues, and circular queues.
45  *
46  * A singly-linked list is headed by a single forward pointer. The elements
47  * are singly linked for minimum space and pointer manipulation overhead at
48  * the expense of O(n) removal for arbitrary elements. New elements can be
49  * added to the list after an existing element or at the head of the list.
50  * Elements being removed from the head of the list should use the explicit
51  * macro for this purpose for optimum efficiency. A singly-linked list may
52  * only be traversed in the forward direction.  Singly-linked lists are ideal
53  * for applications with large datasets and few or no removals or for
54  * implementing a LIFO queue.
55  *
56  * A singly-linked tail queue is headed by a pair of pointers, one to the
57  * head of the list and the other to the tail of the list. The elements are
58  * singly linked for minimum space and pointer manipulation overhead at the
59  * expense of O(n) removal for arbitrary elements. New elements can be added
60  * to the list after an existing element, at the head of the list, or at the
61  * end of the list. Elements being removed from the head of the tail queue
62  * should use the explicit macro for this purpose for optimum efficiency.
63  * A singly-linked tail queue may only be traversed in the forward direction.
64  * Singly-linked tail queues are ideal for applications with large datasets
65  * and few or no removals or for implementing a FIFO queue.
66  *
67  * A list is headed by a single forward pointer (or an array of forward
68  * pointers for a hash table header). The elements are doubly linked
69  * so that an arbitrary element can be removed without a need to
70  * traverse the list. New elements can be added to the list before
71  * or after an existing element or at the head of the list. A list
72  * may only be traversed in the forward direction.
73  *
74  * A tail queue is headed by a pair of pointers, one to the head of the
75  * list and the other to the tail of the list. The elements are doubly
76  * linked so that an arbitrary element can be removed without a need to
77  * traverse the list. New elements can be added to the list before or
78  * after an existing element, at the head of the list, or at the end of
79  * the list. A tail queue may be traversed in either direction.
80  *
81  * A circle queue is headed by a pair of pointers, one to the head of the
82  * list and the other to the tail of the list. The elements are doubly
83  * linked so that an arbitrary element can be removed without a need to
84  * traverse the list. New elements can be added to the list before or after
85  * an existing element, at the head of the list, or at the end of the list.
86  * A circle queue may be traversed in either direction, but has a more
87  * complex end of list detection.
88  *
89  * For details on the use of these macros, see the queue(3) manual page.
90  *
91  *
92  *			SLIST	LIST	STAILQ	TAILQ	CIRCLEQ
93  * _HEAD		+	+	+	+	+
94  * _HEAD_INITIALIZER	+	+	+	+	+
95  * _ENTRY		+	+	+	+	+
96  * _INIT		+	+	+	+	+
97  * _EMPTY		+	+	+	+	+
98  * _FIRST		+	+	+	+	+
99  * _NEXT		+	+	+	+	+
100  * _PREV		-	-	-	+	+
101  * _LAST		-	-	+	+	+
102  * _FOREACH		+	+	+	+	+
103  * _FOREACH_REVERSE	-	-	-	+	+
104  * _INSERT_HEAD		+	+	+	+	+
105  * _INSERT_BEFORE	-	+	-	+	+
106  * _INSERT_AFTER	+	+	+	+	+
107  * _INSERT_TAIL		-	-	+	+	+
108  * _REMOVE_HEAD		+	-	+	-	-
109  * _REMOVE		+	+	+	+	+
110  *
111  */
112 
113 /*
114  * Singly-linked List declarations.
115  */
116 #define	SLIST_HEAD(name, type)						\
117 struct name {								\
118 	struct type *slh_first;	/* first element */			\
119 }
120 
121 #define	SLIST_HEAD_INITIALIZER(head)					\
122 	{ NULL }
123 
124 #define	SLIST_ENTRY(type)						\
125 struct {								\
126 	struct type *sle_next;	/* next element */			\
127 }
128 
129 /*
130  * Singly-linked List functions.
131  */
132 #define	SLIST_EMPTY(head)	((head)->slh_first == NULL)
133 
134 #define	SLIST_FIRST(head)	((head)->slh_first)
135 
136 #define	SLIST_FOREACH(var, head, field)					\
137 	for ((var) = SLIST_FIRST((head));				\
138 	    (var);							\
139 	    (var) = SLIST_NEXT((var), field))
140 
141 #define	SLIST_INIT(head) do {						\
142 	SLIST_FIRST((head)) = NULL;					\
143 } while (0)
144 
145 #define	SLIST_INSERT_AFTER(slistelm, elm, field) do {			\
146 	SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);	\
147 	SLIST_NEXT((slistelm), field) = (elm);				\
148 } while (0)
149 
150 #define	SLIST_INSERT_HEAD(head, elm, field) do {			\
151 	SLIST_NEXT((elm), field) = SLIST_FIRST((head));			\
152 	SLIST_FIRST((head)) = (elm);					\
153 } while (0)
154 
155 #define	SLIST_NEXT(elm, field)	((elm)->field.sle_next)
156 
157 #define	SLIST_REMOVE(head, elm, type, field) do {			\
158 	if (SLIST_FIRST((head)) == (elm)) {				\
159 		SLIST_REMOVE_HEAD((head), field);			\
160 	}								\
161 	else {								\
162 		struct type *curelm = SLIST_FIRST((head));		\
163 		while (SLIST_NEXT(curelm, field) != (elm))		\
164 			curelm = SLIST_NEXT(curelm, field);		\
165 		SLIST_NEXT(curelm, field) =				\
166 		    SLIST_NEXT(SLIST_NEXT(curelm, field), field);	\
167 	}								\
168 } while (0)
169 
170 #define	SLIST_REMOVE_HEAD(head, field) do {				\
171 	SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);	\
172 } while (0)
173 
174 /*
175  * Singly-linked Tail queue declarations.
176  */
177 #define	STAILQ_HEAD(name, type)						\
178 struct name {								\
179 	struct type *stqh_first;/* first element */			\
180 	struct type **stqh_last;/* addr of last next element */		\
181 }
182 
183 #define	STAILQ_HEAD_INITIALIZER(head)					\
184 	{ NULL, &(head).stqh_first }
185 
186 #define	STAILQ_ENTRY(type)						\
187 struct {								\
188 	struct type *stqe_next;	/* next element */			\
189 }
190 
191 /*
192  * Singly-linked Tail queue functions.
193  */
194 #define	STAILQ_EMPTY(head)	((head)->stqh_first == NULL)
195 
196 #define	STAILQ_FIRST(head)	((head)->stqh_first)
197 
198 #define	STAILQ_FOREACH(var, head, field)				\
199 	for((var) = STAILQ_FIRST((head));				\
200 	   (var);							\
201 	   (var) = STAILQ_NEXT((var), field))
202 
203 #define	STAILQ_INIT(head) do {						\
204 	STAILQ_FIRST((head)) = NULL;					\
205 	(head)->stqh_last = &STAILQ_FIRST((head));			\
206 } while (0)
207 
208 #define	STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {		\
209 	if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
210 		(head)->stqh_last = &STAILQ_NEXT((elm), field);		\
211 	STAILQ_NEXT((tqelm), field) = (elm);				\
212 } while (0)
213 
214 #define	STAILQ_INSERT_HEAD(head, elm, field) do {			\
215 	if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL)	\
216 		(head)->stqh_last = &STAILQ_NEXT((elm), field);		\
217 	STAILQ_FIRST((head)) = (elm);					\
218 } while (0)
219 
220 #define	STAILQ_INSERT_TAIL(head, elm, field) do {			\
221 	STAILQ_NEXT((elm), field) = NULL;				\
222 	*(head)->stqh_last = (elm);					\
223 	(head)->stqh_last = &STAILQ_NEXT((elm), field);			\
224 } while (0)
225 
226 #define	STAILQ_LAST(head, type, field)					\
227 	(STAILQ_EMPTY(head) ?						\
228 		NULL :							\
229 	        ((struct type *)					\
230 		((char *)((head)->stqh_last) - __offsetof(struct type, field))))
231 
232 #define	STAILQ_NEXT(elm, field)	((elm)->field.stqe_next)
233 
234 #define	STAILQ_REMOVE(head, elm, type, field) do {			\
235 	if (STAILQ_FIRST((head)) == (elm)) {				\
236 		STAILQ_REMOVE_HEAD(head, field);			\
237 	}								\
238 	else {								\
239 		struct type *curelm = STAILQ_FIRST((head));		\
240 		while (STAILQ_NEXT(curelm, field) != (elm))		\
241 			curelm = STAILQ_NEXT(curelm, field);		\
242 		if ((STAILQ_NEXT(curelm, field) =			\
243 		     STAILQ_NEXT(STAILQ_NEXT(curelm, field), field)) == NULL)\
244 			(head)->stqh_last = &STAILQ_NEXT((curelm), field);\
245 	}								\
246 } while (0)
247 
248 #define	STAILQ_REMOVE_HEAD(head, field) do {				\
249 	if ((STAILQ_FIRST((head)) =					\
250 	     STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL)		\
251 		(head)->stqh_last = &STAILQ_FIRST((head));		\
252 } while (0)
253 
254 #define	STAILQ_REMOVE_HEAD_UNTIL(head, elm, field) do {			\
255 	if ((STAILQ_FIRST((head)) = STAILQ_NEXT((elm), field)) == NULL)	\
256 		(head)->stqh_last = &STAILQ_FIRST((head));		\
257 } while (0)
258 
259 /*
260  * List declarations.
261  */
262 #define	LIST_HEAD(name, type)						\
263 struct name {								\
264 	struct type *lh_first;	/* first element */			\
265 }
266 
267 #define	LIST_HEAD_INITIALIZER(head)					\
268 	{ NULL }
269 
270 #define	LIST_ENTRY(type)						\
271 struct {								\
272 	struct type *le_next;	/* next element */			\
273 	struct type **le_prev;	/* address of previous next element */	\
274 }
275 
276 /*
277  * List functions.
278  */
279 
280 #define	LIST_EMPTY(head)	((head)->lh_first == NULL)
281 
282 #define	LIST_FIRST(head)	((head)->lh_first)
283 
284 #define	LIST_FOREACH(var, head, field)					\
285 	for ((var) = LIST_FIRST((head));				\
286 	    (var);							\
287 	    (var) = LIST_NEXT((var), field))
288 
289 #define	LIST_INIT(head) do {						\
290 	LIST_FIRST((head)) = NULL;					\
291 } while (0)
292 
293 #define	LIST_INSERT_AFTER(listelm, elm, field) do {			\
294 	if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
295 		LIST_NEXT((listelm), field)->field.le_prev =		\
296 		    &LIST_NEXT((elm), field);				\
297 	LIST_NEXT((listelm), field) = (elm);				\
298 	(elm)->field.le_prev = &LIST_NEXT((listelm), field);		\
299 } while (0)
300 
301 #define	LIST_INSERT_BEFORE(listelm, elm, field) do {			\
302 	(elm)->field.le_prev = (listelm)->field.le_prev;		\
303 	LIST_NEXT((elm), field) = (listelm);				\
304 	*(listelm)->field.le_prev = (elm);				\
305 	(listelm)->field.le_prev = &LIST_NEXT((elm), field);		\
306 } while (0)
307 
308 #define	LIST_INSERT_HEAD(head, elm, field) do {				\
309 	if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)	\
310 		LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
311 	LIST_FIRST((head)) = (elm);					\
312 	(elm)->field.le_prev = &LIST_FIRST((head));			\
313 } while (0)
314 
315 #define	LIST_NEXT(elm, field)	((elm)->field.le_next)
316 
317 #define	LIST_REMOVE(elm, field) do {					\
318 	if (LIST_NEXT((elm), field) != NULL)				\
319 		LIST_NEXT((elm), field)->field.le_prev = 		\
320 		    (elm)->field.le_prev;				\
321 	*(elm)->field.le_prev = LIST_NEXT((elm), field);		\
322 } while (0)
323 
324 /*
325  * Tail queue declarations.
326  */
327 #define	TAILQ_HEAD(name, type)						\
328 struct name {								\
329 	struct type *tqh_first;	/* first element */			\
330 	struct type **tqh_last;	/* addr of last next element */		\
331 }
332 
333 #define	TAILQ_HEAD_INITIALIZER(head)					\
334 	{ NULL, &(head).tqh_first }
335 
336 #define	TAILQ_ENTRY(type)						\
337 struct {								\
338 	struct type *tqe_next;	/* next element */			\
339 	struct type **tqe_prev;	/* address of previous next element */	\
340 }
341 
342 /*
343  * Tail queue functions.
344  */
345 #define	TAILQ_EMPTY(head)	((head)->tqh_first == NULL)
346 
347 #define	TAILQ_FIRST(head)	((head)->tqh_first)
348 
349 #define	TAILQ_FOREACH(var, head, field)					\
350 	for ((var) = TAILQ_FIRST((head));				\
351 	    (var);							\
352 	    (var) = TAILQ_NEXT((var), field))
353 
354 #define	TAILQ_FOREACH_REVERSE(var, head, headname, field)		\
355 	for ((var) = TAILQ_LAST((head), headname);			\
356 	    (var);							\
357 	    (var) = TAILQ_PREV((var), headname, field))
358 
359 #define	TAILQ_INIT(head) do {						\
360 	TAILQ_FIRST((head)) = NULL;					\
361 	(head)->tqh_last = &TAILQ_FIRST((head));			\
362 } while (0)
363 
364 #define	TAILQ_INSERT_AFTER(head, listelm, elm, field) do {		\
365 	if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
366 		TAILQ_NEXT((elm), field)->field.tqe_prev = 		\
367 		    &TAILQ_NEXT((elm), field);				\
368 	else								\
369 		(head)->tqh_last = &TAILQ_NEXT((elm), field);		\
370 	TAILQ_NEXT((listelm), field) = (elm);				\
371 	(elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);		\
372 } while (0)
373 
374 #define	TAILQ_INSERT_BEFORE(listelm, elm, field) do {			\
375 	(elm)->field.tqe_prev = (listelm)->field.tqe_prev;		\
376 	TAILQ_NEXT((elm), field) = (listelm);				\
377 	*(listelm)->field.tqe_prev = (elm);				\
378 	(listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);		\
379 } while (0)
380 
381 #define	TAILQ_INSERT_HEAD(head, elm, field) do {			\
382 	if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)	\
383 		TAILQ_FIRST((head))->field.tqe_prev =			\
384 		    &TAILQ_NEXT((elm), field);				\
385 	else								\
386 		(head)->tqh_last = &TAILQ_NEXT((elm), field);		\
387 	TAILQ_FIRST((head)) = (elm);					\
388 	(elm)->field.tqe_prev = &TAILQ_FIRST((head));			\
389 } while (0)
390 
391 #define	TAILQ_INSERT_TAIL(head, elm, field) do {			\
392 	TAILQ_NEXT((elm), field) = NULL;				\
393 	(elm)->field.tqe_prev = (head)->tqh_last;			\
394 	*(head)->tqh_last = (elm);					\
395 	(head)->tqh_last = &TAILQ_NEXT((elm), field);			\
396 } while (0)
397 
398 #define	TAILQ_LAST(head, headname)					\
399 	(*(((struct headname *)((head)->tqh_last))->tqh_last))
400 
401 #define	TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
402 
403 #define	TAILQ_PREV(elm, headname, field)				\
404 	(*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
405 
406 #define	TAILQ_REMOVE(head, elm, field) do {				\
407 	if ((TAILQ_NEXT((elm), field)) != NULL)				\
408 		TAILQ_NEXT((elm), field)->field.tqe_prev = 		\
409 		    (elm)->field.tqe_prev;				\
410 	else								\
411 		(head)->tqh_last = (elm)->field.tqe_prev;		\
412 	*(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);		\
413 } while (0)
414 
415 /*
416  * Circular queue declarations.
417  */
418 #define	CIRCLEQ_HEAD(name, type)					\
419 struct name {								\
420 	struct type *cqh_first;		/* first element */		\
421 	struct type *cqh_last;		/* last element */		\
422 }
423 
424 #define	CIRCLEQ_HEAD_INITIALIZER(head)					\
425 	{ (void *)&(head), (void *)&(head) }
426 
427 #define	CIRCLEQ_ENTRY(type)						\
428 struct {								\
429 	struct type *cqe_next;		/* next element */		\
430 	struct type *cqe_prev;		/* previous element */		\
431 }
432 
433 /*
434  * Circular queue functions.
435  */
436 #define	CIRCLEQ_EMPTY(head)	((head)->cqh_first == (void *)(head))
437 
438 #define	CIRCLEQ_FIRST(head)	((head)->cqh_first)
439 
440 #define	CIRCLEQ_FOREACH(var, head, field)				\
441 	for ((var) = CIRCLEQ_FIRST((head));				\
442 	    (var) != (void *)(head) || ((var) = NULL);			\
443 	    (var) = CIRCLEQ_NEXT((var), field))
444 
445 #define	CIRCLEQ_FOREACH_REVERSE(var, head, field)			\
446 	for ((var) = CIRCLEQ_LAST((head));				\
447 	    (var) != (void *)(head) || ((var) = NULL);			\
448 	    (var) = CIRCLEQ_PREV((var), field))
449 
450 #define	CIRCLEQ_INIT(head) do {						\
451 	CIRCLEQ_FIRST((head)) = (void *)(head);				\
452 	CIRCLEQ_LAST((head)) = (void *)(head);				\
453 } while (0)
454 
455 #define	CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {		\
456 	CIRCLEQ_NEXT((elm), field) = CIRCLEQ_NEXT((listelm), field);	\
457 	CIRCLEQ_PREV((elm), field) = (listelm);				\
458 	if (CIRCLEQ_NEXT((listelm), field) == (void *)(head))		\
459 		CIRCLEQ_LAST((head)) = (elm);				\
460 	else								\
461 		CIRCLEQ_PREV(CIRCLEQ_NEXT((listelm), field), field) = (elm);\
462 	CIRCLEQ_NEXT((listelm), field) = (elm);				\
463 } while (0)
464 
465 #define	CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do {		\
466 	CIRCLEQ_NEXT((elm), field) = (listelm);				\
467 	CIRCLEQ_PREV((elm), field) = CIRCLEQ_PREV((listelm), field);	\
468 	if (CIRCLEQ_PREV((listelm), field) == (void *)(head))		\
469 		CIRCLEQ_FIRST((head)) = (elm);				\
470 	else								\
471 		CIRCLEQ_NEXT(CIRCLEQ_PREV((listelm), field), field) = (elm);\
472 	CIRCLEQ_PREV((listelm), field) = (elm);				\
473 } while (0)
474 
475 #define	CIRCLEQ_INSERT_HEAD(head, elm, field) do {			\
476 	CIRCLEQ_NEXT((elm), field) = CIRCLEQ_FIRST((head));		\
477 	CIRCLEQ_PREV((elm), field) = (void *)(head);			\
478 	if (CIRCLEQ_LAST((head)) == (void *)(head))			\
479 		CIRCLEQ_LAST((head)) = (elm);				\
480 	else								\
481 		CIRCLEQ_PREV(CIRCLEQ_FIRST((head)), field) = (elm);	\
482 	CIRCLEQ_FIRST((head)) = (elm);					\
483 } while (0)
484 
485 #define	CIRCLEQ_INSERT_TAIL(head, elm, field) do {			\
486 	CIRCLEQ_NEXT((elm), field) = (void *)(head);			\
487 	CIRCLEQ_PREV((elm), field) = CIRCLEQ_LAST((head));		\
488 	if (CIRCLEQ_FIRST((head)) == (void *)(head))			\
489 		CIRCLEQ_FIRST((head)) = (elm);				\
490 	else								\
491 		CIRCLEQ_NEXT(CIRCLEQ_LAST((head)), field) = (elm);	\
492 	CIRCLEQ_LAST((head)) = (elm);					\
493 } while (0)
494 
495 #define	CIRCLEQ_LAST(head)	((head)->cqh_last)
496 
497 #define	CIRCLEQ_NEXT(elm,field)	((elm)->field.cqe_next)
498 
499 #define	CIRCLEQ_PREV(elm,field)	((elm)->field.cqe_prev)
500 
501 #define	CIRCLEQ_REMOVE(head, elm, field) do {				\
502 	if (CIRCLEQ_NEXT((elm), field) == (void *)(head))		\
503 		CIRCLEQ_LAST((head)) = CIRCLEQ_PREV((elm), field);	\
504 	else								\
505 		CIRCLEQ_PREV(CIRCLEQ_NEXT((elm), field), field) =	\
506 		    CIRCLEQ_PREV((elm), field);				\
507 	if (CIRCLEQ_PREV((elm), field) == (void *)(head))		\
508 		CIRCLEQ_FIRST((head)) = CIRCLEQ_NEXT((elm), field);	\
509 	else								\
510 		CIRCLEQ_NEXT(CIRCLEQ_PREV((elm), field), field) =	\
511 		    CIRCLEQ_NEXT((elm), field);				\
512 } while (0)
513 
514 #ifdef _KERNEL
515 
516 /*
517  * XXX insque() and remque() are an old way of handling certain queues.
518  * They bogusly assumes that all queue heads look alike.
519  */
520 
521 struct quehead {
522 	struct quehead *qh_link;
523 	struct quehead *qh_rlink;
524 };
525 
526 #ifdef	__GNUC__
527 
528 static __inline void
529 insque(void *a, void *b)
530 {
531 	struct quehead *element = (struct quehead *)a,
532 		 *head = (struct quehead *)b;
533 
534 	element->qh_link = head->qh_link;
535 	element->qh_rlink = head;
536 	head->qh_link = element;
537 	element->qh_link->qh_rlink = element;
538 }
539 
540 static __inline void
541 remque(void *a)
542 {
543 	struct quehead *element = (struct quehead *)a;
544 
545 	element->qh_link->qh_rlink = element->qh_rlink;
546 	element->qh_rlink->qh_link = element->qh_link;
547 	element->qh_rlink = 0;
548 }
549 
550 #else /* !__GNUC__ */
551 
552 void	insque __P((void *a, void *b));
553 void	remque __P((void *a));
554 
555 #endif /* __GNUC__ */
556 
557 #endif /* _KERNEL */
558 
559 #endif /* !_SYS_QUEUE_H_ */
560