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      1 /*	$NetBSD: container_of.h,v 1.1 2024/10/08 22:53:20 christos Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2024 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * Redistribution and use in source and binary forms, with or without
      8  * modification, are permitted provided that the following conditions
      9  * are met:
     10  * 1. Redistributions of source code must retain the above copyright
     11  *    notice, this list of conditions and the following disclaimer.
     12  * 2. Redistributions in binary form must reproduce the above copyright
     13  *    notice, this list of conditions and the following disclaimer in the
     14  *    documentation and/or other materials provided with the distribution.
     15  *
     16  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     17  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     18  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     19  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     20  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     21  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     22  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     23  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     24  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     25  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     26  * POSSIBILITY OF SUCH DAMAGE.
     27  */
     28 
     29 #ifndef _SYS_CONTAINER_OF_H_
     30 #define _SYS_CONTAINER_OF_H_
     31 
     32 #include <sys/stddef.h>
     33 
     34 /*
     35  * Return the container of an embedded struct.  Given x = &c->f,
     36  * container_of(x, T, f) yields c, where T is the type of c.  Example:
     37  *
     38  *	struct foo { ... };
     39  *	struct bar {
     40  *		int b_x;
     41  *		struct foo b_foo;
     42  *		...
     43  *	};
     44  *
     45  *	struct bar b;
     46  *	struct foo *fp = &b.b_foo;
     47  *
     48  * Now we can get at b from fp by:
     49  *
     50  *	struct bar *bp = container_of(fp, struct bar, b_foo);
     51  *
     52  * The 0*sizeof((PTR) - ...) causes the compiler to warn if the type of
     53  * *fp does not match the type of struct bar::b_foo.
     54  * We skip the validation for coverity runs to avoid warnings.
     55  */
     56 #if defined(__COVERITY__) || defined(__LGTM_BOT__)
     57 #define __validate_container_of(PTR, TYPE, FIELD) 0
     58 #define __validate_const_container_of(PTR, TYPE, FIELD) 0
     59 #else
     60 #define __validate_container_of(PTR, TYPE, FIELD)			\
     61     (0 * sizeof((PTR) - &((TYPE *)(((char *)(PTR)) -			\
     62     offsetof(TYPE, FIELD)))->FIELD))
     63 #define __validate_const_container_of(PTR, TYPE, FIELD)			\
     64     (0 * sizeof((PTR) - &((const TYPE *)(((const char *)(PTR)) -	\
     65     offsetof(TYPE, FIELD)))->FIELD))
     66 #endif
     67 
     68 #define	container_of(PTR, TYPE, FIELD)					\
     69     ((TYPE *)(((char *)(PTR)) - offsetof(TYPE, FIELD))			\
     70 	+ __validate_container_of(PTR, TYPE, FIELD))
     71 #define	const_container_of(PTR, TYPE, FIELD)				\
     72     ((const TYPE *)(((const char *)(PTR)) - offsetof(TYPE, FIELD))	\
     73 	+ __validate_const_container_of(PTR, TYPE, FIELD))
     74 
     75 #endif /* !_SYS_CONTAINER_OF_H_ */
     76