container_of.h

 1/* SPDX-License-Identifier: GPL-2.0 */
 2#ifndef _LINUX_CONTAINER_OF_H
 3#define _LINUX_CONTAINER_OF_H
 4
 5#include <linux/build_bug.h>
 6#include <linux/stddef.h>
 7
 8#define typeof_member(T, m)	typeof(((T*)0)->m)
 9
10/**
11 * container_of - cast a member of a structure out to the containing structure
12 * @ptr:	the pointer to the member.
13 * @type:	the type of the container struct this is embedded in.
14 * @member:	the name of the member within the struct.
15 *
16 * WARNING: any const qualifier of @ptr is lost.
17 * Do not use container_of() in new code.
18 */
19#define container_of(ptr, type, member) ({				\
20	void *__mptr = (void *)(ptr);					\
21	static_assert(__same_type(*(ptr), ((type *)0)->member) ||	\
22		      __same_type(*(ptr), void),			\
23		      "pointer type mismatch in container_of()");	\
24	((type *)(__mptr - offsetof(type, member))); })
25
26/**
27 * container_of_const - cast a member of a structure out to the containing
28 *			structure and preserve the const-ness of the pointer
29 * @ptr:		the pointer to the member
30 * @type:		the type of the container struct this is embedded in.
31 * @member:		the name of the member within the struct.
32 *
33 * Always prefer container_of_const() instead of container_of() in new code.
34 */
35#define container_of_const(ptr, type, member)				\
36	_Generic(ptr,							\
37		const typeof(*(ptr)) *: ((const type *)container_of(ptr, type, member)),\
38		default: ((type *)container_of(ptr, type, member))	\
39	)
40
41#endif	/* _LINUX_CONTAINER_OF_H */