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   */
18  #define container_of(ptr, type, member) ({				\
19  	void *__mptr = (void *)(ptr);					\
20  	static_assert(__same_type(*(ptr), ((type *)0)->member) ||	\
21  		      __same_type(*(ptr), void),			\
22  		      "pointer type mismatch in container_of()");	\
23  	((type *)(__mptr - offsetof(type, member))); })
24  
25  /**
26   * container_of_const - cast a member of a structure out to the containing
27   *			structure and preserve the const-ness of the pointer
28   * @ptr:		the pointer to the member
29   * @type:		the type of the container struct this is embedded in.
30   * @member:		the name of the member within the struct.
31   */
32  #define container_of_const(ptr, type, member)				\
33  	_Generic(ptr,							\
34  		const typeof(*(ptr)) *: ((const type *)container_of(ptr, type, member)),\
35  		default: ((type *)container_of(ptr, type, member))	\
36  	)
37  
38  #endif	/* _LINUX_CONTAINER_OF_H */
39