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 */ 42