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/* SPDX-License-Identifier: GPL-2.0 */
/**
* @file container_of.h
* @brief Provides type-aware container and member offset macros.
*/
#ifndef _CONTAINER_OF_H
#define _CONTAINER_OF_H
#include <stddef.h>
/** @brief Checks whether two expressions have compatible types. */
#define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
/** @brief Computes a member offset using the compiler builtin. */
#undef offsetof
#define offsetof(TYPE, MEMBER) __builtin_offsetof(TYPE, MEMBER)
/** @brief Obtains the type of a member of a structure type. */
#define typeof_member(T, m) typeof(((T*)0)->m)
/**
* @brief Converts a pointer to a structure member to its containing object.
* @param ptr A pointer to the member.
* @param type The type of the containing structure.
* @param member The member name within `type`.
*
* The macro performs a compile-time type compatibility check before applying
* the member offset.
*/
#define container_of(ptr, type, member) ({ \
_Static_assert(__same_type(*(ptr), typeof_member(type, member)) || \
__same_type(*(ptr), void), \
"pointer type mismatch in container_of()"); \
(type *)((void *)(ptr) - offsetof(type, member)); })
/**
* @brief Converts a member pointer while preserving its const qualification.
* @param ptr A pointer to the member.
* @param type The type of the containing structure.
* @param member The member name within `type`.
*/
#define container_of_const(ptr, type, member) \
_Generic(ptr, \
const typeof(*(ptr)) *: ((const type *)container_of(ptr, type, member)),\
default: ((type *)container_of(ptr, type, member)) \
)
#endif /* _CONTAINER_OF_H */
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