stddef.h

  1/* SPDX-License-Identifier: GPL-2.0 */
  2#ifndef _LINUX_STDDEF_H
  3#define _LINUX_STDDEF_H
  4
  5#include <uapi/linux/stddef.h>
  6
  7#undef NULL
  8#define NULL ((void *)0)
  9
 10enum {
 11	false	= 0,
 12	true	= 1
 13};
 14
 15#undef offsetof
 16#define offsetof(TYPE, MEMBER)	__builtin_offsetof(TYPE, MEMBER)
 17
 18/**
 19 * sizeof_field() - Report the size of a struct field in bytes
 20 *
 21 * @TYPE: The structure containing the field of interest
 22 * @MEMBER: The field to return the size of
 23 */
 24#define sizeof_field(TYPE, MEMBER) sizeof((((TYPE *)0)->MEMBER))
 25
 26/**
 27 * offsetofend() - Report the offset of a struct field within the struct
 28 *
 29 * @TYPE: The type of the structure
 30 * @MEMBER: The member within the structure to get the end offset of
 31 */
 32#define offsetofend(TYPE, MEMBER) \
 33	(offsetof(TYPE, MEMBER)	+ sizeof_field(TYPE, MEMBER))
 34
 35/**
 36 * struct_group() - Wrap a set of declarations in a mirrored struct
 37 *
 38 * @NAME: The identifier name of the mirrored sub-struct
 39 * @MEMBERS: The member declarations for the mirrored structs
 40 *
 41 * Used to create an anonymous union of two structs with identical
 42 * layout and size: one anonymous and one named. The former can be
 43 * used normally without sub-struct naming, and the latter can be
 44 * used to reason about the start, end, and size of the group of
 45 * struct members.
 46 */
 47#define struct_group(NAME, MEMBERS...)	\
 48	__struct_group(/* no tag */, NAME, /* no attrs */, MEMBERS)
 49
 50/**
 51 * struct_group_attr() - Create a struct_group() with trailing attributes
 52 *
 53 * @NAME: The identifier name of the mirrored sub-struct
 54 * @ATTRS: Any struct attributes to apply
 55 * @MEMBERS: The member declarations for the mirrored structs
 56 *
 57 * Used to create an anonymous union of two structs with identical
 58 * layout and size: one anonymous and one named. The former can be
 59 * used normally without sub-struct naming, and the latter can be
 60 * used to reason about the start, end, and size of the group of
 61 * struct members. Includes structure attributes argument.
 62 */
 63#define struct_group_attr(NAME, ATTRS, MEMBERS...) \
 64	__struct_group(/* no tag */, NAME, ATTRS, MEMBERS)
 65
 66/**
 67 * struct_group_tagged() - Create a struct_group with a reusable tag
 68 *
 69 * @TAG: The tag name for the named sub-struct
 70 * @NAME: The identifier name of the mirrored sub-struct
 71 * @MEMBERS: The member declarations for the mirrored structs
 72 *
 73 * Used to create an anonymous union of two structs with identical
 74 * layout and size: one anonymous and one named. The former can be
 75 * used normally without sub-struct naming, and the latter can be
 76 * used to reason about the start, end, and size of the group of
 77 * struct members. Includes struct tag argument for the named copy,
 78 * so the specified layout can be reused later.
 79 */
 80#define struct_group_tagged(TAG, NAME, MEMBERS...) \
 81	__struct_group(TAG, NAME, /* no attrs */, MEMBERS)
 82
 83/**
 84 * DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
 85 *
 86 * @TYPE: The type of each flexible array element
 87 * @NAME: The name of the flexible array member
 88 *
 89 * In order to have a flexible array member in a union or alone in a
 90 * struct, it needs to be wrapped in an anonymous struct with at least 1
 91 * named member, but that member can be empty.
 92 */
 93#define DECLARE_FLEX_ARRAY(TYPE, NAME) \
 94	__DECLARE_FLEX_ARRAY(TYPE, NAME)
 95
 96/**
 97 * __TRAILING_OVERLAP() - Overlap a flexible-array member with trailing
 98 *			  members.
 99 *
100 * Creates a union between a flexible-array member (FAM) in a struct and a set
101 * of additional members that would otherwise follow it.
102 *
103 * @TYPE: Flexible structure type name, including "struct" keyword.
104 * @NAME: Name for a variable to define.
105 * @FAM: The flexible-array member within @TYPE
106 * @ATTRS: Any struct attributes (usually empty)
107 * @MEMBERS: Trailing overlapping members.
108 */
109#define __TRAILING_OVERLAP(TYPE, NAME, FAM, ATTRS, MEMBERS)			\
110	union {									\
111		TYPE NAME;							\
112		struct {							\
113			unsigned char __offset_to_FAM[offsetof(TYPE, FAM)];	\
114			MEMBERS							\
115		} ATTRS;							\
116	}
117
118/**
119 * TRAILING_OVERLAP() - Overlap a flexible-array member with trailing members.
120 *
121 * Creates a union between a flexible-array member (FAM) in a struct and a set
122 * of additional members that would otherwise follow it.
123 *
124 * @TYPE: Flexible structure type name, including "struct" keyword.
125 * @NAME: Name for a variable to define.
126 * @FAM: The flexible-array member within @TYPE
127 * @MEMBERS: Trailing overlapping members.
128 */
129#define TRAILING_OVERLAP(TYPE, NAME, FAM, MEMBERS)				\
130	__TRAILING_OVERLAP(TYPE, NAME, FAM, /* no attrs */, MEMBERS)
131
132#endif