1/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
2#ifndef _LINUX_STDDEF_H
3#define _LINUX_STDDEF_H
4
5
6
7#ifndef __always_inline
8#define __always_inline __inline__
9#endif
10
11/**
12 * __struct_group() - Create a mirrored named and anonyomous struct
13 *
14 * @TAG: The tag name for the named sub-struct (usually empty)
15 * @NAME: The identifier name of the mirrored sub-struct
16 * @ATTRS: Any struct attributes (usually empty)
17 * @MEMBERS: The member declarations for the mirrored structs
18 *
19 * Used to create an anonymous union of two structs with identical layout
20 * and size: one anonymous and one named. The former's members can be used
21 * normally without sub-struct naming, and the latter can be used to
22 * reason about the start, end, and size of the group of struct members.
23 * The named struct can also be explicitly tagged for layer reuse, as well
24 * as both having struct attributes appended.
25 */
26#define __struct_group(TAG, NAME, ATTRS, MEMBERS...) \
27 union { \
28 struct { MEMBERS } ATTRS; \
29 struct TAG { MEMBERS } ATTRS NAME; \
30 }
31
32/**
33 * __DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
34 *
35 * @TYPE: The type of each flexible array element
36 * @NAME: The name of the flexible array member
37 *
38 * In order to have a flexible array member in a union or alone in a
39 * struct, it needs to be wrapped in an anonymous struct with at least 1
40 * named member, but that member can be empty.
41 */
42#define __DECLARE_FLEX_ARRAY(TYPE, NAME) \
43 struct { \
44 struct { } __empty_ ## NAME; \
45 TYPE NAME[]; \
46 }
47#endif
48

source code of include/linux/stddef.h