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