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libbpf: Extract common user-facing helpers

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LIBBPF_API and DECLARE_LIBBPF_OPTS are needed in many public libbpf API
headers. Extract them into libbpf_common.h to avoid unnecessary
interdependency between btf.h, libbpf.h, and bpf.h or code duplication.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191214014341.3442258-6-andriin@fb.com
This commit is contained in:
Andrii Nakryiko 2019-12-13 17:43:29 -08:00 committed by Alexei Starovoitov
parent 917f6b7b07
commit 544402d4b4
4 changed files with 44 additions and 34 deletions
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6
tools/lib/bpf/bpf.h
View File

@ -28,14 +28,12 @@
#include <stddef.h>
#include <stdint.h>
#include "libbpf_common.h"
#ifdef __cplusplus
extern "C" {
#endif
#ifndef LIBBPF_API
#define LIBBPF_API __attribute__((visibility("default")))
#endif
struct bpf_create_map_attr {
const char *name;
enum bpf_map_type map_type;

6
tools/lib/bpf/btf.h
View File

@ -8,14 +8,12 @@
#include <linux/btf.h>
#include <linux/types.h>
#include "libbpf_common.h"
#ifdef __cplusplus
extern "C" {
#endif
#ifndef LIBBPF_API
#define LIBBPF_API __attribute__((visibility("default")))
#endif
#define BTF_ELF_SEC ".BTF"
#define BTF_EXT_ELF_SEC ".BTF.ext"
#define MAPS_ELF_SEC ".maps"

28
tools/lib/bpf/libbpf.h
View File

@ -17,14 +17,12 @@
#include <sys/types.h> // for size_t
#include <linux/bpf.h>
#include "libbpf_common.h"
#ifdef __cplusplus
extern "C" {
#endif
#ifndef LIBBPF_API
#define LIBBPF_API __attribute__((visibility("default")))
#endif
enum libbpf_errno {
__LIBBPF_ERRNO__START = 4000,
@ -67,28 +65,6 @@ struct bpf_object_open_attr {
enum bpf_prog_type prog_type;
};
/* Helper macro to declare and initialize libbpf options struct
*
* This dance with uninitialized declaration, followed by memset to zero,
* followed by assignment using compound literal syntax is done to preserve
* ability to use a nice struct field initialization syntax and **hopefully**
* have all the padding bytes initialized to zero. It's not guaranteed though,
* when copying literal, that compiler won't copy garbage in literal's padding
* bytes, but that's the best way I've found and it seems to work in practice.
*
* Macro declares opts struct of given type and name, zero-initializes,
* including any extra padding, it with memset() and then assigns initial
* values provided by users in struct initializer-syntax as varargs.
*/
#define DECLARE_LIBBPF_OPTS(TYPE, NAME, ...) \
struct TYPE NAME = ({ \
memset(&NAME, 0, sizeof(struct TYPE)); \
(struct TYPE) { \
.sz = sizeof(struct TYPE), \
__VA_ARGS__ \
}; \
})
struct bpf_object_open_opts {
/* size of this struct, for forward/backward compatiblity */
size_t sz;

38
tools/lib/bpf/libbpf_common.h Normal file
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@ -0,0 +1,38 @@
/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
/*
* Common user-facing libbpf helpers.
*
* Copyright (c) 2019 Facebook
*/
#ifndef __LIBBPF_LIBBPF_COMMON_H
#define __LIBBPF_LIBBPF_COMMON_H
#ifndef LIBBPF_API
#define LIBBPF_API __attribute__((visibility("default")))
#endif
/* Helper macro to declare and initialize libbpf options struct
*
* This dance with uninitialized declaration, followed by memset to zero,
* followed by assignment using compound literal syntax is done to preserve
* ability to use a nice struct field initialization syntax and **hopefully**
* have all the padding bytes initialized to zero. It's not guaranteed though,
* when copying literal, that compiler won't copy garbage in literal's padding
* bytes, but that's the best way I've found and it seems to work in practice.
*
* Macro declares opts struct of given type and name, zero-initializes,
* including any extra padding, it with memset() and then assigns initial
* values provided by users in struct initializer-syntax as varargs.
*/
#define DECLARE_LIBBPF_OPTS(TYPE, NAME, ...) \
struct TYPE NAME = ({ \
memset(&NAME, 0, sizeof(struct TYPE)); \
(struct TYPE) { \
.sz = sizeof(struct TYPE), \
__VA_ARGS__ \
}; \
})
#endif /* __LIBBPF_LIBBPF_COMMON_H */