diff mbox series

[v2,bpf-next,4/6] libbpf: Make DECLARE_LIBBPF_OPTS available in bpf.h

Message ID db7f94fd1735a28b6729a7f908c1a219af046dec.1576193131.git.rdna@fb.com
State Changes Requested
Delegated to: BPF Maintainers
Headers show
Series bpf: Support replacing cgroup-bpf program in MULTI mode | expand

Commit Message

Andrey Ignatov Dec. 12, 2019, 11:30 p.m. UTC 
DECLARE_LIBBPF_OPTS is the way to use option structures in a backward
compatible and extensible way. It's available only in libbpf.h.  Though
public interfaces in bpf.h have the same requirement  to accept options
in a way that can be simply extended w/o introducing new xattr-functions
every time.

libbpf.c depends on bpf.h, hence to share the macros a couple of options
exist:
* either a common header should be introduced;
* or the macro can be moved to bpf.h and used by libbpf.h from there;

The former seems to be an overkill, so do the latter:
* move DECLARE_LIBBPF_OPTS from libbpf.h to bpf.h;
* move `#include "bpf.h"` from libbpf.c to libbpf.h not to break users
  of the macro who already include only libbpf.h.

That makes the macro available to use in bpf.{h,c} and should not break
those who already use it.

Signed-off-by: Andrey Ignatov <rdna@fb.com>
---
 tools/lib/bpf/bpf.h    | 22 ++++++++++++++++++++++
 tools/lib/bpf/libbpf.c |  1 -
 tools/lib/bpf/libbpf.h | 24 ++----------------------
 3 files changed, 24 insertions(+), 23 deletions(-)

Comments

Andrii Nakryiko Dec. 13, 2019, 6:53 a.m. UTC | #1 
On Thu, Dec 12, 2019 at 3:34 PM Andrey Ignatov <rdna@fb.com> wrote:
>
> DECLARE_LIBBPF_OPTS is the way to use option structures in a backward
> compatible and extensible way. It's available only in libbpf.h.  Though
> public interfaces in bpf.h have the same requirement  to accept options
> in a way that can be simply extended w/o introducing new xattr-functions
> every time.
>
> libbpf.c depends on bpf.h, hence to share the macros a couple of options
> exist:
> * either a common header should be introduced;
> * or the macro can be moved to bpf.h and used by libbpf.h from there;
>
> The former seems to be an overkill, so do the latter:
> * move DECLARE_LIBBPF_OPTS from libbpf.h to bpf.h;
> * move `#include "bpf.h"` from libbpf.c to libbpf.h not to break users
>   of the macro who already include only libbpf.h.
>
> That makes the macro available to use in bpf.{h,c} and should not break
> those who already use it.
>
> Signed-off-by: Andrey Ignatov <rdna@fb.com>
> ---

LGTM.

Acked-by: Andrii Nakryiko <andriin@fb.com>

>  tools/lib/bpf/bpf.h    | 22 ++++++++++++++++++++++
>  tools/lib/bpf/libbpf.c |  1 -
>  tools/lib/bpf/libbpf.h | 24 ++----------------------
>  3 files changed, 24 insertions(+), 23 deletions(-)
>

[...]
diff mbox series

Patch

diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 3c791fa8e68e..5cfe6e0a1aef 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -36,6 +36,28 @@  extern "C" {
 #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__					    \
+		};							    \
+	})
+
 struct bpf_create_map_attr {
 	const char *name;
 	enum bpf_map_type map_type;
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 920d4e06a5f9..9d788c1b9874 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -46,7 +46,6 @@ 
 #include <gelf.h>
 
 #include "libbpf.h"
-#include "bpf.h"
 #include "btf.h"
 #include "str_error.h"
 #include "libbpf_internal.h"
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 0dbf4bfba0c4..03189880d99e 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -17,6 +17,8 @@ 
 #include <sys/types.h>  // for size_t
 #include <linux/bpf.h>
 
+#include "bpf.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -67,28 +69,6 @@  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;