libbpf: Introduce bpf_object__btf

Add new accessor for bpf_object to get opaque struct btf * from it.

struct btf * is needed for all operations with BTF and it's present in
bpf_object. The only thing missing is a way to get it.

Example use-case is to get BTF key_type_id and value_type_id for a map in
bpf_object. It can be done with btf__get_map_kv_tids() but that function
requires struct btf *.

Similar API can be added for struct btf_ext but no use-case for it yet.

Signed-off-by: Andrey Ignatov <rdna@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/lib/bpf/libbpf.c

@@ -2331,6 +2331,11 @@ unsigned int bpf_object__kversion(struct bpf_object *obj)
 	return obj ? obj->kern_version : 0;
 }
 
+struct btf *bpf_object__btf(struct bpf_object *obj)
+{
+	return obj ? obj->btf : NULL;
+}
+
 int bpf_object__btf_fd(const struct bpf_object *obj)
 {
 	return obj->btf ? btf__fd(obj->btf) : -1;

tools/lib/bpf/libbpf.h

@@ -89,6 +89,9 @@ LIBBPF_API int bpf_object__load(struct bpf_object *obj);
 LIBBPF_API int bpf_object__unload(struct bpf_object *obj);
 LIBBPF_API const char *bpf_object__name(struct bpf_object *obj);
 LIBBPF_API unsigned int bpf_object__kversion(struct bpf_object *obj);
+
+struct btf;
+LIBBPF_API struct btf *bpf_object__btf(struct bpf_object *obj);
 LIBBPF_API int bpf_object__btf_fd(const struct bpf_object *obj);
 
 LIBBPF_API struct bpf_program *

tools/lib/bpf/libbpf.map

@@ -132,6 +132,7 @@ LIBBPF_0.0.2 {
 		bpf_probe_prog_type;
 		bpf_map__resize;
 		bpf_map_lookup_elem_flags;
+		bpf_object__btf;
 		bpf_object__find_map_fd_by_name;
 		bpf_get_link_xdp_id;
 		btf__dedup;