[PATCH bpf-next 5/6] libbpf: add split BTF support for btf__load_from_kernel_by_id()

[Quentin Monnet <quentin@isovalent.com>]

Add a new API function btf__load_from_kernel_by_id_split(), which takes
a pointer to a base BTF object in order to support split BTF objects
when retrieving BTF information from the kernel.

Reference: https://github.com/libbpf/libbpf/issues/314

Signed-off-by: Quentin Monnet <quentin@isovalent.com>
---
 tools/lib/bpf/btf.c      | 10 ++++++++--
 tools/lib/bpf/btf.h      |  2 ++
 tools/lib/bpf/libbpf.map |  1 +
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 05b63b63083a..15967dd80ffb 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -1383,7 +1383,8 @@ struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf)
 	return btf;
 }
 
-int btf__load_from_kernel_by_id(__u32 id, struct btf **btf)
+int btf__load_from_kernel_by_id_split(__u32 id, struct btf **btf,
+				      struct btf *base_btf)
 {
 	struct btf *res;
 	int err, btf_fd;
@@ -1393,7 +1394,7 @@ int btf__load_from_kernel_by_id(__u32 id, struct btf **btf)
 	if (btf_fd < 0)
 		return libbpf_err(-errno);
 
-	res = btf_get_from_fd(btf_fd, NULL);
+	res = btf_get_from_fd(btf_fd, base_btf);
 	err = libbpf_get_error(res);
 
 	close(btf_fd);
@@ -1407,6 +1408,11 @@ int btf__load_from_kernel_by_id(__u32 id, struct btf **btf)
 int btf__get_from_id(__u32, struct btf **)
 	__attribute__((alias("btf__load_from_kernel_by_id")));
 
+int btf__load_from_kernel_by_id(__u32 id, struct btf **btf)
+{
+	return btf__load_from_kernel_by_id_split(id, btf, NULL);
+}
+
 int btf__get_map_kv_tids(const struct btf *btf, const char *map_name,
 			 __u32 expected_key_size, __u32 expected_value_size,
 			 __u32 *key_type_id, __u32 *value_type_id)
diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
index 522277b16a88..62291d3cc9c6 100644
--- a/tools/lib/bpf/btf.h
+++ b/tools/lib/bpf/btf.h
@@ -71,6 +71,8 @@ LIBBPF_API const char *btf__str_by_offset(const struct btf *btf, __u32 offset);
 LIBBPF_API LIBBPF_DEPRECATED("the name was confusing and will be removed in the future libbpf versions, please use btf__load_from_kernel_by_id() instead")
 int btf__get_from_id(__u32 id, struct btf **btf);
 LIBBPF_API int btf__load_from_kernel_by_id(__u32 id, struct btf **btf);
+LIBBPF_API int btf__load_from_kernel_by_id_split(__u32 id, struct btf **btf,
+						 struct btf *base_btf);
 LIBBPF_API int btf__get_map_kv_tids(const struct btf *btf, const char *map_name,
 				    __u32 expected_key_size,
 				    __u32 expected_value_size,
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index a687cc63cd80..f8420a6d7872 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -379,5 +379,6 @@ LIBBPF_0.5.0 {
 LIBBPF_0.6.0 {
 	global:
 		btf__load_from_kernel_by_id;
+		btf__load_from_kernel_by_id_split;
 		btf__load_into_kernel;
 } LIBBPF_0.5.0;
-- 
2.30.2