libbpf: Rename btf__get_from_id() as btf__load_from_kernel_by_id()

Rename function btf__get_from_id() as btf__load_from_kernel_by_id() to
better indicate what the function does. Change the new function so that,
instead of requiring a pointer to the pointer to update and returning
with an error code, it takes a single argument (the id of the BTF
object) and returns the corresponding pointer. This is more in line with
the existing constructors.

The other tools calling the (soon-to-be) deprecated btf__get_from_id()
function will be updated in a future commit.

References:

- https://github.com/libbpf/libbpf/issues/278
- https://github.com/libbpf/libbpf/wiki/Libbpf:-the-road-to-v1.0#btfh-apisSigned-off-by: Quentin Monnet <quentin@isovalent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20210729162028.29512-4-quentin@isovalent.com

tools/lib/bpf/btf.c

@@ -1383,21 +1383,30 @@ struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf)
 	return btf;
 }
 
-int btf__get_from_id(__u32 id, struct btf **btf)
+struct btf *btf__load_from_kernel_by_id(__u32 id)
 {
-	struct btf *res;
-	int err, btf_fd;
+	struct btf *btf;
+	int btf_fd;
 
-	*btf = NULL;
 	btf_fd = bpf_btf_get_fd_by_id(id);
 	if (btf_fd < 0)
-		return libbpf_err(-errno);
-
-	res = btf_get_from_fd(btf_fd, NULL);
-	err = libbpf_get_error(res);
+		return libbpf_err_ptr(-errno);
 
+	btf = btf_get_from_fd(btf_fd, NULL);
 	close(btf_fd);
 
+	return libbpf_ptr(btf);
+}
+
+int btf__get_from_id(__u32 id, struct btf **btf)
+{
+	struct btf *res;
+	int err;
+
+	*btf = NULL;
+	res = btf__load_from_kernel_by_id(id);
+	err = libbpf_get_error(res);
+
 	if (err)
 		return libbpf_err(err);
 

tools/lib/bpf/btf.h

@@ -44,6 +44,9 @@ LIBBPF_API struct btf *btf__parse_elf_split(const char *path, struct btf *base_b
 LIBBPF_API struct btf *btf__parse_raw(const char *path);
 LIBBPF_API struct btf *btf__parse_raw_split(const char *path, struct btf *base_btf);
 
+LIBBPF_API struct btf *btf__load_from_kernel_by_id(__u32 id);
+LIBBPF_API int btf__get_from_id(__u32 id, struct btf **btf);
+
 LIBBPF_API int btf__finalize_data(struct bpf_object *obj, struct btf *btf);
 LIBBPF_API int btf__load(struct btf *btf);
 LIBBPF_API int btf__load_into_kernel(struct btf *btf);
@@ -67,7 +70,6 @@ LIBBPF_API void btf__set_fd(struct btf *btf, int fd);
 LIBBPF_API const void *btf__get_raw_data(const struct btf *btf, __u32 *size);
 LIBBPF_API const char *btf__name_by_offset(const struct btf *btf, __u32 offset);
 LIBBPF_API const char *btf__str_by_offset(const struct btf *btf, __u32 offset);
-LIBBPF_API int btf__get_from_id(__u32 id, struct btf **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,

tools/lib/bpf/libbpf.c

@@ -8316,7 +8316,7 @@ static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
 {
 	struct bpf_prog_info_linear *info_linear;
 	struct bpf_prog_info *info;
-	struct btf *btf = NULL;
+	struct btf *btf;
 	int err;
 
 	info_linear = bpf_program__get_prog_info_linear(attach_prog_fd, 0);
@@ -8333,7 +8333,8 @@ static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
 		pr_warn("The target program doesn't have BTF\n");
 		goto out;
 	}
-	if (btf__get_from_id(info->btf_id, &btf)) {
+	btf = btf__load_from_kernel_by_id(info->btf_id);
+	if (libbpf_get_error(btf)) {
 		pr_warn("Failed to get BTF of the program\n");
 		goto out;
 	}

tools/lib/bpf/libbpf.map

@@ -375,6 +375,7 @@ LIBBPF_0.5.0 {
 		bpf_map_lookup_and_delete_elem_flags;
 		bpf_program__attach_kprobe_opts;
 		bpf_object__gen_loader;
+		btf__load_from_kernel_by_id;
 		btf__load_into_kernel;
 		btf_dump__dump_type_data;
 		libbpf_set_strict_mode;