libbpf: add API to load extra BTF

Add btf__load_btf_extra() function to load extra BTF relative to
base passed in.  Base can be vmlinux or module BTF.

Signed-off-by: Alan Maguire <[email protected]>

Author: alan-maguire

tools/lib/bpf/btf.c

@@ -5783,6 +5783,14 @@ struct btf *btf__load_module_btf(const char *module_name, struct btf *vmlinux_bt
 	return btf__parse_split(path, vmlinux_btf);
 }
 
+struct btf *btf__load_btf_extra(const char *name, struct btf *base)
+{
+	char path[80];
+
+	snprintf(path, sizeof(path), "/sys/kernel/btf_extra/%s", name);
+	return btf__parse_split(path, base);
+}
+
 int btf_ext_visit_type_ids(struct btf_ext *btf_ext, type_id_visit_fn visit, void *ctx)
 {
 	const struct btf_ext_info *seg;

tools/lib/bpf/btf.h

@@ -138,6 +138,7 @@ LIBBPF_API struct btf *btf__parse_raw_split(const char *path, struct btf *base_b
 
 LIBBPF_API struct btf *btf__load_vmlinux_btf(void);
 LIBBPF_API struct btf *btf__load_module_btf(const char *module_name, struct btf *vmlinux_btf);
+LIBBPF_API struct btf *btf__load_btf_extra(const char *name, struct btf *base);
 
 LIBBPF_API struct btf *btf__load_from_kernel_by_id(__u32 id);
 LIBBPF_API struct btf *btf__load_from_kernel_by_id_split(__u32 id, struct btf *base_btf);

tools/lib/bpf/libbpf.map

@@ -456,4 +456,5 @@ LIBBPF_1.7.0 {
 		btf__add_loc_proto_param;
 		btf__add_locsec;
 		btf__add_locsec_loc;
+		btf__load_btf_extra;
 } LIBBPF_1.6.0;