libbpf: fix check for presence of associated BTF for map creation

Kernel internally checks that either key or value type ID is specified,
before using btf_fd. Do the same in libbpf's map creation code for
determining when to retry map creation w/o BTF.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: fba01a06 ("libbpf: use negative fd to specify missing BTF")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/lib/bpf/libbpf.c

@@ -1736,7 +1736,7 @@ bpf_object__create_maps(struct bpf_object *obj)
 		create_attr.key_size = def->key_size;
 		create_attr.value_size = def->value_size;
 		create_attr.max_entries = def->max_entries;
-		create_attr.btf_fd = -1;
+		create_attr.btf_fd = 0;
 		create_attr.btf_key_type_id = 0;
 		create_attr.btf_value_type_id = 0;
 		if (bpf_map_type__is_map_in_map(def->type) &&
@@ -1750,11 +1750,12 @@ bpf_object__create_maps(struct bpf_object *obj)
 		}
 
 		*pfd = bpf_create_map_xattr(&create_attr);
-		if (*pfd < 0 && create_attr.btf_fd >= 0) {
+		if (*pfd < 0 && (create_attr.btf_key_type_id ||
+				 create_attr.btf_value_type_id)) {
 			cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
 			pr_warning("Error in bpf_create_map_xattr(%s):%s(%d). Retrying without BTF.\n",
 				   map->name, cp, errno);
-			create_attr.btf_fd = -1;
+			create_attr.btf_fd = 0;
 			create_attr.btf_key_type_id = 0;
 			create_attr.btf_value_type_id = 0;
 			map->btf_key_type_id = 0;
@@ -2045,7 +2046,7 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
 	load_attr.license = license;
 	load_attr.kern_version = kern_version;
 	load_attr.prog_ifindex = prog->prog_ifindex;
-	load_attr.prog_btf_fd = prog->btf_fd;
+	load_attr.prog_btf_fd = prog->btf_fd >= 0 ? prog->btf_fd : 0;
 	load_attr.func_info = prog->func_info;
 	load_attr.func_info_rec_size = prog->func_info_rec_size;
 	load_attr.func_info_cnt = prog->func_info_cnt;