[PATCH v2 bpf-next] libbpf: Ensure undefined bpf_attr field stays 0

[Martin KaFai Lau <martin.lau@linux.dev>]

From: Martin KaFai Lau <martin.lau@kernel.org>

The commit 9e926acda0c2 ("libbpf: Find correct module BTFs for struct_ops maps and progs.")
sets a newly added field (value_type_btf_obj_fd) to -1 in libbpf when
the caller of the libbpf's bpf_map_create did not define this field by
passing a NULL "opts" or passing in a "opts" that does not cover this
new field. OPT_HAS(opts, field) is used to decide if the field is
defined or not:

	((opts) && opts->sz >= offsetofend(typeof(*(opts)), field))

Once OPTS_HAS decided the field is not defined, that field should
be set to 0. For this particular new field (value_type_btf_obj_fd),
its corresponding map_flags "BPF_F_VTYPE_BTF_OBJ_FD" is not set.
Thus, the kernel does not treat it as a fd field.

Cc: Kui-Feng Lee <thinker.li@gmail.com>
Reported-by: Andrii Nakryiko <andrii@kernel.org>
Fixes: 9e926acda0c2 ("libbpf: Find correct module BTFs for struct_ops maps and progs.")
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
---
v2: Improve the commit message

 tools/lib/bpf/bpf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 3a35472a17c5..b133acfe08fb 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -192,7 +192,7 @@ int bpf_map_create(enum bpf_map_type map_type,
 	attr.btf_key_type_id = OPTS_GET(opts, btf_key_type_id, 0);
 	attr.btf_value_type_id = OPTS_GET(opts, btf_value_type_id, 0);
 	attr.btf_vmlinux_value_type_id = OPTS_GET(opts, btf_vmlinux_value_type_id, 0);
-	attr.value_type_btf_obj_fd = OPTS_GET(opts, value_type_btf_obj_fd, -1);
+	attr.value_type_btf_obj_fd = OPTS_GET(opts, value_type_btf_obj_fd, 0);
 
 	attr.inner_map_fd = OPTS_GET(opts, inner_map_fd, 0);
 	attr.map_flags = OPTS_GET(opts, map_flags, 0);
-- 
2.34.1