[v2] selftests/bpf: Fix the issue where the error code is 0

[PATCH v2 bpf-next] selftests/bpf: Fix the issue where the error code is 0

Posted by Feng Yang 1 month ago

From: Feng Yang <yangfeng@kylinos.cn>

The error message printed here only uses the previous err value,
which results in it being printed as 0.
Fix this issue by using libbpf_get_error to retrieve the error.

Fix before:
run_subtest:FAIL:1019 bpf_map__attach_struct_ops failed for map pro_epilogue: err=0

Fix after:
run_subtest:FAIL:1019 bpf_map__attach_struct_ops failed for map pro_epilogue: err=-9

Signed-off-by: Feng Yang <yangfeng@kylinos.cn>
---
Changes in v2:
- Use libbpf_get_error, thanks: Alexei Starovoitov.
- Link to v1: https://lore.kernel.org/all/20250828081507.1380218-1-yangfeng59949@163.com/
---
 tools/testing/selftests/bpf/test_loader.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/test_loader.c b/tools/testing/selftests/bpf/test_loader.c
index 78423cf89e01..b8e102eb0908 100644
--- a/tools/testing/selftests/bpf/test_loader.c
+++ b/tools/testing/selftests/bpf/test_loader.c
@@ -1082,8 +1082,8 @@ void run_subtest(struct test_loader *tester,
 			}
 			link = bpf_map__attach_struct_ops(map);
 			if (!link) {
-				PRINT_FAIL("bpf_map__attach_struct_ops failed for map %s: err=%d\n",
-					   bpf_map__name(map), err);
+				PRINT_FAIL("bpf_map__attach_struct_ops failed for map %s: err=%ld\n",
+					   bpf_map__name(map), libbpf_get_error(link));
 				goto tobj_cleanup;
 			}
 			links[links_cnt++] = link;
-- 
2.25.1

Re: [PATCH v2 bpf-next] selftests/bpf: Fix the issue where the error code is 0

Posted by Andrii Nakryiko 3 weeks, 6 days ago

On Thu, Aug 28, 2025 at 6:41 PM Feng Yang <yangfeng59949@163.com> wrote:
>
> From: Feng Yang <yangfeng@kylinos.cn>
>
> The error message printed here only uses the previous err value,
> which results in it being printed as 0.
> Fix this issue by using libbpf_get_error to retrieve the error.
>
> Fix before:
> run_subtest:FAIL:1019 bpf_map__attach_struct_ops failed for map pro_epilogue: err=0
>
> Fix after:
> run_subtest:FAIL:1019 bpf_map__attach_struct_ops failed for map pro_epilogue: err=-9
>
> Signed-off-by: Feng Yang <yangfeng@kylinos.cn>
> ---
> Changes in v2:
> - Use libbpf_get_error, thanks: Alexei Starovoitov.
> - Link to v1: https://lore.kernel.org/all/20250828081507.1380218-1-yangfeng59949@163.com/
> ---
>  tools/testing/selftests/bpf/test_loader.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/test_loader.c b/tools/testing/selftests/bpf/test_loader.c
> index 78423cf89e01..b8e102eb0908 100644
> --- a/tools/testing/selftests/bpf/test_loader.c
> +++ b/tools/testing/selftests/bpf/test_loader.c
> @@ -1082,8 +1082,8 @@ void run_subtest(struct test_loader *tester,
>                         }
>                         link = bpf_map__attach_struct_ops(map);
>                         if (!link) {
> -                               PRINT_FAIL("bpf_map__attach_struct_ops failed for map %s: err=%d\n",
> -                                          bpf_map__name(map), err);
> +                               PRINT_FAIL("bpf_map__attach_struct_ops failed for map %s: err=%ld\n",
> +                                          bpf_map__name(map), libbpf_get_error(link));

since libbpf 1.0 all that libbpf_get_error() is doing is returning
-errno if link is NULL. It's kind of discouraged now because it's too
easy to miss its reliance on errno. So let's use -errno here directly.

pw-bot: cr

>                                 goto tobj_cleanup;
>                         }
>                         links[links_cnt++] = link;
> --
> 2.25.1
>