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

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Message-Id: <20250828081507.1380218-1-yangfeng59949@163.com>
Date: Thu, 28 Aug 2025 16:15:07 +0800
From: Feng Yang <yangfeng59949@....com>
To: ast@...nel.org,
	daniel@...earbox.net,
	john.fastabend@...il.com,
	andrii@...nel.org,
	martin.lau@...ux.dev,
	eddyz87@...il.com,
	song@...nel.org,
	yonghong.song@...ux.dev,
	kpsingh@...nel.org,
	sdf@...ichev.me,
	haoluo@...gle.com,
	jolsa@...nel.org
Cc: bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: [PATCH bpf-next] selftests/bpf: Fix the issue where the error code is 0

From: Feng Yang <yangfeng@...inos.cn>

The error message printed here only uses the previous err value,
which results in it being printed as 0.
When bpf_map__attach_struct_ops encounters an error,
it uses libbpf_err_ptr(err) to set errno = -err and returns NULL.
Therefore, strerror(errno) can be used to fix this issue.

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: Bad file descriptor

Signed-off-by: Feng Yang <yangfeng@...inos.cn>
---
 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 f361c8aa1daf..686a7d7f87b1 100644
--- a/tools/testing/selftests/bpf/test_loader.c
+++ b/tools/testing/selftests/bpf/test_loader.c
@@ -1008,8 +1008,8 @@ 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: %s\n",
+					   bpf_map__name(map), strerror(errno));
 				goto tobj_cleanup;
 			}
 			links[links_cnt++] = link;
-- 
2.27.0