[PATCH bpf v4 3/4] selftests/bpf: improve unexpected success reporting in test_syctl

[Ilya Leoshkevich <iii@xxxxxxxxxxxxx>]

When tests fail because sysctl() unexpectedly succeeds, they print an
inappropriate "Unexpected failure" message and a random errno. Zero
out errno before calling sysctl() and replace the message with
"Unexpected success".

Fixes: 1f5fa9ab6e2e ("selftests/bpf: Test BPF_CGROUP_SYSCTL")
Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
---
 tools/testing/selftests/bpf/test_sysctl.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/test_sysctl.c b/tools/testing/selftests/bpf/test_sysctl.c
index 908f327839d5..106644f7e73e 100644
--- a/tools/testing/selftests/bpf/test_sysctl.c
+++ b/tools/testing/selftests/bpf/test_sysctl.c
@@ -1499,6 +1499,7 @@ static int run_test_case(int cgfd, struct sysctl_test *test)
 			goto err;
 	}
 
+	errno = 0;
 	if (access_sysctl(sysctl_path, test) == -1) {
 		if (test->result == OP_EPERM && errno == EPERM)
 			goto out;
@@ -1507,7 +1508,7 @@ static int run_test_case(int cgfd, struct sysctl_test *test)
 	}
 
 	if (test->result != SUCCESS) {
-		log_err("Unexpected failure");
+		log_err("Unexpected success");
 		goto err;
 	}
 
-- 
2.21.0