[PATCH v4 bpf-next] selftests/bpf: livepatch_trampoline: skip when prerequisites are missing

[Sun Jian <sun.jian.kdev@gmail.com>]

livepatch_trampoline relies on livepatch sysfs and livepatch-sample.ko.
When CONFIG_LIVEPATCH is disabled or the samples module isn't built, the
test fails with ENOENT and causes false failures in minimal CI configs.

Skip the test when livepatch sysfs or the sample module is unavailable.
Also avoid writing to livepatch sysfs when it's not present.

Signed-off-by: Sun Jian <sun.jian.kdev@gmail.com>
---
v4:
  - Drop redundant <errno.h> and <unistd.h> includes; both are already included by test_progs.h (per Jiayuan Chen)
  - Tested: ./test_progs -t livepatch_trampoline -vv (SKIP when livepatch-sample.ko missing)

v3:
  - Skip on -ENOENT from load_livepatch() instead of duplicating module path logic (suggested by Jiri Olsa)
  - Tested: ./test_progs -t livepatch_trampoline (SKIP when livepatch-sample.ko missing)

v2:
  - Skip when /sys/kernel/livepatch is missing
  - Guard sysfs write in unload_livepatch() when enabled knob is absent

v3: https://lore.kernel.org/bpf/20260309033712.728133-1-sun.jian.kdev@gmail.com/
v2: https://patchwork.kernel.org/project/netdevbpf/patch/20260305030258.5273-1-sun.jian.kdev@gmail.com/
v1: https://patchew.org/linux/20260227042354.20926-1-sun.jian.kdev@gmail.com/

 .../bpf/prog_tests/livepatch_trampoline.c     | 20 +++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/livepatch_trampoline.c b/tools/testing/selftests/bpf/prog_tests/livepatch_trampoline.c
index 72aa5376c30e..0a12af924a99 100644
--- a/tools/testing/selftests/bpf/prog_tests/livepatch_trampoline.c
+++ b/tools/testing/selftests/bpf/prog_tests/livepatch_trampoline.c
@@ -5,6 +5,8 @@
 #include "testing_helpers.h"
 #include "livepatch_trampoline.skel.h"
 
+#define LIVEPATCH_ENABLED_PATH "/sys/kernel/livepatch/livepatch_sample/enabled"
+
 static int load_livepatch(void)
 {
 	char path[4096];
@@ -19,7 +21,8 @@ static int load_livepatch(void)
 static void unload_livepatch(void)
 {
 	/* Disable the livepatch before unloading the module */
-	system("echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled");
+	if (!access(LIVEPATCH_ENABLED_PATH, F_OK))
+		system("echo 0 > " LIVEPATCH_ENABLED_PATH);
 
 	unload_module("livepatch_sample", env_verbosity > VERBOSE_NONE);
 }
@@ -81,9 +84,22 @@ static void __test_livepatch_trampoline(bool fexit_first)
 void test_livepatch_trampoline(void)
 {
 	int retry_cnt = 0;
+	int err;
+
+	/* Skip if kernel was built without CONFIG_LIVEPATCH */
+	if (access("/sys/kernel/livepatch", F_OK)) {
+		test__skip();
+		return;
+	}
 
 retry:
-	if (load_livepatch()) {
+	err = load_livepatch();
+	if (err) {
+		if (err == -ENOENT) {
+			test__skip();
+			return;
+		}
+
 		if (retry_cnt) {
 			ASSERT_OK(1, "load_livepatch");
 			goto out;

base-commit: 1f318b96cc84d7c2ab792fcc0bfd42a7ca890681
-- 
2.43.0