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

["Jiayuan Chen" <jiayuan.chen@linux.dev>]

March 9, 2026 at 18:44, "Sun Jian" <sun.jian.kdev@gmail.com mailto:sun.jian.kdev@gmail.com?to=%22Sun%20Jian%22%20%3Csun.jian.kdev%40gmail.com%3E > wrote:


> 
> 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;
> + }
>  


I think Jiri's suggestion in v2 means that you should drop the path check 
here and in unload_livepatch() and just keep checking -ENOENT.

-ENOENT returned by load_livepatch() means the ko doesn't exist,
which happens when either CONFIG_LIVEPATCH is disabled or livepatch_sample 
is not compiled.


>  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
>