linux-kernel - Re: [PATCH 3/3] selftests: cachestat: test for cachestat availability

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Date:   Tue, 15 Aug 2023 16:25:54 -0700
From:   Nhat Pham <nphamcs@...il.com>
To:     Andre Przywara <andre.przywara@....com>
Cc:     Shuah Khan <shuah@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] selftests: cachestat: test for cachestat availability

On Tue, Aug 15, 2023 at 8:56 AM Andre Przywara <andre.przywara@....com> wrote:
>
> As cachestat is a new syscall, it won't be available on older kernels,
> for instance those running on a build machine. In this case, a run
> reports all tests as "not ok" at the moment.
Interesting - I was under the assumption that if you backported the
selftests for cachestat, you would also backport the syscall's implementation
and wiring.

But yeah, I guess if you build with !CONFIG_CACHESTAT_SYSCALL,
these tests would fail.
>
> Test for the cachestat syscall availability first, before doing further
> tests, and bail out early with a TAP SKIP comment.
>
> This also uses the opportunity to add the proper TAP headers, and add
> one check for the syscall error handling (illegal file descriptor).
Thanks for the addition!
>
> Signed-off-by: Andre Przywara <andre.przywara@....com>
> ---
>  .../selftests/cachestat/test_cachestat.c      | 22 ++++++++++++++++++-
>  1 file changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/cachestat/test_cachestat.c b/tools/testing/selftests/cachestat/test_cachestat.c
> index a5a4ac8dcb76c..77620e7ecf562 100644
> --- a/tools/testing/selftests/cachestat/test_cachestat.c
> +++ b/tools/testing/selftests/cachestat/test_cachestat.c
> @@ -15,6 +15,8 @@
>
>  #include "../kselftest.h"
>
> +#define NR_TESTS       8
> +
>  static const char * const dev_files[] = {
>         "/dev/zero", "/dev/null", "/dev/urandom",
>         "/proc/version", "/proc"
> @@ -235,7 +237,25 @@ bool test_cachestat_shmem(void)
>
>  int main(void)
>  {
> -       int ret = 0;
> +       int ret;
> +
> +       ksft_print_header();
> +
> +       ret = syscall(__NR_cachestat, -1, NULL, NULL, 0);
> +       if (ret == -1 && errno == ENOSYS) {
nit: if (ret && errno == ENOSYS) sounds cleaner, but up to you.
> +               printf("1..0 # Skipped: cachestat syscall not available\n");
nit: perhaps ksft_print_msg()?
> +               return KSFT_SKIP;
> +       }
> +
> +       ksft_set_plan(NR_TESTS);
> +
> +       if (ret == -1 && errno == EBADF) {
> +               ksft_test_result_pass("bad file descriptor recognized\n");
> +               ret = 0;
> +       } else {
> +               ksft_test_result_fail("bad file descriptor ignored\n");
> +               ret = 1;
> +       }
Nice!
>
>         for (int i = 0; i < 5; i++) {
>                 const char *dev_filename = dev_files[i];
> --
> 2.25.1
>
Nitpicking aside:
Acked-by: Nhat Pham <nphamcs@...il.com>