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

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Date:   Wed, 16 Aug 2023 11:11:49 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Andre Przywara <andre.przywara@....com>,
        Shuah Khan <shuah@...nel.org>, Nhat Pham <nphamcs@...il.com>,
        Johannes Weiner <hannes@...xchg.org>
Cc:     linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH 3/3] selftests: cachestat: test for cachestat availability

On 8/15/23 09:56, Andre Przywara 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.
> 
> 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).
> 
> 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) {
> +		printf("1..0 # Skipped: cachestat syscall not available\n");
> +		return KSFT_SKIP;
What happens when other errors besides ENOSYS? The test shouldn't
continue.

> +	}
> +
> +	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;
> +	}
>   
>   	for (int i = 0; i < 5; i++) {
>   		const char *dev_filename = dev_files[i];

thanks,
-- Shuah