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

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Message-ID: <c1fd09a3-3c15-62b7-fbae-2ea04cbe06e8@linuxfoundation.org>
Date:   Thu, 17 Aug 2023 12:01:58 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Andre Przywara <andre.przywara@....com>
Cc:     Shuah Khan <shuah@...nel.org>, Nhat Pham <nphamcs@...il.com>,
        Johannes Weiner <hannes@...xchg.org>,
        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 8/17/23 08:47, Andre Przywara wrote:
> On Wed, 16 Aug 2023 11:11:49 -0600
> Shuah Khan <skhan@...uxfoundation.org> wrote:
> 
> Hi,
> 
>> 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.
> 
> -1 is an illegal file descriptor, and this is checked below (still using
> the same ret and errno), but reported using the normal framework.
> This check above is done early, before we even announce the plan, so that
> we can skip *all* of the tests, since they don't make any sense when the
> syscall is not available at all.
> 
> Does that make sense?
> 

Yup. I will apply this for Linux 6.6-rc1. You will get patchbot notification
shortly.

thanks,
-- Shuah