Re: [PATCH 1/3] selftests/mm: check a valid fd with negative value

[Wei Yang <richard.weiyang@gmail.com>]

On Wed, Jul 16, 2025 at 10:52:21AM +0200, David Hildenbrand wrote:
>On 16.07.25 10:27, Wei Yang wrote:
>> fd 0 is usually occupied by stdin, which is not expected to be returned
>> by open(). But 0 is still a valid fd.
>> 
>> Check the valid fd with negative value like other places.
>> 
>> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
>> Cc: Rik van Riel <riel@surriel.com>
>> Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
>> Cc: Vlastimil Babka <vbabka@suse.cz>
>> Cc: Harry Yoo <harry.yoo@oracle.com>
>> ---
>>   tools/testing/selftests/mm/ksm_functional_tests.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
>> index d8bd1911dfc0..6da5c3340e10 100644
>> --- a/tools/testing/selftests/mm/ksm_functional_tests.c
>> +++ b/tools/testing/selftests/mm/ksm_functional_tests.c
>> @@ -81,7 +81,7 @@ static long get_my_ksm_zero_pages(void)
>>   	ssize_t read_size;
>>   	unsigned long my_ksm_zero_pages;
>> -	if (!proc_self_ksm_stat_fd)
>> +	if (proc_self_ksm_stat_fd < 0)
>>   		return 0;
>
>Only test_unmerge_zero_pages() calls get_my_ksm_zero_pages(). And there, we
>have
>
>if (proc_self_ksm_stat_fd < 0) {
>	ksft_test_result_skip("open(\"/proc/self/ksm_stat\") failed\n");
>	return;
>}
>
>As the fd is opened after others, we should never get fd=0.
>

You are right.

>So probably, this should just be handled as part of factoring it out, no need
>for this change upfront AFAIKS.
>

My intention of this change is, we plan to move get_my_ksm_zero_pages() into a
standalone helper and will open and check the fd there. To make following
change consistent, I split it out.

If you think it is not necessary, will drop this.

>-- 
>Cheers,
>
>David / dhildenb

-- 
Wei Yang
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