linux-kernel - Re: [PATCH RESEND] selftests: Suppress unused variable warning

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Message-ID: <f73fa51e-87e5-4805-bbbc-a7af9b50a1d8@linuxfoundation.org>
Date: Thu, 19 Jun 2025 15:40:46 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: John Hubbard <jhubbard@...dia.com>,
 Chen Linxuan <chenlinxuan@...ontech.com>
Cc: Shuah Khan <shuah@...nel.org>, Christian Brauner <brauner@...nel.org>,
 Amir Goldstein <amir73il@...il.com>, Miklos Szeredi <mszeredi@...hat.com>,
 Jan Kara <jack@...e.cz>, zhanjun@...ontech.com, niecheng1@...ontech.com,
 linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
 Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH RESEND] selftests: Suppress unused variable warning

On 6/19/25 13:00, John Hubbard wrote:
> On 6/19/25 10:00 AM, Shuah Khan wrote:
>> On 6/19/25 01:46, Chen Linxuan wrote:
>>> On Thu, Jun 19, 2025 at 5:23 AM Shuah Khan <skhan@...uxfoundation.org> wrote:
>>>> On 6/9/25 20:07, Chen Linxuan wrote:
> ...
>>>>> diff --git a/tools/testing/selftests/filesystems/mount-notify/mount- notify_test.c b/tools/testing/selftests/filesystems/mount-notify/ mount-notify_test.c
>>>>> index 63ce708d93ed0..34afe27b7978f 100644
>>>>> --- a/tools/testing/selftests/filesystems/mount-notify/mount- notify_test.c
>>>>> +++ b/tools/testing/selftests/filesystems/mount-notify/mount- notify_test.c
>>>>> @@ -465,7 +465,9 @@ TEST_F(fanotify, rmdir)
>>>>>        ASSERT_GE(ret, 0);
>>>>>
>>>>>        if (ret == 0) {
>>>>> -             chdir("/");
>>>>> +             // Suppress -Wunused-result
>>>>> +             // Ref: https://gcc.gnu.org/bugzilla/show_bug.cgi? id=66425#c34
>>>>> +             (void) !chdir("/");
> 
> This is quite ugly. :)
> 
>>>>>> Why not fix the problem the right way by checking the return value.
>>>> Suppressing the error isn't useful.
>>>
>>> The code is already handling cleanup in error cases,
>>> and I don't think checking the result of chdir would be useful here.
>>
> 
> Why not just fail with the appropriate test result, if chdir() fails
> here, instead of making a bit of a mess with odd void casts to a
> negated return value, and a reference to a compiler bug report?
> 
> Really, Shuah is putting you on the right path here.

Ha. I didn't ask to suppress the error with the cast. I asked
to check the return and fail.

> 
>> We check for chdir() in several tools in the kernel. Add a check for
>> it instead of suppressing the [-Wunused-result] - suppressing doesn't
>> do any good.

This is what I said.

thanks,
-- Shuah