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

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Message-ID: <91817e12-54c4-4241-b895-2e452a00e0c4@nvidia.com>
Date: Thu, 19 Jun 2025 12:00:58 -0700
From: John Hubbard <jhubbard@...dia.com>
To: Shuah Khan <skhan@...uxfoundation.org>,
 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
Subject: Re: [PATCH RESEND] selftests: Suppress unused variable warning

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.

> 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.
> 
> thanks,
> -- Shuah
> 
> 

thanks,
-- 
John Hubbard