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

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Message-ID: <265ebc1f-b0c0-4c57-92b2-41714469c7f5@linuxfoundation.org>
Date: Thu, 19 Jun 2025 11:00:25 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: Chen Linxuan <chenlinxuan@...ontech.com>
Cc: Shuah Khan <shuah@...nel.org>, Christian Brauner <brauner@...nel.org>,
 Amir Goldstein <amir73il@...il.com>, John Hubbard <jhubbard@...dia.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 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:
>>> When running `make kselftest`, the following compilation warning was encountered:
>>>
>>> mount-notify_test.c: In function ‘fanotify_rmdir’:
>>> mount-notify_test.c:490:17: warning: ignoring return value of ‘chdir’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
>>>     490 |                 chdir("/");
>>>         |                 ^~~~~~~~~~
>>>
>>> This patch addresses the warning by
>>> explicitly suppressing the unused result of the `chdir` function.
>>>
>>> Signed-off-by: Chen Linxuan <chenlinxuan@...ontech.com>
>>> ---
>>>    .../selftests/filesystems/mount-notify/mount-notify_test.c    | 4 +++-
>>>    1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> 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("/");
>>>> 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.

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