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

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Message-ID: <CAC1kPDPg0AN9Ft3SNM6JDcZf=XD1oinqeAMzuRpZF3nzemZ=Kg@mail.gmail.com>
Date: Thu, 19 Jun 2025 15:46:43 +0800
From: Chen Linxuan <chenlinxuan@...ontech.com>
To: Shuah Khan <skhan@...uxfoundation.org>
Cc: Chen Linxuan <chenlinxuan@...ontech.com>, 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
Subject: Re: [PATCH RESEND] selftests: Suppress unused variable warning

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.

>
>
> >               unshare(CLONE_NEWNS);
> >               mount("", "/", NULL, MS_REC|MS_PRIVATE, NULL);
> >               umount2("/a", MNT_DETACH);
>
> thanks,
> -- Shuah
>
>