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From:   Arnd Bergmann <arnd@kernel.org>
Date:   Mon, 22 Mar 2021 19:24:51 +0100
Message-ID: <CAK8P3a3hQKASNVp0VsFYteGh6Mav3=iNZT5n2eWzFieH0hpXjQ@mail.gmail.com>
Subject: Re: [PATCH] audit: avoid -Wempty-body warning
To:     Richard Guy Briggs <rgb@redhat.com>
Cc:     Paul Moore <paul@paul-moore.com>, Eric Paris <eparis@redhat.com>,
        Jules Irenge <jbi.octave@gmail.com>, linux-audit@redhat.com,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Mon, Mar 22, 2021 at 6:58 PM Richard Guy Briggs <rgb@redhat.com> wrote:
>
> On 2021-03-22 17:28, Arnd Bergmann wrote:
> > On Mon, Mar 22, 2021 at 3:33 PM Richard Guy Briggs <rgb@redhat.com> wrote:
> > > > Change the macros to use the usual "do { } while (0)" instead, and change a
> > > > few more that were (void)0, for consistency.
> > >
> > > So what about audit_put_watch() and audit_get_watch() which are set to
> > > {}?   (And all of include/linux/audit.h that uses the latter...)  Does
> > > this only matter if they are the only action called in an if or loop?
> >
> > I missed those, thanks for pointing it out. I sent a v2 patch now.
>
> Ok, cool, that looks more consistent.  Can you answer my question about
> include/linux/audit.h and exactly what conditions require
> "do { } while (0)" over "{ }"?

This is the usual way of constructing a C expression that can be used
e.g. in

   if (x)
          foo();
   else
          bar();

If foo() is defined as '{}', this causes a syntax error.

         Arnd