linux-kernel - Re: [PATCH] xfs: Add missing braces around xfs_scrub_agfl

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Date:   Thu, 01 Feb 2018 09:24:12 -0800
From:   Joe Perches <joe@...ches.com>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>,
        Arnd Bergmann <arnd@...db.de>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xfs: Add missing braces around xfs_scrub_agfl_info
 initializer

On Thu, 2018-02-01 at 09:08 -0800, Darrick J. Wong wrote:
> On Thu, Feb 01, 2018 at 12:31:36PM +0100, Arnd Bergmann wrote:
> > On Thu, Feb 1, 2018 at 11:23 AM, Geert Uytterhoeven
> > <geert@...ux-m68k.org> wrote:
> > > With gcc-4.1.2:
> > > 
> > >     fs/xfs/scrub/agheader.c: In function ‘xfs_scrub_agfl’:
> > >     fs/xfs/scrub/agheader.c:770: warning: missing braces around initializer
> > >     fs/xfs/scrub/agheader.c:770: warning: (near initialization for ‘sai.oinfo’)
> > > 
> > > The first member of struct xfs_scrub_agfl_info is no longer an integral
> > > type, but a struct.  Add the missing curly braces to fix this.
> > 
> > I suspect gcc-4.5 is affected as well, but not 4.6+
> > 
> > > --- a/fs/xfs/scrub/agheader.c
> > > +++ b/fs/xfs/scrub/agheader.c
> > > @@ -767,7 +767,7 @@ int
> > >  xfs_scrub_agfl(
> > >         struct xfs_scrub_context        *sc)
> > >  {
> > > -       struct xfs_scrub_agfl_info      sai = { 0 };
> > > +       struct xfs_scrub_agfl_info      sai = { { 0 } };
> > >         struct xfs_agf                  *agf;
> > 
> > Looks ok to me, but
> > 
> >         struct xfs_scrub_agfl_info      sai = { };
> > 
> > might be slightly better in case the first member changes again.
> 
> Frankly I'd rather see it changed to memset(&sai, 0, sizeof(sai)); and
> stop having to field all these gcc warnings that vary depending on
> compiler version...

trivia:

memset should also be preferred if the structure
could be copied to userspace as the "= {}" is not
guaranteed to zero any possible padding or member
alignment holes.