Re: [Xen-devel] [PATCH 12/12] xen-blkfront: Avoid that gcc 7 warns about fall-through when building with W=1

[Roger Pau Monn303251 <roger.pau@xxxxxxxxxx>]

On Fri, Aug 18, 2017 at 12:46:23PM +0100, Anthony PERARD wrote:
> On Fri, Aug 18, 2017 at 09:54:01AM +0100, Roger Pau Monn303251 wrote:
> > On Thu, Aug 17, 2017 at 04:23:11PM -0700, Bart Van Assche wrote:
> > > Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxx>
> > > Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > > Cc: Roger Pau Monn303251 <roger.pau@xxxxxxxxxx>
> > > Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
> > > ---
> > >  drivers/block/xen-blkfront.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> > > index 98e34e4c62b8..270019e3e5d8 100644
> > > --- a/drivers/block/xen-blkfront.c
> > > +++ b/drivers/block/xen-blkfront.c
> > > @@ -2456,7 +2456,7 @@ static void blkback_changed(struct xenbus_device 
> > > *dev,
> > >   case XenbusStateClosed:
> > >           if (dev->state == XenbusStateClosed)
> > >                   break;
> > > -         /* Missed the backend's Closing state -- fallthrough */
> > > +         /* fall through */
> > 
> > This is losing information present in the original comment. Would
> > splitting the comment into two make gcc happy?
> 
> What about:
> 
> -             /* Missed the backend's Closing state -- fallthrough */
> +             /* fallthrough -- Missed the backend's Closing state */
> 
> FIY:
> https://gcc.gnu.org/onlinedocs/gcc-7.2.0/gcc/Warning-Options.html#index-Wimplicit-fallthrough
> 
> A dash seems to be needed between "fall through" and a extra comment,
> with fallthrough first.

I think so, according to the documentation -Wimplicit-fallthrough=3 is
enabled with -Wextra, and requires having "fallthrough" first. Your
proposed change seems fine to me.

Roger.

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