Re: [PATCH 4/9v2] usb: host: ehci.h: fix single statement macros

[Sergei Shtylyov]

On 12/10/2015 05:56 PM, Geyslan G. Bem wrote:

> > > > > > Don't use the 'do {} while (0)' wrapper in a single statement macro.
> > > > > >
> > > > > > Caught by checkpatch: "WARNING: Single statement macros should not
> > > > > > use a do {} while (0) loop"
> > > > > >
> > > > > > Signed-off-by: Geyslan G. Bem <geyslan@xxxxxxxxx>
> > > > > > ---
> > > > > >     drivers/usb/host/ehci.h | 4 ++--
> > > > > >     1 file changed, 2 insertions(+), 2 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/usb/host/ehci.h b/drivers/usb/host/ehci.h
> > > > > > index cfeebd8..945000a 100644
> > > > > > --- a/drivers/usb/host/ehci.h
> > > > > > +++ b/drivers/usb/host/ehci.h
> > > > > > @@ -244,9 +244,9 @@ struct ehci_hcd {                   /* one per
> > > > > > controller */
> > > > > >           /* irq statistics */
> > > > > >     #ifdef EHCI_STATS
> > > > > >           struct ehci_stats       stats;
> > > > > > -#      define COUNT(x) do { (x)++; } while (0)
> > > > > > +#      define COUNT(x) ((x)++)
> > > > > >     #else
> > > > > > -#      define COUNT(x) do {} while (0)
> > > > > > +#      define COUNT(x) ((void) 0)
> > > > >
> > > > >
> > > > >
> > > > >      Why not just empty #define?
> > > >
> > > >
> > > > Indeed. I'll change it.
> > > > Tks Sergei.
> > >
> > >
> > > Since COUNT is not used to return the empty #define is ok. Another way
> > > is to use #define COUNT(x) (0) to get a 0 when necessary to read
> > > returns.

> >     Just 0, no parens please.

> Ok, no parens, since there's no evaluation.

   It's because the literals don't need parens at all.

> Then my change is:
>
> -#      define COUNT(x) do { (x)++; } while (0)
> +#      define COUNT(x) (++(x))
>   #else
> -#      define COUNT(x) do {} while (0)
> +#      define COUNT(x) 0
>
> Pre-increment allowing to return the updated x.

   Why if there was a post-increment before?

   Anyway, this talk is quite pointless since the macro didn't return any 
value anyway.

MBR, Sergei

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