Re: [PATCH v4 1/2] sunrpc: fix unused variable warnings by using no_printk

[Sean Chang]

On Sat, Feb 28, 2026 at 2:15 AM David Laight
<david.laight.linux@xxxxxxxxx> wrote:
>
> On Fri, 27 Feb 2026 18:57:33 +0100
> Andrew Lunn <andrew@xxxxxxx> wrote:
>
> > > >  # define ifdebug(fac)            if (0)
> > > > -# define dfprintk(fac, fmt, ...) do {} while (0)
> > > > -# define dfprintk_rcu(fac, fmt, ...)     do {} while (0)
> > > > +# define dfprintk(fac, fmt, ...) no_printk(fmt, ##__VA_ARGS__)
> > > > +# define dfprintk_rcu(fac, fmt, ...)     no_printk(fmt, ##__VA_ARGS__)
> > >
> > > You can omit fmt, then you don't need the ##
> > > #define dfprintk(fac, ...)  no_printk(__VA_ARGS__)
> >
> > /*
> >  * Dummy printk for disabled debugging statements to use whilst maintaining
> >  * gcc's format checking.
> >  */
> > #define no_printk(fmt, ...)                           \
> > ({                                                    \
> >       if (0)                                          \
> >               _printk(fmt, ##__VA_ARGS__);            \
> >       0;                                              \
> > })
> >
> > Without fmt, gcc cannot do format checking. Or worse, it takes the
> > first member of __VA_ARGS__ as the format, and gives spurious errors?
>
> By the time the compiler looks at it the pre-processor has expanded
> __VA_ARGS__.
> So it doesn't matter that the format string is in the __VA_ARGS__
> list rather than preceding it.
>

Hi David,
Thanks for the explanation. I agree that since __VA_ARGS__ will
always contain the format string in this context, the ## and explicit
fmt are indeed redundant. Since no_printk itself already handles
the ##__VA_ARGS__ logic internally, there's no need to duplicate
it in the dfprintk definition.

I'll switch to the simpler in v5:
-# define dfprintk(fac, fmt, ...)            no_printk(fmt, ##__VA_ARGS__)
-# define dfprintk_rcu(fac, fmt, ...)     no_printk(fmt, ##__VA_ARGS__)
+#define dfprintk(fac, ...)                   no_printk(__VA_ARGS__)
+# define dfprintk_rcu(fac, ...)           no_printk(__VA_ARGS__)

Best regards,
Sean