linux-kernel - Re: [PATCH v1] cleanup: adjust scoped_guard() to avoid potential warning

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Message-ID: <Zv7ZsieITDle2lgl@smile.fi.intel.com>
Date: Thu, 3 Oct 2024 20:51:46 +0300
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	linux-kernel@...r.kernel.org, amadeuszx.slawinski@...ux.intel.com,
	Tony Nguyen <anthony.l.nguyen@...el.com>,
	nex.sw.ncis.osdt.itp.upstreaming@...el.com, netdev@...r.kernel.org,
	Markus Elfring <Markus.Elfring@....de>, Kees Cook <kees@...nel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH v1] cleanup: adjust scoped_guard() to avoid potential
 warning

On Thu, Oct 03, 2024 at 04:12:21PM +0200, Peter Zijlstra wrote:
> On Thu, Oct 03, 2024 at 03:46:24PM +0300, Andy Shevchenko wrote:
> > On Thu, Oct 03, 2024 at 03:43:17PM +0300, Andy Shevchenko wrote:
> > > On Thu, Oct 03, 2024 at 01:39:06PM +0200, Przemek Kitszel wrote:

...

> > > > +#define __scoped_guard_labeled(_label, _name, args...)			\
> > > > +	for (CLASS(_name, scope)(args);					\
> > > > +	     __guard_ptr(_name)(&scope) || !__is_cond_ptr(_name);	\
> > > > +		     ({ goto _label; }))				\
> > > > +		if (0)							\
> > > > +		_label:							\
> > > > +			break;						\
> > > > +		else
> > > 
> > > I believe the following will folow more the style we use in the kernel:
> > > 
> > > #define __scoped_guard_labeled(_label, _name, args...)			\
> > > 	for (CLASS(_name, scope)(args);					\
> > > 	     __guard_ptr(_name)(&scope) || !__is_cond_ptr(_name);	\
> > > 		     ({ goto _label; }))				\
> > > 		if (0) {						\
> > > _label:									\
> > > 			break;						\
> > > 		} else
> > > 
> 
> Yeah, needs braces like that. I'm not super opposed to this, however, 
> 
> > And FWIW:
> > 1) still NAKed;
> 
> I would really like to understand why you don't like this; care to
> elaborate Andy?

To me the idea of

int my_foo(...)
{
	NOT_my_foo_macro(...)
		return X;
}

is counter intuitive from C programming. Without knowing the magic behind the
scenes of NOT_my_foo_macro() I would eager to ask for adding a dead code like

int my_foo(...)
{
	NOT_my_foo_macro(...)
		return X;
	return 0;
}

What I would agree on is

int my_foo(...)
{
	return NOT_my_foo_macro(..., X);
}

Or just using guard()().

-- 
With Best Regards,
Andy Shevchenko