linux-kernel - Re: [PATCH] checkpatch giving bogus advice (was staging: goldfish: Fix minor coding style)

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Message-ID: <20141215130346.GB18251@hudson.localdomain>
Date:	Mon, 15 Dec 2014 05:03:46 -0800
From:	Jeremiah Mahler <jmmahler@...il.com>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Cc:	Loic Pefferkorn <loic@...cp.eu>, gregkh@...uxfoundation.org,
	alan@...ux.intel.com, jun.j.tian@...el.com,
	octavian.purdila@...el.com, nnk@...gle.com,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
	apw@...onical.com, joe@...ches.com
Subject: Re: [PATCH] checkpatch giving bogus advice (was staging: goldfish:
 Fix minor coding style)

On Mon, Dec 15, 2014 at 11:44:21AM +0000, One Thousand Gnomes wrote:
> On Sat, 13 Dec 2014 11:46:47 -0800
> Jeremiah Mahler <jmmahler@...il.com> wrote:
> 
> > Loïc,
> > 
> > On Sat, Dec 13, 2014 at 07:22:38PM +0100, Loic Pefferkorn wrote:
> > > > Whose convention is this?  I can't find any mention in
> > > > Documention/CodingStyle. checkpatch.pl doesn't complain about them.
> > > > And there are almost three thousand examples in staging which don't
> > > > use this convention.
> > > > 
> > > >   linux-next$ grep -r "== NULL" drivers/staging/* | wc -l
> > > >   2844
> > > 
> > > Hi Jeremiah,
> > > 
> > > Thanks for your feedback.
> > > 
> > > I have used checkpatch.pl with the --strict flag:
> 
> checkpatch.pl is a bit dubious at the best of times - you can't automate
> taste without an AI ;). With --strict it's a positive hazard.
> 
> Those kind of small cleanups really only make sense if you are doing big
> changes to the code itself anyway and are doing testing and all the rest.
> 
> In this case I'd say checkpatch.pl is actually wrong because in the
> general case it's better to compare with NULL in C
> 
> If you write
> 
>           if (!x)
> 
> and accidentally use a non-pointer type you don't get a warning. If you
> try and compare a non pointer type to NULL you usually do. So the NULL
> comparison avoids accidents.
> 
> The historical reason for it being done in C was I think to avoid the
> 
>           if (x = NULL) 
> 
> bug, but gcc will shout at you for that these days.
> 

Or another way mentioned in K&R that produces a compile error

            if (NULL = x) 

> Alan
> 
> 
> 

-- 
- Jeremiah Mahler
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