linux-kernel - Re: [PATCH] video/saa7164: Fix sparse warning: Using plain integer as NULL pointer

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Date:	Tue, 25 Jan 2011 19:30:13 -0500
From:	Andy Walls <awalls@...metrocast.net>
To:	Devin Heitmueller <dheitmueller@...nellabs.com>
Cc:	Peter Hüwe <PeterHuewe@....de>,
	Julia Lawall <julia@...u.dk>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org,
	Steven Toth <stoth@...nellabs.com>, Tejun Heo <tj@...nel.org>,
	Dan Carpenter <error27@...il.com>
Subject: Re: [PATCH] video/saa7164: Fix sparse warning: Using plain integer
 as NULL pointer

On Tue, 2011-01-25 at 18:05 -0500, Devin Heitmueller wrote:
> On Tue, Jan 25, 2011 at 5:54 PM, Peter Hüwe <PeterHuewe@....de> wrote:
> > Hi Julia,
> >
> > thanks for your input.
> > So do I understand you correctly if I say
> > if(!x) is better than if(x==NULL) in any case?

The machine code should be equivalent in size and speed.


> > Or only for the kmalloc family?
> >
> > Do you remember the reason why !x should be preferred?
> >
> > In Documentation/CodingStyle ,  Chapter 7: Centralized exiting of functions
> > there is a function fun with looks like this:
> > int fun(int a)
> > {
> >    int result = 0;
> >    char *buffer = kmalloc(SIZE);
> >
> >    if (buffer == NULL)
> >        return -ENOMEM;

> >
> > -->  So   if (buffer == NULL) is in the official CodingStyle - maybe we should
> > add a paragraph there as well ;)


CodingStyle shouldn't specify anything on the matter.  There is no
overall, optimal choice for all contexts.   Arguing either way is as
pointless as the Lilliputians' little-end vs. big-end dispute.


> To my knowledge, the current CodingStyle doesn't enforce a particular
> standard in this regard, leaving it at the discretion of the author.

Correct, it does not.  I just checked CodingStyle and checkpatch
yesterday.


> Whether to do (!foo) or (foo == NULL) is one of those debates people
> have similar to whether to use tabs as whitespace.  People have
> differing opinions and there is no clearly "right" answer.

It depends on one's measurement criteria for "optimizing" the written
form of source code.

I prefer more explicit statement of action is taking place over
statements with fewer characters.  It usually saves me time when
revisiting code.

More genrally I prefer any coding practice that saves me time when
revisiting code.  (Note the word "me" carries a lot of context with it.)

Ambiguity and implicit behaviors ultimately waste my time.


>   Personally
> I strongly prefer (foo == NULL) as it makes it blindingly obvious that
> it's a pointer comparison, whereas (!foo) leaves you wondering whether
> it's an integer or pointer comparison.

<usenet>
Me too.
</usenet>


> All that said, you shouldn't submit patches which arbitrarily change
> from one format to the other.  With regards to the proposed patch, you
> should follow whatever style the author employed in the rest of the
> file.

That is another reasonable critereon in "optimizing" the written form of
the source code.  I tend to give it less weight though.


Regards,
Andy

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