linux-kernel - Re: [PATCH 01/12] staging: lustre: fid: Use !x to check for kzalloc failure

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Date:	Tue, 23 Jun 2015 11:35:42 +0200 (CEST)
From:	Julia Lawall <julia.lawall@...6.fr>
To:	Dan Carpenter <dan.carpenter@...cle.com>
cc:	"Dilger, Andreas" <andreas.dilger@...el.com>,
	Julia Lawall <Julia.Lawall@...6.fr>,
	"Drokin, Oleg" <oleg.drokin@...el.com>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lustre-devel@...ts.lustre.org" <lustre-devel@...ts.lustre.org>
Subject: Re: [PATCH 01/12] staging: lustre: fid: Use !x to check for kzalloc
 failure

On Tue, 23 Jun 2015, Dan Carpenter wrote:

> On Tue, Jun 23, 2015 at 08:25:05AM +0000, Dilger, Andreas wrote:
> > I've found in the past that developers can introduce bugs when they treat
> > return values as boolean when they really aren't.
>
> I can imagine a bug like that where a function can return 0-2 and people
> do:
>
> 	if (ret)
>
> instead of:
>
> 	if (ret == 1)
>
> but that bug is something else besides pointers so it doesn't apply
> here.
>
> What someone should do is try to measure it scientifically where we
> flash some code on the screen and you have to press J for NULL and K for
> non-NULL and we time it to the hundredth of a second.  I have a feeling
> that (NULL != foo) is the worst way to write it because of the double
> negative Yoda code.
>
> Yoda code is the most useless thing ever.  I have actually measured this
> and we introduce about 2 = vs == bugs per year.  It's probably less now
> that we have so many static checks against it.  But people decided that
> Yoda code was a good idea based on their gut instead of using statistics
> and measurements and science.

In 2007, Al Viro said (https://lkml.org/lkml/2007/7/27/103):

Idiomatic form for "has allocation succeeded?" is neither "if (p != 0)"
nor "if (p != NULL)".  It's simply "if (p)".


>From the point of view of looking at kernel code, x == NULL for the result
of kmalloc etc looks verbose and distracting.

julia
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