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

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Message-Id: <201101252354.31217.PeterHuewe@gmx.de>
Date:	Tue, 25 Jan 2011 23:54:30 +0100
From:	Peter Hüwe <PeterHuewe@....de>
To:	Julia Lawall <julia@...u.dk>
Cc:	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

Am Dienstag 25 Januar 2011, 23:20:44 schrieb Julia Lawall:
> On Tue, 25 Jan 2011, Peter Huewe wrote:
> > This patch fixes the warning "Using plain integer as NULL pointer",
> > generated by sparse, by replacing the offending 0s with NULL.
> 
> I recall (a number of years ago) being told that for things like kmalloc,
> the proper test was !x, not x == NULL.
> 
> julia
> 


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?

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;

    if (condition1) {
        while (loop1) {
            ...
        }
        result = 1;
        goto out;
    }
    ...
out:
    kfree(buffer);
    return result;
}


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


Don't get me wrong, I just want to learn ;)


Thanks,
Peter

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