Re: [PATCH] video/saa7164: Fix sparse warning: Using plain integer

Julia Lawall
2011-01-26T05:59:39Z

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On Tue, 25 Jan 2011, Peter Hüwe wrote:

> 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?

No.

> Or only for the kmalloc family?
>
> Do you remember the reason why !x should be preferred?

Because it is a function call, and NULL represents failure of that
function, not an actual NULL value.

Here is an email that explains that:

http://lkml.org/lkml/2007/7/27/103

Here is the beginning of the thread:

http://lkml.org/lkml/2007/7/27/75

julia

> 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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