linux-kernel - Re: [PATCH] staging: vboxvideo: vbox_main: Remove unnecessary local variable

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Date:   Thu, 10 Jan 2019 22:44:08 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Sidong Yang <realwakka@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: vboxvideo: vbox_main: Remove unnecessary local
 variable

On Thu, Jan 10, 2019 at 05:00:24PM +0000, Sidong Yang wrote:
> I think you just point out that my code isn't obvious because the
> function returns negative error codes. I agree with you. But what if
> change my code like if(hgsmi_query_conf() != 0). 
> 

That's even worse!  :P

You should do comparisons with zero when you are talking about zero
meaning the number zero.  In this case, hgsmi_query_conf() returns "zezro
meaning success" not "zero meaning the number zero".  How many bytes?
Zero.  That is the number zero.

!= zero is a double negative, because NOT and ZERO are negatives.  If
double negatives simplified the code we would add four of them instead
of just the one:

	if ((((hgsmi_query_conf() != 0) != 0) != 0) != 0) {

See?  Adding != 0 doesn't make it simpler...

The other place where != 0 is appropriate besides talking about the
number is when you're using a strcmp() function because it works like
this:

	if (strcmp(a, b) < 0) {  <-- means a < b
	if (strcmp(a, b) == 0) { <-- means a == b
	if (strcmp(a, b) != 0) { <-- means a != b

regards,
dan carpenter