linux-kernel - Re: [PATCH] staging: fsl-mc: fix fsl_mc_is

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Message-ID: <20170816120654.p3mpezb3zr2eqxvw@mwanda>
Date:   Wed, 16 Aug 2017 15:06:54 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Colin King <colin.king@...onical.com>
Cc:     Stuart Yoder <stuyoder@...il.com>,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Wei Yongjun <weiyongjun1@...wei.com>,
        devel@...verdev.osuosl.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: fsl-mc: fix fsl_mc_is_allocatable strcmps

On Wed, Aug 16, 2017 at 12:44:51PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> The previous fix removed the equal to zero comparisons by the strcmps and
> now the function always returns true. Fix this by adding in the missing
> logical negation operators.
> 
> Detected by CoverityScan, CID#1452267 ("Constant expression result")
> 
> Fixes: b93ad9a067e1 ("staging: fsl-mc: be consistent when checking strcmp() return")

Ugh...  I did review the original patch at all.  Sorry.  It's better to
use "== 0" because it's idiomatic.

	strcmp(foo, bar) == 0 means foo == bar
	strcmp(foo, bar) != 0 means foo != bar
	strcmp(foo, bar) < 0 means foo < bar alphabetically.

It's way more readable.  strcmp() bugs are fairly common when people
don't use == 0 and != 0.  There are other places where != 0 hurts
readability, such as checking for errors:

	if (frob() != 0) {

In this case, frob() is returning negative error codes, but it's not
really returning the number zero, it's returning "success".  So it
should be:

	ret = frob();
	if (ret) {

Comparing against NULL really doesn't add anything either.  But if
you're talking about the number zero then you should use == 0.

	if (len == 0)
		return 0;

regards,
dan carpenter