linux-kernel - Re: [lustre-devel] [PATCH 21/40] staging: lustre: improve LNet clean up code and API

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Date:	Wed, 2 Dec 2015 16:59:30 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Alexander Zarochentsev <alexander.zarochentsev@...gate.com>
Cc:	James Simmons <jsimmons@...radead.org>, devel@...verdev.osuosl.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Oleg Drokin <oleg.drokin@...el.com>,
	Amir Shehata <amir.shehata@...el.com>,
	lustre-devel@...ts.lustre.org
Subject: Re: [lustre-devel] [PATCH 21/40] staging: lustre: improve LNet clean
 up code and API

On Wed, Dec 02, 2015 at 04:20:59PM +0300, Alexander Zarochentsev wrote:
> >  BAD:   if (rc != 0)
> > GOOD:   if (rc)
> 
> The latest suggestion is not correct,
> from http://wiki.lustre.org/Lustre_Coding_Guidelines :
> Conditional boolean (if (expr)), scalar (if (val != 0)) and pointer
> (if (ptr != NULL)) expressions should be written consistently.

Kernel style trumps Lustre style.  Double negative don't not hurt
readability.  != NULL is a checkpatch.pl warning.  Also comparisons like
== false or == true are checkpatch warnings.

I can think of two places where comparing with zero is appropriate and
those are:

1)  If you are talking about the numer zero.

	if (x == 0 || x == 2)

2) strcmp() and other *cmp() functions.

	if (strcmp(foo, bar) == 0)   /* foo and bar are the same */
	if (strcmp(foo, bar) < 0)    /* foo less than bar */
	if (strcmp(foo, bar) != 0)   /* foo not the same as bar */

For "if (rc) {" a zero return doesn't mean zero, it means success so
comparing against zero is bad style.

regards,
dan carpenter

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