linux-kernel - Re: [PATCH] checkpatch: Flag code that returns a negative number

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Message-ID: <1464969664.11800.9.camel@perches.com>
Date:	Fri, 03 Jun 2016 09:01:04 -0700
From:	Joe Perches <joe@...ches.com>
To:	"Andrew F. Davis" <afd@...com>, Nishanth Menon <nm@...com>,
	Andy Whitcroft <apw@...onical.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] checkpatch: Flag code that returns a negative number

On Fri, 2016-06-03 at 10:49 -0500, Andrew F. Davis wrote:
> On 06/03/2016 10:41 AM, Joe Perches wrote:
> > On Fri, 2016-06-03 at 10:25 -0500, Nishanth Menon wrote:
> > > In some functions, returning a -ve decimal value is actually a valid
> > > return condition when the function is returning a value, however, it
> > > can also be misused for returning an error value that should ideally
> > > be a valid error code defined in include/uapi/asm-generic/errno-base.h
> > > or include/uapi/asm-generic/errno.h
> > > 
> > > Considering typical newbie error of doing the following:
> > > int fn(void)
> > > {
> > > 	/* ... error condition ... */
> > > 	return -1;
> > > }
> > > 
> > > void fn1(void)
> > > {
> > > 	/* some code */
> > > 	if (fn() < 0) {
> > > 		pr_err("Error occurred\n");
> > > 		return;
> > > 	}
> > > 	/* other cases... */
> > > }
> > > 
> > > Flag this as a check case for developer verification.
> > I think it's not a newbie error to have a -1 return and it
> > seems like rather too many cases to even suggest be changed.
> > 
> > $ git grep -E "\breturn\s+\-\s*[0-9]+" * | grep -v "^tools" | wc -l
> > 8388
> > 
> A quick look over some of these cases show many *should* be replaced
> with proper error codes.
> 
> Removing the simple -1 case, which is often used for signaling one level
> up of an error, gives better results though:
> 
> $ git grep -E "\breturn\s+\-\s*[2-9][0-9]*" * | grep -v "^tools" | wc -l
> 189

I did more or less the same grep, and that's somewhat true.
-1 though is very common and doesn't need to be replaced.

$ git grep -E "\breturn\s+\-\s*[0-9]+\s*;" * | grep -v "^tools" | grep -vP "return\s*\-1;" | wc -l
211

Looking at some of the specific instances of negative return values
instead of the line counts though may show otherwise.

-EFOO errors aren't always better.