linux-kernel - Re: [PATCH V2] checkpatch: Flag code that returns a negative number less than 1

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Message-ID: <1464986529.11800.24.camel@perches.com>
Date:	Fri, 03 Jun 2016 13:42:09 -0700
From:	Joe Perches <joe@...ches.com>
To:	Nishanth Menon <nm@...com>, Andy Whitcroft <apw@...onical.com>
Cc:	linux-kernel@...r.kernel.org, afd@...com,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH V2] checkpatch: Flag code that returns a negative number
 less than 1

On Fri, 2016-06-03 at 15:02 -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. The notable exception is "-1"
> which has quiet a history of usage as pointed out by Joe Perches.
> 
> Considering typical error of doing the following:
> int fn(void)
> {
> 	/* ... error condition ... */
> 	return -2;
> }
> 
> 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.
> 
> The check is done for negative values less than 1 and tools
> directory is exempt from this requirement based on Joe Perches'
> suggestion.
> 
> Suggested-by: Joe Perches <joe@...ches.com>

No, I didn't suggest this.
I'm not at all sure it's even a good idea.

> Signed-off-by: Nishanth Menon <nm@...com>
> ---
> Changes in V2:
> 	- change in regex for check for check for less than 1
> 	- Update in commit message to the effect
> 	- Added Suggested-by for Joe's recommendation on regex.
> 
> V1: https://patchwork.kernel.org/patch/9153345/
> 
>  scripts/checkpatch.pl | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 4904ced676d4..a2e677b5fd78 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -4351,6 +4351,12 @@ sub process {
>  			}
>  		}
>  
> +# return with a value is not usually a good sign, unless the function is supposed to return a value
> +		if ($realfile !~ /^tools/ && defined($stat) && $stat =~ /^.\s*return\s*-\s*(?!1\b)\d+\s*;/s) {

I think
	if ($realfile != /^tools/ && $line =~ /\breturn\s*-\s*(?!1\b)\d+\s*;/
would be better as it would catch return -2 in a macro or a
multi-line statement like
	if (<foo>) return -2;

> +			CHK("RETURN_NUMBER",
> +			    "Suspect error return with a value, If this is error value, refer to include/uapi/asm-generic/errno-base.h  and include/uapi/asm-generic/errno.h\n" . $herecurr);

That's an awfully long message.

Maybe something like:
	"Perhaps better to use standard ERRNO system error symbols"