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

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Date:	Fri, 03 Jun 2016 08:41:33 -0700
From:	Joe Perches <joe@...ches.com>
To:	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 10:25 -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


> diff --git 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 (defined($stat) && $stat =~ /^.\s*return\s*-[0-9]+\s*;/s) {
> +			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);
> +		}
> +
>  # unnecessary return in a void function
>  # at end-of-function, with the previous line a single leading tab, then return;
>  # and the line before that not a goto label target like "out:"