linux-kernel - Re: [PATCH v2 3/2] lib/uuid.c: Silence an unchecked return value warning

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Date:	Sun, 05 Jun 2016 17:21:04 +0300
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	George Spelvin <linux@...encehorizons.net>
Cc:	bjorn@...k.no, linux-kernel@...r.kernel.org,
	matt@...eblueprint.co.uk, rv@...musvillemoes.dk
Subject: Re: [PATCH v2 3/2] lib/uuid.c: Silence an unchecked return value
 warning

On Sat, 2016-06-04 at 09:16 -0400, George Spelvin wrote:
> Andy Shevchenko pointed out that __uuid_to_bin doesn't need to check
> the return value from hex2bin(), because the preceding uuid_is_valid()
> check already took care of that.
> 
> But hex2bin() is declared __must_check, so checking anyway is the
> simplest way to silence the warning.
> 
> This cancels a small fraction of the the space savings, but not all:
> 
> 	vs. previous patch		vs. before patch series
> 	Before  After   Delta   Percent	Orig.	Delta
> Percent
> x86-32	90	 96	 +6	6.7%	122	-
> 26	-21.3%
> x86-64	90	 96	 +6	6.7%	127     -31	
> -24.4%
> arm	92	104	+12	13.0%	116     -12	
> -10.3%
> thumb	50	 62	+12	24.0%	100     -38	
> -38.0%
> arm64	116	124	 +8	6.9%	148     -24	
> -16.2%
> 
> Signed-off-by: George Spelvin <linux@...encehorizons.net>
> ---
>  lib/uuid.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/uuid.c b/lib/uuid.c
> index 93945915..1a6dbbd2 100644
> --- a/lib/uuid.c
> +++ b/lib/uuid.c
> @@ -104,7 +104,8 @@ static int __uuid_to_bin(const char uuid[36], __u8
> b[16], const u8 pos[16])
>  		return -EINVAL;
>  
>  	for (i = 0; i < 16; i++)
> -		hex2bin(b + i, uuid + pos[i], 1);
> +		if (hex2bin(b + i, uuid + pos[i], 1) < 0)
> +			return -EINVAL;

Which I against of. Please, use normal hex_to_bin() calls here.

Compiler will inline it anyway, but at least will not do second check
for nothing.

>  
>  	return 0;
>  }

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy