Re: [PATCH 3/3] lib/uuid: avoid double traversal in __uuid_parse()

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 12 Mar 2026 18:41:13 +0000 Josh Law <hlcj1234567@gmail.com> wrote:

> __uuid_parse() calls uuid_is_valid() to walk all 36 characters for
> format validation, then walks the string a second time to parse the
> hex bytes.  Combine both passes into one: validate each hex digit
> inline via hex_to_bin() return value and check the four dash positions
> after the loop.
> 
> uuid_is_valid() remains exported unchanged for callers that only need
> validation without parsing.
> 
> --- a/lib/uuid.c
> +++ b/lib/uuid.c
> @@ -108,16 +108,20 @@ static int __uuid_parse(const char *uuid, __u8 b[16], const u8 ei[16])
>  	static const u8 si[16] = {0,2,4,6,9,11,14,16,19,21,24,26,28,30,32,34};
>  	unsigned int i;
>  
> -	if (!uuid_is_valid(uuid))
> -		return -EINVAL;
> -
>  	for (i = 0; i < 16; i++) {
>  		int hi = hex_to_bin(uuid[si[i] + 0]);
>  		int lo = hex_to_bin(uuid[si[i] + 1]);
>  
> +		if (hi < 0 || lo < 0)
> +			return -EINVAL;
> +
>  		b[ei[i]] = (hi << 4) | lo;
>  	}
>  
> +	if (uuid[8] != '-' || uuid[13] != '-' ||
> +	    uuid[18] != '-' || uuid[23] != '-')
> +		return -EINVAL;
> +
>  	return 0;

This rather messifies the code, and for what?  Is this in any way a hot
path?