Re: [PATCH 2/8] lib: printf code %pUs for GUID text representation

[AKASHI Takahiro <takahiro.akashi@linaro.org>]

On Sun, Jan 16, 2022 at 04:14:35PM +0100, Heinrich Schuchardt wrote:
> In different places text representations are used for GUIDs, e.g.
> 
> * command efidebug
> * command part list for GPT partitions
> 
> To allow reducing code duplication introduce a new printf code %pUs.
> It will call uuid_guid_get_str() to get a text representation. If none is
> found it will fallback to %pUl and print a hexadecimal representation.

I think the idea is good.
Moreover, when you add a new format specifier to printf() routine,
it would also be good to add a document so that people won't bustle
around the code to find an appropriate format string.
Not only to "%pU*", but also others including "%pD" and "%ls" that you added.

# See linux's Documentation/core-api/printk-formats.rst.

-Takahiro Akashi


> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
> ---
>  lib/vsprintf.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index de9f236b90..2c0cc1647e 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -255,8 +255,8 @@ static char *number(char *buf, char *end, u64 num,
>  	return buf;
>  }
>  
> -static char *string(char *buf, char *end, char *s, int field_width,
> -		int precision, int flags)
> +static char *string(char *buf, char *end, const char *s, int field_width,
> +		    int precision, int flags)
>  {
>  	int len, i;
>  
> @@ -387,12 +387,14 @@ static char *ip4_addr_string(char *buf, char *end, u8 *addr, int field_width,
>   *   %pUB:   01020304-0506-0708-090A-0B0C0D0E0F10
>   *   %pUl:   04030201-0605-0807-090a-0b0c0d0e0f10
>   *   %pUL:   04030201-0605-0807-090A-0B0C0D0E0F10
> + *   %pUs:   GUID text representation if known or fallback to %pUl
>   */
>  static char *uuid_string(char *buf, char *end, u8 *addr, int field_width,
>  			 int precision, int flags, const char *fmt)
>  {
>  	char uuid[UUID_STR_LEN + 1];
>  	int str_format;
> +	const char *str;
>  
>  	switch (*(++fmt)) {
>  	case 'L':
> @@ -404,6 +406,13 @@ static char *uuid_string(char *buf, char *end, u8 *addr, int field_width,
>  	case 'B':
>  		str_format = UUID_STR_FORMAT_STD | UUID_STR_UPPER_CASE;
>  		break;
> +	case 's':
> +		str = uuid_guid_get_str(addr);
> +		if (str)
> +			return string(buf, end, str,
> +				      field_width, precision, flags);
> +		str_format = UUID_STR_FORMAT_GUID;
> +		break;
>  	default:
>  		str_format = UUID_STR_FORMAT_STD;
>  		break;
> -- 
> 2.33.1
>