[PATCH v3 2/7] lib/vsprintf: Add support for generic FOURCCs by extending %p4cc

[Petr Mladek]

On Tue 2022-11-08 16:33:22, Russell King wrote:
> From: Hector Martin <marcan at marcan.st>
> 
> %p4cc is designed for DRM/V4L2 FOURCCs with their specific quirks, but
> it's useful to be able to print generic 4-character codes formatted as
> an integer. Extend it to add format specifiers for printing generic
> 32-bit FOURCCs with various endian semantics:
> 
> %p4ch   Host-endian
> %p4cl	Little-endian
> %p4cb	Big-endian
> %p4cr	Reverse-endian
> 
> The endianness determines how bytes are interpreted as a u32, and the
> FOURCC is then always printed MSByte-first (this is the opposite of
> V4L/DRM FOURCCs). This covers most practical cases, e.g. %p4cr would
> allow printing LSByte-first FOURCCs stored in host endian order
> (other than the hex form being in character order, not the integer
> value).
> 
> Signed-off-by: Hector Martin <marcan at marcan.st>
> Signed-off-by: Russell King (Oracle) <rmk+kernel at armlinux.org.uk>

Reviewed-by: Petr Mladek <pmladek at suse.com>

See one nit below.

> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1762,27 +1762,50 @@ char *fourcc_string(char *buf, char *end, const u32 *fourcc,
>  	char output[sizeof("0123 little-endian (0x01234567)")];
>  	char *p = output;
>  	unsigned int i;
> +	bool pixel_fmt = false;
>  	u32 orig, val;
>  
> -	if (fmt[1] != 'c' || fmt[2] != 'c')
> +	if (fmt[1] != 'c')
>  		return error_string(buf, end, "(%p4?)", spec);
>  
>  	if (check_pointer(&buf, end, fourcc, spec))
>  		return buf;
>  
>  	orig = get_unaligned(fourcc);
> -	val = orig & ~BIT(31);
> +	switch (fmt[2]) {
> +	case 'h':
> +		val = orig;
> +		break;
> +	case 'r':
> +		val = orig = swab32(orig);

I do not like much these multi assignments. I think that the result
was not even defined in some older C standards. Though, I can't find
it now. And even make W=3 does not warn about it.

> +		break;
> +	case 'l':
> +		val = orig = le32_to_cpu(orig);
> +		break;
> +	case 'b':
> +		val = orig = be32_to_cpu(orig);
> +		break;

Best Regards,
Petr