Re: [PATCH 0/2] xen/common: llc-coloring parser fixes

[Jan Beulich <jbeulich@xxxxxxxx>]

On 18.05.2026 08:42, Mykola Kvach wrote:
> On Mon, May 18, 2026 at 9:20 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>> On 16.05.2026 17:03, Mykola Kvach wrote:
>>> This small series fixes two issues in parse_color_config().
>>>
>>> The first patch makes parse failures leave the caller-visible color count
>>> at zero.  This prevents a rejected command-line value from leaving a
>>> partially parsed configuration behind for later init paths to consume.
>>>
>>> The second patch rejects empty color tokens.  Previously, delimiters in
>>> places where a color value was expected could be interpreted as color 0,
>>> because simple_strtoul() returns zero without advancing the input pointer.
>>> The patch checks that each parsed color value consumed input.  It also
>>> adds the missing newline to the DT color parsing error message.
>>>
>>> Mykola Kvach (2):
>>>   xen/common: llc-coloring: clear color count on parse failure
>>>   xen/common: llc-coloring: reject empty color tokens
>>
>> For both of these, a question which isn't even considered in the reasoning
>> is whether the present behavior may be intentional. Especially for the 2nd
>> ISTR Stefano(?) not so long ago indicating that the behavior is indeed
>> intended to be this way. That may have been somewhere on Matrix rather than
>> on the list, though.
> 
> Thank you for pointing this out.
> 
> For the first patch, my reasoning was that returning an error while
> leaving a partially parsed caller-visible color count behind looks
> surprising. If the value is rejected, I think later init paths should
> not be able to consume the partially parsed state.
> 
> For the second patch, my reasoning was that the current behavior looks
> accidental rather than an intentional extension of the syntax.

That was my impression as well, hence why I had raised the question back
then.

> The parser comment says:
> 
> COLOR_CONFIGURATION ::= COLOR | RANGE,...,COLOR | RANGE
> RANGE ::= COLOR-COLOR
> 
> The user guide also describes this as a comma-separated list of colors
> or ranges, with ranges written as hyphen-separated inclusive intervals.
> I don't see an empty-token production there.

What you quote is insufficient to determine: COLOR may be allowed to be
<nothing>. Iirc the reasoning went in particular towards a range with
merely the upper end specified being something (halfway) meaningful.

Jan