Re: [PATCH] libxl: respect unset video_memkb for Dom0

[Jan Beulich <jbeulich@xxxxxxxx>]

On 28.08.2025 03:12, Jason Andryuk wrote:
> On 2025-08-27 01:56, Jan Beulich wrote:
>> Without this, Dom0 will have have a curiously off-by-1 target_memkb
>> value displayed by "xl list -l".
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> Reviewed-by: Jason Andryuk <jason.andryuk@xxxxxxx>

Thanks.

> In theory, b_info->video_memkb should have been defaulted to 0.

I don't think 0 would be a legitimate default; it might be for Dom0, but
not generally.

>  In 
> practice you found it isn't.  xen-init-dom0 could probably use some fixing.

Right, kind of as per the latter of the two post-commit-message remarks.

>> ---
>> In retrieve_domain_configuration_end(), isn't it the wrong way round to
>> set both ->b_info.target_memkb and ->b_info.max_memkb only after calling
>> libxl__get_targetmem_fudge(), when that uses the two fields? This way we
>> could as well use ->b_info->video_memkb directly there.
> 
> I think it's attempting to read the current values from xenstore, in 
> case they changed via xl mem-set, and then putting them into the d_config.

That's my understanding too, yet it still makes little sense to me to
invoke a function when data it consumes isn't set (yet).

Jan

>> Of course this may point at a bigger problem, as other fields may
>> similarly never be set for Dom0.