Re: [PATCH v8 3/3] xen/domain: introduce CONFIG_MAX_DOMID

[Jan Beulich <jbeulich@xxxxxxxx>]

On 22.05.2025 20:08, dmkhn@xxxxxxxxx wrote:
> On Thu, May 22, 2025 at 09:01:51AM +0200, Jan Beulich wrote:
>> On 22.05.2025 02:09, dmkhn@xxxxxxxxx wrote:
>>> On Wed, May 21, 2025 at 09:31:34AM +0200, Jan Beulich wrote:
>>>> On 21.05.2025 02:00, dmkhn@xxxxxxxxx wrote:
>>>>> --- a/xen/common/Kconfig
>>>>> +++ b/xen/common/Kconfig
>>>>> @@ -576,4 +576,11 @@ config BUDDY_ALLOCATOR_SIZE
>>>>>     Amount of memory reserved for the buddy allocator to serve Xen heap,
>>>>>     working alongside the colored one.
>>>>>
>>>>> +config MAX_DOMID
>>>>> + int "Maximum number of user domains"
>>>>> + range 1 32752
>>>>> + default 32752
>>>>> + help
>>>>> +   Specifies the maximum number of domains a user can create.
>>>>
>>>> My prior comment remains: The description and help needs to be accurate, in
>>>> order to not cause any confusion. In a true dom0less environment I'm not
>>>> sure the "user" can create any domains (post boot, that is). And when there
>>>> is Dom0 (or late hwdom), the number specified already isn't the number of
>>>> domains one can create (again, post boot, which is how I understand "user
>>>> domains"). If someone picked 1 as the value here, it's unclear to me how
>>>> late hwdom or dom0less would work in the first place.
>>>
>>> Do you think something like the following will be more accurate?
>>>
>>>     config MAX_DOMID
>>>        int "Maximum number of domains"
>>>        range 1 32752
>>>        default 32752
>>>        help
>>>          Specifies the maximum number of domains: dom0 or late hwdom,
>>>          predefined domains, post-boot domains, excluding Xen system domains
>>>          (domid >= DOMID_FIRST_RESERVED).
>>
>> Especially the mention of DOMID_FIRST_RESERVED is too much of an 
>> implementation
>> detail here, imo. Beyond that - maybe, but I'm not overly happy this way 
>> either.
> 
> Will the following description will be satisfactory?
> 
> config MAX_DOMID
>        int "Maximum domain ID"
>        range 1 32752
>        default 32752
>        help
>          Specifies the maximum domain ID (dom0 or late hwdom, predefined
>          domains, post-boot domains, excluding Xen system domains).

This is better, yes, yet ...

>> As an aside - MAX_DOMID and "Maximum number of domains" are conflicting
>> with one another, too: Do you mean "maximum ID" or "maximum number of"? The 
>> two
>> are different by 1.
> 
> That would be "maximum ID", thank you.

... imo asking for "maximum" of something is perhaps a little odd. Asking for
"number of" is the more usual thing imo.

Yet as before - I remain unconvinced we need such a Kconfig setting in the first
place.

Jan