Re: [RFC PATCH v3 16/19] qmp: add query-cpu-props-info command

Khushit Shah <[email protected]> writes:

>> On 4 Aug 2026, at 12:15 PM, Markus Armbruster <[email protected]> wrote:
>> 
>> !-------------------------------------------------------------------|
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>> 
>> Khushit Shah <[email protected]> writes:
>> 
>>> Introduce the 'query-cpu-props-info' QMP command. For CPU model
>>> properties it reports the type (boolean or number) and the set of values
>>> supported under the active accelerator and host.
>>> 
>>> For numbers the supported values are expressed as a list of inclusive
>>> {min, max} ranges; for booleans as the list of allowed true/false
>>> values.
>>> 
>>> The command and its return types (CpuPropertyType, CpuPropertyInfo and
>>> friends) are defined in qapi/machine.json rather than an Arm-specific
>>> schema, since the concept applies to other targets (e.g. x86, riscv)
>>> too. Target that do not implement it return an error.
>>> 
>>> The Arm/KVM implementation spins up a scratch "host" vCPU object,
>>> walks its QOM properties: SYSREG_ ID-register fields become 'number'
>>> properties whose ranges come from arm_field_get_supported_values(),
>>> and the advertised feature toggles become 'boolean' properties.
>>> 
>>> Signed-off-by: Khushit Shah <[email protected]>
>> 
>> This explains what the command does and how it's implemented.  It's
>> silent on the most important aspect: why do we want the command?  What
>> is its intended purpose?
>
> Will add something like:
>
> This helps the management stack to discover which values are supported
> for a given CPU property. This is especially important for non-boolean
> properties, where knowing that the host has value 'x' does not inherently
> reveal the full range of valid values supported on the host.

Better.  Perhaps throw in an example if you can come up with a simple
one.