Re: Purpose of QOM properties registered at realize time?

[Paolo Bonzini]

On 07/10/20 15:02, Eduardo Habkost wrote:
> On Wed, Oct 07, 2020 at 02:04:23PM +0200, Paolo Bonzini wrote:
>> On 07/10/20 00:06, Eduardo Habkost wrote:
>>> Hi,
>>>
>>> While trying to understand how QOM properties are used in QEMU, I
>>> stumbled upon multiple cases where alias properties are added at
>>> realize time.
>>>
>>> Now, I don't understand why those properties exist.  As the
>>> properties are added at realize time, I assume they aren't
>>> supposed to be touched by the user at all.  If they are not
>>> supposed to be touched by the user, what exactly is the purpose
>>> of those QOM properties?
>>
>> In the case of GPIOs, I think they will be used by other devices that
>> are added afterwards.
> 
> Do you know how exactly are they used?  Is this always wrapped
> behind a specific API for GPIOs, or the devices can look for the
> properties directly?

It is always wrapped, but (as far as I recall, because I have never
worked with GPIOs) they are intentionally QOM properties and not just as
an implementation detail.  It's meant to be accessible to the user if
only through qom-get/qom-set.

Paolo

> I'm concerned by the possibility of having QOM properties as an
> undocumented part of an internal API.