Re: Purpose of QOM properties registered at realize time?

[Eduardo Habkost]

On Wed, Oct 07, 2020 at 03:55:58PM +0200, Paolo Bonzini wrote:
> 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.

Being accessible for debugging would be OK.  I'm just worried
about dynamic QOM properties being part of a stable and supported
API.

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

-- 
Eduardo