Re: [PATCH v2 05/10] qom: Create object-property-ptr.[ch]

[Peter Xu <peterx@redhat.com>]

On Wed, Jun 10, 2026 at 05:15:59PM +0100, Daniel P. Berrangé wrote:
> On Tue, Jun 09, 2026 at 01:25:09PM -0400, Peter Xu wrote:
> > Create object-property-ptr.[ch] files to include all the helpers for
> > object_property_add*_ptr().
> > 
> > These set of helpers are handy because they look extremely familiar with
> > qdev-properties, allowing the caller to provide a pointer and it will
> > manage all the setters and getters.
> > 
> > The follow up patches may introduce more of such helpers.  Since object.c
> > has been already too big, split that part out.
> 
> The "ptr" helpers are all instance level properties which is a concept
> we discourage from new usage, in favour of class level properties.
> 
> I don't think we should be adding more "ptr" helpers, but rather
> planning to eliminiate the (surprisingly little) usage of the
> existing ones.

The other way to do similar thing is qdev's offset way, but IMHO that's
more awkward to remember an offset of a pointer then do math everytime.
Essentially, from technical pov we need at least one uintptr_t to store
either (1) offset, or (2) field pointer when there's a field that is bound
to a prop.  IMHO (2) can be better otherwise we'll need to do all the maths
to calculate offsets then when access we add the offset back and do a force
cast.  It seems not necessary.

OTOH, I still see value on non-class instance properties (that sometimes we
don't even want to have some props avail for the class, but conditional to
some instances when created dynamically).  If that is needed, IMHO it's
fine we still provide per-instance properties.

Is there any pointer I can read about the discussion previously on this?

Thanks,

-- 
Peter Xu