Re: [PATCH 2/2] qom: Manage references to embedded child objects

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, Jun 15, 2026 at 01:11:07PM +0900, Akihiko Odaki wrote:
> Problem
> =======
> 
> The Rust wrapper for object_ref() is marked unsafe and has:
> > The object must not be embedded in another unless the outer
> > object is guaranteed to have a longer lifetime.
> 
> In other words, object_ref() does not work for embedded objects and
> does not keep embedded objects alive. MemoryRegion has its own
> memory_region_ref() helper to call object_ref() on its owner for this
> reason.
> 
> However, this is insufficient to avoid calling object_ref() for all
> embedded objects. For example, consider an embedded Device that has a
> MemoryRegion. When referencing a MemoryRegion for guest memory access,
> QEMU automatically references the owning Device to keep the MemoryRegion
> alive. However, that reference is ineffective if the Device itself is
> embedded, because object_ref() does not keep the containing storage
> alive.

Do we know how many examples we have of embedding objects inside
another ?

I would much prefer if we forbid the embedding of objects. It is
horrible design practice to have some QOM objects which can be
freed via reference count and some which cannot.

With regards,
Daniel
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