Re: [Qemu-devel] [PATCH 12/23] hyperv: make HvSintRoute reference-counted

[Eduardo Habkost]

On Wed, Jun 14, 2017 at 07:23:56PM +0300, Roman Kagan wrote:
> On Wed, Jun 14, 2017 at 10:53:25AM -0300, Eduardo Habkost wrote:
> > On Tue, Jun 06, 2017 at 09:19:37PM +0300, Roman Kagan wrote:
> > > Multiple entities (e.g. VMBus devices) can use the same SINT route.  To
> > > make their lives easier in maintaining SINT route ownership, make it
> > > reference-counted.  Adjust the respective API names accordingly.
> > > 
> > > Signed-off-by: Roman Kagan <address@hidden>
> > 
> > Isn't it easier to reuse existing refcounting infrastructure
> > here?  Is it overkill to make it a QOM object? (struct Object has
> > 40 bytes)
> 
> Normally the guests use a sint route per cpu or less.  So no, the space
> overhead is not an issue.
> 
> I also wanted to reuse regular QOM refcounting so I QOM-ified it at
> first.  However, while hammering out the design, I found no appropriate
> place in the QOM hierachy where to stick these objects so we dropped the
> idea.
> 
> If I get your proposal right you suggest to leave it unattached instead.
> That should probably work; however, looking at all the boilerplate code
> this would entail, including OBJECT casts, I'm not sure it would save
> anything.  Do you think it's worth reworking into QOM?

I just noticed I didn't reply to this, sorry.  I'm also not sure it is
worth reworking into QOM, so I guess it's up to you.

About placing the object in the QOM hierarchy, I don't think that would
be a problem.  Objects without a parent are safer, as long as reference
counting is properly tracked.

About the OBJECT casts, I guess that's a common issue.  I'm considering
proposing making object_ref()/object_unref() macros that use OBJECT()
automatically.

-- 
Eduardo