Re: [Qemu-devel] [PATCH 01/16] qdev: fix hot-unplug

[Paolo Bonzini <pbonzini@redhat.com>]

On 02/04/2012 04:03 AM, Anthony Liguori wrote:
> There's no object_ref() in qdev_device_add().  The 2 references come
> from adding a child link to /peripheral and via object_new().

Sure, but there's when the object_new() reference becomes unreachable. 
At this point, if it weren't for /peripheral the device should have 
disappeared.

> object_free() drops a reference (it's called in qdev_device_del()) and
> in the process of calling object_free(), it also calls object_unparent()
> which will drop the reference from the parent.
>
> I'm not thrilled about the way reference counting is done now.  Perhaps
> we should do a gobject style floating reference...

I'm not sure that's a problem.  Rather, the problem is that we are 
(still) mixing manual memory management and refcounting by making 
object_delete drop a reference.

Can you remind me of why you have object_unref separate from 
object_delete?  Is it because you must not delete objects that were 
object_initialize'd rather than object_new'd?  Perhaps we can take care 
of that with a flag elsewhere saying "do not free this object when 
object_unref drops the last ref" (only finalize it).

Thanks for analyzing the behavior.  We don't have to get it right 
immediately as long as we know what's going on, the transition is not 
complete anyway.

Paolo