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Date: Mon, 27 Aug 2012 14:09:30 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [RFC PATCH 0/9] qom: improve reference counting
 and hotplug
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To: =?ISO-8859-1?Q?Andreas_F=E4rber?= <afaerber@suse.de>
Cc: Liu Ping Fan <pingfank@linux.vnet.ibm.com>, liu ping fan <qemulist@gmail.com>, Anthony Liguori <anthony@codemonkey.ws>, qemu-devel@nongnu.org

Il 27/08/2012 13:46, Andreas F=E4rber ha scritto:
>>> >>
>>> >> Since link and child properties all hold references, in order to a=
ctually free
>>> >> an object, we need to break those links.  User created devices end=
 up as
>>> >> children of a container.  But child properties cannot be removed w=
hich means
>>> >> there's no obvious way to remove the reference and ultimately free=
 the object.
>>> >>
>> > Why? Since we call _add_child() in qdev_device_add(), why can not we
>> > call object_property_del_child() for qmp_device_del(). Could you
>> > explain it more detail?
> Seconded. If we hot-unplug a device, we should surely remove its child<=
>
> property from /machine/unassigned or parent bus or whatever.

Sure, as soon as the device is ejected by the guest.  But until that
point we need to keep the device in the QOM tree so that: 1) it has a
canonical path; 2) it can be examined; 3) it keeps children alive.

> Why is it that child<> properties cannot be removed?

Yeah, I didn't quite understand the difference between unparenting and
setting the child property to NULL.

Paolo