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


From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH 01/16] qdev: fix hot-unplug
Date: Sat, 04 Feb 2012 01:27:39 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:9.0) Gecko/20111222 Thunderbird/9.0

On 02/03/2012 03:27 PM, Anthony Liguori wrote:
On 02/02/2012 10:45 AM, Paolo Bonzini wrote:
The reference that is returned by qdev_device_add is never given
back, so that device_del does not cause the refcount to go to zero
(and thus does nothing).

Signed-off-by: Paolo Bonzini<address@hidden>

This isn't needed in qom-upstream.14. Here's why:

object_init does not increase the reference count

object_property_add_child increases the reference count
object_new increases the reference count

object_delete decrements the reference count
object_property_del_child decreases the reference count

object_delete calls object_property_del_child(obj->parent, obj)

qdev_device_add calls object_new and object_property_add_child
-> ref == 2

qdev_device_del calls object_delete
-> ref -= 2

In qom-upstream.13, object_delete wasn't calling
object_property_del_child which is why you saw the behavior you did.
This problem would still exist with a composed device so dropping the
reference here isn't enough.

I trust you for now. :)

It really seems like my patch is obviously correct so, if it's not needed anymore there may be another bug elsewhere that masks it.

Paolo




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