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

[Anthony Liguori]

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.

Regards,

Anthony Liguori

> ---
>   vl.c |    1 +
>   1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/vl.c b/vl.c
> index d88a18c..c63af69 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -1746,6 +1746,7 @@ static int device_init_func(QemuOpts *opts, void *opaque)
>       dev = qdev_device_add(opts);
>       if (!dev)
>           return -1;
> +    object_unref(OBJECT(dev));
>       return 0;
>   }