Re: [Qemu-devel] Object instantiation vs. device realization: what to do when?

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 14 Feb 2019 17:58:06 +0100
Paolo Bonzini <pbonzini@redhat.com> wrote:

> On 14/02/19 17:21, Markus Armbruster wrote:
> >  * As an interim step, the #DeviceState:realized property can also be
> >  * set with qdev_init_nofail().
> >  * In the future, devices will propagate this state change to their children
> >  * and along busses they expose.
> > 
> > This sentence is five years old.  Any progress?  If not, any intentions
> > to make progress?  
> 
> Good news, it's done!  What we still don't do is removing
> qdev_init_nofail and realizing the whole machine in one fell swoop.
> 
> Bad news, it's been done for five years:
> 
>     commit 5c21ce77d7e5643089ceec556c0408445d017f32
>     Author: Bandan Das <bsd@redhat.com>
>     Date:   Wed Mar 12 21:02:12 2014 +0100
> 
>     qdev: Realize buses on device realization
> 
>     Integrate (un)realization of child buses with
>     realization/unrealization
>     of the device hosting them. Code in device_unparent() is reordered
>     for unrealization of buses to work as part of device unrealization.
> 
>     That way no changes need to be made to bus instantiation.
> 
>     Signed-off-by: Bandan Das <bsd@redhat.com>
>     Signed-off-by: Andreas Färber <afaerber@suse.de>
> 
> so I don't expect that the next step will ever happen...

that isn't really used (realize part) last time we've looked at it
https://www.mail-archive.com/qemu-devel@nongnu.org/msg570424.html


> >  * The point in time will be deferred to machine creation, so that values
> >  * set in @realize will not be introspectable beforehand. Therefore devices
> >  * must not create children during @realize; they should initialize them via
> >  * object_initialize() in their own #TypeInfo.instance_init and forward the
> >  * realization events appropriately.
> > 
> > This is mostly greek to me.  Pity the developer who knows less about
> > qdev than I do.  
> 
> The first part refers to what virtio_instance_init_common does:
> 
>     object_initialize(vdev, vdev_size, vdev_name);
>     object_property_add_child(proxy_obj, "virtio-backend", OBJECT(vdev),
>                               NULL);
>     object_unref(OBJECT(vdev));
> 
> The second part doesn't apply to virtio because it has a bus (so the
> code from the above commit handles recursive realization automatically).
> 
> hw/sd/milkymist-memcard.c has an example of this:
> 
>     object_property_set_bool(OBJECT(carddev), true, "realized", &err);
> 
> but it should create the device in milkymist_memcard_init rather than
> milkymist_memcard_realize, in order to obey the directives of the sacred
> book of QEMU.
> 
> Paolo
>