Re: [Qemu-devel] KVM call agenda for Tuesday 7

[Anthony Liguori]

On 02/07/2012 12:17 PM, Andreas Färber wrote:
> Am 07.02.2012 19:01, schrieb Anthony Liguori:
> > On 02/07/2012 07:45 AM, Andreas Färber wrote:
> > > http://lists.gnu.org/archive/html/qemu-devel/2012-01/msg04065.html
> > >
> > > How is the realize step (DeviceState::init) supposed to translate to
> > > Object-derived classes (e.g., CPU) and where to draw the line between
> > > initfn and realize.
> >
> > Realize probably should be folded into Object or some intermediate object.
> >
> > The idea is that there will be a realized boolean property.  When the
> > level changes, it will invoke a realize() or unrealize() method
> > depending on the direction.  DeviceState will implement realize() and
> > invoke init().  For unrealize(), it will invoke exit().
>
> That's fine. Question is, who is in charge of setting the realized
> property

Ideally, the user, but there is a lot of refactoring to get there.

Realize should propagate through the composition tree (in such a way that it can 
be overridden, of course).

> and some rules of what do we put in initfn and what in realize.

instance_init:
 - initialize fields that don't depend on properties
 - install properties
 - initialize children

realize:
 - validate all properties have sane values
 - perform initialization that depends on properties
 - take any actions that would logically "start" the device
 - propagate to children

unrealize:
 - take any actions that would logically "stop" the device
 - propagate to children
 - restore fields to the values after reset

finalize:
 - take any actions that would logically "stop" the device
 - free any sources of the device

What we think of reset today is unrealize().  What with thing of as qdev_init is 
instance_init + realize.

One thing I'd like to do is make the default implementation of unrealize() 
essentially be finalize + reinit in the same memory location.  This would make 
it so that the vast majority of devices would not need to implement reset.

> Take the CPU, should CPU reset be done in realize or initfn?

Forget about reset as you know it.  initfn should initialize state.  Realize 
should only deal with starting the VM.

> realize
> might overwrite values set by the user after initfn but would provide us
> with a reproducible state wrt reboot.
>
> Starting the VCPU thread would definitely be for realize, but currently
> this is all done from cpu_*_init() and having sequential calls to initfn
> and realize doesn't offer any advantage over doing it all in initfn.

In general, if something can be done in initfn, it should be done there.

> So given we do the split, who knows about these objects to call their
> realize function?

'/' is an object (it's a container).  It will have a realize property that it 
propagates to all of it's children.

So a user simply has to set /.realize = true and that will realize the entire 
graph of objects.

> Will there be some global QOM logic that calls realize
> on all objects instantiated so far (any ordering constraints then?) or
> is everyone themselves responsible for making this work, i.e. must I
> keep a global list of all CPUs initfn'ed to have their realize method
> called later?

Nope, it all will just magically work.

Regards,

Anthony Liguori

> Andreas