Re: [Qemu-devel] [RFC] QEMU Object Model status/merge plan

[Anthony Liguori]

On 12/13/2011 05:35 AM, Stefan Hajnoczi wrote:
> On Mon, Dec 12, 2011 at 7:36 PM, Anthony Liguori<address@hidden>  wrote:
> > I choose the serial device to showcase what we'll eventually be able to do.
> >   The three relevant files are:
> >
> > https://github.com/aliguori/qemu/blob/qom-next/hw/isa-serial.c
> >
> > https://github.com/aliguori/qemu/blob/qom-next/hw/mm-serial.c
> >
> > https://github.com/aliguori/qemu/blob/qom-next/hw/serial.c
>
> I'm not sure I understand how init functions are called for derived
> classes.

There are three types of init functions:

class_init
==========

This lives in (TypeInit) and is called when a class is first created for a type. 
 It is only ever called once.  Within this function, you should override any 
methods in your base classes and set default implementations for any methods you 
implement.

instance_init
=============

This is the constructor for a type.  It is called when an object is created and 
chained such that the base class constructors are called first to initialize the 
object.

DeviceState::init
=================

This is the qdev initialize function.  It is called sometime after properties 
are set and before the guest starts running for the first time.  Long term, I 
plan to change this to "DeviceState::realize" and remove explicit calls to 
qdev_init() in favor of a propagated realize signal.

But for now, I'm trying to avoid churn in the tree.

> On one hand mm-serial.c calls its superclass init function,
> on the other hand isa-bus.c:isa_qdev_init() calls an init function
> that its child class must provide.  One is calling its parent, the
> other is calling its child.  Is there a consistent way of doing this
> and what did I miss :)?

Yes, this is all DeviceState::init.  This is what is called when you invoke 
qdev_init().  Right now, you have to do it explicitly and in the case of 
composition, since the device is creating another device, it must be the one 
that calls qdev_init() for that device.

In the case of inheritance, we're just calling the superclass's init function 
because DeviceState::init is just a normal method so we have to explicitly chain 
it if we want that behavior.

Regards,

Anthony Liguori

> Stefan