Re: [Qemu-devel] [PATCH 07/23] target-i386: convert cpuid features into properties

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 3 Oct 2012 13:54:34 -0300
Eduardo Habkost <ehabkost@redhat.com> wrote:

> On Wed, Oct 03, 2012 at 06:24:11PM +0200, Igor Mammedov wrote:
> > On Wed, 03 Oct 2012 17:20:46 +0200
> > Paolo Bonzini <pbonzini@redhat.com> wrote:
> > 
> > > Il 03/10/2012 17:03, Eduardo Habkost ha scritto:
> > > > On Tue, Oct 02, 2012 at 05:38:45PM -0300, Eduardo Habkost wrote:
> > > >> (Now replying on the right thread, to keep the discussion in the
> > > >> right place. I don't know how I ended up replying to a pre-historic
> > > >> version of the patch, sorry.)
> > > >>
> > > >> On Tue, Oct 02, 2012 at 05:36:59PM +0200, Igor Mammedov wrote:
> > > >> [...]
> > > >>> @@ -1938,6 +2043,12 @@ static void x86_cpu_initfn(Object *obj)
> > > >>>      object_property_add(obj, "tsc-frequency", "int",
> > > >>>                          x86_cpuid_get_tsc_freq,
> > > >>>                          x86_cpuid_set_tsc_freq, NULL, NULL, NULL);
> > > >>> +    x86_register_cpuid_properties(obj, feature_name);
> > > >>> +    x86_register_cpuid_properties(obj, ext_feature_name);
> > > >>> +    x86_register_cpuid_properties(obj, ext2_feature_name);
> > > >>> +    x86_register_cpuid_properties(obj, ext3_feature_name);
> > > >>> +    x86_register_cpuid_properties(obj, kvm_feature_name);
> > > >>> +    x86_register_cpuid_properties(obj, svm_feature_name);
> > > >>
> > > >> Stupid question about qdev:
> > > >>
> > > >> - qdev_prop_set_globals() is called from device_initfn()
> > > >> - device_initfn() is called before the child class instance_init()
> > > >>   function (x86_cpu_initfn())
> > > >> - So, qdev_prop_set_globals() gets called before the CPU class
> > > >>   properties are registered.
> > > >>
> > > >> So this would defeat the whole point of all the work we're doing,
> > > >> that is to allow compatibility bits to be set as machine-type global
> > > >> properties. But I don't know what's the right solution here.
> > > >>
> > > >> Should the qdev_prop_set_globals() call be moved to qdev_init()
> > > >> instead? Should the CPU properties be registered somewhere else?
> > > 
> > > Properties should be registered (for all objects, not just CPUs) in the
> > > instance_init function.  This is device_initfn.
> > > 
> > > I would add an instance_postinit function that is called at the end of
> > > object_initialize_with_type, that is after instance_init, and in the
> > > opposite order (i.e. from the leaf to the root).
> > 
> > You've meant something like that?
> > 
> 
> That's almost exactly the same code I wrote here. :-)
> 
> The only difference is that I added post_init to the struct Object
> documentation comments, and added a unit test. The unit test required
> the qdev-core/qdev split, so we could compile it without bringing too
> many dependencies. I will submit it soon.
> 
After irc discussion, Anthony suggested to use static properties instead of
dynamic ones that we use now. 

But  qdev_prop_set_globals() in device_initfn() is still causes problems even
with static properties.

For x86 CPU classes we were going dynamically generate CPU classes and store
pointer to appropriate cpudef from builtin_x86_defs in class field for each
CPU class and then init default feature words values from this field int
x86_cpu_initfn().

However with qdev_prop_set_globals() in device_initfn() that is called before
x86_cpu_initfn() it won't work because defaults in x86_cpu_initfn() will
overwrite whatever was set by qdev_prop_set_globals().

IMHO from general POV it's not correct to set properties before object is
completely created.
But Anthony wants to keep qdev_prop_set_globals() qdev only thing, so could
we move it from device_initfn() to qdev_init() or some other place then?