Re: [Qemu-devel] [PATCH v6 11/10] migration: add comment for TYPE_MIGRATE

[Peter Xu]

On Wed, Jun 28, 2017 at 12:37:04PM -0300, Eduardo Habkost wrote:
> On Wed, Jun 28, 2017 at 03:15:44PM +0800, Peter Xu wrote:
> > It'll be strange that the migration object inherits TYPE_DEVICE. Add
> > some explanations to it.
> > 
> > Signed-off-by: Peter Xu <address@hidden>
> > ---
> >  migration/migration.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/migration/migration.c b/migration/migration.c
> > index b1b0825..2398a9d 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -2046,6 +2046,14 @@ static void migration_instance_init(Object *obj)
> >  
> >  static const TypeInfo migration_type = {
> >      .name = TYPE_MIGRATION,
> > +    /*
> > +     * NOTE: "migration" itself is not really a device. We used
> 
> I suggest extending this as:
> 
>   TYPE_MIGRATION is not really a device, as the object is not created
>   using qdev_create(), it is not attached to the qdev device tree, and
>   it is never realized.
> 
> 
> > +     * TYPE_DEVICE here only to leverage some existing QDev features
> > +     * like "-global" properties, and HW_COMPAT_* fields (which are
> > +     * finally applied as global properties as well). If one day the
> > +     * global property feature can be migrated from QDev to QObject in
> > +     * general, then we can switch to QObject as well.
> > +     */
> 
> QOM objects (qom/object.h) are not QObject (qapi/qmp/qobject.h).  People
> often confuse them with each other.  (It probably doesn't help that both
> are described as "QEMU Object Model" at their headers.)

Indeed. Sorry I got confused.

> 
> I suggest rewriting it as:
> 
>   If one day we allow non-device QOM objects to use the global property
>   system, we can switch this from TYPE_DEVICE to TYPE_OBJECT."

For the comment for this patch (and patch 10 on "properties" and
"globals"), I both agree. Again, I'll see what's the best way to fix
them.  Thanks,

-- 
Peter Xu