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

[Eduardo Habkost]

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.)

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."


>      .parent = TYPE_DEVICE,
>      .class_init = migration_class_init,
>      .class_size = sizeof(MigrationClass),
> -- 
> 2.7.4
> 

-- 
Eduardo