Re: [RFC PATCH 0/3] qdev: Introduce QDEV_DECLARE_DEV_BUS_TYPES() macro

[Daniel P . Berrangé]

On Wed, Mar 01, 2023 at 03:42:44PM +0100, Igor Mammedov wrote:
> On Mon, 13 Feb 2023 11:56:06 +0100
> Philippe Mathieu-Daudé <philmd@linaro.org> wrote:
> 
> > Experiment after discussing with Thomas around qdev_get_parent_bus:
> > https://lore.kernel.org/qemu-devel/ad356f64-dca0-8117-d22a-a530e620ddb0@redhat.com/
> > 
> > When a QDev plug on a QBus, we'll always use qdev_get_parent_bus()
> > at least once with this type. Why not provide a consistent defined
> > macro instead of:
> >  1/ adding an inlined helper such usb_bus_from_device()
> >     or scsi_bus_from_device() with different type checks,
> >  2/ open-code calls to qdev_get_parent_bus() with unsafe casts
> > ?
> > 
> > This RFC series introduce a QDev-equivalent of QOM DECLARE_TYPES
> > macro, to be used with a (device, bus) tuple, and declaring the
> > equivalent device_GET_BUS() macro.
> it's already bad having 2 ways to declare types (though SIMPLE was a huge LOC 
> saving)
> so question is where do we stop (API explosion ain't a good thing either).
> 
> I my opinion this is just code churn for nor tangible benefit,
> given how qdev_get_parent_bus() is used.

Right so in the USB conversion the only improvement is the elimination of
this method:

-static inline USBBus *usb_bus_from_device(USBDevice *d)
-{
-    return DO_UPCAST(USBBus, qbus, qdev_get_parent_bus(DEVICE(d)));
-}

It strikes me that we don't have especially many (bus-type, device-type)
pairs that would benefit from this macro.

With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|