Re: [Qemu-devel] [PATCH] virtio: make bindings typesafe

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Dec 18, 2012 at 01:13:18AM +0100, Andreas Färber wrote:
> Am 17.12.2012 23:58, schrieb Michael S. Tsirkin:
> > On Mon, Dec 17, 2012 at 11:08:43PM +0100, Andreas Färber wrote:
> >> Am 17.12.2012 22:18, schrieb Michael S. Tsirkin:
> >>> On Mon, Dec 17, 2012 at 10:13:11PM +0100, Andreas Färber wrote:
> >>>> Am 17.12.2012 21:48, schrieb Michael S. Tsirkin:
> >>>>> On Mon, Dec 17, 2012 at 07:25:08PM +0100, Andreas Färber wrote:
> >>>>>> Am 17.12.2012 19:21, schrieb Paolo Bonzini:
> >>>>>>> Il 17/12/2012 18:55, Andreas Färber ha scritto:
> >>>>>>>> Am 17.12.2012 16:45, schrieb Michael S. Tsirkin:
> >>>>>>>>> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> >>>>>>>>> index 3ea4140..63ae888 100644
> >>>>>>>>> --- a/hw/virtio-pci.c
> >>>>>>>>> +++ b/hw/virtio-pci.c
> >>>>>>>>> @@ -98,34 +98,34 @@ bool virtio_is_big_endian(void);
> >>>>>>>>>  
> >>>>>>>>>  /* virtio device */
> >>>>>>>>>  
> >>>>>>>>> -static void virtio_pci_notify(void *opaque, uint16_t vector)
> >>>>>>>>> +static void virtio_pci_notify(DeviceState *d, uint16_t vector)
> >>>>>>>>>  {
> >>>>>>>>> -    VirtIOPCIProxy *proxy = opaque;
> >>>>>>>>> +    VirtIOPCIProxy *proxy = container_of(d, VirtIOPCIProxy, pci_dev.qdev);
> >>>>>>>>
> >>>>>>>> Nack. This is going the wrong direction QOM-wise and you among all
> >>>>>>>> others know that from PCI host bridges!
> >>>>>>>
> >>>>>>> Well, that's just a difference of VIRTIO_PCI_PROXY(d) vs. container_of.
> >>>>>>
> >>>>>> VIRTIO_PCI_PROXY(d) would be acceptable, sure. But as-is this patch just
> >>>>>> pushes unnecessary work on Fred, me, you or anyone else who works with QOM.
> >>>>>
> >>>>> What's VIRTIO_PCI_PROXY? Note this is data path we do not want extra
> >>>>> code.
> >>>>
> >>>> My complaint is the direct access of pci_dev, qdev, etc. parent fields
> >>>> in many places as the main change of this patch. Those mean more places
> >>>> to touch in a future patch.
> >>>>
> >>>> Use of any new-style macro hiding these - wherever the particular one
> >>>> suggested may be defined or whether it needs to be added - is better.
> >>>>
> >>>> If performance of dynamic_cast is an issue - something I'd leave you to
> >>>> discuss with Anthony - you can just do a C cast directly. Just don't
> >>>> spread this qdev paradigm further please.
> >>>
> >>> OK so just
> >>>
> >>> #define VIRTIO_PCI_PROXY(d) container_of(d, VirtIOPCIProxy, pci_dev.qdev)
> >>>
> >>> is OK with you?
> >>
> >> Well, at least it's better than inlining it...
> >>
> >> I would've expected to see VIRTIO_PCI_PROXY(obj) defined as
> >> OBJECT_CHECK(VirtIOPCIProxy, (obj), TYPE_something) somewhere.
> >>
> >> If, as you imply with "data path", this were a problem, you could just
> >> do VirtIOPCIProxy *proxy = (VirtIOPCIProxy *)d inline to allow for
> >> VIRTIO_PCI_PROXY() to be used in the QOM sense elsewhere.
> > 
> > I don't get it - where?
> > Since we don't do runtime checks we need container_of -
> > safer than a plain cast.
> >
> > Anyway, when you start doing your QOM conversions it will be
> > easy to do what you like.
> 
> I don't get what you don't get

Wha'ts the QOM way to get virtio pci proxy from
devicestate?
C cast is not what I am looking for.