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

[Andreas Färber]

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.

Regards,
Andreas

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