Re: [Qemu-devel] Virtio-pci issue

[Evgeny Voevodin <e.voevodin@samsung.com>]

On 23.05.2012 17:36, Stefan Hajnoczi wrote:
> On Thu, May 10, 2012 at 12:24 PM, Evgeny Voevodin
> <e.voevodin@samsung.com>  wrote:
>> Hi, guys!
>>
>> While trying to refactor virtio-pci as continuation of my RFC
>> virtio-mmio patch series:
>> http://lists.gnu.org/archive/html/qemu-devel/2012-04/msg03665.html
>> I've faced a problem.
>>
>> I try to create virtio-pci-transport device to which virtio-blk,net,etc
>> could be connected. Any board could create as many transport devices as
>> it wants and then any actual back-end could be connected to that
>> transport through a provided virtio-pci.x bus. virtio-pci-transport is
>> derived from TYPE_PCI_DEVICE.
>> The problem is that if I create transport devices and wish to connect
>> back-ends to them, each back-end would set its properties to the class,
>> not to the object.
>> For example, vendor_id property is different for blk and net, but since
>> they are both have same class PCIDeviceClass, they share that property.
>>
>> How to deal with this?
> I think you are asking how a virtio-pci adapter can have device_id
> value that depends on its VirtioDevice (not known at compile-time and
> different between virtio-pci adapters).
>
> You should be able to set the PCI device ID at runtime:
>
> pci_config_set_device_id(pci_dev->config, device_id_from_virtio_device);
>
> Take a look at hw/pci.c:pci_qdev_init().  The order of operations is important:
>
> 1. do_pci_register_device() sets up default values from PCIDeviceClass.
> 2. ->init(pci_dev) gets called, this is where your init code gets executed.
>
> So it should be fine to set the PCI device ID at runtime from
> VirtioPCIAdapter::init().
>
> Stefan
>

Oh, thanks a lot, Stefan! As soon as I have a time to continue 
refactoring, I'll check this functionality.
And also there is another problem that I've faced with. It is the 
ability to plug as many pci back-ends as board wants.
I mean that if for each back-end board should create a transport, then 
user have to know maximum number of transport instances
created by board. In the case of mmio transport I think that it's a 
correct behaviour, but for pci transport seems not.

-- 
Kind regards,
Evgeny Voevodin,
Leading Software Engineer,
ASWG, Moscow R&D center, Samsung Electronics
e-mail: e.voevodin@samsung.com