Re: [Qemu-devel] [RFC PATCH v6 0/6] Virtio refactoring.

["KONRAD Frédéric" <fred.konrad@greensocs.com>]

On 07/01/2013 20:58, Michael S. Tsirkin wrote:
> On Tue, Dec 18, 2012 at 12:30:20PM +0100, KONRAD Frédéric wrote:
>> On 18/12/2012 12:01, Michael S. Tsirkin wrote:
>>> On Tue, Dec 18, 2012 at 10:33:37AM +0000, Peter Maydell wrote:
>>>> On 17 December 2012 15:45, Michael S. Tsirkin <mst@redhat.com> wrote:
>>>>> Is the point to allow virtio-mmio?  Why can't virtio-mmio be just
>>>>> another bus, like a pci bus, and another binding, like the virtio-pci
>>>>> binding?
>>>> (a) the current code is really not very nice because it's not
>>>> actually a proper set of QOM/qdev devices
>>>> (b) unlike PCI, you can't create sysbus devices on the
>>>> command line, because they don't correspond to a user
>>>> pluggable bit of hardware. We don't want users to have to know
>>>> an address and IRQ number for each virtio-mmio device (especially
>>>> since these are board specific); instead the board can create
>>>> and wire up transport devices wherever is suitable, and the
>>>> user just creates the backend (which is plugged into the virtio bus).
>>>>
>>>> -- PMM
>>> This is what I am saying: create your own bus and put
>>> your devices there. Allocate resources when you init
>>> a device.
>>>
>>> Instead you seem to want to expose a virtio device as two devices to
>>> user - if true this is not reasonable.
>>>
>> The modifications will be transparent to the user, as we will keep
>> virtio-x-pci devices.
> Then what's the point of all this?
>
> -device virtio-pci,id=transport1 -device virtio-net,bus=transport1
>
> or
>
> -device virtio-mmio,id=transport1 -device virtio-net,bus=transport1
>
> Is simply an insane way to create a network device.
>
To recap :

The idea is to have a virtio-bus between the transport device
(like pci, mmio,... ).

Then we can have a platform with several virtio-mmio and then virtio-bus 
slot.

At the end user can add a virtio-device in the command line with -device
parameter without recompiling the platform. That is not possible with just
creating the virtio-x-mmio devices. The bus= option can be used to
select the bus slot, but I'm not sure it is usefull.

The series keep the virtio-x-pci devices :
eg : step 11/61 for virtio-blk
So -device virtio-blk-pci or -device virtio-blk-s390 works as before.

Of course -device virtio-pci,id=transport1 -device 
virtio-net,bus=transport1 is
possible but why using this command line when we could simply do :
-device virtio-net-pci ?

Fred