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

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

On 08/01/2013 15:02, Michael S. Tsirkin wrote:
> On Tue, Jan 08, 2013 at 10:56:54AM +0100, KONRAD Frédéric wrote:
>> 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.
> pci uses addr option for this, I am guessing mmio can do the same.
>
>> 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
> Adding multiple ways to do one thing is a bad idea.
> I'm fine with modeling virtio by multiple devices
> internally, but exposing this to user is a mistake,
> we might rework this even more and command line
> has to be supported indefinitely.
>
for the moment all virtio-x-pci devices extend virtio-pci.
So why not abstracting virtio-pci ?
Then there is only one way to add a virtio-x-pci device.