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

[Anthony Liguori <aliguori@us.ibm.com>]

"Michael S. Tsirkin" <mst@redhat.com> writes:

> 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.

virtio-pci is pluggable into a bus, virtio-mmio is not.  There is a
fixed number of them for a specific board and you have the option to add
virtio devices to the ones that already exist.

virtio is a mess in its current state.  Large swaths are not qdev'ified
and we jump through hoops to try to set properties.

I can't imagine how you can look at this cleanup and not understand why
it's nicer...

Regards,

Anthony Liguori

>
> -- 
> MST