Re: [Qemu-devel] Virtio refactoring.

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

On 13/11/2012 16:32, Cornelia Huck wrote:
> On Tue, 13 Nov 2012 15:27:57 +0100
> KONRAD Frédéric <fred.konrad@greensocs.com> wrote:
>
>> To fix this, an idea is to use a new qbus named VirtioBus to link virtio-pci
>> or virtio-mmio with all the virtio backend ( VirtioDevice ). So
>> "virtio-pci" and
>> "virtio-mmio" will have a VirtioBus.
> Just to spell this out:
>
> We'd go from
>
> system bus
> -> virtio transport bridge dev (virtio-xxx-bridge)
>     -> virtio transport bus (virtio-xxx-bus)
>        -> virtio transport dev (virtio-<type>-xxx)
>
> to
>
> system bus
> -> virtio transport bridge dev (virtio-bridge-xxx)
>     -> virtio bus (virtio-bus-xxx)
>        -> virtio dev (virtio-<type>-xxx)
>
> ?
I'm not sure of what you mean,.. do you mean for s390 ?

for the moment we have e.g : virtio-blk-pci ( in virtio-pci.c )

and we want virtio-pci -> virtio-bus -> virtio-blk.

( or virtio-mmio -> virtio-bus -> virtio-blk. for pci-less system. )

>
> Would this also mean we could have several virtio-busses with different
> transports?
I think so.
>
>> To do that we will do the following things in the right order :
>>       * Introduce a new VirtioBus ( same way as scsi-bus.c ), with
>> VirtIODevice
>>         interface :
>>            -> callback to completely abstract the VirtioDevice from
>> VirtioPCI.
>>            -> for the queue, load/save the queue/config, features, ...,
>> other ?
>>       * Add a VirtioBus to the VirtioPCIProxy. ( virtio-pci.c ) :
>>            -> moving all to the newer callback.
>>       * For each of the virtio-device : ( virtio-x.c )
>>            -> making a separate class for virtio-x which is a VirtioDevice.
>>            -> making a virtio-x-pci which has a virtio-x.
>>       * Create virtio-mmio ( virtio-mmio.c ).
>>
>> Is it the right approach ? Do I miss something ?
> What of the alias handling? Can this be killed once everything has been
> converted?
Which alias ?
>
>> When it will work, we must be sure of :
>>
>> -> migration compatibility.
>> -> not breaking the s390 transport.
>> -> compatibility with s390 ccw.
> There shouldn't be major problems rebasing the virtio-ccw code on top
> of this rework (though I'd probably try to keep the basic channel I/O
> support separate from this patchset).
>