Re: [Qemu-devel] [PATCH 2/4] s390-virtio-bus: move common virtio properties to virtio s390 device class

[Ming Lei]

On Tue, Jun 17, 2014 at 6:40 PM, Ming Lei <address@hidden> wrote:
> On Tue, Jun 17, 2014 at 6:25 PM, Cornelia Huck <address@hidden> wrote:
>> On Tue, 17 Jun 2014 18:15:39 +0800
>> Ming Lei <address@hidden> wrote:
>>
>>> On Tue, Jun 17, 2014 at 4:46 PM, Cornelia Huck <address@hidden> wrote:
>>> >>
>>> >> Looks like s390 virtio-blk never enables the two common features, is
>>> >> there any reason the two features can't be supported by s390?
>>> >
>>> > Indirect descriptors are fine. event_idx will not work IIUC because we
>>> > always need to do a sync before we see changes, and this needs an
>>> > interrupt to trigger.
>>>
>>> Sounds like the old s390 isn't cache coherent? Because you mean
>>> write in one side can only be observed from another side with an
>>> explicit notification or interrupt.
>>>
>>> On arm/arm64, we didn't see any problem with event_idx.
>>
>> But you probably have the queues in guest memory, as on other
>> transports (including virtio-ccw)? The old s390-virtio transport keeps
>> the devices and their virtqueues in a memory area behind the guest
>> memory - the guest does not see that memory directly, but a sync has to
>> be performed to see virtqueue movement (see s390_virtio_device_sync()).
>
> OK, it looks like a real physical device, :-)
>
> I will keep s390-virtio as it is, thanks for your explanation.

BTW, do you want me to add DEFINE_VIRTIO_COMMON_FEATURES()
to s390_virtio_net_properties and s390_virtio_scsi_properties since
I remove them from their default properties?

Thanks,
--
Ming Lei