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

[Cornelia Huck]

On Tue, 17 Jun 2014 18:45:09 +0800
Ming Lei <address@hidden> wrote:

> 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?

It might be better to remove them for good :)

Nobody has probably tried to use them for some time...
I just start a very minimal guest with a virtio-console and a
virtio-blk device. Don't know whether Alex has a more advanced setup
at hand?