Re: [PATCH RFC] virtio-fs: force virtio 1.x usage

[Michael S. Tsirkin]

On Wed, Jul 01, 2020 at 06:19:17PM +0200, Cornelia Huck wrote:
> On Tue, 30 Jun 2020 09:04:38 -0400
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > On Tue, Jun 30, 2020 at 02:25:04PM +0200, Cornelia Huck wrote:
> 
> > > What bothers me most is that you need to explicitly request a device to
> > > be modern-only, while that should be the default for any newly added
> > > device. Hence the approach with the centralized list of device types
> > > mentioned in a parallel thread. The main problem with that is that the
> > > proxy device starts getting realized before the virtio device with its
> > > id is present... I failed to find a solution so far. But I'd really
> > > like an approach that can work for all transports.  
> > 
> > So how about simply validating that the device is modern only,
> > unless it's one of the whitelist?
> 
> Who would do the validation, the virtio core? How can it distinguish
> between transitional and non-transitional? But maybe I'm just not
> getting your idea.

OK I've been thinking about two ideas, we can use them both:
1. virtio core: that can detect VIRTIO_1 being clear
in virtio_validate_features.
2. transports: could use a core API to detect whether
device can be a legacy one, to block device creation.


> Also, ccw does not currently have a way to explicitly configure a
> device non-transitional; the revisions can be used to fence off newer
> features, going down to legacy-only, but fencing off older features is
> not possible (that is only done by the device, if it has no legacy
> support).

I guess for ccw only option 1 works.

-- 
MST