On Mon, Aug 19, 2013 at 03:20:49PM +0200, Cornelia Huck wrote:
> On Mon, 19 Aug 2013 16:05:43 +0300
> "Michael S. Tsirkin" <> wrote:
>
> > > One idea might be that all devices start out in 'legacy mode' and we
> > > add either a feature bit or a new channel command that switches to
> > > 'standard mode'. Old hosts would reject that command, while old guests
> > > would simply not issue it.
> > >
> > > Another idea is to look at the read_conf/write_conf channel commands
> > > and introduce a new pair of read_conf_le/write_conf_le commands. Again,
> > > compatibility would be achived via the host doing command rejects.
> > >
> > > We also have the possibility to convey extra information about the
> > > control unit (the device) in the 'extended sense id data' via the sense
> > > id command. Basically, we can encode some supported channel commands in
> > > there, but we would need a new command type for that architectured.
> > > We'd still need to rely on the command rejects mentioned above, though.
> >
> > If guest can discover whether host supports the new layout,
> > why would there be any rejects?
>
> If we want to support old guests on new hosts, we'll have to rely on
> this.
I would expect old guests not to issue old commands, if new
host supports that why would there be rejects?
