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Subject: Re: [virtio-comment] virtio and endian-ness
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" <mst@redhat.com> 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?
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