[libvirt] [PATCHv5 00/13] qemu: allow disabling certain virtio revisions

[Peter Krempa]

On Wed, Sep 07, 2016 at 16:13:57 +0100, Daniel Berrange wrote:
> On Wed, Sep 07, 2016 at 05:10:01PM +0200, Peter Krempa wrote:
> > On Wed, Aug 24, 2016 at 00:20:42 +0200, Ján Tomko wrote:
> > > https://bugzilla.redhat.com/show_bug.cgi?id=1227354

[...]

> > Obviously making the user responsible for correct setting is much
> > easier.
> > 
> > Sigh. It'd be great if somebody else could also state their opinion on
> > this. I can't say that I'm a big fan of this approach but it looks like
> > as if it would be the only sensible one.
> 
> I tend to agree. I'd be incredibly happy if we didn't add any of this to
> the XML and would simply "do the best thing" automatically.
> 
> I'm particularly not a fan of adding something "just in case there is a
> bug"

Yep, that's why I don't see a reason for using --disable-modern in
libvirt. It does not have any value besides working around "possible bugs".

On the other hand, I'm kind of worried that with "--disable-legacy" we
are entering the domain of policy decisions as it's uncertain to me
whether:
* Enabling it would break guests with very old drivers.
* Guest firmware actually supports the modern mode (both ovmf and bios)
* other possible caveats that I can't think of right now

In such case we'd need to expose a knob to set it, but I'd prefer
dropping the possibility to use legacy mode only since it's of no value.

Peter