[Libguestfs] [PATCH] v2v: Set machine type explicitly for outputs which support it (RHBZ#1581428).

[Richard W.M. Jones]

On Tue, Jun 19, 2018 at 11:43:38AM +0100, Daniel P. Berrangé wrote:
> I'd encourage apps to check the capabilities XML to see what
> machine types are available.

One issue is we don't always have access to the target hypervisor.

For example in the Glance case we have to write something which will
be picked up by Nova much later:

> > +        "hw_machine_type",
> > +        (match guestcaps.gcaps_machine with
> > +         | I440FX -> "pc"
> > +         | Q35 -> "q35"
> > +         | Virt -> "virt");

I read the Nova code and it seems very ad-hoc.  As far as I can tell
these strings are eventually passed down to libvirt.  However libvirt
capabilities doesn't advertise these machine types exactly, but
something more like "pc-q35-2.6".  Does libvirt map "q35" to something
intelligent?

In any case it's not passed to libvirt before Nova has also done
various ad-hoc stuff based on substrings.  For example Nova will only
add PCIe root ports to a guest if the machine type has "q35" as a
substring.

I can see many ways this could all go horribly wrong.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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