[libvirt] [PATCH v2 06/15] qemu: Defer capability check to command line generation time

[Andrea Bolognani]

On Mon, 2018-02-19 at 07:24 +0100, Peter Krempa wrote:
> On Fri, Feb 16, 2018 at 17:28:03 +0100, Andrea Bolognani wrote:
> > Validate time is a bit too early to check whether the required
> > capabilities are available, since the QEMU binary might have
> > been updated or replaced by the time we are asked to run the
> > guest.
> 
> So are you having problem with the fact that the definition will be
> rejected right away and not just when you try to start it?
> 
> Validate is re-run when starting the VM so a downgrade is handled
> properly.

Right, but isn't checking for QEMU capabilities at validate time
unreasonably strict? A guest which uses eg. an invalid combination
of machine type and architecture will never become valid at a later
point, but a guest should not be considered invalid just because
the QEMU binary you happened to have installed at the time you
defined it lacked some features - the guest itself is perfectly
valid, it just can't be run :)

-- 
Andrea Bolognani / Red Hat / Virtualization