On Thu, Feb 01, 2018 at 02:44:03PM +0100, Andrea Bolognani wrote:
On Thu, 2018-02-01 at 12:54 +0000, Daniel P. Berrangé wrote:
If an application breaks based on the USB controller being either present or not present, then they shouldn't be relying on libvirt's default but rather explicitly opt either in or out.
It is not merely the mgmt application that may break, but the guest OS inside too. When we suddenly expose new hardware to a guest that was not previously present you can certainly trigger latent problems in the guest OS. It could slow boot at a key phase, or trigger loading of bad drivers, or any number of other things that can occurr when you change hardware visible to an OS.
Note that I'm not advocating adding controllers or any other hardware to *existing* guests - that would clearly be a guest ABI breakage and thus Extremely Bad™. For newly-defined guests, however, none of the above applies AFAICT.
There's no practical way to distinguish an existing guest from a new guest being provisioned. With transient domains they are one & the same. Even with persistent guests the distinction is far from clear. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|