Re: [libvirt] [RFC] Question regarding the validity of QEMU capabilities

On Fri, Oct 20, 2017 at 01:10:14PM +0200, Pavel Hrdina wrote: > On Fri, Oct 20, 2017 at 12:59:51PM +0200, Marc Hartmayer wrote: > > Hi all, > > > > the actual capabilities of QEMU are depending on the host. This > > includes dependencies like which kernel modules are loaded or which > > kernel parameters are used (e.g. kvm.nested). Therefore, after a > > restart we cannot be sure that the QEMU capabilities remain the same. > > > > How can we solve this problem? > > Hi, > > thanks for bringing up this issue, we kind of already know about it > but it's good idea to discuss it publicly. > > > > > I have come up with two ways: > > - reprobe the capabilities with every host reboot > > This is the solution that was agreed on but nobody was motivated enough > to write the code :). Reprobing QEMU is quite heavy. I wonder if we should change slightly. Make our capabilities cache *only* contain stuff reported by the QEMU binary. For other stuff we detect from the host, never cache it.