On Thu, Feb 21, 2013 at 11:58:18 -0300, Eduardo Habkost wrote:
> = Querying host capabilities =
> Requirement: libvirt needs to know which feature can really be enabled, before
> it tries to start a VM, and before it tries to start a live-migration process.
> The set of available capabilities depend on:
>   • Host CPU (hardware) capabilities;
>   • Kernel capabilities (reported by GET_SUPPORTED_CPUID);
>   • QEMU capabilities;
>   • Specific configuration options (e.g. in-kernel IRQ chip is required for
>     some features).

Actually, one more thing. Can any of these requirements change while a
host is up and QEMU is not upgraded? I believe, host CPU capabilities
can only change when the host starts. Kernel capabilities are a bit less
clear since I guess they could possibly change when kvm module is
unloaded and loaded back with a different options. QEMU capabilities
should only change when different version is installed. And the specific
configuration options are the most unclear to me. The reason I'm asking
is whether libvirt could run-time cache CPU definitions (including all
model details) in the same way we currently cache QEMU capabilities,
such as availability of specific QMP commands.


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