[libvirt] ARM KVM GICv3 Support

[Peter Maydell]

On 5 January 2016 at 17:58, Andrea Bolognani <abologna at redhat.com> wrote:
> On Tue, 2016-01-05 at 14:47 +0100, Christoffer Dall wrote:
>> Why can libvirt not just run the tool and parse its output?  That's what
>> I understood was done for other things, but perhaps I misunderstood.
>
> It's the other way around: the tool uses libvirt to implement its
> checks. Running a command and parsing its output makes sense when the
> binary (as is the case for QEMU) is developed by a third party; if
> you control both pieces, it's usually better to stick to C and avoid
> spawning extra processes.

That argument suggests libvirt should just go ahead and do the
ioctls to check for GICv2/v3 support, rather than spawning a
separate QEMU binary to do the check for it ?

> I realized the information is already sort of exposed by QEMU:
>
>   $ qemu-system-aarch64 -machine virt,?
>   ...
>   virt.gic-version=string (Set GIC version. Valid values are 2, 3 and host)
>   ...
>
> Not the best format to parse, but the information is there. And we
> already have some code to extract such parameters from QEMU using QMP's
> query-command-line-options command![1]

Note that helpstring will tell you whether the qemu you have supports
the machine parameter, but not whether the host CPU supports
GICv2 or 3 (or both) -- it's just a fixed string.

thanks
-- PMM