Re: [libvirt] ARM KVM GICv3 Support

On Tue, 2016-01-05 at 18:14 +0000, Peter Maydell 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 ? libvirt already has to spawn QEMU and run QMP commands to probe for dozens of other capabilities, so we have very robust code to do that. Most importantly, as I wrote in a previous mail, if the check is done by QEMU we remove the risk of it and libvirt ever disagreeing.