Re: [libvirt] PATCH: Be more flexible in emulator choice on x86 archs

Currently we are pretty strict about what emulator binary we allow for QEMU guests on x86 arches. In particular, for arch+domain type combos: - i686+qemu must use 'qemu' binary - x86_64+qemu must use 'qemu-system-x86_64' binary - kvm must use 'qemu-kvm' or 'kvm' binaries - i686+kvm on x86_64 host is not allowed These restrictions are overkill because - i686+qemu could use 'qemu-system-x86_64' if '-cpu qemu32' is added - i686+qemu could use 'qemu-kvm' if '-cpu qemu32 -no-kvm' is added - x86_64+qemu could use 'qemu-kvm' if '-no-kvm' is added - i686+kvm on x86_64 host can be used if '-cpu qemu32' is added This patch makes QEMU driver more flexible in this way when setting up its capabilities information. It also makes it aware of the -no-kvm and -cpu flag, using them where required by the os type + arch + emulator combinations specified in the guest XML. This should finally remove the confusion where a user in virt-manager selectrs 'i686' and then wonders why we've disallowed choice of 'kvm'. It also fixes 'virsh version' when only qemu-kvm is installed. The matrix should now work thus: 1. qemu, qemu-system-x86_64, qemu-kvm all available qemu+i686 => qemu qemu+x86_64 => qemu-system-x86_64 kvm+i686 => qemu-kvm -cpu qemu32 kvm+x86_64 => qemu-kvm 2. qemu, qemu-kvm available qemu+i686 => qemu qemu+x86_64 => qemu-kvm -no-kvm kvm+i686 => qemu-kvm -cpu qemu32 kvm+x86_64 => qemu-kvm 3. qemu-system-x86_64, qemu-kvm available qemu+i686 => qemu-system-x86_64 -cpu qemu32 qemu+x86_64 => qemu-system-x86_64 kvm+i686 => qemu-kvm -cpu qemu32 kvm+x86_64 => qemu-kvm 4. qemu-kvm available qemu+i686 => qemu-kvm -no-kvm -cpu qemu32 qemu+x86_64 => qemu-kvm -no-kvm kvm+i686 => qemu-kvm -cpu qemu32 kvm+x86_64 => qemu-kvm The only real remaining problem is that we don't cope with scenario where the KVM enabled binary is called 'qemu-system-x64_64' instead of 'qemu-kvm' or 'kvm'.