Re: [libvirt] [PATCH v7 1/4] arm: qmp: add query-gic-capabilities interface

This patch add "query-gic-capabilities" but does not implemnet it. The

command is ARM-only. The command will return a list of GICCapability struct that describes all GIC versions that current QEMU and system support. Libvirt is possibly the first consumer of this new command. Before this patch, user will successfully configure all kinds of GIC devices for ARM guests, no matter whether current QEMU/kernel support it. If the specified GIC version/type is not supported, user will got an ambiguous "QEMU boot failure" when trying to start the VM. This is not user-friendly. With this patch, libvirt should be able to query which type (and which version) of GIC device that we support. Use this information, libvirt can warn the user during configuration of guests when specified GIC device type is not supported. Or better, we can just list those versions that we support, and filter out those not-supported ones. For example, if we got the query result: {"return": [{"emulated": false, "version": 3, "kernel": true}, {"emulated": true, "version": 2, "kernel": false}]} Then it means that we support emulated GIC version 2 using: qemu-system-aarch64 -M virt,accel=tcg,gic-version=2 ... or kvm-accelerated GIC version 3 using: qemu-system-aarch64 -M virt,accel=kvm,gic-version=3 ...

If we specify other explicit GIC version rather than the above, QEMU will not be able to boot. Besides, the community is working on a more generic way to query these kind of information. However, due to the eagerness of this command, we decided to first implement this ad-hoc one, then when the generic method is ready, we can move on to that one smoothly. Signed-off-by: Peter Xu <peterx(a)redhat.com&gt; ---