Re: [libvirt] [Qemu-devel] [RFC PATCH 0/2] ARM: add QMP command to query GIC version

> AFAIK, the current situation of libvirt passing the GIC version to > QEMU and simply reporting in case of failure is not unprecedented > and there are a few cases where probing in advance would simply not > be feasible. >  > Any probing code added to libvirt would have to be kept around > forever to ensure compatibility with current QEMU versions, so it > should IMHO be seen as a last resort in case we can't live without > GIC version probing while it's being implemented, properly, in QEMU.   If libvirt is the most possible consumer for the new command, I think it might not be too hard to keep the compatibility of all possible versions of QEMU. E.g., after we have got a better way to query GIC version other than query-gic-capability, we can do something like this in libvirt:   - try query-gic-capability    - if supported -> [got GIC version]    - if not supported -> try the new method      - if supported -> [got GIC version]      - if not supported -> [not support]   During the time when QEMU has both methods working (before obsoleting the query-gic-capability QMP command), QEMU will make sure querying in both way will get exactly the same results.