[libvirt] [PATCH] Refresh QEMU driver caps in getCapabilities

Hi all, The attached patch fixes QEMU getCapabilities to refresh caps before returning them to the user. Currently the capabilities are only refreshed once (at daemon startup), which means libvirtd needs to be restarted to pick up changes if QEMU or KVM are installed while the daemon is running. See: https://bugzilla.redhat.com/show_bug.cgi?id=460649 There are several things 'wrong' with this change: - We reset/rescan fields that won't change (host arch, mac address prefix). This should be fixed at some point, but isn't a big deal since total performance impact is negligible (see below). - We only refresh the capabilities when the user calls getCapabilities, which means we are still carrying around stale caps prior to that, which is what libvirt validates against. In practice, virt-manager and virt-install both call getCapabilities often so this isn't an issue, though the caps internal API should probably address this at some point. To test the performance impact, I used a simple python script: import libvirt conn = libvirt.open("qemu:///system") for i in range(0, 30): conn.getCapabilities() The time difference was on average .02 seconds slower, which I think is negligible. If at somepoint in the future, capabilities generation becomes smarter (searching PATH emulators, scraping device list output, etc.) it might be worth re-checking the time impact. But for now it doesn't seem to be an issue. Thanks, Cole