Re: [PATCH v6 1/4] qemu_capabilities: introduce QEMU_CAPS_ACCEL

From: Hyman Huang(黄勇) <huangy81(a)chinatelecom.cn&gt; since the "-machine" option for accelerators is legacy, "-accel" option may be a better mechanism. following are details: https://lore.kernel.org/qemu-devel/3aa73987-40e8-3619-0723-9f17f73850bd@r... this patch introduce QEMU_CAPS_ACCEL capability to tell if we're dealing new enough QEMU so that we can replace '-machine accel' with '-accel'. there were two phases of -accel support in QEMU: - 2.9 to 4.2: only one -accel option supported; specifying a fallback couldn't be done with -accel and required the older "-machine accel=tcg:kvm" instead. - 5.0 or newer: multiple -accel options supported, e.g. "-accel tcg -accel kvm" and it would be possible to distinguish them, for example using QOM properties. however libvirt only ever specifies one accelerator so it makes no difference. since the oldest supported qemu by libvirt is qemu-2.11, so modify capability test cases with QEMU version >= 2.11.0 carefully.