On Mon, Jan 11, 2021 at 10:14:58 +0100, Paolo Bonzini wrote: > On 11/01/21 09:35, J�¡n Tomko wrote: > >> This unfortunately cannot be done unconditionally.� You need to probe > >> for the availability of -accel, using something like > > > > What are we probing for? > > Existence of "-accel". "-accel" allows configuration of > accelerator-specific, machine-independent properties. In the past they > went in -machine but the two have been separate since 5.0 (with > backwards-compatible glue). > > 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. We use a fallback for capabilities probing (in qemuProcessQMPLaunch) so in case the old -machine type,accel=... way is going to be deprecated, we need to be able to detect whether multiple -accel options are allowed and use -machine otherwise. Jirka
