[libvirt] QEMU capabilities vs machine types

Dear list, I've ran into the following bug [1]. The problem is, even though we check whether memory-backend-{ram,file} devices are supported, qemu fails to start. As I see it, on one hand, qemu lies about supported devices (when I imitated libvirt capabilities check by hand on the command line). But on the other hand, libvirt is using '-M none' so even if qemu is fixed, the domain would be unable to start anyway. So I believe my question is, does anybody have a bright idea how to fix this? I don't think we want to extend our capabilities from a list to a matrix (where a machine type would select a list). Moreover, querying and creating the matrix would take ages. But then again, machine type is important. Maybe not so for -x86_64 but for -arm definitely! Or? Michal 1: https://bugzilla.redhat.com/show_bug.cgi?id=1191567