[Qemu-devel] machines and versions - why so many?

[Alexey Kardashevskiy <aik@ozlabs.ru>]

Hi!

I have been hearing recently that we (server PPC) should have more that
just one pseries machine in QEMU because this is what everybody else does :)

My current understanding is that multiple machines (like
pc-i440fx-1.4..2.1, and many others) are needed:

1) for the -nodefaults case when a lot of devices are still created and
there is no other way to configure them;

in "pseries", only CPU + empty VIO + empty PCI buses are created,
everything else can be created explicitly; nothing to tweak;

2) to enable/disable CPUID_EXT_xxx bits (saw in x86);

in "pseries", there is a "compat" property on CPU and that seems to be enough;

3) for devices which are created explicitly and for which we want some
capabilities be disabled and we do not want to bother about this every time
we run QEMU;

ok, this one makes some sense for "pseries" to have (and upcoming
endianness register on VGA seems to be the case) but it seems that adding a
"compat" or "feature" property to the VGA device (and other devices which
deal with this kind of compatibility) is still more architecturally correct
thing to do, and let libvirt deal with the rest.

Since I (almost) always miss the bigger picture, what do I miss now? :) Thanks!


-- 
Alexey