[Qemu-devel] [PATCH 0/22] Refactor machine support

[Anthony Liguori]

This series introduces a rather radical change in the way we deal with machine
definitions in QEMU.  Here are the features this series introduces:

 - Machines are definable via a -machine-def option or a [machine-def] config
   stanza
 - Parameters such as -kernel, -initrd, -append, -m, -acpi-enable, -enable-kvm,
   and potentially many more are now support via a config
 - It's possible to set a default block format (ide, scsi, virtio) for a machine
 - It's possible to make kvm enablement a property of a machine type.  The
   support modes are KVM enabled, TCG enabled, and KVM enabled with TCG
   fallback.
 - All properties of the default machine type are overridable via global config.
   IOW, you can make KVM enablement default without touching the source code.
   You can also increase the default ram size without touching any code.

Conceptually, it works by introducing a MachineCore concept.  A MachineCore is
a function that is able to create a machine based on a set of user specified
parameters.  These parameters may be high level properties (like ram size) or
qdev global properties (virtio-blk-pci.vectors).

A builtin Machine is an instance of a MachineCore that has a set of default
parameters set.

The concept of MachineCore is *not* a stop-gap measure for proper qdev
conversion.  Rather, the idea behind MachineCore is that it's a device tree
builder.

You certainly could still have a machine described purely by a device tree and
qdev properties but that's not enough to represent the UI that we currently
expose.  We need a way convert user visible operations like enable usb to
platform specific operations like add a PIIX3 USB hub.  This is what a
MachineCore does.