Enhancement Request: Support configuration of default storage controller and type VirtIO

[VanNostrand]

I want to configure the default storage controller to be of type virtio but at the moment it seems to be impossible to configure the default storage controller in any way.
I mean I can create a new virtualbox instance with vagrant, open the GUI and just switch the type from AHCI to virtio-scsi. It is trivial and the VM works - but there is no such function in vagrant.

In the Vagrantfile I could always add a controller via e.g.

vb.customize ["storagectl", :id, "--name", "VirtIO Controller", "--add", "virtio", "--controller", "VirtIO"]

but the default SATA AHCI controller has already been created before that happens.
It also means the default disk is attached to that controller automatically and I have no chance to plug it into the other one.
And when I remove the SATA AHCI controller via vagrant then the system has no disk attached.

And if I try to attach the system disk that has previously and automatically been created I found out that either Vagrant or Virtualbox always tries to look in the current directory for the vmdk file instead of ~/.VirtualBox/Machines/myvm/. I tried to trick it by providing a path with a couple of ../../../ entries to ensure the path points to the box.vmdk in the ~/.VirtualBox/Machines/myvm/ subdirectory but then the VirtualBox tooling tells me that this file was supposed to not be attached to that controller because some of its dumb xml files says so (sorry, I did not keep the error, because I was about to shoot the computer after 12 hours of dealing with that issue) and in another approach I also specified the disk's UUID, which according to the VBoxManage help would be a valid option, but VBoxManage tried to treat that UUID as a literal filename...

I am not sure how Vagrant exactly configures the default controller and disk. In action.rb I can see this:

      b.use CleanupDisks
      b.use Disk
      b.use Customize, "pre-boot"
      b.use Boot
      b.use Customize, "post-boot"

and if all customize commands are implied to be used in the pre-boot stage (like setting the amount of CPUs and RAM size etc), then I have no influence on setting the default disk.

When I grep through the sources, the virtio driver is never mentioned anywhere too. I can see the following:

  class StorageController
    IDE_CONTROLLER_TYPES = ["PIIX4", "PIIX3", "ICH6"].map(&:freeze).freeze
    SATA_CONTROLLER_TYPES = ["IntelAhci"].map(&:freeze).freeze
    SCSI_CONTROLLER_TYPES = [ "LsiLogic", "BusLogic"].map(&:freeze).freeze

But there is no virtio. My storagectl from above probably just works because it is passed 1:1 to VBoxManage somehow:

VBoxManage storagectl <uuid | vmname> <--name=controller-name> [--add= floppy | ide | pcie | sas | sata | scsi | usb ] [--controller= BusLogic | I82078 | ICH6 | IntelAhci | LSILogic | LSILogicSAS | NVMe | PIIX3 | PIIX4 | USB | VirtIO ] [--bootable= on | off ] [--hostiocache= on | off ] [--portcount=count] [--remove] [--rename=new-controller-name]