_: {

  microvm = {
    interfaces = [
      {
        type = "user";

        # interface name on the host
        id = "vm-a1";

        # Ethernet address of the MicroVM's interface, not the host's
        #
        # Locally administered have one of 2/6/A/E in the second nibble.
        mac = "02:00:00:00:00:01";
      }
    ];
    volumes = [
      {
        mountPoint = "/var";
        image = "var.img";
        size = 256;
      }
    ];
    shares = [
      {
        # use proto = "virtiofs" for MicroVMs that are started by systemd
        proto = "9p";
        tag = "ro-store";
        # a host's /nix/store will be picked up so that no
        # squashfs/erofs will be built for it.
        source = "/nix/store";
        mountPoint = "/nix/.ro-store";
      }
    ];

    # "qemu" has 9p built-in!
    hypervisor = "qemu";
    socket = "control.socket";
  };
}