+Starting with qemu version 2.7 usb-bot and usb-uas devices can be
+hotplugged. In the hotplug case they are added with "attached =
+false" so the guest will not see the device until the "attached"
+property is explicitly set to true. That allows to attach one or more
+scsi devices before making the device visible to the guest, i.e. the
+workflow looks like this:
+
+ (1) device-add usb-bot,id=foo
+ (2) device-add scsi-{hd,cd},bus=foo.0,lun=0
+ (2b) optionally add more devices (luns 1 ... 15).
+ (3) scripts/qmp/qom-set foo.attached = true
+