A slot is the hotpluggable entity. Open your computer and you can
actually see them.
QEMU doesn't really know that.
How can that be? Do we signal hotplug notifications to a function or
to a slot?
Can we hotplug a single function in an already occupied slot?
What I meant to say: we have no concept of "slot" in the higher level
interfaces, we have only bus and device.
If a PCI device has multiple functions, we have a separate qdev device
for each function. You can't unplug a "slot" (concept doesn't exist in
qdev), only a qdev device. Naturally, when you unplug a qdev device,
all functions in the same PCI slot need to go. This happens deep down
in the bowels of ACPI, in piix4_device_hotplug(). qdev is not aware of
this magic relation between the qdev devices for functions in the same
slot.