Pattern: FOO's PCIDeviceInfo method exit is virtio_FOO_exit_pci(), which calls virtio_FOO_exit() and virtio_exit_pci().
virtio_{net,serial}_exit() call virtio_cleanup(). virtio_blk_exit() doesn't. Why? virtio-balloon-pci uses virtio_exit_pci() as exit method. No virtio_cleanup()? virtio-9p-pci doesn't have an exit method. Doesn't feel right. I suspect these three leak memory or worse on hot unplug.