[libvirt] It's said 'when the guest has PCI passthrough devices in use, operations like migration/save/restore are not possible.' where are the corresponding codes in xen? '

It's said 'when the guest has PCI passthrough devices in use, operations like migration/save/restore are not possible.' where are the corresponding codes in xen?  I'm wondering how xend/xenlight tells whether a guest has a pci passthu device in use or not.        thank you in advance!  已从三星手机发送