Re: [libvirt] [PATCH v2] xen: Prevent updating device when attaching a device

When attaching a device that already exists, xend driver updates the device with "device_configure", it causes problems (e.g. for disk device, 'device_configure' only can be used to update device like CDROM), on the other hand, we provide additional API (virDomainUpdateDevice) to update device, this fix is to raise up errors instead of updating the existed device which is not CDROM device. Changes from v1 to v2: - allow update CDROM