[libvirt] How to make udev not touch my device?

Hey udev developers, I'm a libvirt developer and I've been facing an interesting issue recently. Libvirt is a library for managing virtual machines and as such allows basically any device to be exposed to a virtual machine. For instance, a virtual machine can use /dev/sdX as its own disk. Because of security reasons we allow users to configure their VMs to run under different UID/GID and also SELinux context. That means that whenever a VM is being started up, libvirtd (our daemon we have) relabels all the necessary paths that QEMU process (representing VM) can touch. However, I'm facing an issue that I don't know how to fix. In some cases QEMU can close & reopen a block device. However, closing a block device triggers an event and hence if there is a rule that sets a security label on a device the QEMU process is unable to reopen the device again. My question is, whet we can do to prevent udev from mangling with our security labels that we've set on the devices? One of the ideas our lead developer had was for libvirt to set some kind of udev label on devices managed by libvirt (when setting up security labels) and then whenever udev sees such labelled device it won't touch it at all (this could be achieved by a rule perhaps?). Later, when domain is shutting down libvirt removes that label. But I don't think setting an arbitrary label on devices is supported, is it? Michal