[libvirt-users] fstrim support in libvirt/qemu guests

Hi, I'm trying to find out how to enable fstrim support for libvirt/qemu guests. Specifically I'm trying to enable this on a CentOS 7 host (qemu 1.5). I searched the web but only found very vague information and no clear documentation on the requirements or how to modify the guest xml to enable discard/fstrim support. Can someone point me in the right direction? Regards, Dennis