[libvirt] How to call QEMU with -snapshot ?

Hi, I want to execute qemu (actually is KVM, qemu-system_x86-64) with -snapshot. Is there any way to do that? I tried following ways, and none works: - Put -snapshot in <emulator> in configuration file. - Create a script calling "qemu -snapshot", and rename it to qemu-system_x86-64 (and of course i rename the original one to smt else, and let my scrip call that) In all these cases, I got error about parsing for QEMU version. Thanks, J