Virtual Machine Manager vs. qemu-kvm commandline issue (tap xor snapshot)

I want to experiment with pacemaker, and for that I’d like to start kvm virtual machines with the snapshot option, so that as soon as I stop the vm, all changes are gone and I can start over.

Since I couldn’t figure out how to setup networking (vm - vm and vm - public) with a kvm commandline without disturbing the Network Manager, I used the Virtual Machine Manager (VMM) for this.

It works now, but I cant see how to use the snapshot option with the VMM.
On the other hand, I cant see how I start the resulting vm from the commandline.
When I look at the process list, I see the command with these network options:

-netdev tap,fd=21,id=hostnet0 
-device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:45:30:b0,bus=pci.0,addr=0x3 
-netdev tap,fd=22,id=hostnet1 
-device virtio-net-pci,netdev=hostnet1,id=net1,mac=52:54:00:84:5b:bc,bus=pci.0,addr=0x6 

How would I go about these fd=nn things on the commandline?
I guess I somehow have to start the tap devices before, but how?

Ok, still dont know how to setup the tap devices, but that is pretty much obsolete now, because I found out about virsh:

virsh list --all

virsh snapshot-create DOMAINNAME

virsh start DOMAINNAME

virsh destroy DOMAINNAME

virsh snapshot-revert DOMAINNAME SNAPSHOTNAME

so, virt-manager + virsh = best of both worlds … COOL!