Ok, I understand it.
I manually create a tap device and I added it to my bridge, can you please
at least tell me how am I supposed to use it with virt-manager? With plain
qemu I simply use -net nic,model=virtio -net
tap,ifname=tap0,script=no,downscript=no,vhost=on but I didn't find how to
use tap0 with the virt-manager graphical interface.
Niccolò