Use a NFS mount via loopback for testing file system operations.
By changing files directly on the server and accessing them on the
client or vice versa, specific kernel behavior can be triggered.
Especially using file mmap(2) over NFS is tested.

These tests must be run as root, on a system with a free vnd0 slot.
They create an entry in /etc/exports and start NFS server daemons
for a loopback mount.