Currently, we mount local drives with the "nolock" option. Perhaps we should consider adding file locking support. Citrix added this feature some while ago. For us, it's fairly difficult to support this. unfs3 does not support this, neither does the old unfsd (although the README says Kirch made some progress). The biggest problem, though, is that the NLM protocol, as far as I understand, requires more or less direct network connectivity between the client and server. So, SSH tunnels will most likely not work.
The NLM protocol is (was?) not freely available, but it's documented in our book "NFS Illustrated". Also, there is http://www.swb.de/personal/okir/lockd.html.
