idmap question

[Herb Lewis]

I was starting to play around with the new idmap stuff in 3.0.25
so I can figure out how it works but I'm having a problem
getting the right parameters in smb.conf.  I was trying to
use something other than tdb (tried nss) but I must be missing
something basic - lack of documentation doesn't help :-)

I first tried just

idmap backend = nss

but that among other things says that is depricated. So then I
tried

idmap domains = default
idmap config default: backend = nss

and that complains

ERROR: Initialization failed for alloc backend tdb
Aborting IDMAP Initialization ...

So if I wanted to setup a simple test to use nss backend
(basically so I can figure out how to write a new one for
our systems) what do I need to have in smb.conf?