[Samba] VFS for Samba 3 or 4

[Daniel Iwan]

I'm intending to write a VFS module for Samba and my question is: should I
be writing it as a samba3 module or rather samba4 ntvfs?
Initially I plan to deploy Samba 3 but in the nearest future it will be
definitely Samba 4 due to it's ActiveDirectory support.
Is writing ntvfs modules actually recommended or is it too low level and
something like POSIX abstraction would be more appropriate?
If I write it as Samba3 module how much effort is required to migrate it to
 POSIX compliant module for Samba 4 and eventually ntvfs module?

Regards
Daniel