I'm going to use original NetBSD implementation as a base of my port and use FreeBSD port as additional source of information. PUFFS has straightforward design, as name suggests it's "pass-to-userspace framework file system". I also propose to port librefuse library emulating FUSE API. Porting PUFFS can be considered a first step in adding support for file systems as user space servers (http://www.netbsd.org/docs/puffs/rump.html). VFS in Dragonfly is rather different from NetBSD: * Adds new vnode operations, replacing old versions * Different vnode locking scheme * Different file name cache/lookup scheme I'd like to make PUFFS interface identical to kernel level VFS implementation and add wrappers at user level similar to vop_compat_*. That would allow to have rump port easily which would allow to test new file system code as a user space process without addition overhead.