Besides the example DOS file system that comes with the BeOS developers stuff, there's also a CD-ROM file system example. If you installed the optional stuff on the BeOS 5.0 Pro CD-ROM (or the developer's kit from the free site), it's at: /boot/optional/sample-code/add-ons/iso9660
On BeBits you can get source code examples from a few programs, such as AtheOS FS (app 2028 on BeBits). There used to be a copy of NTFS too with source (app 620 on BeBits), but the site seems to be down. There are also other file systems there, but source is not included (some have it available on request).
Another useful source of information is the BeOS developer library web site. It has some articles on file systems, the most relevant being the One File Network File System, which shows one way of combining a user space program with a kernel file system stub. Another good one is about the FSP (file system protocol). The prior issue describes what features the BFS supports. There are lots of other tangentially related articles, such as ones on device drivers, programming in kernel mode, debugging, etc.
There's also the very good Practical File System Design book by Dominic Giampaolo, from Morgan Kaufmann Publishers, read their catalog entry for more info about the book.
Finally, there's Alexander G. M. Smith's ongoing documentation of the file system API, condensed from all these sources and from his continuing experiences with trying to write a RAM file system. You can get the StyledEdit text file with the October 18 2001 version or check the BeOS directory on his site for newer versions.
Last updated November 11, 2001 by AGMS.