File System development is very difficult and time consuming. Even small changes to existing file systems require deep understanding of kernel internals, making the barrier to entry for new developers high.
Moreover, porting file system code from one operating system to another is almost as difficult as the first port. Past proposals to provide extensible (stackable) file system interfaces would have simplified the development of new file systems.
These proposals, however, advocated massive changes to existing operating system interfaces and existing file systems; operating system vendors and maintainers resist making any large changes to their kernels because of stability and performance concerns. As a result, file system development is still a difficult, long, and non-portable process.
The FiST (File System Translator) system combines two methods to solve the above problems in a novel way: a set of stackable file system templates for each operating system, and a high-level language that can describe stackable file systems in a cross-platform portable fashion.
Using FiST, stackable file systems need only be described once. FiST's code generation tool, fistgen, compiles a single file system description into loadable kernel modules for several operating systems (currently Solaris, Linux, and FreeBSD).
The project demonstrates that with FiST, code size and development time are reduced significantly, while imposing a small performance overhead of only 1-2%. These benefits are achieved, as well as portability, without changing existing operating systems or file system.
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