File-system development with stackable layers

Abstract

Filing services have experienced a number of innovations in recent years, but many of these promising ideas have failed to enter into broad use. One reason is that current filing environments present several barriers to new development. For example, file systems today typically stand alone instead of building on the work of others, and support of new filing services often requires changes that invalidate existing work. Stackable file-system design addresses these issues in several ways. Complex filing services are constructed from layer “building blocks,” each of which may be provided by independent parties. There are no syntactic constraints to layer order, and layers can occupy different address spaces, allowing very flexible layer configuration. Independent layer evolution and development are supported by an extensible interface bounding each layer. This paper discusses stackable layering in detail and presents design techniques it enables. We describe an implementation providing these facilities that exhibits very high performance. By lowering barriers to new filing design, stackable layering offers the potential of broad third-party file-system development not feasible today.