Knit: component composition for systems software
Alastair Reid, Matthew Flatt, Leigh B. Stoller, Jay Lepreau, Eric N. Eide · 2000
Knit is a new component definition and linking language for systems code. Knit helps make C code more understandable and reusable by third parties, helps eliminate much of the performance overhead of componentization, detects subtle errors in component composition that cannot be caught with normal component type systems, and provides a foundation for developing future analyses over C-based components, such as cross-component optimization. The language is especially designed for use with component kits, where standard linking tools provide inadequate support for component configuration. In particular, we developed Knit for use with the OSKit, a large collection of components for building low-level systems. However, Knit is not OSKit-specific, and we have implemented parts of the Click modular router in terms of Knit components to illustrate the expressiveness and flexibility of our language. This paper provides an overview of the Knit language and its applications. 1 Components for Systems Software Software components can reduce development time by providing programmers with prepackaged chunks of reusable code. The key to making software components work is to define components that are general enough to be useful in many contexts, but simple enough that programmers can understand and use the components’ interfaces. Historically, developers have seen great success with components only in the limited form of libraries. The implementor of a library provides services to unknown clients, but builds on top of an existing, known layer of services. For example, the X11 library builds on the C library. A component implementor, in contrast, provides services to an unknown client while simulta-