Hybrid Resource Control for Fast-Path Active Extensions

Parveen K Patel
School of Computing
University of Utah, Salt Lake City, UT 84112

Master's Thesis
December, 2003


The ability of active networks technology to allow customized router computation critically depends on having resource control techniques that prevent buggy, malicious, or greedy code from affecting the integrity or availability of the router's resources. It is hard to choose between static and dynamic checking for resource control. Dynamic checking has the advantage of basing its decisions on precise real-time information about what the extension is doing but causes runtime overhead and asynchronous termination. Static checking, on the other hand, has the advantage of avoiding asynchronous termination and runtime overhead, but is overly conservative. This thesis presents a hybrid solution: static checking is used to reject extremely resource-greedy code from the kernel fast path, while dynamic checking is used to enforce overall resource control. The hybrid solution uses a restricted programming model that guarantees termination. It leverages the termination guarantee to reduce the overhead of runtime checks and to avoid asynchronous termination.

This thesis also presents a design and initial implementation of the key parts of the hybrid resource control technique in a router toolkit called RBClick. RBClick is an extension of the Click modular router toolkit, customized for active networking in Janos, an active network operating system. Untrusted extension code is written in a resource-bounded version of Cyclone, a type-safe version of C. RBClick would allow users to download new router extensions directly into the Janos kernel. The thesis shows, by presenting an analysis of existing and new extensions, that hybrid resource control can be successfully applied to many classes of extensions. Further, as compared to the dynamic resource control in Janos, the hybrid solution can improve the performance of router extensions by up to a factor of two.

The full thesis is available in gzip'ed Postscript and PDF formats.