General-purpose operating systems are ill-equipped to meet the quality of service (QoS) requirements of complex real-time applications. Consequently, many classes of real-time applications have either been carefully developed to compensate for inadequate system support, or they have been developed to run on special purpose systems. This paper focuses on a safe extension architecture for general purpose systems, to allow applications to customize the behavior of the system for their individual needs. Using Linux as the basis for our work, we describe how application programmers can safely ncorporate ?service extensions? into the kernel, so that application-specific QoS guarantees can be provided. We introduce the notion of ?QoS safety ?, which is concerned with meeting the QoS constraints of applications while maintaining system integrity.

Our safe extension architecture supports the dynamic-linking of code into the address space of the kernel, to affect service management decisions. Extensions are written in a type-safe language, to monitor and adapt resource usage on behalf of specific applications. Experimental results show that safe kernel extensions can lead to fewer service violations (and, hence, better qualities of service) for real-time tasks, compared to user-level methods that monitor and adapt system resources.