Generic User-Level PCI Drivers

Linux has become a popular foundation for systems with real-time requirements such as industrial control applications. In order to run such workloads on Linux, the kernel needs to provide certain properties, such as low interrupt latencies. For this purpose, the kernel has been thoroughly examined, tuned, and verified. This examination includes all aspects of the kernel, including the device drivers necessary to run the system. However, hardware may change and therefore require device driver updates or replacements. Such an update might require reevaluation of the whole kernel because of the tight integration of device drivers into the system and the manyfold ways of potential interactions. This approach is time-consuming and might require revalidation by a third party. To mitigate these costs, we propose to run device drivers in user-space applications. This allows to rely on the unmodified and already analyzed latency characteristics of the kernel when updating drivers, so that only the drivers themselves remain in the need of evaluation. In this paper, we present the Device Driver Environment (DDE), which uses the UIO framework supplemented by some modifications, which allow running any recent PCI driver from the Linux kernel without modifications in user space. We report on our implementation, discuss problems related to DMA from user space and evaluate the achieved performance.