Introduction to I/O kit fundamentals, 2006. Experiments show that as much as 65% of driver code can be removed from the kernel without affecting common-case performance, and that only 1-6 percent of the code requires annotations. To achieve compatibility, we present DriverSlicer, a tool that splits existing kernel drivers into a kernel-level component and a user-level component using a small number of programmer annotations. This allows data-handling operations critical to I/O performance to run at full speed, while management operations such as initialization and configuration run at reduced speed in user-level. This paper introduces the Microdrivers architecture that achieves high performance and compatibility by leaving critical path code in the kernel and moving the rest of the driver code to a user-mode process. User-mode drivers have long been seen as a solution to this problem, but suffer from either poor performance or new interfaces that require a rewrite of existing drivers. Faults in kernel drivers can cause the entire operating system to crash. Driver programmers are unable to use user-mode development tools and must instead use cumbersome kernel tools. However, this comes at the price of decreased reliability and increased programming difficulty. Device drivers commonly execute in the kernel to achieve high performance and easy access to kernel services.
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