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Device Access and the I/O Kit

In Mac OS X, kernel space is the protected memory partition in which the kernel resides, while user space is memory outside the kernel’s partition. Most device drivers reside in kernel space, typically because they take primary interrupts (which requires them to live in the kernel) or because their primary client resides in the kernel (such as a device driver for an Ethernet card that resides in the kernel because the network stacks reside there).

Because only code running in the kernel can directly access hardware devices, Mac OS X provides two mechanisms that allow your application or other user-space code to make use of kernel-resident drivers and other kernel services. These mechanisms are I/O Kit device interfaces and POSIX support, using device files.

This chapter summarizes fundamental I/O Kit concepts and terms and describes some of the actions the I/O Kit takes to support devices attached to a Mac OS X computer. Then, it introduces device interfaces and device files, describing how they work and where they fit into the I/O Kit’s layered, runtime architecture.

Contents:

I/O Kit Summary
Device Interfaces and Device Files

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