The role of device drivers
As mentioned in Chapter 4, Porting and Configuring the Kernel, one of the functions of the kernel is to encapsulate the many hardware interfaces of a computer system and present them in a consistent manner to user-space programs. There are frameworks designed to make it easy to write the interface logic for a device in the kernel and you can integrate it with the kernel: this is a device driver, the piece of code that mediates between the kernel above it and the hardware below. A device driver is a piece of software that controls physical devices such as a UART or an MMC controller, or virtual devices such as the null device (/dev/null
) or a ramdisk. One driver may control multiple devices of the same kind.
Kernel device driver code runs at a high privilege level, as does the rest of the kernel. It has full access to the processor address space and hardware registers. It can handle interrupts and DMA transfers. It can make use of the sophisticated kernel infrastructure...