LinuxDeviceDriver幻灯片.ppt

Linux Device Driver Writing a real world device driver for embedded Linux. Outline Concept Kernel Module Char Device Driver Interrupt Handling I/O Management Allocating Memory Block Device Driver Network Device Driver Concept The role of device driver To allow interaction with hardware devices. Providing mechanism, not policy. What capabilities are to be provided? ? Mechanism How those capabilities can be used? ? Policy Writing a Linux device driver Pre-requisites C programming Microprocessor programming Important concepts User space vs. kernel space Concept (Cont.) Execution paths: From user to kernel Concept (Cont.) Classes of devices Characters devices Can be accessed as a stream of bytes. Such a driver usually implements at least the open, close, read, and write system calls. Example: RTC driver. Block devices A device (e.g., a disk) that can host a filesystem. Example: Ramdisk driver. Network interfaces In charge of sending and receiving data packets, driven by the network subsystem of the kernel. Example: Network card driver. Concept (Cont.) A device driver is a kernel module. A kernel module is a device driver? Not necessarily so. Example: ext3 file system module Outline Concept Kernel Module Character Device Driver Interrupt Handling I/O Management Allocating Memory Block Device Driver Network Device Driver Kernel Module The first kernel module “Hello, world” Kernel Module (Cont.) How to compile # gcc -c hello.c -D__KERNEL__  -DMODULE -o hello.o How to insert into kernel # insmod ./hello.o How to remove from kernel # rmmod hello Kernel Module (Cont.) Kernel module vs Application Application Run in user space. Perform a task from beginning to end. Linked to the appropriate library such as libc. Kernel Module Run in kernel space. Register itself in order to serve future requests. Linked only to the kernel, and the only functions it can call are the ones exported by the kernel. Kernel Module (Cont.) Kernel Module (Cont.) Just about all module code h