Creating a Linu Device Driver Welcome to Utah State University创建一个Linu设备驱动程序 欢迎来到犹他州立大学.doc

Creating a Linux Device Driver Much of the following was taken from “The Linux Kernel Module Programming Guide” by Peter Salzman (/LDP/lkmpg/) 1. Define the hardware device. This requires specifying the name of the device and major and minor device numbers. Normally, device numbers are assigned to a manufacturer and are unique for each device. Fortunately, Linux has reserved some device numbers for demonstrations and experiments: Major 60-63 and minor 0-255. Devices are normally defined by special files in /dev. A program reads or writes to a device by treating it as a ‘file’. Devices are specified to be character- or block- oriented depending upon whether they need a buffering. To define a simple device, use mknod as superuser. The following example defines /dev/my_device as character oriented with major and minor numbers of 60 and 128. $ mknod /dev/my_device c 60 128 2. Write a device driver A device driver program is an example of a Linux module. A module is different from a user-program in that a) there is no main(), b) each module must include members init_module() and cleanup_module(), and c) a module may not call library functions – only functions available in the kernel as listed in /proc/ksyms. The init_module() function is invoked when the module is installed. The cleanup_module() is invoked when the driver is removed. The primary responsibility of the init_module() function is to register the module as the device driver for the hardware device you defined in step #1 above. For a character device, this is done with the register_chrdev(). The arguments to this function are the major device number, the name of the device (used in the mknod command), and a struct file_operations structure that Linux will add to the master device table. The minor number isn’t really used by Linux – it is available to the device driver to differentiate between a family of similar devices. As such, family of devices sharing the same major number may be serviced by a s