最简单的内核字符设备驱动

这是参考《Linux设备驱动程序》第三版写的一个简单的字符设备驱动程序，简直简单得无与伦比，不过也算是2.6内核风格的了。实现的功能是当应用程序读此设备时，返回26个英文字母。

第一步，建立一个字符设备文件：
mknod /dev/scull c 200 0
chmod 666 /dev/scull

以下是驱动源码，scull.c
/****************************Begin**************************/
#include <linux/init.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <asm/uaccess.h>

#define DEV_MAJOR 200
#define DEV_MINOR 0
MODULE_LICENSE("Dual BSD/GPL");

char *buffer = "abcdefghijklmnopqrstuvwxyz";

static int scull_open( struct inode *scull_inode, struct file *scull_file );
static int scull_release( struct inode *scull_inode, struct file *scull_file );
static ssize_t scull_read( struct file *p_file, char *u_buffer, size_t count, loff_t *ppos );

dev_t scull_dev;
struct cdev *scull_cdev;
struct file_operations scull_fops = {
    owner : THIS_MODULE,
    read : scull_read,
//    .write = scull_write,
    open : scull_open,
    release : scull_release,   
};

static int scull_open( struct inode *p_inode, struct file *p_file )
{
    return( 0 );
}

static int scull_release( struct inode *p_inode, struct file *p_file )
{
    return( 0 );
}

static ssize_t scull_read( struct file *p_file, char *u_buffer, size_t count, loff_t *ppos )
{
    int rc;
    rc = copy_to_user( u_buffer, buffer, count );
    return( rc );
}

static int scull_init( void )
{
    scull_dev = MKDEV( DEV_MAJOR, DEV_MINOR );
    register_chrdev_region( scull_dev, 1, "scull" );
   
    scull_cdev = cdev_alloc();
    scull_cdev->owner = THIS_MODULE;
    scull_cdev->ops = &scull_fops;
    cdev_init( scull_cdev, &scull_fops );
    cdev_add( scull_cdev, scull_dev, 1 );
   
    return( 0 );
}

static void scull_exit( void )
{
    cdev_del( scull_cdev );
   
    unregister_chrdev_region( scull_dev, 1 );
}

module_init(scull_init);
module_exit(scull_exit);
/***************************END*****************************/

以下是Makefile：
/***************************Begin*****************************/
KERNELDIR := /usr/src/linux-2.6.16-beyond/
obj-m := scull.o
default:
    $(MAKE) -C $(KERNELDIR) M=`pwd` modules
/***************************END*****************************/

以下是测试程序：
/***************************Begin*****************************/
#include <linux/fs.h>
#include <stdio.h>

int main()
{
    char buffer[64];
    int count;
   
    int fd;
    fd = open( "/dev/scull", 0 );
    read( fd, buffer, 20 );
    printf( "%s", buffer );
    close( fd );
    return( 0 );
}
/***************************END*****************************/

完成了，是不是简单得令人发指啊？