LInux 字符设备驱动程序

#include <linux/module.h>

#include <linux/init.h>

#include <linux/fs.h>

#include <asm/uaccess.h>

MODULE_LICENSE("GPL");// 设置这个模块的协议为 GPL

#define MAJOR_NUM 2918 //主设备号

//声明Read函数
static ssize_t device_read(struct file *, char *, size_t, loff_t*);
//声明Write函数
static ssize_t device_write(struct file *, const char *, size_t, loff_t*);

//初始化字符设备驱动的file_operations结构体

struct file_operations device_fops =

{
.read=device_read,
.write=device_write,
};

static int device_var = 0; //"globalvar"设备的全局变量

static int __init device_init(void)
{
int ret;
//注册设备驱动
ret = register_chrdev(MAJOR_NUM, "device", &device_fops);
if (ret)
{
printk("device register failure");
}
else
{
printk("device register success");
}
return ret;
}

static void __exit device_exit(void)
{
int ret = 0;
//注销设备驱动
unregister_chrdev(MAJOR_NUM, "device");
if (ret)
{
printk("device unregister failure");
}
else
{
printk("device unregister success");
}
}
//READ
static ssize_t device_read(struct file *filp, char *buf, size_t len, loff_t *off)
{
//将device_var从内核空间复制到用户空间
if (copy_to_user(buf, &device_var, sizeof(int)))
{
return - EFAULT;
}
return sizeof(int);
}
static ssize_t device_write(struct file *filp, const char *buf, size_t len, loff_t *off)
{
//将用户空间的数据复制到内核空间的device_var
if (copy_from_user(&device_var, buf, sizeof(int)))
{
return - EFAULT;
}
return sizeof(int);
}
module_init(device_init);
module_exit(device_exit);

编译为模块：

命令为：make -C /lib/modules/3.0.0-7-generic/build M(等号)/home/shi/c_dev/modules

Makefile为

 

# From《Linux Device Drivers》3rd Edition
# Makefile
ifneq ($(KERNELRELEASE),)
# call from kernel build system

obj-m   := device.o

else

KERNELDIR ?= /lib/modules/$(shell uname -r)/build
PWD       := $(shell pwd)

default:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules

endif

完成之后，讲模块加入到内核中去

sudo insmod ./device.ko

查看所有模块

lsmod

删除模块

sudo rmmod ./device.ko

测试程序

 

#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <fcntl.h>
main()
{
int fd,num;
//打开"/dev/device"
fd = open("/dev/device", O_RDWR, S_IRUSR | S_IWUSR);
if (fd != 0)
{
//初次读device
read(fd, &num, sizeof(int));
printf("The device is %d\n", num);
//写device
printf("Please input the num written to device\n");
scanf("%d", &num);
write(fd, &num, sizeof(int));
//再次读device
read(fd, &num, sizeof(int));
printf("The device is %d\n", num);
//关闭"/dev/device"
close(fd);
}
else
{
printf("Device open failure\n");
}
}

运行结果

shi@smkoo:~/c_dev$ ./test
The device is 134514219
Please input the num written to device
1
The device is 1