/* GlobalCharDev.c */
#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>#include <asm/uaccess.h>#define DEV_NAME "GlobalChar"static ssize_t GlobalRead(struct file *, char *, size_t, loff_t *);
static ssize_t GlobalWrite(struct file *, const char *, size_t,loff_t *);static int char_major = 0;
static int GlobalData = 0; /* "GlobalChar"设备的全局变量 *//* 初始化字符设备驱动的 file_operations 结构体 */
struct file_operations globalchar_fops =
{.read = GlobalRead,.write = GlobalWrite
};/* 模块初始化 */
static int __init GlobalChar_init(void)
{int ret;ret = register_chrdev(char_major, DEV_NAME, &globalchar_fops);/* 注册设备驱动，_driver_char_misc.c 第290行参考  */if(ret < 0 )printk(KERN_ALERT "GlobalChar Reg Fail\n");else{printk(KERN_ALERT "GlobalChar Reg Success\n");char_major = ret;printk(KERN_ALERT "Major = %d\n", char_major);}return ret;
}/* 模块卸载函数 */
static void __exit GlobalChar_exit(void)
{unregister_chrdev(char_major, DEV_NAME); /* 注销设备驱动 */return;
}/* 模块驱动读函数 */
static ssize_t GlobalRead(struct file *file, char *buf, size_t len, loff_t *off)
{if (copy_to_user(buf, &GlobalData ,sizeof(int)))  {/* 从内核复制 GlobalData 到用户空间*/return -EFAULT;}return sizeof(int);
}/* 模块驱动写函数 */
static ssize_t GlobalWrite(struct file *file, const char *buf, size_t len, loff_t *off)
{if (copy_from_user(&GlobalData, buf, sizeof(int))){/* 从用户复制 GlobalData 到内核 */return -EFAULT;}return sizeof(int);
}module_init(GlobalChar_init);
module_exit(GlobalChar_exit);MODULE_LICENSE("GPL");
MODULE_AUTHOR("dongjin");

ifneq ($(KERNELRELEASE),)    obj-m := GlobalCharDev.o
else# KERNELDIR ?= /lib/modules/$(shell uname -r)/buildKERNELDIR ?= /usr/src/linux-headers-$(shell uname -r)       //这两个都可以PWD := $(shell pwd)default:$(MAKE) -C $(KERNELDIR) M=$(PWD) modulesclean:rm -rf rm -rf *.ko *.mod* *.o* *.sy*
endif

root@ubuntu:/home/arm/data/char_driver# make
make -C /usr/src/linux-headers-4.4.0-31-generic M=/home/arm/data/char_driver modules
make[1]: 正在进入目录 `/usr/src/linux-headers-4.4.0-31-generic'
  CC [M]  /home/arm/data/char_driver/GlobalCharDev.oBuilding modules, stage 2.MODPOST 1 modulesLD [M]  /home/arm/data/char_driver/GlobalCharDev.ko
make[1]:正在离开目录 `/usr/src/linux-headers-4.4.0-31-generic'

/* GlobaiCharText.c 测试文件*/#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>#define DEV_NAME "/dev/GlobalChar"int main()
{int fd, num;/* 打开设备文件 */fd = open(DEV_NAME, O_RDWR, S_IRUSR | S_IWUSR);if(fd < 0){printf("Open Device Fail!\n");return -1;}/* 读取当前设备数值 */read(fd, &num, sizeof(int));printf("The GlobalChar is %d\n", num);printf("Please input a numble written to GlobalChar: ");scanf("%d", &num);/* 写入新的数值 */write(fd, &num, sizeof(int));/* 重新读取数值 */read(fd, &num, sizeof(int));printf("The GlobalChar is %d\n", num);close(fd);return 0;}

root@ubuntu:/home/arm/data/char_driver# ./a.out
The GlobalChar is 0
Please input a numble written to GlobalChar: 111
The GlobalChar is 111