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#include <linux/module.h>#include <linux/init.h>#include <linux/fs.h>#include <asm/uaccess.h>#include <linux/syscalls.h>MODULE_LICENSE("GPL");#define MAJOR_NUM 100int g_val;static ssize_t global_read(struct file *filp, char __user *buf, size_t len, loff_t *off){int ret;char val[20];printk(KERN_ERR "###### global_read \n");sprintf(val, "%d\n", g_val);ret = simple_read_from_buffer(buf, len, off, val, strlen(val));return ret;}static ssize_t global_write(struct file *filp, const char __user *buf, size_t len, loff_t *off){int  ret, temp;char val[20];//simple_write_to_buffer(void *to, size_t available, loff_t *ppos,const void __user *from, size_t count);ret = simple_write_to_buffer(val, strlen(val), off, buf, len);sscanf(val, "%d", &temp);g_val = temp;return ret;}struct file_operations fileops = {.read = global_read,.write = global_write,};static int __init globalvar_init(void){int reg;g_val = 0;printk(KERN_ERR "golabvar_init \n");reg = register_chrdev(MAJOR_NUM, "globalvar", &fileops);if(reg){printk(KERN_ERR "register_chrdev fail \n");}else{printk(KERN_ERR "register_chrdev sucess \n");}sys_mknodat(AT_FDCWD, "/dev/xxx", O_RDWR | O_CREAT, 100);return 0;} static void __exit globalvar_exit(void){printk("golabvar_exit \n");unregister_chrdev(MAJOR_NUM, "globalvar");}module_init(globalvar_init);module_exit(globalvar_exit);