#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>static ssize_t light_read(struct file *, char __user *, size_t, loff_t *);
static ssize_t light_write(struct file *, const char __user *, size_t,loff_t *);static int light_open(struct inode *, struct file *);
static int light_release(struct inode *, struct file *);static long light_unlocked_ioctl(struct file *, unsigned int, unsigned long);struct file_operations light_fops = {.owner = THIS_MODULE,.read = light_read,.write = light_write,.open = light_open,.release = light_release,.unlocked_ioctl = light_unlocked_ioctl,// all others are NULL
};#define BUFFER_SIZE 64
#define SUCCESS 0

#include <asm-generic/uaccess.h>
#include <linux/timer.h>
#include "light.h"/********* light status *******/
enum light_enum {ALL_ZERO = 1, // every time got zeroALL_ONE = 3, // every time got ONEALTERNATIVE = 5, // got 1,0,1,0...
};static enum light_enum light_flag = ALTERNATIVE;
static int lastword = 0;
static int Device_Open = 0;
static int BASE_ADDR = 0x378;extern struct file_operations light_fops;/******************************/
static struct timer_list light_timer;
static int SLEEP_INTERVAL = 500;int rounds = 1;void light_timer_callback(unsigned long data) {char output;
//  printk("my_timer_callback called (%ld).\n", jiffies);switch (light_flag) {case ALL_ONE:output = 0xff;break;case ALL_ZERO:output = 0;break;case ALTERNATIVE:output = lastword == 0 ? 0 : 0xff;lastword ^= 1;break;default:printk("see error flag.\n");return;}outb(output, BASE_ADDR);// need to send a 0x00 signal to stop thatmod_timer(&light_timer,jiffies + msecs_to_jiffies(SLEEP_INTERVAL * rounds));
}
/******************************//******* light functions *******/
// read the round number, nothing to do with count
static ssize_t light_read(struct file * file, char __user * buf, size_t count,loff_t * pos) {int len;char kbuf[BUFFER_SIZE];printk("read inside the kernel\n");if (!Device_Open) {printk("device not opened\n");return -1;}if (rounds > 100) {printk("rounds too big\n");return -1;}kbuf[0] = (char) rounds;kbuf[1] = 0;len = 1;copy_to_user(buf, kbuf, len);printk("read %d chars from kernel\n", len);return len;
}// write the type, not implemented yet
static ssize_t light_write(struct file * file, const char __user * buf,size_t count, loff_t * pos) {char kbuf[BUFFER_SIZE];int tmp;printk("write inside the kernel\n");if (!access_ok(VERIFY_WRITE, buf, count))return -EFAULT;if (!Device_Open) {printk("device not opened\n");return -1;}if (count == 0) {return -EFAULT;}if (copy_from_user(kbuf, buf, count))return -EFAULT;tmp = kbuf[0];if (0 < tmp && tmp < 100) {printk("modify interval rounds from %d to %d\n", rounds, tmp);rounds = tmp;}return 1;
}static int light_open(struct inode * inode, struct file * file) {if (Device_Open)return -EBUSY;Device_Open++;try_module_get(THIS_MODULE);return SUCCESS;
}
static int light_release(struct inode * inode, struct file * file) {Device_Open--;module_put(THIS_MODULE);return 0;
}// set flat to ALL_ONE, ALL_ZERO or ALTERNATIVE
static long light_unlocked_ioctl(struct file * file, unsigned int cmd,unsigned long arg) {switch (cmd) {case ALL_ONE:case ALL_ZERO:case ALTERNATIVE:printk("change status from %d to %d\n", light_flag, cmd);light_flag = cmd;break;default:printk("meet error %d, %ld\n", cmd, arg);return -1;}return SUCCESS;
}/********* light end *******//********* dev control *******/
static int Major;
#define DEVICE_NAME "light_test"int light_init(void) {Major = register_chrdev(0, DEVICE_NAME, &light_fops);if (Major < 0) {printk("Registering the character device failed with %d/n", Major);return Major;}printk("create a dev file with mknod /dev/? c %d 0.\n", Major);printk("ZERO %d, ONE %d, ALTER %d\n", ALL_ZERO, ALL_ONE, ALTERNATIVE);setup_timer( &light_timer, light_timer_callback, 0);mod_timer(&light_timer,jiffies + msecs_to_jiffies(SLEEP_INTERVAL * rounds));return 0;
}void light_exit(void) {int ret = 1;while (ret) {ret = del_timer(&light_timer);printk("The timer is still in use...\n");}printk("unregister_chrdev: %d\n", Major);unregister_chrdev(Major, DEVICE_NAME);
}
/********* dev control end*******/module_init(light_init);
module_exit(light_exit);

ifneq ($(KERNELRELEASE),)
# kbuild part of makefile
obj-m  := light.oelse
# normal makefileKDIR ?= /lib/modules/`uname -r`/builddefault:$(MAKE) -C $(KDIR) M=$$PWD modules
endif