#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/cdev.h>
#include <asm/uaccess.h>
#define     TEST_DEVICE_NAME    "test_dev"
#define        BUFF_SZ                1024

/*全局变量*/
static struct cdev test_dev;
unsigned int major =0;
static char *data = NULL;

/*读函数*/
static ssize_t test_read(struct file *file, 
                                 char *buf, size_t count, loff_t *f_pos)
{
    int len;
    if (count < 0 )
    {
        return -EINVAL;
    }
    len = strlen(data);
    count = (len > count)?count:len;
    if (copy_to_user(buf, data, count)) /* 将内核缓冲的数据拷贝到用户空间*/
    {
        return -EFAULT;
    }
    return count;
}
/*写函数*/
static ssize_t test_write(struct file *file, const char *buffer, 
                                       size_t count, loff_t *f_pos)
{
    if(count < 0)
    {
        return -EINVAL;
    }
    memset(data, 0, BUFF_SZ);
        count = (BUFF_SZ > count)?count:BUFF_SZ;
    if (copy_from_user(data, buffer, count)) /* 将用户缓冲的数据复制到内核空间*/
    {
        return -EFAULT;
    }
    return count;
}
/*打开函数*/
static int test_open(struct inode *inode, struct file *file)
{
    printk("This is open operation\n");
    /* 分配并初始化缓冲区*/
    data = (char*)kmalloc(sizeof(char) * BUFF_SZ, GFP_KERNEL);
    if (!data)
    {
        return -ENOMEM;
    }
    memset(data, 0, BUFF_SZ); 
    return 0;
}
/*关闭函数*/
static int test_release(struct inode *inode,struct file *file)
{
    printk("This is release operation\n");
 if (data)
    {
        kfree(data); /* 释放缓冲区*/
        data = NULL; /* 防止出现野指针 */
    }
    return 0;
}
/* 创建、初始化字符设备，并且注册到系统*/
static void test_setup_cdev(struct cdev *dev, int minor,
        struct file_operations *fops)
{
    int err, devno = MKDEV(major, minor);
    cdev_init(dev, fops);
    dev->owner = THIS_MODULE;
    dev->ops = fops;
    err = cdev_add (dev, devno, 1);
    if (err)
    {
        printk (KERN_NOTICE "Error %d adding test %d", err, minor);
    }
}

/* 虚拟设备的file_operations结构 */
static struct file_operations test_fops = 
{
    .owner   = THIS_MODULE,
    .read    = test_read,
    .write   = test_write,
    .open    = test_open,
    .release = test_release,
};

/*模块注册入口*/
int init_module(void)
{
    int result;
    dev_t dev = MKDEV(major, 0);

    if (major)
    {/* 静态注册一个设备，设备号先前指定好，并设定设备名，用cat /proc/devices来查看 */
        result = register_chrdev_region(dev, 1, TEST_DEVICE_NAME);
    }
    else 
    {
        result = alloc_chrdev_region(&dev, 0, 1, TEST_DEVICE_NAME);
    }

    if (result < 0) 
    {
        printk(KERN_WARNING "Test device: unable to get major %d\n", major);
        return result;
    }
    test_setup_cdev(&test_dev, 0, &test_fops);
    printk("The major of the test device is %d\n", major);
    return 0;
}

/*卸载模块*/
void cleanup_module(void) 
{
    cdev_del(&test_dev);
    unregister_chrdev_region(MKDEV(major, 0), 1);
    printk("Test device uninstalled\n");
}