/**
 * @file    demo_misc.c
 * @author  Rick Chan (cy187lion@sina.com)
 * @brief   Linux misc driver demo.
            在 Linux 驱动中，会把一些无法归类的设备定义为混杂设备，它们是拥
            有着共同的特性的简单字符设备。它们的特点是共享统一的主设备号 10，
            但每个设备可以选择一个单独的次设备号。

            通常情况下，一个字符设备都不得不在初始化的过程中进行下面的步骤：

            1.通过alloc_chrdev_region()分配主/次设备号
            2.使用cdev_init()和cdev_add()来以一个字符设备注册自己

            而一个misc驱动，则可以只用一个调用misc_register()来完成这所有
            的步骤。

            所有的 miscdevice 设备形成一个链表，对设备访问时，内核根据次设
            备号查找对应的 miscdevice 设备，然后调用其 file_operations 
            中注册的文件操作方法进行操作。
 * @version 0.1.1
 * @date    2020-04-27
 * 
 * @copyright Copyright (c) 2020
 * 
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/miscdevice.h>
#include <linux/uaccess.h>

MODULE_AUTHOR("Rick Chan");
MODULE_LICENSE("GPL");

#define DEMO_MAGIC     'R'
#define DEMO_IOC_SIZE   8
#define DEMO_CTL_IOC   _IOC(_IOC_READ|_IOC_WRITE, DEMO_MAGIC, 0, DEMO_IOC_SIZE)
#define DEMO_CTL_IO    _IO(DEMO_MAGIC, 1)
#define DEMO_CTL_IOR   _IOR(DEMO_MAGIC, 2, uint16_t)
#define DEMO_CTL_IOW   _IOW(DEMO_MAGIC, 3, int32_t)
#define DEMO_CTL_IOWR  _IOWR(DEMO_MAGIC, 4, uint32_t)
#define DEMO_CTL_MAX    5

static int demo_open(struct inode *inode, struct file* filp)
{
    return 0;
}

static int demo_release(struct inode *inode, struct file* filp)
{
    return 0;
}

static loff_t demo_llseek(struct file *filp, loff_t offset, int origin)
{
    return filp->f_pos;
}

static ssize_t demo_read(struct file *filp, char __user *buffer, size_t count, loff_t *offset)
{
    const char __user *p = buffer;
    return p-buffer;
}

static ssize_t demo_write(struct file *filp, const char __user *buffer, size_t count, loff_t *offset)
{
    const char __user *p = buffer;
    return p-buffer;
}

static long demo_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
    static int err = 0;

    // 检测 cmd 合法性.
    if(DEMO_MAGIC!=_IOC_TYPE(cmd)) 
        return -EINVAL;
    if(DEMO_CTL_MAX<_IOC_NR(cmd)) 
        return -EINVAL;

    // 根据命令类型, 检测参数空间是否可以访问.
    if(_IOC_DIR(cmd)&_IOC_READ)
        err = !access_ok(VERIFY_WRITE, (void *)arg, _IOC_SIZE(cmd));
    else if(_IOC_DIR(cmd)&_IOC_WRITE)
        err = !access_ok(VERIFY_READ, (void *)arg, _IOC_SIZE(cmd));

    if (err) 
        return -EFAULT;

    // 根据命令, 来选择执行哪个分支.
    switch(cmd)
    {
    case DEMO_CTL_IOC:
       {
        uint8_t tmp[DEMO_IOC_SIZE];
        copy_from_user(&tmp, (void*)arg, _IOC_SIZE(cmd));
        copy_to_user((void*)arg, &tmp, _IOC_SIZE(cmd));
    }
        break;
    case DEMO_CTL_IO:
        break;
    case DEMO_CTL_IOR:
    {
        uint16_t tmp = 0x55AA;
        copy_to_user((void*)arg, &tmp, _IOC_SIZE(cmd));
    }
        break;
    case DEMO_CTL_IOW:
    {
        int32_t tmp = 0;
        copy_from_user(&tmp, (void*)arg, _IOC_SIZE(cmd));
    }
        break;
    case DEMO_CTL_IOWR:
    {
        uint32_t tmp = 0;
        copy_from_user(&tmp, (void*)arg, _IOC_SIZE(cmd));
        copy_to_user((void*)arg, &tmp, _IOC_SIZE(cmd));
    }
        break;
    default:
        return -ENOIOCTLCMD;
    }
    return 0;
}

static int demo_mmap(struct file* filp, struct vm_area_struct* vma)
{
    return 0;
}

static struct file_operations demo_fops = {
    .owner          = THIS_MODULE,
    .open           = demo_open,
    .release        = demo_release,
    .llseek         = demo_llseek,
    .read           = demo_read,
    .write          = demo_write,
    .unlocked_ioctl = demo_ioctl,
    .mmap           = demo_mmap
};

static struct miscdevice demo_dev = {
    .minor  = MISC_DYNAMIC_MINOR,   // Dynamically allocate minor.
    .name   = "demo_misc",
    .fops   = &demo_fops,
};

static int __init demo_init(void)
{
    misc_register(&demo_dev);   // 注册混杂设备驱动.
    return 0;
}

static void __exit demo_exit(void)
{
    misc_deregister(&demo_dev); // 撤销混杂设备驱动.
}

module_init(demo_init);
module_exit(demo_exit);