/**
 * @file    demo_char.c
 * @author  Rick Chan (cy187lion@sina.com)
 * @brief   Linux char driver demo.
 * @version 0.1.0
 * @date    2020-04-27
 * 
 * @copyright Copyright (c) 2020
 * 
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <linux/uaccess.h>
#include <linux/fs.h>

#include <linux/slab.h>
#include <linux/device.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
#define DEMO_MODULE_NAME    "demo_char"

#define DEMO_DEV_CNT    2

// This is a test.
#define DEMO_DATA_SIZE  5

static int demo_major = 0;

struct demo_dev
{
    struct cdev cdev;
    struct device *dev;
    // This is a test.
    char demo_text[DEMO_DATA_SIZE];
};

struct class *class;
struct demo_dev* demo_devp;

static int demo_open(struct inode *inode, struct file* filp)
{
    struct demo_dev *demo;
    demo = container_of(inode->i_cdev, struct demo_dev, cdev);
    filp->private_data = demo;

    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)
{
    struct demo_dev *devp = filp->private_data;
    loff_t ret;

    (void)devp;
    // This is a test.
    switch(origin)
    {
    case 0:     // 从文件开头开始偏移
        if(offset<0)
        {
            ret = -EINVAL;
            break;
        }
        if((unsigned int)offset>DEMO_DATA_SIZE)
        {
            ret = -EINVAL;
            break;
        }
        filp->f_pos = (unsigned int)offset;
        ret = filp->f_pos;
        break;
    case 1:     // 从当前位置开始偏移
        if((filp->f_pos+offset)>DEMO_DATA_SIZE)
        {
            ret = -EINVAL;
            break;
        }
        if((filp->f_pos+offset)<0)
        {
            ret = -EINVAL;
            break;
        }
        filp->f_pos += offset;
        ret = filp->f_pos;
        break;
    default:
        ret = -EINVAL;
    }

    return ret;
    return filp->f_pos;
}

static ssize_t demo_read(struct file *filp, char __user *buffer, size_t count, loff_t *position)
{
    struct demo_dev *devp = filp->private_data;
    loff_t p = *position;
    ssize_t ret = 0;

    // This is a test.
    // 分析和获取有效的读长度
    if(DEMO_DATA_SIZE<=p)       // 要读的偏移位置越界
        return 0;               // End of a file
    if(DEMO_DATA_SIZE<(count+p))  // 要读的字节数太大
        count = DEMO_DATA_SIZE-p;

    if(copy_to_user((void*)buffer, &devp->demo_text[p], count))
        ret = -EFAULT;
    else
    {
        *position += count;
        ret = count;
    }
    return ret;
}

static ssize_t demo_write(struct file *filp, const char __user *buffer, size_t count, loff_t *position)
{
    struct demo_dev *devp = filp->private_data;
    const char __user *p = buffer;

    (void)devp;
    return p-buffer;
}

static long demo_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
    struct demo_dev *devp = filp->private_data;
    (void)devp;

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

    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)
{
    struct demo_dev *devp = filp->private_data;
    (void)devp;

    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 int demo_setup_cdev(struct demo_dev *devp, int index)
{
    char name[16];
    int err, devno = MKDEV(demo_major, index);

    cdev_init(&devp->cdev, &demo_fops);
    devp->cdev.owner = THIS_MODULE;
    devp->cdev.ops = &demo_fops;
    err = cdev_add(&devp->cdev, devno, 1);
    if(err)
    {
        printk(KERN_ERR "demo add cdev:%d error:%d.\r\n", index, err);
        goto out_cdev;
    }

    // 创建设备节点
    memset(name, 0, 16);
    sprintf(name, DEMO_MODULE_NAME"%d", index);
    printk(KERN_INFO "demo new dev name:%s", name);
    devp->dev = device_create(class, NULL, devp->cdev.dev, NULL, name);
    // This is a test.
    devp->demo_text[DEMO_DATA_SIZE-2] = '\n';
    devp->demo_text[DEMO_DATA_SIZE-1] = 0;
    sprintf(devp->demo_text, "%d", index);
    return 0;
out_cdev:
    cdev_del(&devp->cdev);
    kfree(devp);
    return err;
}

static int __init demo_init(void)
{
    int err, i;
    dev_t devno = MKDEV(demo_major, 0);

    if(demo_major)  // 使用固定主设备号
        err = register_chrdev_region(devno, DEMO_DEV_CNT, DEMO_MODULE_NAME);
    else            // 动态分配主设备号
    {
        err = alloc_chrdev_region(&devno, 0, DEMO_DEV_CNT, DEMO_MODULE_NAME);
        demo_major = MAJOR(devno);
    }

    if(err<0)
        return err;

    demo_devp = kzalloc(DEMO_DEV_CNT*sizeof(struct demo_dev), GFP_KERNEL);
    if(!demo_devp)
    {
        err = -ENOMEM;
        goto out;
    }

    // 创建设备类, 子设备属于同一个设备类
    class = class_create(THIS_MODULE, DEMO_MODULE_NAME);
    for(i=0; i<DEMO_DEV_CNT; i++)
    {
        err = demo_setup_cdev(&demo_devp[i], i);
        if(err)
            goto out_class;
    }

    return 0;

out_class:
    class_destroy(class);
out:
    unregister_chrdev_region(devno, DEMO_DEV_CNT);
    return err;
}

static void demo_clean_cdev(struct demo_dev *devp)
{
    device_destroy(class, devp->cdev.dev);
    cdev_del(&devp->cdev);
}

static void __exit demo_exit(void)
{
    int i;

    for(i=0; i<DEMO_DEV_CNT; i++)
        demo_clean_cdev(&demo_devp[i]);

    class_destroy(class);
    kfree(demo_devp);
    unregister_chrdev_region(MKDEV(demo_major, 0), DEMO_DEV_CNT);
}

// insmod 时可传入参数
module_param(demo_major, int, S_IRUGO);

module_init(demo_init);
module_exit(demo_exit);