原创 Linux 字符设备驱动的组成

//1、字符设备驱动模块加载与卸载函数

//设备结构

struct XXX_dev                                    
{                                                       
  struct cdev cdev; /*cdev结构体*/                       
  ...
}XXX_dev  ;

/*设备驱动模块加载函数*/
static int __int XXX_init(void)
{

  ...
  cdev_init(&XXX_dev.cdev, &XXX_fops);   //初始化cdev

  /* 申请设备号*/
  if (XXX_major)
    result = register_chrdev_region(XXX_dev_no, 1, DEV_NAME);
  else  /* 动态申请设备号 */
  {
    result = alloc_chrdev_region(&XXX_dev_no, 0, 1, DEV_NAME);
    globalmem_major = MAJOR(devno);
  } 

  ret = cdev_add(&dev->cdev, devno, 1);
  ...
}

/*模块卸载函数*/
static void __exit XXX_exit(void)
{

  unregister_chrdev_region(XXX_dev_no, 1); /*释放设备号*/
  cdev_del(&XXX_devp.cdev);   /*注销cdev*/
  ...

}

//文件设备驱动的file_operations结构体中成员函数

/*读函数*/
static ssize_t XXX_read(struct file *filp, char __user *buf, size_t count,
  loff_t *ppos)
{
  ...

  /*内核空间->用户空间*/
   copy_to_user(buf, ..., ...)

  ...

}

/*写函数*/
static ssize_t globalmem_write(struct file *filp, const char __user *buf,
  size_t count, loff_t *ppos)
{
  ...
    
  /*用户空间->内核空间*/
  copy_from_user(..., buf, ...)

  ...
}

/* ioctl设备控制函数 */
static int globalmem_ioctl(struct inode *inodep, struct file *filp, unsigned
  int cmd, unsigned long arg)
{
  ...

  switch (cmd)
  {
    case XXX_CMD1:
      ...
      break;

   ...

    default:
      return  - ENOTTY;
  }
  return 0;
}
//字符设备驱动文件操作结构体模板

/*文件操作结构体*/
static const struct file_operations globalmem_fops =
{
  .owner = THIS_MODULE,
  .read = XXX_read,
  .write = XXX_write,
  .ioctl = XXX_ioctl,
  ...
};