#ifndef _IOCTL_CHAR_DEVICE_H_
#define _IOCTL_CHAR_DEVICE_H_

#include <linux/ioctl.h>

/**
 *  ioctl constants are defined in this header file for our
 *  char_driver_ioctl driver.
 * 
 *  This file explains how the constants are defined with
 *  the use of inline comments
 */

/**
 *  Constants have to be globally unique. Though this is not
 *  compulsory, it is necessary. This is because of the simple
 *  reason: we do not want our commands to clash with the commands
 *  in other drivers. we don't want the right command doing to
 *  the wrong driver or vice-versa
 */

/**
 *  We have to base our constants based on a magic number. 
 */

#define DEMO_IOCTL_MAGIC 'a'

/**
 * Defining constants requires us to decide following values
 * 
 * 1. type or magic number (type)
 * 2. sequence number which is eight bits wide. This means
 *    we can have up to 256 ioctl commands (nr)
 * 3. direction if the arg is involed, whether we are reading
 *    or writing
 * 4. size(composition) of the argument.
 * 
 *  To arrive at unique numbers easily we use the following macros
 *  _IO(type, nr); -> no data is passed from kernel to user space, just like void function
 *  _IOW(type, nr, dataitem) the fourth item calculated using sizeof -> to read from user to kernel
 *  _IOR(type, nr, dataitem) -> to write to user from kernel
 *  _IOWR(type, nr, dataitem) -> to do both read and write
 */

#define WR_VALUE _IOW(DEMO_IOCTL_MAGIC, 1, int32_t *)
#define RD_VALUE _IOR(DEMO_IOCTL_MAGIC, 2, int32_t *)
 
#endif