lkmpg/examples/chardev.h

/*
 *  chardev.h - the header file with the ioctl definitions.
 *
 *  The declarations here have to be in a header file, because
 *  they need to be known both to the kernel module
 *  (in chardev.c) and the process calling ioctl (ioctl.c)
 */

#ifndef CHARDEV_H
#define CHARDEV_H

#include <linux/ioctl.h>

/*
 * The major device number. We can't rely on dynamic
 * registration any more, because ioctls need to know
 * it.
 */
#define MAJOR_NUM 100

/*
 * Set the message of the device driver
 */
#define IOCTL_SET_MSG _IOW(MAJOR_NUM, 0, char *)
/*
 * _IOW means that we're creating an ioctl command
 * number for passing information from a user process
 * to the kernel module.
 *
 * The first arguments, MAJOR_NUM, is the major device
 * number we're using.
 *
 * The second argument is the number of the command
 * (there could be several with different meanings).
 *
 * The third argument is the type we want to get from
 * the process to the kernel.
 */

/*
 * Get the message of the device driver
 */
#define IOCTL_GET_MSG _IOR(MAJOR_NUM, 1, char *)
/*
 * This IOCTL is used for output, to get the message
 * of the device driver. However, we still need the
 * buffer to place the message in to be input,
 * as it is allocated by the process.
 */

/*
 * Get the n'th byte of the message
 */
#define IOCTL_GET_NTH_BYTE _IOWR(MAJOR_NUM, 2, int)
/*
 * The IOCTL is used for both input and output. It
 * receives from the user a number, n, and returns
 * Message[n].
 */

/*
 * The name of the device file
 */
#define DEVICE_FILE_NAME "char_dev"

#endif