void set_brightness(int fd, int p)
{
	struct v4l2_queryctrl queryctrl;
	struct v4l2_control control;

	int s = ((255*p)/100);

	memset (&queryctrl, 0, sizeof (queryctrl));
	queryctrl.id = V4L2_CID_BRIGHTNESS;

	if (-1 == ioctl (fd, VIDIOC_QUERYCTRL, &queryctrl)) {
		if (errno != EINVAL) {
			perror ("VIDIOC_QUERYCTRL");
			return;
		} else {
			printf ("V4L2_CID_BRIGHTNESS is not supported\n");
		}
	} else if (queryctrl.flags & V4L2_CTRL_FLAG_DISABLED) {
		printf ("V4L2_CID_BRIGHTNESS is not supported\n");
	} else {
		memset (&control, 0, sizeof (control));
		control.id = V4L2_CID_BRIGHTNESS;
		control.value = (queryctrl.minimum + (s * queryctrl.step));

		if (-1 == ioctl (fd, VIDIOC_S_CTRL, &control)) {
			perror ("VIDIOC_S_CTRL");
			return;
		}
	}
}