/*
 * This module implements the basic serial port opening operation.
 */

#include <sys/types.h>
#include <sys/file.h>
#include <sys/ioctl.h>
#include <linux/serial.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int target_fd;

open_serial_port(ttyport)
	char *ttyport;
{
	struct serial_struct kernel_serial_settings;

	target_fd = open(ttyport, O_RDWR|O_NONBLOCK);
	if (target_fd < 0) {
		perror(ttyport);
		exit(1);
	}
	ioctl(target_fd, TIOCEXCL);
	/*
	 * It appears that some miscreants have modified recent Linux kernel
	 * versions (newer than linux-4.4.14 of Slackware 14.2) to insert
	 * a delay of 10 ms before select system call returns when serial
	 * input is ready; this Linux kernel misbehaviour majorly slows down
	 * many of our operations.  It appears that we need to set the
	 * ASYNC_LOW_LATENCY flag in TIOCSSERIAL in order to get the old
	 * sane behaviour back.
	 */
	ioctl(target_fd, TIOCGSERIAL, &kernel_serial_settings);
	kernel_serial_settings.flags |= ASYNC_LOW_LATENCY;
	ioctl(target_fd, TIOCSSERIAL, &kernel_serial_settings);
	return 0;
}