/*
 * tty line discipline example
 *
 * Copyright (C) 2016  Krzysztof Mazur <krzysiek@podlesie.net>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 */

#define pr_fmt(fmt) "ldisc-example: " fmt
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/tty.h>
#include <asm/uaccess.h>

#ifndef N_EXAMPLE
#define N_EXAMPLE 26
#endif

static int ringdev_ldisc_open(struct tty_struct *tty)
{
	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;

	if (!tty->ops->write)
		return -EOPNOTSUPP;

	pr_info("ldisc open\n");
	tty->receive_room = 65536;	/* We don't flow control */
	return 0;
}

static void ringdev_ldisc_close(struct tty_struct *tty)
{
	pr_info("ldisc close\n");
}

static int ringdev_ldisc_hangup(struct tty_struct *tty)
{
	pr_info("ldisc hangup\n");
	return 0;
}


static void ringdev_receive_buf(struct tty_struct *tty, const unsigned char *cp,
		char *fp, int count)
{
	while (count--) {
		if (fp && *fp++) {
			pr_info("error %02x\n", *fp);
			cp++;
			continue;
		}
		pr_info("received %02x\n", *cp++);
	}
}

static void ringdev_write_wakeup(struct tty_struct *tty)
{
}

static struct tty_ldisc_ops ringdev_ldisc = {
	.owner 		= THIS_MODULE,
	.magic 		= TTY_LDISC_MAGIC,
	.name 		= "ringdev",
	.open 		= ringdev_ldisc_open,
	.hangup	 	= ringdev_ldisc_hangup,
	.close	 	= ringdev_ldisc_close,
	.ioctl		= tty_mode_ioctl,
	.receive_buf	= ringdev_receive_buf,
	.write_wakeup	= ringdev_write_wakeup,
};

static int __init ringdev_init(void)
{
	int ret;

	ret = tty_register_ldisc(N_EXAMPLE, &ringdev_ldisc);
	if (ret) {
		pr_err("can't register line discipline (err = %d)\n", ret);
		goto out;
	}
	return 0;

out:
	return ret;
}

static void __exit ringdev_exit(void)
{
	tty_unregister_ldisc(N_EXAMPLE);
}

module_init(ringdev_init);
module_exit(ringdev_exit);

MODULE_DESCRIPTION("tty line discripline example");
MODULE_AUTHOR("Krzysztof Mazur <krzysiek@podlesie.net>");
MODULE_LICENSE("GPL");