/*
   *  linux/drivers/char/ttyprintk.c
   *
   *  Copyright (C) 2010  Samo Pogacnik
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the smems of the GNU General Public License as published by
   * the Free Software Foundation; version 2 of the License.
   */
  
  /*
   * This pseudo device allows user to make printk messages. It is possible
   * to store "console" messages inline with kernel messages for better analyses
   * of the boot process, for example.
   */
  
  #include <linux/device.h>
  #include <linux/serial.h>
  #include <linux/tty.h>

  #include <linux/module.h>

  
  struct ttyprintk_port {
  	struct tty_port port;
  	struct mutex port_write_mutex;
  };
  
  static struct ttyprintk_port tpk_port;
  
  /*
   * Our simple preformatting supports transparent output of (time-stamped)
   * printk messages (also suitable for logging service):
   * - any cr is replaced by nl
   * - adds a ttyprintk source tag in front of each line

   * - too long message is fragmented, with '\'nl between fragments
   * - TPK_STR_SIZE isn't really the write_room limiting factor, because

   *   it is emptied on the fly during preformatting.
   */
  #define TPK_STR_SIZE 508 /* should be bigger then max expected line length */
  #define TPK_MAX_ROOM 4096 /* we could assume 4K for instance */

  static int tpk_curr;

  static char tpk_buffer[TPK_STR_SIZE + 4];
  
  static void tpk_flush(void)
  {
  	if (tpk_curr > 0) {
  		tpk_buffer[tpk_curr] = '\0';
  		pr_info("[U] %s
  ", tpk_buffer);
  		tpk_curr = 0;
  	}
  }

  static int tpk_printk(const unsigned char *buf, int count)
  {

  	int i = tpk_curr;
  
  	if (buf == NULL) {

  		tpk_flush();

  		return i;
  	}
  
  	for (i = 0; i < count; i++) {

  		if (tpk_curr >= TPK_STR_SIZE) {

  			/* end of tmp buffer reached: cut the message in two */

  			tpk_buffer[tpk_curr++] = '\\';
  			tpk_flush();
  		}
  
  		switch (buf[i]) {
  		case '\r':
  			tpk_flush();
  			if ((i + 1) < count && buf[i + 1] == '
  ')
  				i++;
  			break;
  		case '
  ':
  			tpk_flush();
  			break;
  		default:
  			tpk_buffer[tpk_curr++] = buf[i];
  			break;

  		}
  	}
  
  	return count;
  }
  
  /*
   * TTY operations open function.
   */
  static int tpk_open(struct tty_struct *tty, struct file *filp)
  {
  	tty->driver_data = &tpk_port;
  
  	return tty_port_open(&tpk_port.port, tty, filp);
  }
  
  /*
   * TTY operations close function.
   */
  static void tpk_close(struct tty_struct *tty, struct file *filp)
  {
  	struct ttyprintk_port *tpkp = tty->driver_data;
  
  	mutex_lock(&tpkp->port_write_mutex);
  	/* flush tpk_printk buffer */
  	tpk_printk(NULL, 0);
  	mutex_unlock(&tpkp->port_write_mutex);
  
  	tty_port_close(&tpkp->port, tty, filp);
  }
  
  /*
   * TTY operations write function.
   */
  static int tpk_write(struct tty_struct *tty,
  		const unsigned char *buf, int count)
  {
  	struct ttyprintk_port *tpkp = tty->driver_data;
  	int ret;
  
  
  	/* exclusive use of tpk_printk within this tty */
  	mutex_lock(&tpkp->port_write_mutex);
  	ret = tpk_printk(buf, count);
  	mutex_unlock(&tpkp->port_write_mutex);
  
  	return ret;
  }
  
  /*
   * TTY operations write_room function.
   */
  static int tpk_write_room(struct tty_struct *tty)
  {
  	return TPK_MAX_ROOM;
  }
  
  /*
   * TTY operations ioctl function.
   */

  static int tpk_ioctl(struct tty_struct *tty,

  			unsigned int cmd, unsigned long arg)
  {
  	struct ttyprintk_port *tpkp = tty->driver_data;
  
  	if (!tpkp)
  		return -EINVAL;
  
  	switch (cmd) {
  	/* Stop TIOCCONS */
  	case TIOCCONS:
  		return -EOPNOTSUPP;
  	default:
  		return -ENOIOCTLCMD;
  	}
  	return 0;
  }
  
  static const struct tty_operations ttyprintk_ops = {
  	.open = tpk_open,
  	.close = tpk_close,
  	.write = tpk_write,
  	.write_room = tpk_write_room,
  	.ioctl = tpk_ioctl,
  };

  static const struct tty_port_operations null_ops = { };

  
  static struct tty_driver *ttyprintk_driver;
  
  static int __init ttyprintk_init(void)
  {
  	int ret = -ENOMEM;

  	mutex_init(&tpk_port.port_write_mutex);

  	ttyprintk_driver = tty_alloc_driver(1,
  			TTY_DRIVER_RESET_TERMIOS |
  			TTY_DRIVER_REAL_RAW |
  			TTY_DRIVER_UNNUMBERED_NODE);

  	if (IS_ERR(ttyprintk_driver))
  		return PTR_ERR(ttyprintk_driver);

  	tty_port_init(&tpk_port.port);

  	tpk_port.port.ops = &null_ops;

  	ttyprintk_driver->driver_name = "ttyprintk";
  	ttyprintk_driver->name = "ttyprintk";
  	ttyprintk_driver->major = TTYAUX_MAJOR;
  	ttyprintk_driver->minor_start = 3;

  	ttyprintk_driver->type = TTY_DRIVER_TYPE_CONSOLE;
  	ttyprintk_driver->init_termios = tty_std_termios;
  	ttyprintk_driver->init_termios.c_oflag = OPOST | OCRNL | ONOCR | ONLRET;

  	tty_set_operations(ttyprintk_driver, &ttyprintk_ops);

  	tty_port_link_device(&tpk_port.port, ttyprintk_driver, 0);

  
  	ret = tty_register_driver(ttyprintk_driver);
  	if (ret < 0) {
  		printk(KERN_ERR "Couldn't register ttyprintk driver
  ");
  		goto error;
  	}

  	return 0;
  
  error:
  	put_tty_driver(ttyprintk_driver);

  	tty_port_destroy(&tpk_port.port);

  	return ret;
  }

  
  static void __exit ttyprintk_exit(void)
  {
  	tty_unregister_driver(ttyprintk_driver);
  	put_tty_driver(ttyprintk_driver);
  	tty_port_destroy(&tpk_port.port);
  }

  device_initcall(ttyprintk_init);

  module_exit(ttyprintk_exit);
  
  MODULE_LICENSE("GPL");