如何创建一个最小的串口、TTY设备包括虚拟控制台，串口以及伪终端设备的驱动程序

来源：LINUX设备驱动程序第三版配套源码

Table of Contents

tiny_serial.c

tiny_tty.c

makefile

---

tiny_serial.c

/*
 * Tiny Serial driver
 *
 * Copyright (C) 2002-2004 Greg Kroah-Hartman ([email protected])
 *
 *	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, version 2 of the License.
 *
 * This driver shows how to create a minimal serial driver.  It does not rely on
 * any backing hardware, but creates a timer that emulates data being received
 * from some kind of hardware.
 *	这个驱动程序展示了如何创建一个最小的串行驱动程序。
 *	它不依赖于任何支持硬件，而是创建一个计时器来模拟从某种硬件接收的数据。
 */

#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <linux/serial.h>
#include <linux/serial_core.h>
#include <linux/module.h>


#define DRIVER_AUTHOR "Greg Kroah-Hartman <[email protected]>"
#define DRIVER_DESC "Tiny serial driver"

/* Module information */
MODULE_AUTHOR( DRIVER_AUTHOR );
MODULE_DESCRIPTION( DRIVER_DESC );
MODULE_LICENSE("GPL");

#define DELAY_TIME		HZ * 2	/* 2 seconds per character */
#define TINY_DATA_CHARACTER	't'

#define TINY_SERIAL_MAJOR	240	/* experimental range */
#define TINY_SERIAL_MINORS	1	/* only have one minor */
#define UART_NR			1	/* only use one port */

#define TINY_SERIAL_NAME	"ttytiny"

#define MY_NAME			TINY_SERIAL_NAME

static struct timer_list *timer;

static void tiny_stop_tx(struct uart_port *port, unsigned int tty_stop)
{
}

static void tiny_stop_rx(struct uart_port *port)
{
}

static void tiny_enable_ms(struct uart_port *port)
{
}

static void tiny_tx_chars(struct uart_port *port)
{
	struct circ_buf *xmit = &port->info->xmit;
	int count;

	if (port->x_char) {
		pr_debug("wrote %2x", port->x_char);
		port->icount.tx++;
		port->x_char = 0;
		return;
	}
	if (uart_circ_empty(xmit) || uart_tx_stopped(port)) {
		tiny_stop_tx(port, 0);
		return;
	}

	count = port->fifosize >> 1;
	do {
		pr_debug("wrote %2x", xmit->buf[xmit->tail]);
		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
		port->icount.tx++;
		if (uart_circ_empty(xmit))
			break;
	} while (--count > 0);

	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
		uart_write_wakeup(port);

	if (uart_circ_empty(xmit))
		tiny_stop_tx(port, 0);
}

static void tiny_start_tx(struct uart_port *port, unsigned int tty_start)
{
}

static void tiny_timer(unsigned long data)
{
	struct uart_port *port;
	struct tty_struct *tty;


	port = (struct uart_port *)data;
	if (!port)
		return;
	if (!port->info)
		return;
	tty = port->info->tty;
	if (!tty)
		return;

	/* add one character to the tty port */
	/* this doesn't actually push the data through unless tty->low_latency is set */
	tty_insert_flip_char(tty, TINY_DATA_CHARACTER, 0);

	tty_flip_buffer_push(tty);

	/* resubmit the timer again */
	timer->expires = jiffies + DELAY_TIME;
	add_timer(timer);

	/* see if we have any data to transmit */
	tiny_tx_chars(port);
}

static unsigned int tiny_tx_empty(struct uart_port *port)
{
	return 0;
}

static unsigned int tiny_get_mctrl(struct uart_port *port)
{
	return 0;
}

static void tiny_set_mctrl(struct uart_port *port, unsigned int mctrl)
{
}

static void tiny_break_ctl(struct uart_port *port, int break_state)
{
}

static void tiny_set_termios(struct uart_port *port,
			     struct termios *new, struct termios *old)
{
	int baud, quot, cflag = new->c_cflag;
	/* get the byte size */
	switch (cflag & CSIZE) {
	case CS5:
		printk(KERN_DEBUG " - data bits = 5\n");
		break;
	case CS6:
		printk(KERN_DEBUG " - data bits = 6\n");
		break;
	case CS7:
		printk(KERN_DEBUG " - data bits = 7\n");
		break;
	default: // CS8
		printk(KERN_DEBUG " - data bits = 8\n");
		break;
	}

	/* determine the parity */
	if (cflag & PARENB)
		if (cflag & PARODD)
			pr_debug(" - parity = odd\n");
		else
			pr_debug(" - parity = even\n");
	else
		pr_debug(" - parity = none\n");

	/* figure out the stop bits requested */
	if (cflag & CSTOPB)
		pr_debug(" - stop bits = 2\n");
	else
		pr_debug(" - stop bits = 1\n");

	/* figure out the flow control settings */
	if (cflag & CRTSCTS)
		pr_debug(" - RTS/CTS is enabled\n");
	else
		pr_debug(" - RTS/CTS is disabled\n");

	/* Set baud rate */
        baud = uart_get_baud_rate(port, new, old, 0, port->uartclk/16);
        quot = uart_get_divisor(port, baud);
	
	//UART_PUT_DIV_LO(port, (quot & 0xff));
	//UART_PUT_DIV_HI(port, ((quot & 0xf00) >> 8));
}

static int tiny_startup(struct uart_port *port)
{
	/* this is the first time this port is opened */
	/* do any hardware initialization needed here */

	/* create our timer and submit it */
	if (!timer) {
		timer = kmalloc(sizeof(*timer), GFP_KERNEL);
		if (!timer)
			return -ENOMEM;
	}
	timer->data = (unsigned long)port;
	timer->expires = jiffies + DELAY_TIME;
	timer->function = tiny_timer;
	add_timer(timer);
	return 0;
}

static void tiny_shutdown(struct uart_port *port)
{
	/* The port is being closed by the last user. */
	/* Do any hardware specific stuff here */

	/* shut down our timer */
	del_timer(timer);
}

static const char *tiny_type(struct uart_port *port)
{
	return "tinytty";
}

static void tiny_release_port(struct uart_port *port)
{

}

static int tiny_request_port(struct uart_port *port)
{
	return 0;
}

static void tiny_config_port(struct uart_port *port, int flags)
{
}

static int tiny_verify_port(struct uart_port *port, struct serial_struct *ser)
{
	return 0;
}

static struct uart_ops tiny_ops = {
	.tx_empty	= tiny_tx_empty,
	.set_mctrl	= tiny_set_mctrl,
	.get_mctrl	= tiny_get_mctrl,
	.stop_tx	= tiny_stop_tx,
	.start_tx	= tiny_start_tx,
	.stop_rx	= tiny_stop_rx,
	.enable_ms	= tiny_enable_ms,
	.break_ctl	= tiny_break_ctl,
	.startup	= tiny_startup,
	.shutdown	= tiny_shutdown,
	.set_termios	= tiny_set_termios,
	.type		= tiny_type,
	.release_port	= tiny_release_port,
	.request_port	= tiny_request_port,
	.config_port	= tiny_config_port,
	.verify_port	= tiny_verify_port,
};

static struct uart_port tiny_port = {
	.ops		= &tiny_ops,
};

static struct uart_driver tiny_reg = {
	.owner		= THIS_MODULE,
	.driver_name	= TINY_SERIAL_NAME,
	.dev_name	= TINY_SERIAL_NAME,
	.major		= TINY_SERIAL_MAJOR,
	.minor		= TINY_SERIAL_MINORS,
	.nr		= UART_NR,
};

static int __init tiny_init(void)
{
	int result;

	printk(KERN_INFO "Tiny serial driver loaded\n");

	result = uart_register_driver(&tiny_reg);
	if (result)
		return result;

	result = uart_add_one_port(&tiny_reg, &tiny_port);
	if (result)
		uart_unregister_driver(&tiny_reg);

	return result;
}

module_init(tiny_init);

tiny_tty.c

/*
 * Tiny TTY driver
 *
 * Copyright (C) 2002-2004 Greg Kroah-Hartman ([email protected])
 *
 *	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, version 2 of the License.
 *
 * This driver shows how to create a minimal tty driver.  It does not rely on
 * any backing hardware, but creates a timer that emulates data being received
 * from some kind of hardware.
 */

#include <linux/config.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/wait.h>
#include <linux/tty.h>
#include <linux/tty_driver.h>
#include <linux/tty_flip.h>
#include <linux/serial.h>
#include <asm/uaccess.h>


#define DRIVER_VERSION "v2.0"
#define DRIVER_AUTHOR "Greg Kroah-Hartman <[email protected]>"
#define DRIVER_DESC "Tiny TTY driver"

/* Module information */
MODULE_AUTHOR( DRIVER_AUTHOR );
MODULE_DESCRIPTION( DRIVER_DESC );
MODULE_LICENSE("GPL");

#define DELAY_TIME		HZ * 2	/* 2 seconds per character */
#define TINY_DATA_CHARACTER	't'

#define TINY_TTY_MAJOR		240	/* experimental range */
#define TINY_TTY_MINORS		4	/* only have 4 devices */

struct tiny_serial {
	struct tty_struct	*tty;		/* pointer to the tty for this device */
	int			open_count;	/* number of times this port has been opened */
	struct semaphore	sem;		/* locks this structure */
	struct timer_list	*timer;

	/* for tiocmget and tiocmset functions */
	int			msr;		/* MSR shadow */
	int			mcr;		/* MCR shadow */

	/* for ioctl fun */
	struct serial_struct	serial;
	wait_queue_head_t	wait;
	struct async_icount	icount;
};

static struct tiny_serial *tiny_table[TINY_TTY_MINORS];	/* initially all NULL */


static void tiny_timer(unsigned long timer_data)
{
	struct tiny_serial *tiny = (struct tiny_serial *)timer_data;
	struct tty_struct *tty;
	int i;
	char data[1] = {TINY_DATA_CHARACTER};
	int data_size = 1;

	if (!tiny)
		return;

	tty = tiny->tty;

	/* send the data to the tty layer for users to read.  This doesn't
	 * actually push the data through unless tty->low_latency is set */
	for (i = 0; i < data_size; ++i) {
		if (tty->flip.count >= TTY_FLIPBUF_SIZE)
			tty_flip_buffer_push(tty);
		tty_insert_flip_char(tty, data[i], TTY_NORMAL);
	}
	tty_flip_buffer_push(tty);

	/* resubmit the timer again */
	tiny->timer->expires = jiffies + DELAY_TIME;
	add_timer(tiny->timer);
}

static int tiny_open(struct tty_struct *tty, struct file *file)
{
	struct tiny_serial *tiny;
	struct timer_list *timer;
	int index;

	/* initialize the pointer in case something fails */
	tty->driver_data = NULL;

	/* get the serial object associated with this tty pointer */
	index = tty->index;
	tiny = tiny_table[index];
	if (tiny == NULL) {
		/* first time accessing this device, let's create it */
		tiny = kmalloc(sizeof(*tiny), GFP_KERNEL);
		if (!tiny)
			return -ENOMEM;

		init_MUTEX(&tiny->sem);
		tiny->open_count = 0;
		tiny->timer = NULL;

		tiny_table[index] = tiny;
	}

	down(&tiny->sem);

	/* save our structure within the tty structure */
	tty->driver_data = tiny;
	tiny->tty = tty;

	++tiny->open_count;
	if (tiny->open_count == 1) {
		/* this is the first time this port is opened */
		/* do any hardware initialization needed here */

		/* create our timer and submit it */
		if (!tiny->timer) {
			timer = kmalloc(sizeof(*timer), GFP_KERNEL);
			if (!timer) {
				up(&tiny->sem);
				return -ENOMEM;
			}
			tiny->timer = timer;
		}
		tiny->timer->data = (unsigned long )tiny;
		tiny->timer->expires = jiffies + DELAY_TIME;
		tiny->timer->function = tiny_timer;
		add_timer(tiny->timer);
	}

	up(&tiny->sem);
	return 0;
}

static void do_close(struct tiny_serial *tiny)
{
	down(&tiny->sem);

	if (!tiny->open_count) {
		/* port was never opened */
		goto exit;
	}

	--tiny->open_count;
	if (tiny->open_count <= 0) {
		/* The port is being closed by the last user. */
		/* Do any hardware specific stuff here */

		/* shut down our timer */
		del_timer(tiny->timer);
	}
exit:
	up(&tiny->sem);
}

static void tiny_close(struct tty_struct *tty, struct file *file)
{
	struct tiny_serial *tiny = tty->driver_data;

	if (tiny)
		do_close(tiny);
}	

static int tiny_write(struct tty_struct *tty, 
		      const unsigned char *buffer, int count)
{
	struct tiny_serial *tiny = tty->driver_data;
	int i;
	int retval = -EINVAL;

	if (!tiny)
		return -ENODEV;

	down(&tiny->sem);

	if (!tiny->open_count)
		/* port was not opened */
		goto exit;

	/* fake sending the data out a hardware port by
	 * writing it to the kernel debug log.
	 */
	printk(KERN_DEBUG "%s - ", __FUNCTION__);
	for (i = 0; i < count; ++i)
		printk("%02x ", buffer[i]);
	printk("\n");
		
exit:
	up(&tiny->sem);
	return retval;
}

static int tiny_write_room(struct tty_struct *tty) 
{
	struct tiny_serial *tiny = tty->driver_data;
	int room = -EINVAL;

	if (!tiny)
		return -ENODEV;

	down(&tiny->sem);
	
	if (!tiny->open_count) {
		/* port was not opened */
		goto exit;
	}

	/* calculate how much room is left in the device */
	room = 255;

exit:
	up(&tiny->sem);
	return room;
}

#define RELEVANT_IFLAG(iflag) ((iflag) & (IGNBRK|BRKINT|IGNPAR|PARMRK|INPCK))

static void tiny_set_termios(struct tty_struct *tty, struct termios *old_termios)
{
	unsigned int cflag;

	cflag = tty->termios->c_cflag;

	/* check that they really want us to change something */
	if (old_termios) {
		if ((cflag == old_termios->c_cflag) &&
		    (RELEVANT_IFLAG(tty->termios->c_iflag) == 
		     RELEVANT_IFLAG(old_termios->c_iflag))) {
			printk(KERN_DEBUG " - nothing to change...\n");
			return;
		}
	}

	/* get the byte size */
	switch (cflag & CSIZE) {
		case CS5:
			printk(KERN_DEBUG " - data bits = 5\n");
			break;
		case CS6:
			printk(KERN_DEBUG " - data bits = 6\n");
			break;
		case CS7:
			printk(KERN_DEBUG " - data bits = 7\n");
			break;
		default:
		case CS8:
			printk(KERN_DEBUG " - data bits = 8\n");
			break;
	}
	
	/* determine the parity */
	if (cflag & PARENB)
		if (cflag & PARODD)
			printk(KERN_DEBUG " - parity = odd\n");
		else
			printk(KERN_DEBUG " - parity = even\n");
	else
		printk(KERN_DEBUG " - parity = none\n");

	/* figure out the stop bits requested */
	if (cflag & CSTOPB)
		printk(KERN_DEBUG " - stop bits = 2\n");
	else
		printk(KERN_DEBUG " - stop bits = 1\n");

	/* figure out the hardware flow control settings */
	if (cflag & CRTSCTS)
		printk(KERN_DEBUG " - RTS/CTS is enabled\n");
	else
		printk(KERN_DEBUG " - RTS/CTS is disabled\n");
	
	/* determine software flow control */
	/* if we are implementing XON/XOFF, set the start and 
	 * stop character in the device */
	if (I_IXOFF(tty) || I_IXON(tty)) {
		unsigned char stop_char  = STOP_CHAR(tty);
		unsigned char start_char = START_CHAR(tty);

		/* if we are implementing INBOUND XON/XOFF */
		if (I_IXOFF(tty))
			printk(KERN_DEBUG " - INBOUND XON/XOFF is enabled, "
				"XON = %2x, XOFF = %2x", start_char, stop_char);
		else
			printk(KERN_DEBUG" - INBOUND XON/XOFF is disabled");

		/* if we are implementing OUTBOUND XON/XOFF */
		if (I_IXON(tty))
			printk(KERN_DEBUG" - OUTBOUND XON/XOFF is enabled, "
				"XON = %2x, XOFF = %2x", start_char, stop_char);
		else
			printk(KERN_DEBUG" - OUTBOUND XON/XOFF is disabled");
	}

	/* get the baud rate wanted */
	printk(KERN_DEBUG " - baud rate = %d", tty_get_baud_rate(tty));
}

/* Our fake UART values */
#define MCR_DTR		0x01
#define MCR_RTS		0x02
#define MCR_LOOP	0x04
#define MSR_CTS		0x08
#define MSR_CD		0x10
#define MSR_RI		0x20
#define MSR_DSR		0x40

static int tiny_tiocmget(struct tty_struct *tty, struct file *file)
{
	struct tiny_serial *tiny = tty->driver_data;

	unsigned int result = 0;
	unsigned int msr = tiny->msr;
	unsigned int mcr = tiny->mcr;

	result = ((mcr & MCR_DTR)  ? TIOCM_DTR  : 0) |	/* DTR is set */
             ((mcr & MCR_RTS)  ? TIOCM_RTS  : 0) |	/* RTS is set */
             ((mcr & MCR_LOOP) ? TIOCM_LOOP : 0) |	/* LOOP is set */
             ((msr & MSR_CTS)  ? TIOCM_CTS  : 0) |	/* CTS is set */
             ((msr & MSR_CD)   ? TIOCM_CAR  : 0) |	/* Carrier detect is set*/
             ((msr & MSR_RI)   ? TIOCM_RI   : 0) |	/* Ring Indicator is set */
             ((msr & MSR_DSR)  ? TIOCM_DSR  : 0);	/* DSR is set */

	return result;
}

static int tiny_tiocmset(struct tty_struct *tty, struct file *file,
                         unsigned int set, unsigned int clear)
{
	struct tiny_serial *tiny = tty->driver_data;
	unsigned int mcr = tiny->mcr;

	if (set & TIOCM_RTS)
		mcr |= MCR_RTS;
	if (set & TIOCM_DTR)
		mcr |= MCR_RTS;

	if (clear & TIOCM_RTS)
		mcr &= ~MCR_RTS;
	if (clear & TIOCM_DTR)
		mcr &= ~MCR_RTS;

	/* set the new MCR value in the device */
	tiny->mcr = mcr;
	return 0;
}

static int tiny_read_proc(char *page, char **start, off_t off, int count,
                          int *eof, void *data)
{
	struct tiny_serial *tiny;
	off_t begin = 0;
	int length = 0;
	int i;

	length += sprintf(page, "tinyserinfo:1.0 driver:%s\n", DRIVER_VERSION);
	for (i = 0; i < TINY_TTY_MINORS && length < PAGE_SIZE; ++i) {
		tiny = tiny_table[i];
		if (tiny == NULL)
			continue;

		length += sprintf(page+length, "%d\n", i);
		if ((length + begin) > (off + count))
			goto done;
		if ((length + begin) < off) {
			begin += length;
			length = 0;
		}
	}
	*eof = 1;
done:
	if (off >= (length + begin))
		return 0;
	*start = page + (off-begin);
	return (count < begin+length-off) ? count : begin + length-off;
}

#define tiny_ioctl tiny_ioctl_tiocgserial
static int tiny_ioctl(struct tty_struct *tty, struct file *file,
                      unsigned int cmd, unsigned long arg)
{
	struct tiny_serial *tiny = tty->driver_data;

	if (cmd == TIOCGSERIAL) {
		struct serial_struct tmp;

		if (!arg)
			return -EFAULT;

		memset(&tmp, 0, sizeof(tmp));

		tmp.type		= tiny->serial.type;
		tmp.line		= tiny->serial.line;
		tmp.port		= tiny->serial.port;
		tmp.irq			= tiny->serial.irq;
		tmp.flags		= ASYNC_SKIP_TEST | ASYNC_AUTO_IRQ;
		tmp.xmit_fifo_size	= tiny->serial.xmit_fifo_size;
		tmp.baud_base		= tiny->serial.baud_base;
		tmp.close_delay		= 5*HZ;
		tmp.closing_wait	= 30*HZ;
		tmp.custom_divisor	= tiny->serial.custom_divisor;
		tmp.hub6		= tiny->serial.hub6;
		tmp.io_type		= tiny->serial.io_type;

		if (copy_to_user((void __user *)arg, &tmp, sizeof(struct serial_struct)))
			return -EFAULT;
		return 0;
	}
	return -ENOIOCTLCMD;
}
#undef tiny_ioctl

#define tiny_ioctl tiny_ioctl_tiocmiwait
static int tiny_ioctl(struct tty_struct *tty, struct file *file,
                      unsigned int cmd, unsigned long arg)
{
	struct tiny_serial *tiny = tty->driver_data;

	if (cmd == TIOCMIWAIT) {
		DECLARE_WAITQUEUE(wait, current);
		struct async_icount cnow;
		struct async_icount cprev;

		cprev = tiny->icount;
		while (1) {
			add_wait_queue(&tiny->wait, &wait);
			set_current_state(TASK_INTERRUPTIBLE);
			schedule();
			remove_wait_queue(&tiny->wait, &wait);

			/* see if a signal woke us up */
			if (signal_pending(current))
				return -ERESTARTSYS;

			cnow = tiny->icount;
			if (cnow.rng == cprev.rng && cnow.dsr == cprev.dsr &&
			    cnow.dcd == cprev.dcd && cnow.cts == cprev.cts)
				return -EIO; /* no change => error */
			if (((arg & TIOCM_RNG) && (cnow.rng != cprev.rng)) ||
			    ((arg & TIOCM_DSR) && (cnow.dsr != cprev.dsr)) ||
			    ((arg & TIOCM_CD)  && (cnow.dcd != cprev.dcd)) ||
			    ((arg & TIOCM_CTS) && (cnow.cts != cprev.cts)) ) {
				return 0;
			}
			cprev = cnow;
		}

	}
	return -ENOIOCTLCMD;
}
#undef tiny_ioctl

#define tiny_ioctl tiny_ioctl_tiocgicount
static int tiny_ioctl(struct tty_struct *tty, struct file *file,
                      unsigned int cmd, unsigned long arg)
{
	struct tiny_serial *tiny = tty->driver_data;

	if (cmd == TIOCGICOUNT) {
		struct async_icount cnow = tiny->icount;
		struct serial_icounter_struct icount;

		icount.cts	= cnow.cts;
		icount.dsr	= cnow.dsr;
		icount.rng	= cnow.rng;
		icount.dcd	= cnow.dcd;
		icount.rx	= cnow.rx;
		icount.tx	= cnow.tx;
		icount.frame	= cnow.frame;
		icount.overrun	= cnow.overrun;
		icount.parity	= cnow.parity;
		icount.brk	= cnow.brk;
		icount.buf_overrun = cnow.buf_overrun;

		if (copy_to_user((void __user *)arg, &icount, sizeof(icount)))
			return -EFAULT;
		return 0;
	}
	return -ENOIOCTLCMD;
}
#undef tiny_ioctl

/* the real tiny_ioctl function.  The above is done to get the small functions in the book */
static int tiny_ioctl(struct tty_struct *tty, struct file *file,
                      unsigned int cmd, unsigned long arg)
{
	switch (cmd) {
	case TIOCGSERIAL:
		return tiny_ioctl_tiocgserial(tty, file, cmd, arg);
	case TIOCMIWAIT:
		return tiny_ioctl_tiocmiwait(tty, file, cmd, arg);
	case TIOCGICOUNT:
		return tiny_ioctl_tiocgicount(tty, file, cmd, arg);
	}

	return -ENOIOCTLCMD;
}

static struct tty_operations serial_ops = {
	.open = tiny_open,
	.close = tiny_close,
	.write = tiny_write,
	.write_room = tiny_write_room,
	.set_termios = tiny_set_termios,
};

static struct tty_driver *tiny_tty_driver;

static int __init tiny_init(void)
{
	int retval;
	int i;

	/* allocate the tty driver */
	tiny_tty_driver = alloc_tty_driver(TINY_TTY_MINORS);
	if (!tiny_tty_driver)
		return -ENOMEM;

	/* initialize the tty driver */
	tiny_tty_driver->owner = THIS_MODULE;
	tiny_tty_driver->driver_name = "tiny_tty";
	tiny_tty_driver->name = "ttty";
	tiny_tty_driver->devfs_name = "tts/ttty%d";
	tiny_tty_driver->major = TINY_TTY_MAJOR,
	tiny_tty_driver->type = TTY_DRIVER_TYPE_SERIAL,
	tiny_tty_driver->subtype = SERIAL_TYPE_NORMAL,
	tiny_tty_driver->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_NO_DEVFS,
	tiny_tty_driver->init_termios = tty_std_termios;
	tiny_tty_driver->init_termios.c_cflag = B9600 | CS8 | CREAD | HUPCL | CLOCAL;
	tty_set_operations(tiny_tty_driver, &serial_ops);

	/* hack to make the book purty, yet still use these functions in the
	 * real driver.  They really should be set up in the serial_ops
	 * structure above... */
	tiny_tty_driver->read_proc = tiny_read_proc;
	tiny_tty_driver->tiocmget = tiny_tiocmget;
	tiny_tty_driver->tiocmset = tiny_tiocmset;
	tiny_tty_driver->ioctl = tiny_ioctl;

	/* register the tty driver */
	retval = tty_register_driver(tiny_tty_driver);
	if (retval) {
		printk(KERN_ERR "failed to register tiny tty driver");
		put_tty_driver(tiny_tty_driver);
		return retval;
	}

	for (i = 0; i < TINY_TTY_MINORS; ++i)
		tty_register_device(tiny_tty_driver, i, NULL);

	printk(KERN_INFO DRIVER_DESC " " DRIVER_VERSION);
	return retval;
}

static void __exit tiny_exit(void)
{
	struct tiny_serial *tiny;
	int i;

	for (i = 0; i < TINY_TTY_MINORS; ++i)
		tty_unregister_device(tiny_tty_driver, i);
	tty_unregister_driver(tiny_tty_driver);

	/* shut down all of the timers and free the memory */
	for (i = 0; i < TINY_TTY_MINORS; ++i) {
		tiny = tiny_table[i];
		if (tiny) {
			/* close the port */
			while (tiny->open_count)
				do_close(tiny);

			/* shut down our timer and free the memory */
			del_timer(tiny->timer);
			kfree(tiny->timer);
			kfree(tiny);
			tiny_table[i] = NULL;
		}
	}
}

module_init(tiny_init);
module_exit(tiny_exit);

makefile

# Comment/uncomment the following line to disable/enable debugging
#DEBUG = y


# Add your debugging flag (or not) to CFLAGS
ifeq ($(DEBUG),y)
  DEBFLAGS = -O -g -DSCULL_DEBUG # "-O" is needed to expand inlines
else
  DEBFLAGS = -O2
endif

CFLAGS += $(DEBFLAGS)
CFLAGS += -I..

ifneq ($(KERNELRELEASE),)
# call from kernel build system

obj-m	:= tiny_tty.o tiny_serial.o

else

KERNELDIR ?= /lib/modules/$(shell uname -r)/build
PWD       := $(shell pwd)

default:
	$(MAKE) -C $(KERNELDIR) M=$(PWD) modules

endif



clean:
	rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions

depend .depend dep:
	$(CC) $(CFLAGS) -M *.c > .depend


ifeq (.depend,$(wildcard .depend))
include .depend
endif