n_hdlc.c

讲述linux的初始化过程

 * 	
 * Arguments:	 	tty		pointer to tty isntance data
 * 			data		pointer to received data
 * 			flags		pointer to flags for data
 * 			count		count of received data in bytes
 * 	
 * Return Value:	None
 */
static void n_hdlc_tty_receive(struct tty_struct *tty,
	const __u8 * data, char *flags, int count)
{
	register struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
	register N_HDLC_BUF *buf;

	if (debuglevel >= DEBUG_LEVEL_INFO)	
		printk("%s(%d)n_hdlc_tty_receive() called count=%d\n",
			__FILE__,__LINE__, count);
		
	/* This can happen if stuff comes in on the backup tty */
	if (n_hdlc == 0 || tty != n_hdlc->tty)
		return;
		
	/* verify line is using HDLC discipline */
	if (n_hdlc->magic != HDLC_MAGIC) {
		printk("%s(%d) line not using HDLC discipline\n",
			__FILE__,__LINE__);
		return;
	}
	
	if ( count>maxframe ) {
		if (debuglevel >= DEBUG_LEVEL_INFO)	
			printk("%s(%d) rx count>maxframesize, data discarded\n",
			       __FILE__,__LINE__);
		return;
	}

	/* get a free HDLC buffer */	
	buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
	if (!buf) {
		/* no buffers in free list, attempt to allocate another rx buffer */
		/* unless the maximum count has been reached */
		if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT)
			buf = (N_HDLC_BUF*)kmalloc(N_HDLC_BUF_SIZE,GFP_ATOMIC);
	}
	
	if (!buf) {
		if (debuglevel >= DEBUG_LEVEL_INFO)	
			printk("%s(%d) no more rx buffers, data discarded\n",
			       __FILE__,__LINE__);
		return;
	}
		
	/* copy received data to HDLC buffer */
	memcpy(buf->buf,data,count);
	buf->count=count;

	/* add HDLC buffer to list of received frames */
	n_hdlc_buf_put(&n_hdlc->rx_buf_list,buf);
	
	/* wake up any blocked reads and perform async signalling */
	wake_up_interruptible (&n_hdlc->read_wait);
	wake_up_interruptible (&n_hdlc->poll_wait);
	if (n_hdlc->tty->fasync != NULL)
		kill_fasync (&n_hdlc->tty->fasync, SIGIO, POLL_IN);

}	/* end of n_hdlc_tty_receive() */

/* n_hdlc_tty_read()
 * 
 * 	Called to retreive one frame of data (if available)
 * 	
 * Arguments:
 * 
 * 	tty		pointer to tty instance data
 * 	file		pointer to open file object
 * 	buf		pointer to returned data buffer
 * 	nr		size of returned data buffer
 * 	
 * Return Value:
 * 
 * 	Number of bytes returned or error code
 */
static rw_ret_t n_hdlc_tty_read (struct tty_struct *tty,
	struct file *file, __u8 * buf, rw_count_t nr)
{
	struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
	int error;
	rw_ret_t ret;
	N_HDLC_BUF *rbuf;

	if (debuglevel >= DEBUG_LEVEL_INFO)	
		printk("%s(%d)n_hdlc_tty_read() called\n",__FILE__,__LINE__);
		
	/* Validate the pointers */
	if (!n_hdlc)
		return -EIO;

	/* verify user access to buffer */
	error = verify_area (VERIFY_WRITE, buf, nr);
	if (error != 0) {
		printk(KERN_WARNING"%s(%d) n_hdlc_tty_read() can't verify user "
		"buffer\n",__FILE__,__LINE__);
		return (error);
	}

	for (;;) {
		n_hdlc = tty2n_hdlc (tty);
		if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC ||
			 tty != n_hdlc->tty)
			return 0;

		rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
		if (rbuf)
			break;
			
		/* no data */
		if (file->f_flags & O_NONBLOCK)
			return -EAGAIN;
			
		interruptible_sleep_on (&n_hdlc->read_wait);
		if (signal_pending(current))
			return -EINTR;
	}
		
	if (rbuf->count > nr) {
		/* frame too large for caller's buffer (discard frame) */
		ret = (rw_ret_t)-EOVERFLOW;
	} else {
		/* Copy the data to the caller's buffer */
		COPY_TO_USER(error,buf,rbuf->buf,rbuf->count);
		if (error)
			ret = (rw_ret_t)error;
		else
			ret = (rw_ret_t)rbuf->count;
	}
	
	/* return HDLC buffer to free list unless the free list */
	/* count has exceeded the default value, in which case the */
	/* buffer is freed back to the OS to conserve memory */
	if (n_hdlc->rx_free_buf_list.count > DEFAULT_RX_BUF_COUNT)
		kfree(rbuf);
	else	
		n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,rbuf);
	
	return ret;
	
}	/* end of n_hdlc_tty_read() */

/* n_hdlc_tty_write()
 * 
 * 	write a single frame of data to device
 * 	
 * Arguments:	tty	pointer to associated tty device instance data
 * 		file	pointer to file object data
 * 		data	pointer to transmit data (one frame)
 * 		count	size of transmit frame in bytes
 * 		
 * Return Value:	number of bytes written (or error code)
 */
static rw_ret_t n_hdlc_tty_write (struct tty_struct *tty, struct file *file,
	const __u8 * data, rw_count_t count)
{
	struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
	int error = 0;
	DECLARE_WAITQUEUE(wait, current);
	N_HDLC_BUF *tbuf;

	if (debuglevel >= DEBUG_LEVEL_INFO)	
		printk("%s(%d)n_hdlc_tty_write() called count=%d\n",
			__FILE__,__LINE__,count);
		
	/* Verify pointers */
	if (!n_hdlc)
		return -EIO;

	if (n_hdlc->magic != HDLC_MAGIC)
		return -EIO;

	/* verify frame size */
	if (count > maxframe ) {
		if (debuglevel & DEBUG_LEVEL_INFO)
			printk (KERN_WARNING
				"n_hdlc_tty_write: truncating user packet "
				"from %lu to %d\n", (unsigned long) count,
				maxframe );
		count = maxframe;
	}
	
	add_wait_queue(&n_hdlc->write_wait, &wait);
	set_current_state(TASK_INTERRUPTIBLE);
	
	/* Allocate transmit buffer */
	/* sleep until transmit buffer available */		
	while (!(tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list))) {
		schedule();
			
		n_hdlc = tty2n_hdlc (tty);
		if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC || 
		    tty != n_hdlc->tty) {
			printk("n_hdlc_tty_write: %p invalid after wait!\n", n_hdlc);
			error = -EIO;
			break;
		}
			
		if (signal_pending(current)) {
			error = -EINTR;
			break;
		}
	}

	set_current_state(TASK_RUNNING);
	remove_wait_queue(&n_hdlc->write_wait, &wait);

	if (!error) {		
		/* Retrieve the user's buffer */
		COPY_FROM_USER (error, tbuf->buf, data, count);
		if (error) {
			/* return tx buffer to free list */
			n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,tbuf);
		} else {
			/* Send the data */
			tbuf->count = error = count;
			n_hdlc_buf_put(&n_hdlc->tx_buf_list,tbuf);
			n_hdlc_send_frames(n_hdlc,tty);
		}
	}

	return error;
	
}	/* end of n_hdlc_tty_write() */

/* n_hdlc_tty_ioctl()
 *
 *	Process IOCTL system call for the tty device.
 *
 * Arguments:
 *
 *	tty		pointer to tty instance data
 *	file		pointer to open file object for device
 *	cmd		IOCTL command code
 *	arg		argument for IOCTL call (cmd dependent)
 *
 * Return Value:	Command dependent
 */
static int n_hdlc_tty_ioctl (struct tty_struct *tty, struct file * file,
               unsigned int cmd, unsigned long arg)
{
	struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
	int error = 0;
	int count;
	unsigned long flags;
	
	if (debuglevel >= DEBUG_LEVEL_INFO)	
		printk("%s(%d)n_hdlc_tty_ioctl() called %d\n",
			__FILE__,__LINE__,cmd);
		
	/* Verify the status of the device */
	if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC)
		return -EBADF;

	switch (cmd) {
	case FIONREAD:
		/* report count of read data available */
		/* in next available frame (if any) */
		spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock,flags);
		if (n_hdlc->rx_buf_list.head)
			count = n_hdlc->rx_buf_list.head->count;
		else
			count = 0;
		spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock,flags);
		PUT_USER (error, count, (int *) arg);
		break;

	case TIOCOUTQ:
		/* get the pending tx byte count in the driver */
		count = tty->driver.chars_in_buffer ?
				tty->driver.chars_in_buffer(tty) : 0;
		/* add size of next output frame in queue */
		spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock,flags);
		if (n_hdlc->tx_buf_list.head)
			count += n_hdlc->tx_buf_list.head->count;
		spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock,flags);
		PUT_USER (error, count, (int*)arg);
		break;

	default:
		error = n_tty_ioctl (tty, file, cmd, arg);
		break;
	}
	return error;
	
}	/* end of n_hdlc_tty_ioctl() */

/* n_hdlc_tty_poll()
 * 
 * 	TTY callback for poll system call. Determine which 
 * 	operations (read/write) will not block and return
 * 	info to caller.
 * 	
 * Arguments:
 * 
 * 	tty		pointer to tty instance data
 * 	filp		pointer to open file object for device
 * 	poll_table	wait queue for operations
 * 
 * Return Value:
 * 
 * 	bit mask containing info on which ops will not block
 */
static unsigned int n_hdlc_tty_poll (struct tty_struct *tty,
	 struct file *filp, poll_table * wait)
{
	struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
	unsigned int mask = 0;

	if (debuglevel >= DEBUG_LEVEL_INFO)	
		printk("%s(%d)n_hdlc_tty_poll() called\n",__FILE__,__LINE__);
		
	if (n_hdlc && n_hdlc->magic == HDLC_MAGIC && tty == n_hdlc->tty) {
		/* queue current process into any wait queue that */
		/* may awaken in the future (read and write) */
		poll_wait(filp, &n_hdlc->poll_wait, wait);

		/* set bits for operations that wont block */
		if(n_hdlc->rx_buf_list.head)
			mask |= POLLIN | POLLRDNORM;	/* readable */
		if(tty->flags & (1 << TTY_OTHER_CLOSED))
			mask |= POLLHUP;
		if(tty_hung_up_p(filp))
			mask |= POLLHUP;
		if(n_hdlc->tx_free_buf_list.head)
			mask |= POLLOUT | POLLWRNORM;	/* writable */
	}
	return mask;
}	/* end of n_hdlc_tty_poll() */

/* n_hdlc_alloc()
 * 
 * 	Allocate an n_hdlc instance data structure
 *
 * Arguments:		None
 * Return Value:	pointer to structure if success, otherwise 0	
 */
static struct n_hdlc *n_hdlc_alloc (void)
{
	struct n_hdlc	*n_hdlc;
	N_HDLC_BUF	*buf;
	int		i;
	
	n_hdlc = (struct n_hdlc *)kmalloc(sizeof(struct n_hdlc), GFP_KERNEL);
	if (!n_hdlc)
		return 0;

	memset(n_hdlc, 0, sizeof(*n_hdlc));

	n_hdlc_buf_list_init(&n_hdlc->rx_free_buf_list);
	n_hdlc_buf_list_init(&n_hdlc->tx_free_buf_list);
	n_hdlc_buf_list_init(&n_hdlc->rx_buf_list);
	n_hdlc_buf_list_init(&n_hdlc->tx_buf_list);
	
	/* allocate free rx buffer list */
	for(i=0;i<DEFAULT_RX_BUF_COUNT;i++) {
		buf = (N_HDLC_BUF*)kmalloc(N_HDLC_BUF_SIZE,GFP_KERNEL);
		if (buf)
			n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,buf);
		else if (debuglevel >= DEBUG_LEVEL_INFO)	
			printk("%s(%d)n_hdlc_alloc(), kalloc() failed for rx buffer %d\n",__FILE__,__LINE__, i);
	}
	
	/* allocate free tx buffer list */
	for(i=0;i<DEFAULT_TX_BUF_COUNT;i++) {
		buf = (N_HDLC_BUF*)kmalloc(N_HDLC_BUF_SIZE,GFP_KERNEL);
		if (buf)
			n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,buf);
		else if (debuglevel >= DEBUG_LEVEL_INFO)	
			printk("%s(%d)n_hdlc_alloc(), kalloc() failed for tx buffer %d\n",__FILE__,__LINE__, i);
	}
	
	/* Initialize the control block */
	n_hdlc->magic  = HDLC_MAGIC;

	n_hdlc->flags  = 0;
	init_waitqueue_head(&n_hdlc->read_wait);
	init_waitqueue_head(&n_hdlc->poll_wait);
	init_waitqueue_head(&n_hdlc->write_wait);
	
	return n_hdlc;
	
}	/* end of n_hdlc_alloc() */

/* n_hdlc_buf_list_init()
 * 
 * 	initialize specified HDLC buffer list
 * 	
 * Arguments:	 	list	pointer to buffer list
 * Return Value:	None	
 */
void n_hdlc_buf_list_init(N_HDLC_BUF_LIST *list)
{
	memset(list,0,sizeof(N_HDLC_BUF_LIST));
	spin_lock_init(&list->spinlock);
}	/* end of n_hdlc_buf_list_init() */

/* n_hdlc_buf_put()
 * 
 * 	add specified HDLC buffer to tail of specified list
 * 	
 * Arguments:
 * 
 * 	list	pointer to buffer list
 * 	buf	pointer to buffer
 * 
 * Return Value:	None	
 */
void n_hdlc_buf_put(N_HDLC_BUF_LIST *list,N_HDLC_BUF *buf)
{
	unsigned long flags;
	spin_lock_irqsave(&list->spinlock,flags);
	
	buf->link=NULL;
	if(list->tail)
		list->tail->link = buf;
	else
		list->head = buf;
	list->tail = buf;
	(list->count)++;
	
	spin_unlock_irqrestore(&list->spinlock,flags);
	
}	/* end of n_hdlc_buf_put() */

/* n_hdlc_buf_get()
 * 
 * 	remove and return an HDLC buffer from the
 * 	head of the specified HDLC buffer list
 * 	
 * Arguments:
 * 
 * 	list	pointer to HDLC buffer list
 * 	
 * Return Value:
 * 
 * 	pointer to HDLC buffer if available, otherwise NULL
 */
N_HDLC_BUF* n_hdlc_buf_get(N_HDLC_BUF_LIST *list)
{
	unsigned long flags;
	N_HDLC_BUF *buf;
	spin_lock_irqsave(&list->spinlock,flags);
	
	buf = list->head;
	if (buf) {
		list->head = buf->link;
		(list->count)--;
	}
	if (!list->head)
		list->tail = NULL;
	
	spin_unlock_irqrestore(&list->spinlock,flags);
	return buf;
	
}	/* end of n_hdlc_buf_get() */

static int __init n_hdlc_init(void)
{
	static struct tty_ldisc	n_hdlc_ldisc;
	int    status;

	/* range check maxframe arg */
	if ( maxframe<4096)
		maxframe=4096;
	else if ( maxframe>65535)
		maxframe=65535;

	printk("HDLC line discipline: version %s, maxframe=%u\n", 
		szVersion, maxframe);

	/* Register the tty discipline */
	
	memset(&n_hdlc_ldisc, 0, sizeof (n_hdlc_ldisc));
	n_hdlc_ldisc.magic		= TTY_LDISC_MAGIC;
	n_hdlc_ldisc.name          	= "hdlc";
	n_hdlc_ldisc.open		= n_hdlc_tty_open;
	n_hdlc_ldisc.close		= n_hdlc_tty_close;
	n_hdlc_ldisc.read		= n_hdlc_tty_read;
	n_hdlc_ldisc.write		= n_hdlc_tty_write;
	n_hdlc_ldisc.ioctl		= n_hdlc_tty_ioctl;
	n_hdlc_ldisc.poll		= n_hdlc_tty_poll;
	n_hdlc_ldisc.receive_room	= n_hdlc_tty_room;
	n_hdlc_ldisc.receive_buf	= n_hdlc_tty_receive;
	n_hdlc_ldisc.write_wakeup	= n_hdlc_tty_wakeup;

	status = tty_register_ldisc(N_HDLC, &n_hdlc_ldisc);
	if (!status)
		printk (KERN_INFO"N_HDLC line discipline registered.\n");
	else
		printk (KERN_ERR"error registering line discipline: %d\n",status);

	if (status)
		printk(KERN_INFO"N_HDLC: init failure %d\n", status);
	return (status);
	
}	/* end of init_module() */

static void __exit n_hdlc_exit(void)
{
	int status;
	/* Release tty registration of line discipline */
	if ((status = tty_register_ldisc(N_HDLC, NULL)))
		printk("N_HDLC: can't unregister line discipline (err = %d)\n", status);
	else
		printk("N_HDLC: line discipline unregistered\n");
}

module_init(n_hdlc_init);
module_exit(n_hdlc_exit);