TTY: create drivers/tty and move the tty core files there

The tty code should be in its own subdirectory and not in the char
driver with all of the cruft that is currently there.

Based on work done by Arnd Bergmann <arnd@arndb.de>

Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 1007 insertions, 0 deletions

diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c
new file mode 100644
index 000000000000..47d32281032c
--- /dev/null
+++ b/drivers/tty/n_hdlc.c
@@ -0,0 +1,1007 @@
+/* generic HDLC line discipline for Linux
+ *
+ * Written by Paul Fulghum paulkf@microgate.com
+ * for Microgate Corporation
+ *
+ * Microgate and SyncLink are registered trademarks of Microgate Corporation
+ *
+ * Adapted from ppp.c, written by Michael Callahan <callahan@maths.ox.ac.uk>,
+ *	Al Longyear <longyear@netcom.com>,
+ *	Paul Mackerras <Paul.Mackerras@cs.anu.edu.au>
+ *
+ * Original release 01/11/99
+ *
+ * This code is released under the GNU General Public License (GPL)
+ *
+ * This module implements the tty line discipline N_HDLC for use with
+ * tty device drivers that support bit-synchronous HDLC communications.
+ *
+ * All HDLC data is frame oriented which means:
+ *
+ * 1. tty write calls represent one complete transmit frame of data
+ *    The device driver should accept the complete frame or none of 
+ *    the frame (busy) in the write method. Each write call should have
+ *    a byte count in the range of 2-65535 bytes (2 is min HDLC frame
+ *    with 1 addr byte and 1 ctrl byte). The max byte count of 65535
+ *    should include any crc bytes required. For example, when using
+ *    CCITT CRC32, 4 crc bytes are required, so the maximum size frame
+ *    the application may transmit is limited to 65531 bytes. For CCITT
+ *    CRC16, the maximum application frame size would be 65533.
+ *
+ *
+ * 2. receive callbacks from the device driver represents
+ *    one received frame. The device driver should bypass
+ *    the tty flip buffer and call the line discipline receive
+ *    callback directly to avoid fragmenting or concatenating
+ *    multiple frames into a single receive callback.
+ *
+ *    The HDLC line discipline queues the receive frames in separate
+ *    buffers so complete receive frames can be returned by the
+ *    tty read calls.
+ *
+ * 3. tty read calls returns an entire frame of data or nothing.
+ *    
+ * 4. all send and receive data is considered raw. No processing
+ *    or translation is performed by the line discipline, regardless
+ *    of the tty flags
+ *
+ * 5. When line discipline is queried for the amount of receive
+ *    data available (FIOC), 0 is returned if no data available,
+ *    otherwise the count of the next available frame is returned.
+ *    (instead of the sum of all received frame counts).
+ *
+ * These conventions allow the standard tty programming interface
+ * to be used for synchronous HDLC applications when used with
+ * this line discipline (or another line discipline that is frame
+ * oriented such as N_PPP).
+ *
+ * The SyncLink driver (synclink.c) implements both asynchronous
+ * (using standard line discipline N_TTY) and synchronous HDLC
+ * (using N_HDLC) communications, with the latter using the above
+ * conventions.
+ *
+ * This implementation is very basic and does not maintain
+ * any statistics. The main point is to enforce the raw data
+ * and frame orientation of HDLC communications.
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
+ * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#define HDLC_MAGIC 0x239e
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/types.h>
+#include <linux/fcntl.h>
+#include <linux/interrupt.h>
+#include <linux/ptrace.h>
+
+#undef VERSION
+#define VERSION(major,minor,patch) (((((major)<<8)+(minor))<<8)+(patch))
+
+#include <linux/poll.h>
+#include <linux/in.h>
+#include <linux/ioctl.h>
+#include <linux/slab.h>
+#include <linux/tty.h>
+#include <linux/errno.h>
+#include <linux/smp_lock.h>
+#include <linux/string.h>	/* used in new tty drivers */
+#include <linux/signal.h>	/* used in new tty drivers */
+#include <linux/if.h>
+#include <linux/bitops.h>
+
+#include <asm/system.h>
+#include <asm/termios.h>
+#include <asm/uaccess.h>
+
+/*
+ * Buffers for individual HDLC frames
+ */
+#define MAX_HDLC_FRAME_SIZE 65535 
+#define DEFAULT_RX_BUF_COUNT 10
+#define MAX_RX_BUF_COUNT 60
+#define DEFAULT_TX_BUF_COUNT 3
+
+struct n_hdlc_buf {
+	struct n_hdlc_buf *link;
+	int		  count;
+	char		  buf[1];
+};
+
+#define	N_HDLC_BUF_SIZE	(sizeof(struct n_hdlc_buf) + maxframe)
+
+struct n_hdlc_buf_list {
+	struct n_hdlc_buf *head;
+	struct n_hdlc_buf *tail;
+	int		  count;
+	spinlock_t	  spinlock;
+};
+
+/**
+ * struct n_hdlc - per device instance data structure
+ * @magic - magic value for structure
+ * @flags - miscellaneous control flags
+ * @tty - ptr to TTY structure
+ * @backup_tty - TTY to use if tty gets closed
+ * @tbusy - reentrancy flag for tx wakeup code
+ * @woke_up - FIXME: describe this field
+ * @tbuf - currently transmitting tx buffer
+ * @tx_buf_list - list of pending transmit frame buffers
+ * @rx_buf_list - list of received frame buffers
+ * @tx_free_buf_list - list unused transmit frame buffers
+ * @rx_free_buf_list - list unused received frame buffers
+ */
+struct n_hdlc {
+	int			magic;
+	__u32			flags;
+	struct tty_struct	*tty;
+	struct tty_struct	*backup_tty;
+	int			tbusy;
+	int			woke_up;
+	struct n_hdlc_buf	*tbuf;
+	struct n_hdlc_buf_list	tx_buf_list;
+	struct n_hdlc_buf_list	rx_buf_list;
+	struct n_hdlc_buf_list	tx_free_buf_list;
+	struct n_hdlc_buf_list	rx_free_buf_list;
+};
+
+/*
+ * HDLC buffer list manipulation functions
+ */
+static void n_hdlc_buf_list_init(struct n_hdlc_buf_list *list);
+static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
+			   struct n_hdlc_buf *buf);
+static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
+
+/* Local functions */
+
+static struct n_hdlc *n_hdlc_alloc (void);
+
+/* debug level can be set by insmod for debugging purposes */
+#define DEBUG_LEVEL_INFO	1
+static int debuglevel;
+
+/* max frame size for memory allocations */
+static int maxframe = 4096;
+
+/* TTY callbacks */
+
+static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
+			   __u8 __user *buf, size_t nr);
+static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
+			    const unsigned char *buf, size_t nr);
+static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
+			    unsigned int cmd, unsigned long arg);
+static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
+				    poll_table *wait);
+static int n_hdlc_tty_open(struct tty_struct *tty);
+static void n_hdlc_tty_close(struct tty_struct *tty);
+static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *cp,
+			       char *fp, int count);
+static void n_hdlc_tty_wakeup(struct tty_struct *tty);
+
+#define bset(p,b)	((p)[(b) >> 5] |= (1 << ((b) & 0x1f)))
+
+#define tty2n_hdlc(tty)	((struct n_hdlc *) ((tty)->disc_data))
+#define n_hdlc2tty(n_hdlc)	((n_hdlc)->tty)
+
+static void flush_rx_queue(struct tty_struct *tty)
+{
+	struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
+	struct n_hdlc_buf *buf;
+
+	while ((buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list)))
+		n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, buf);
+}
+
+static void flush_tx_queue(struct tty_struct *tty)
+{
+	struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
+	struct n_hdlc_buf *buf;
+	unsigned long flags;
+
+	while ((buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list)))
+		n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, buf);
+ 	spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
+	if (n_hdlc->tbuf) {
+		n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, n_hdlc->tbuf);
+		n_hdlc->tbuf = NULL;
+	}
+	spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
+}
+
+static struct tty_ldisc_ops n_hdlc_ldisc = {
+	.owner		= THIS_MODULE,
+	.magic		= TTY_LDISC_MAGIC,
+	.name		= "hdlc",
+	.open		= n_hdlc_tty_open,
+	.close		= n_hdlc_tty_close,
+	.read		= n_hdlc_tty_read,
+	.write		= n_hdlc_tty_write,
+	.ioctl		= n_hdlc_tty_ioctl,
+	.poll		= n_hdlc_tty_poll,
+	.receive_buf	= n_hdlc_tty_receive,
+	.write_wakeup	= n_hdlc_tty_wakeup,
+	.flush_buffer   = flush_rx_queue,
+};
+
+/**
+ * n_hdlc_release - release an n_hdlc per device line discipline info structure
+ * @n_hdlc - per device line discipline info structure
+ */
+static void n_hdlc_release(struct n_hdlc *n_hdlc)
+{
+	struct tty_struct *tty = n_hdlc2tty (n_hdlc);
+	struct n_hdlc_buf *buf;
+	
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_release() called\n",__FILE__,__LINE__);
+		
+	/* Ensure that the n_hdlcd process is not hanging on select()/poll() */
+	wake_up_interruptible (&tty->read_wait);
+	wake_up_interruptible (&tty->write_wait);
+
+	if (tty->disc_data == n_hdlc)
+		tty->disc_data = NULL;	/* Break the tty->n_hdlc link */
+
+	/* Release transmit and receive buffers */
+	for(;;) {
+		buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
+		if (buf) {
+			kfree(buf);
+		} else
+			break;
+	}
+	for(;;) {
+		buf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
+		if (buf) {
+			kfree(buf);
+		} else
+			break;
+	}
+	for(;;) {
+		buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
+		if (buf) {
+			kfree(buf);
+		} else
+			break;
+	}
+	for(;;) {
+		buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
+		if (buf) {
+			kfree(buf);
+		} else
+			break;
+	}
+	kfree(n_hdlc->tbuf);
+	kfree(n_hdlc);
+	
+}	/* end of n_hdlc_release() */
+
+/**
+ * n_hdlc_tty_close - line discipline close
+ * @tty - pointer to tty info structure
+ *
+ * Called when the line discipline is changed to something
+ * else, the tty is closed, or the tty detects a hangup.
+ */
+static void n_hdlc_tty_close(struct tty_struct *tty)
+{
+	struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
+
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_tty_close() called\n",__FILE__,__LINE__);
+		
+	if (n_hdlc != NULL) {
+		if (n_hdlc->magic != HDLC_MAGIC) {
+			printk (KERN_WARNING"n_hdlc: trying to close unopened tty!\n");
+			return;
+		}
+#if defined(TTY_NO_WRITE_SPLIT)
+		clear_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
+#endif
+		tty->disc_data = NULL;
+		if (tty == n_hdlc->backup_tty)
+			n_hdlc->backup_tty = NULL;
+		if (tty != n_hdlc->tty)
+			return;
+		if (n_hdlc->backup_tty) {
+			n_hdlc->tty = n_hdlc->backup_tty;
+		} else {
+			n_hdlc_release (n_hdlc);
+		}
+	}
+	
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_tty_close() success\n",__FILE__,__LINE__);
+		
+}	/* end of n_hdlc_tty_close() */
+
+/**
+ * n_hdlc_tty_open - called when line discipline changed to n_hdlc
+ * @tty - pointer to tty info structure
+ *
+ * Returns 0 if success, otherwise error code
+ */
+static int n_hdlc_tty_open (struct tty_struct *tty)
+{
+	struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
+
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_tty_open() called (device=%s)\n",
+		__FILE__,__LINE__,
+		tty->name);
+		
+	/* There should not be an existing table for this slot. */
+	if (n_hdlc) {
+		printk (KERN_ERR"n_hdlc_tty_open:tty already associated!\n" );
+		return -EEXIST;
+	}
+	
+	n_hdlc = n_hdlc_alloc();
+	if (!n_hdlc) {
+		printk (KERN_ERR "n_hdlc_alloc failed\n");
+		return -ENFILE;
+	}
+		
+	tty->disc_data = n_hdlc;
+	n_hdlc->tty    = tty;
+	tty->receive_room = 65536;
+	
+#if defined(TTY_NO_WRITE_SPLIT)
+	/* change tty_io write() to not split large writes into 8K chunks */
+	set_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
+#endif
+	
+	/* flush receive data from driver */
+	tty_driver_flush_buffer(tty);
+		
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_tty_open() success\n",__FILE__,__LINE__);
+		
+	return 0;
+	
+}	/* end of n_tty_hdlc_open() */
+
+/**
+ * n_hdlc_send_frames - send frames on pending send buffer list
+ * @n_hdlc - pointer to ldisc instance data
+ * @tty - pointer to tty instance data
+ *
+ * Send frames on pending send buffer list until the driver does not accept a
+ * frame (busy) this function is called after adding a frame to the send buffer
+ * list and by the tty wakeup callback.
+ */
+static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
+{
+	register int actual;
+	unsigned long flags;
+	struct n_hdlc_buf *tbuf;
+
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_send_frames() called\n",__FILE__,__LINE__);
+ check_again:
+		
+ 	spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
+	if (n_hdlc->tbusy) {
+		n_hdlc->woke_up = 1;
+ 		spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
+		return;
+	}
+	n_hdlc->tbusy = 1;
+	n_hdlc->woke_up = 0;
+	spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
+
+	/* get current transmit buffer or get new transmit */
+	/* buffer from list of pending transmit buffers */
+		
+	tbuf = n_hdlc->tbuf;
+	if (!tbuf)
+		tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
+		
+	while (tbuf) {
+		if (debuglevel >= DEBUG_LEVEL_INFO)	
+			printk("%s(%d)sending frame %p, count=%d\n",
+				__FILE__,__LINE__,tbuf,tbuf->count);
+			
+		/* Send the next block of data to device */
+		tty->flags |= (1 << TTY_DO_WRITE_WAKEUP);
+		actual = tty->ops->write(tty, tbuf->buf, tbuf->count);
+
+		/* rollback was possible and has been done */
+		if (actual == -ERESTARTSYS) {
+			n_hdlc->tbuf = tbuf;
+			break;
+		}
+		/* if transmit error, throw frame away by */
+		/* pretending it was accepted by driver */
+		if (actual < 0)
+			actual = tbuf->count;
+		
+		if (actual == tbuf->count) {
+			if (debuglevel >= DEBUG_LEVEL_INFO)	
+				printk("%s(%d)frame %p completed\n",
+					__FILE__,__LINE__,tbuf);
+					
+			/* free current transmit buffer */
+			n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf);
+			
+			/* this tx buffer is done */
+			n_hdlc->tbuf = NULL;
+			
+			/* wait up sleeping writers */
+			wake_up_interruptible(&tty->write_wait);
+	
+			/* get next pending transmit buffer */
+			tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
+		} else {
+			if (debuglevel >= DEBUG_LEVEL_INFO)	
+				printk("%s(%d)frame %p pending\n",
+					__FILE__,__LINE__,tbuf);
+					
+			/* buffer not accepted by driver */
+			/* set this buffer as pending buffer */
+			n_hdlc->tbuf = tbuf;
+			break;
+		}
+	}
+	
+	if (!tbuf)
+		tty->flags  &= ~(1 << TTY_DO_WRITE_WAKEUP);
+	
+	/* Clear the re-entry flag */
+	spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
+	n_hdlc->tbusy = 0;
+	spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags); 
+	
+        if (n_hdlc->woke_up)
+	  goto check_again;
+
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_send_frames() exit\n",__FILE__,__LINE__);
+		
+}	/* end of n_hdlc_send_frames() */
+
+/**
+ * n_hdlc_tty_wakeup - Callback for transmit wakeup
+ * @tty	- pointer to associated tty instance data
+ *
+ * Called when low level device driver can accept more send data.
+ */
+static void n_hdlc_tty_wakeup(struct tty_struct *tty)
+{
+	struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
+
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_tty_wakeup() called\n",__FILE__,__LINE__);
+		
+	if (!n_hdlc)
+		return;
+
+	if (tty != n_hdlc->tty) {
+		tty->flags &= ~(1 << TTY_DO_WRITE_WAKEUP);
+		return;
+	}
+
+	n_hdlc_send_frames (n_hdlc, tty);
+		
+}	/* end of n_hdlc_tty_wakeup() */
+
+/**
+ * n_hdlc_tty_receive - Called by tty driver when receive data is available
+ * @tty	- pointer to tty instance data
+ * @data - pointer to received data
+ * @flags - pointer to flags for data
+ * @count - count of received data in bytes
+ *
+ * Called by tty low level driver when receive data is available. Data is
+ * interpreted as one HDLC frame.
+ */
+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 struct 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 || 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 = 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 (&tty->read_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 retrieve one frame of data (if available)
+ * @tty - pointer to tty instance data
+ * @file - pointer to open file object
+ * @buf - pointer to returned data buffer
+ * @nr - size of returned data buffer
+ * 	
+ * Returns the number of bytes returned or error code.
+ */
+static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
+			   __u8 __user *buf, size_t nr)
+{
+	struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
+	int ret;
+	struct 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 */
+	if (!access_ok(VERIFY_WRITE, buf, nr)) {
+		printk(KERN_WARNING "%s(%d) n_hdlc_tty_read() can't verify user "
+		"buffer\n", __FILE__, __LINE__);
+		return -EFAULT;
+	}
+
+	tty_lock();
+
+	for (;;) {
+		if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
+			tty_unlock();
+			return -EIO;
+		}
+
+		n_hdlc = tty2n_hdlc (tty);
+		if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC ||
+			 tty != n_hdlc->tty) {
+			tty_unlock();
+			return 0;
+		}
+
+		rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
+		if (rbuf)
+			break;
+			
+		/* no data */
+		if (file->f_flags & O_NONBLOCK) {
+			tty_unlock();
+			return -EAGAIN;
+		}
+			
+		interruptible_sleep_on (&tty->read_wait);
+		if (signal_pending(current)) {
+			tty_unlock();
+			return -EINTR;
+		}
+	}
+		
+	if (rbuf->count > nr)
+		/* frame too large for caller's buffer (discard frame) */
+		ret = -EOVERFLOW;
+	else {
+		/* Copy the data to the caller's buffer */
+		if (copy_to_user(buf, rbuf->buf, rbuf->count))
+			ret = -EFAULT;
+		else
+			ret = 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);
+	tty_unlock();
+	return ret;
+	
+}	/* end of n_hdlc_tty_read() */
+
+/**
+ * n_hdlc_tty_write - write a single frame of data to device
+ * @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
+ * 		
+ * Returns the number of bytes written (or error code).
+ */
+static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
+			    const unsigned char *data, size_t count)
+{
+	struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
+	int error = 0;
+	DECLARE_WAITQUEUE(wait, current);
+	struct n_hdlc_buf *tbuf;
+
+	if (debuglevel >= DEBUG_LEVEL_INFO)	
+		printk("%s(%d)n_hdlc_tty_write() called count=%Zd\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;
+	}
+	
+	tty_lock();
+
+	add_wait_queue(&tty->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))) {
+		if (file->f_flags & O_NONBLOCK) {
+			error = -EAGAIN;
+			break;
+		}
+		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(&tty->write_wait, &wait);
+
+	if (!error) {		
+		/* Retrieve the user's buffer */
+		memcpy(tbuf->buf, data, count);
+
+		/* Send the data */
+		tbuf->count = error = count;
+		n_hdlc_buf_put(&n_hdlc->tx_buf_list,tbuf);
+		n_hdlc_send_frames(n_hdlc,tty);
+	}
+	tty_unlock();
+	return error;
+	
+}	/* end of n_hdlc_tty_write() */
+
+/**
+ * n_hdlc_tty_ioctl - process IOCTL system call for the tty device.
+ * @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)
+ *
+ * Returns command dependent result.
+ */
+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);
+		error = put_user(count, (int __user *)arg);
+		break;
+
+	case TIOCOUTQ:
+		/* get the pending tx byte count in the driver */
+		count = tty_chars_in_buffer(tty);
+		/* 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);
+		error = put_user(count, (int __user *)arg);
+		break;
+
+	case TCFLSH:
+		switch (arg) {
+		case TCIOFLUSH:
+		case TCOFLUSH:
+			flush_tx_queue(tty);
+		}
+		/* fall through to default */
+
+	default:
+		error = n_tty_ioctl_helper(tty, file, cmd, arg);
+		break;
+	}
+	return error;
+	
+}	/* end of n_hdlc_tty_ioctl() */
+
+/**
+ * n_hdlc_tty_poll - TTY callback for poll system call
+ * @tty - pointer to tty instance data
+ * @filp - pointer to open file object for device
+ * @poll_table - wait queue for operations
+ * 
+ * Determine which operations (read/write) will not block and return info
+ * to caller.
+ * Returns a 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, &tty->read_wait, wait);
+		poll_wait(filp, &tty->write_wait, wait);
+
+		/* set bits for operations that won't block */
+		if (n_hdlc->rx_buf_list.head)
+			mask |= POLLIN | POLLRDNORM;	/* readable */
+		if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
+			mask |= POLLHUP;
+		if (tty_hung_up_p(filp))
+			mask |= POLLHUP;
+		if (!tty_is_writelocked(tty) &&
+				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
+ *
+ * Returns a pointer to newly created structure if success, otherwise %NULL
+ */
+static struct n_hdlc *n_hdlc_alloc(void)
+{
+	struct n_hdlc_buf *buf;
+	int i;
+	struct n_hdlc *n_hdlc = kmalloc(sizeof(*n_hdlc), GFP_KERNEL);
+
+	if (!n_hdlc)
+		return NULL;
+
+	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 = 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 = 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;
+	
+	return n_hdlc;
+	
+}	/* end of n_hdlc_alloc() */
+
+/**
+ * n_hdlc_buf_list_init - initialize specified HDLC buffer list
+ * @list - pointer to buffer list
+ */
+static void n_hdlc_buf_list_init(struct n_hdlc_buf_list *list)
+{
+	memset(list, 0, sizeof(*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
+ * @list - pointer to buffer list
+ * @buf	- pointer to buffer
+ */
+static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
+			   struct 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 list
+ * @list - pointer to HDLC buffer list
+ * 
+ * Remove and return an HDLC buffer from the head of the specified HDLC buffer
+ * list.
+ * Returns a pointer to HDLC buffer if available, otherwise %NULL.
+ */
+static struct n_hdlc_buf* n_hdlc_buf_get(struct n_hdlc_buf_list *list)
+{
+	unsigned long flags;
+	struct 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 char hdlc_banner[] __initdata =
+	KERN_INFO "HDLC line discipline maxframe=%u\n";
+static char hdlc_register_ok[] __initdata =
+	KERN_INFO "N_HDLC line discipline registered.\n";
+static char hdlc_register_fail[] __initdata =
+	KERN_ERR "error registering line discipline: %d\n";
+static char hdlc_init_fail[] __initdata =
+	KERN_INFO "N_HDLC: init failure %d\n";
+
+static int __init n_hdlc_init(void)
+{
+	int status;
+
+	/* range check maxframe arg */
+	if (maxframe < 4096)
+		maxframe = 4096;
+	else if (maxframe > 65535)
+		maxframe = 65535;
+
+	printk(hdlc_banner, maxframe);
+
+	status = tty_register_ldisc(N_HDLC, &n_hdlc_ldisc);
+	if (!status)
+		printk(hdlc_register_ok);
+	else
+		printk(hdlc_register_fail, status);
+
+	if (status)
+		printk(hdlc_init_fail, status);
+	return status;
+	
+}	/* end of init_module() */
+
+static char hdlc_unregister_ok[] __exitdata =
+	KERN_INFO "N_HDLC: line discipline unregistered\n";
+static char hdlc_unregister_fail[] __exitdata =
+	KERN_ERR "N_HDLC: can't unregister line discipline (err = %d)\n";
+
+static void __exit n_hdlc_exit(void)
+{
+	/* Release tty registration of line discipline */
+	int status = tty_unregister_ldisc(N_HDLC);
+
+	if (status)
+		printk(hdlc_unregister_fail, status);
+	else
+		printk(hdlc_unregister_ok);
+}
+
+module_init(n_hdlc_init);
+module_exit(n_hdlc_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Paul Fulghum paulkf@microgate.com");
+module_param(debuglevel, int, 0);
+module_param(maxframe, int, 0);
+MODULE_ALIAS_LDISC(N_HDLC);