Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 978 insertions, 0 deletions

diff --git a/drivers/char/n_hdlc.c b/drivers/char/n_hdlc.c
new file mode 100644
index 000000000000..b3dbff1cf967
--- /dev/null
+++ b/drivers/char/n_hdlc.c
@@ -0,0 +1,978 @@
+/* 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
+ * $Id: n_hdlc.c,v 4.8 2003/05/06 21:18:51 paulkf Exp $
+ *
+ * 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
+#define HDLC_VERSION "$Revision: 4.8 $"
+
+#include <linux/config.h>
+#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/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 1
+
+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 int n_hdlc_tty_room(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 struct tty_ldisc 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,
+        .receive_room   = n_hdlc_tty_room,
+        .write_wakeup   = n_hdlc_tty_wakeup,
+};
+
+/**
+ * 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 != NULL && 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;
+        }
+        if (n_hdlc->tbuf)
+                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;
+        
+#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 any pending characters in the driver and discipline. */
+        
+        if (tty->ldisc.flush_buffer)
+                tty->ldisc.flush_buffer (tty);
+
+        if (tty->driver->flush_buffer)
+                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->driver->write(tty, tbuf->buf, tbuf->count);
+                    
+                /* 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_room - Return the amount of space left in the receiver's buffer
+ * @tty - pointer to associated tty instance data
+ *
+ * Callback function from tty driver. Return the amount of space left in the
+ * receiver's buffer to decide if remote transmitter is to be throttled.
+ */
+static int n_hdlc_tty_room(struct tty_struct *tty)
+{
+        if (debuglevel >= DEBUG_LEVEL_INFO)     
+                printk("%s(%d)n_hdlc_tty_room() called\n",__FILE__,__LINE__);
+        /* always return a larger number to prevent */
+        /* throttling of remote transmitter. */
+        return 65536;
+}       /* end of n_hdlc_tty_root() */
+
+/**
+ * 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 == 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 = 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 retreive 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;
+        }
+
+        for (;;) {
+                if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
+                        return -EIO;
+
+                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 (&tty->read_wait);
+                if (signal_pending(current))
+                        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);
+        
+        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;
+        }
+        
+        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))) {
+                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);
+        }
+
+        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->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);
+                error = put_user(count, (int __user *)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
+ * @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(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: version " HDLC_VERSION
+        ", 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_register_ldisc(N_HDLC, NULL);
+
+        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);