n_hdlc.c

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/* generic HDLC line discipline for Linux
 *
 * Written by Paul Fulghum [e-mail]
 * for Microgate Corporation
 *
 * Microgate and SyncLink are registered trademarks of Microgate Corporation
 *
 * Adapted from ppp.c, written by Michael Callahan <[e-mail]>,
 *	Al Longyear <[e-mail]>, Paul Mackerras <[e-mail]>
 *
 * Original release 01/11/99
 * $Id: n_hdlc.c,v 3.2 2000/11/06 22:34:38 paul 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 seperate
 *    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 "3.2"

#include <linux/version.h>
#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/malloc.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 <asm/system.h>
#include <asm/bitops.h>
#include <asm/termios.h>
#include <linux/if.h>

#include <linux/ioctl.h>

#ifdef CONFIG_KERNELD
#include <linux/kerneld.h>
#endif

#include <asm/segment.h>
#define GET_USER(error,value,addr) error = get_user(value,addr)
#define COPY_FROM_USER(error,dest,src,size) error = copy_from_user(dest,src,size) ? -EFAULT : 0
#define PUT_USER(error,value,addr) error = put_user(value,addr)
#define COPY_TO_USER(error,dest,src,size) error = copy_to_user(dest,src,size) ? -EFAULT : 0

#include <asm/uaccess.h>

typedef ssize_t		rw_ret_t;
typedef size_t		rw_count_t;

/*
 * 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


typedef struct _n_hdlc_buf
{
	struct _n_hdlc_buf *link;
	int count;
	char buf[1];
} N_HDLC_BUF;

#define	N_HDLC_BUF_SIZE	(sizeof(N_HDLC_BUF)+maxframe)

typedef struct _n_hdlc_buf_list
{
	N_HDLC_BUF *head;
	N_HDLC_BUF *tail;
	int count;
	spinlock_t spinlock;
	
} N_HDLC_BUF_LIST;

/*
 * Per device instance data structure
 */
struct n_hdlc {
	int		magic;		/* magic value for structure	*/
	__u32		flags;		/* miscellaneous control flags	*/
	
	struct tty_struct *tty;		/* ptr to TTY structure	*/
	struct tty_struct *backup_tty;	/* TTY to use if tty gets closed */
	
	/* Queues for select() functionality */
	wait_queue_head_t read_wait;
	wait_queue_head_t write_wait;
	wait_queue_head_t poll_wait;

	int		tbusy;		/* reentrancy flag for tx wakeup code */
	int		woke_up;
	N_HDLC_BUF	*tbuf;		/* currently transmitting tx buffer */
	N_HDLC_BUF_LIST tx_buf_list;	/* list of pending transmit frame buffers */	
	N_HDLC_BUF_LIST	rx_buf_list;	/* list of received frame buffers */
	N_HDLC_BUF_LIST tx_free_buf_list;	/* list unused transmit frame buffers */	
	N_HDLC_BUF_LIST	rx_free_buf_list;	/* list unused received frame buffers */
};

/*
 * HDLC buffer list manipulation functions
 */
void n_hdlc_buf_list_init(N_HDLC_BUF_LIST *list);
void n_hdlc_buf_put(N_HDLC_BUF_LIST *list,N_HDLC_BUF *buf);
N_HDLC_BUF* n_hdlc_buf_get(N_HDLC_BUF_LIST *list);

/* Local functions */

static struct n_hdlc *n_hdlc_alloc (void);

MODULE_PARM(debuglevel, "i");
MODULE_PARM(maxframe, "i");


/* debug level can be set by insmod for debugging purposes */
#define DEBUG_LEVEL_INFO	1
int debuglevel=0;

/* max frame size for memory allocations */
ssize_t	maxframe=4096;

/* TTY callbacks */

static rw_ret_t n_hdlc_tty_read(struct tty_struct *,
	struct file *, __u8 *, rw_count_t);
static rw_ret_t n_hdlc_tty_write(struct tty_struct *,
	struct file *, const __u8 *, rw_count_t);
static int n_hdlc_tty_ioctl(struct tty_struct *,
	struct file *, unsigned int, unsigned long);
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 *);
static void n_hdlc_tty_close (struct tty_struct *);
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)

/* Define this string only once for all macro invocations */
static char szVersion[] = HDLC_VERSION;

/* n_hdlc_release()
 *
 *	release an 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);
	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 (&n_hdlc->read_wait);
	wake_up_interruptible (&n_hdlc->poll_wait);
	wake_up_interruptible (&n_hdlc->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;
	}
	
	kfree(n_hdlc);
	
}	/* end of n_hdlc_release() */

/* n_hdlc_tty_close()
 *
 *	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 = 0;
		if (tty != n_hdlc->tty)
			return;
		if (n_hdlc->backup_tty) {
			n_hdlc->tty = n_hdlc->backup_tty;
		} else {
			n_hdlc_release (n_hdlc);
			MOD_DEC_USE_COUNT;
		}
	}
	
	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
 * 	
 * Arguments:	tty	pointer to tty info structure
 * Return Value:	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 (major=%u,minor=%u)\n",
		__FILE__,__LINE__,
		MAJOR(tty->device), MINOR(tty->device));
		
	/* 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;
	
	MOD_INC_USE_COUNT;
	
#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 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
 * 	
 * Arguments:		n_hdlc		pointer to ldisc instance data
 * 			tty		pointer to tty instance data
 * Return Value:	None
 */
static void n_hdlc_send_frames (struct n_hdlc *n_hdlc, struct tty_struct *tty)
{
	register int actual;
	unsigned long flags;
	N_HDLC_BUF *tbuf;

	if (debuglevel >= DEBUG_LEVEL_INFO)	
		printk("%s(%d)n_hdlc_send_frames() called\n",__FILE__,__LINE__);
 check_again:
		
	save_flags(flags);
	cli ();
	if (n_hdlc->tbusy) {
		n_hdlc->woke_up = 1;
		restore_flags(flags);
		return;
	}
	n_hdlc->tbusy = 1;
	n_hdlc->woke_up = 0;
	restore_flags(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, 0, 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(&n_hdlc->write_wait);
			wake_up_interruptible(&n_hdlc->poll_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 */
	save_flags(flags);
	cli ();
	n_hdlc->tbusy = 0;
	restore_flags(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. Called when low level
 *	device driver can accept more send data.
 *
 * Arguments:		tty	pointer to associated tty instance data
 * Return Value:	None
 */
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()
 * 
 *	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.
 *
 * Arguments:		tty	pointer to associated tty instance data
 * Return Value:	number of bytes left in receive buffer
 */
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 low level driver when receive data is
 * 	available. Data is interpreted as one HDLC frame.