Merge master.kernel.org:/home/rmk/linux-2.6-serial
[linux-2.6] / drivers / char / n_hdlc.c
1 /* generic HDLC line discipline for Linux
2  *
3  * Written by Paul Fulghum paulkf@microgate.com
4  * for Microgate Corporation
5  *
6  * Microgate and SyncLink are registered trademarks of Microgate Corporation
7  *
8  * Adapted from ppp.c, written by Michael Callahan <callahan@maths.ox.ac.uk>,
9  *      Al Longyear <longyear@netcom.com>,
10  *      Paul Mackerras <Paul.Mackerras@cs.anu.edu.au>
11  *
12  * Original release 01/11/99
13  * $Id: n_hdlc.c,v 4.8 2003/05/06 21:18:51 paulkf Exp $
14  *
15  * This code is released under the GNU General Public License (GPL)
16  *
17  * This module implements the tty line discipline N_HDLC for use with
18  * tty device drivers that support bit-synchronous HDLC communications.
19  *
20  * All HDLC data is frame oriented which means:
21  *
22  * 1. tty write calls represent one complete transmit frame of data
23  *    The device driver should accept the complete frame or none of 
24  *    the frame (busy) in the write method. Each write call should have
25  *    a byte count in the range of 2-65535 bytes (2 is min HDLC frame
26  *    with 1 addr byte and 1 ctrl byte). The max byte count of 65535
27  *    should include any crc bytes required. For example, when using
28  *    CCITT CRC32, 4 crc bytes are required, so the maximum size frame
29  *    the application may transmit is limited to 65531 bytes. For CCITT
30  *    CRC16, the maximum application frame size would be 65533.
31  *
32  *
33  * 2. receive callbacks from the device driver represents
34  *    one received frame. The device driver should bypass
35  *    the tty flip buffer and call the line discipline receive
36  *    callback directly to avoid fragmenting or concatenating
37  *    multiple frames into a single receive callback.
38  *
39  *    The HDLC line discipline queues the receive frames in separate
40  *    buffers so complete receive frames can be returned by the
41  *    tty read calls.
42  *
43  * 3. tty read calls returns an entire frame of data or nothing.
44  *    
45  * 4. all send and receive data is considered raw. No processing
46  *    or translation is performed by the line discipline, regardless
47  *    of the tty flags
48  *
49  * 5. When line discipline is queried for the amount of receive
50  *    data available (FIOC), 0 is returned if no data available,
51  *    otherwise the count of the next available frame is returned.
52  *    (instead of the sum of all received frame counts).
53  *
54  * These conventions allow the standard tty programming interface
55  * to be used for synchronous HDLC applications when used with
56  * this line discipline (or another line discipline that is frame
57  * oriented such as N_PPP).
58  *
59  * The SyncLink driver (synclink.c) implements both asynchronous
60  * (using standard line discipline N_TTY) and synchronous HDLC
61  * (using N_HDLC) communications, with the latter using the above
62  * conventions.
63  *
64  * This implementation is very basic and does not maintain
65  * any statistics. The main point is to enforce the raw data
66  * and frame orientation of HDLC communications.
67  *
68  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
69  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
70  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
71  * DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
72  * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
73  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
74  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
75  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
76  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
77  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
78  * OF THE POSSIBILITY OF SUCH DAMAGE.
79  */
80
81 #define HDLC_MAGIC 0x239e
82 #define HDLC_VERSION "$Revision: 4.8 $"
83
84 #include <linux/config.h>
85 #include <linux/module.h>
86 #include <linux/init.h>
87 #include <linux/kernel.h>
88 #include <linux/sched.h>
89 #include <linux/types.h>
90 #include <linux/fcntl.h>
91 #include <linux/interrupt.h>
92 #include <linux/ptrace.h>
93
94 #undef VERSION
95 #define VERSION(major,minor,patch) (((((major)<<8)+(minor))<<8)+(patch))
96
97 #include <linux/poll.h>
98 #include <linux/in.h>
99 #include <linux/ioctl.h>
100 #include <linux/slab.h>
101 #include <linux/tty.h>
102 #include <linux/errno.h>
103 #include <linux/string.h>       /* used in new tty drivers */
104 #include <linux/signal.h>       /* used in new tty drivers */
105 #include <linux/if.h>
106 #include <linux/bitops.h>
107
108 #include <asm/system.h>
109 #include <asm/termios.h>
110 #include <asm/uaccess.h>
111
112 /*
113  * Buffers for individual HDLC frames
114  */
115 #define MAX_HDLC_FRAME_SIZE 65535 
116 #define DEFAULT_RX_BUF_COUNT 10
117 #define MAX_RX_BUF_COUNT 60
118 #define DEFAULT_TX_BUF_COUNT 1
119
120 struct n_hdlc_buf {
121         struct n_hdlc_buf *link;
122         int               count;
123         char              buf[1];
124 };
125
126 #define N_HDLC_BUF_SIZE (sizeof(struct n_hdlc_buf) + maxframe)
127
128 struct n_hdlc_buf_list {
129         struct n_hdlc_buf *head;
130         struct n_hdlc_buf *tail;
131         int               count;
132         spinlock_t        spinlock;
133 };
134
135 /**
136  * struct n_hdlc - per device instance data structure
137  * @magic - magic value for structure
138  * @flags - miscellaneous control flags
139  * @tty - ptr to TTY structure
140  * @backup_tty - TTY to use if tty gets closed
141  * @tbusy - reentrancy flag for tx wakeup code
142  * @woke_up - FIXME: describe this field
143  * @tbuf - currently transmitting tx buffer
144  * @tx_buf_list - list of pending transmit frame buffers
145  * @rx_buf_list - list of received frame buffers
146  * @tx_free_buf_list - list unused transmit frame buffers
147  * @rx_free_buf_list - list unused received frame buffers
148  */
149 struct n_hdlc {
150         int                     magic;
151         __u32                   flags;
152         struct tty_struct       *tty;
153         struct tty_struct       *backup_tty;
154         int                     tbusy;
155         int                     woke_up;
156         struct n_hdlc_buf       *tbuf;
157         struct n_hdlc_buf_list  tx_buf_list;
158         struct n_hdlc_buf_list  rx_buf_list;
159         struct n_hdlc_buf_list  tx_free_buf_list;
160         struct n_hdlc_buf_list  rx_free_buf_list;
161 };
162
163 /*
164  * HDLC buffer list manipulation functions
165  */
166 static void n_hdlc_buf_list_init(struct n_hdlc_buf_list *list);
167 static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
168                            struct n_hdlc_buf *buf);
169 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
170
171 /* Local functions */
172
173 static struct n_hdlc *n_hdlc_alloc (void);
174
175 /* debug level can be set by insmod for debugging purposes */
176 #define DEBUG_LEVEL_INFO        1
177 static int debuglevel;
178
179 /* max frame size for memory allocations */
180 static int maxframe = 4096;
181
182 /* TTY callbacks */
183
184 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
185                            __u8 __user *buf, size_t nr);
186 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
187                             const unsigned char *buf, size_t nr);
188 static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
189                             unsigned int cmd, unsigned long arg);
190 static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
191                                     poll_table *wait);
192 static int n_hdlc_tty_open(struct tty_struct *tty);
193 static void n_hdlc_tty_close(struct tty_struct *tty);
194 static int n_hdlc_tty_room(struct tty_struct *tty);
195 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *cp,
196                                char *fp, int count);
197 static void n_hdlc_tty_wakeup(struct tty_struct *tty);
198
199 #define bset(p,b)       ((p)[(b) >> 5] |= (1 << ((b) & 0x1f)))
200
201 #define tty2n_hdlc(tty) ((struct n_hdlc *) ((tty)->disc_data))
202 #define n_hdlc2tty(n_hdlc)      ((n_hdlc)->tty)
203
204 static struct tty_ldisc n_hdlc_ldisc = {
205         .owner          = THIS_MODULE,
206         .magic          = TTY_LDISC_MAGIC,
207         .name           = "hdlc",
208         .open           = n_hdlc_tty_open,
209         .close          = n_hdlc_tty_close,
210         .read           = n_hdlc_tty_read,
211         .write          = n_hdlc_tty_write,
212         .ioctl          = n_hdlc_tty_ioctl,
213         .poll           = n_hdlc_tty_poll,
214         .receive_buf    = n_hdlc_tty_receive,
215         .receive_room   = n_hdlc_tty_room,
216         .write_wakeup   = n_hdlc_tty_wakeup,
217 };
218
219 /**
220  * n_hdlc_release - release an n_hdlc per device line discipline info structure
221  * @n_hdlc - per device line discipline info structure
222  */
223 static void n_hdlc_release(struct n_hdlc *n_hdlc)
224 {
225         struct tty_struct *tty = n_hdlc2tty (n_hdlc);
226         struct n_hdlc_buf *buf;
227         
228         if (debuglevel >= DEBUG_LEVEL_INFO)     
229                 printk("%s(%d)n_hdlc_release() called\n",__FILE__,__LINE__);
230                 
231         /* Ensure that the n_hdlcd process is not hanging on select()/poll() */
232         wake_up_interruptible (&tty->read_wait);
233         wake_up_interruptible (&tty->write_wait);
234
235         if (tty != NULL && tty->disc_data == n_hdlc)
236                 tty->disc_data = NULL;  /* Break the tty->n_hdlc link */
237
238         /* Release transmit and receive buffers */
239         for(;;) {
240                 buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
241                 if (buf) {
242                         kfree(buf);
243                 } else
244                         break;
245         }
246         for(;;) {
247                 buf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
248                 if (buf) {
249                         kfree(buf);
250                 } else
251                         break;
252         }
253         for(;;) {
254                 buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
255                 if (buf) {
256                         kfree(buf);
257                 } else
258                         break;
259         }
260         for(;;) {
261                 buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
262                 if (buf) {
263                         kfree(buf);
264                 } else
265                         break;
266         }
267         if (n_hdlc->tbuf)
268                 kfree(n_hdlc->tbuf);
269         kfree(n_hdlc);
270         
271 }       /* end of n_hdlc_release() */
272
273 /**
274  * n_hdlc_tty_close - line discipline close
275  * @tty - pointer to tty info structure
276  *
277  * Called when the line discipline is changed to something
278  * else, the tty is closed, or the tty detects a hangup.
279  */
280 static void n_hdlc_tty_close(struct tty_struct *tty)
281 {
282         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
283
284         if (debuglevel >= DEBUG_LEVEL_INFO)     
285                 printk("%s(%d)n_hdlc_tty_close() called\n",__FILE__,__LINE__);
286                 
287         if (n_hdlc != NULL) {
288                 if (n_hdlc->magic != HDLC_MAGIC) {
289                         printk (KERN_WARNING"n_hdlc: trying to close unopened tty!\n");
290                         return;
291                 }
292 #if defined(TTY_NO_WRITE_SPLIT)
293                 clear_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
294 #endif
295                 tty->disc_data = NULL;
296                 if (tty == n_hdlc->backup_tty)
297                         n_hdlc->backup_tty = NULL;
298                 if (tty != n_hdlc->tty)
299                         return;
300                 if (n_hdlc->backup_tty) {
301                         n_hdlc->tty = n_hdlc->backup_tty;
302                 } else {
303                         n_hdlc_release (n_hdlc);
304                 }
305         }
306         
307         if (debuglevel >= DEBUG_LEVEL_INFO)     
308                 printk("%s(%d)n_hdlc_tty_close() success\n",__FILE__,__LINE__);
309                 
310 }       /* end of n_hdlc_tty_close() */
311
312 /**
313  * n_hdlc_tty_open - called when line discipline changed to n_hdlc
314  * @tty - pointer to tty info structure
315  *
316  * Returns 0 if success, otherwise error code
317  */
318 static int n_hdlc_tty_open (struct tty_struct *tty)
319 {
320         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
321
322         if (debuglevel >= DEBUG_LEVEL_INFO)     
323                 printk("%s(%d)n_hdlc_tty_open() called (device=%s)\n",
324                 __FILE__,__LINE__,
325                 tty->name);
326                 
327         /* There should not be an existing table for this slot. */
328         if (n_hdlc) {
329                 printk (KERN_ERR"n_hdlc_tty_open:tty already associated!\n" );
330                 return -EEXIST;
331         }
332         
333         n_hdlc = n_hdlc_alloc();
334         if (!n_hdlc) {
335                 printk (KERN_ERR "n_hdlc_alloc failed\n");
336                 return -ENFILE;
337         }
338                 
339         tty->disc_data = n_hdlc;
340         n_hdlc->tty    = tty;
341         
342 #if defined(TTY_NO_WRITE_SPLIT)
343         /* change tty_io write() to not split large writes into 8K chunks */
344         set_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
345 #endif
346         
347         /* Flush any pending characters in the driver and discipline. */
348         
349         if (tty->ldisc.flush_buffer)
350                 tty->ldisc.flush_buffer (tty);
351
352         if (tty->driver->flush_buffer)
353                 tty->driver->flush_buffer (tty);
354                 
355         if (debuglevel >= DEBUG_LEVEL_INFO)     
356                 printk("%s(%d)n_hdlc_tty_open() success\n",__FILE__,__LINE__);
357                 
358         return 0;
359         
360 }       /* end of n_tty_hdlc_open() */
361
362 /**
363  * n_hdlc_send_frames - send frames on pending send buffer list
364  * @n_hdlc - pointer to ldisc instance data
365  * @tty - pointer to tty instance data
366  *
367  * Send frames on pending send buffer list until the driver does not accept a
368  * frame (busy) this function is called after adding a frame to the send buffer
369  * list and by the tty wakeup callback.
370  */
371 static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
372 {
373         register int actual;
374         unsigned long flags;
375         struct n_hdlc_buf *tbuf;
376
377         if (debuglevel >= DEBUG_LEVEL_INFO)     
378                 printk("%s(%d)n_hdlc_send_frames() called\n",__FILE__,__LINE__);
379  check_again:
380                 
381         spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
382         if (n_hdlc->tbusy) {
383                 n_hdlc->woke_up = 1;
384                 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
385                 return;
386         }
387         n_hdlc->tbusy = 1;
388         n_hdlc->woke_up = 0;
389         spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
390
391         /* get current transmit buffer or get new transmit */
392         /* buffer from list of pending transmit buffers */
393                 
394         tbuf = n_hdlc->tbuf;
395         if (!tbuf)
396                 tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
397                 
398         while (tbuf) {
399                 if (debuglevel >= DEBUG_LEVEL_INFO)     
400                         printk("%s(%d)sending frame %p, count=%d\n",
401                                 __FILE__,__LINE__,tbuf,tbuf->count);
402                         
403                 /* Send the next block of data to device */
404                 tty->flags |= (1 << TTY_DO_WRITE_WAKEUP);
405                 actual = tty->driver->write(tty, tbuf->buf, tbuf->count);
406                     
407                 /* if transmit error, throw frame away by */
408                 /* pretending it was accepted by driver */
409                 if (actual < 0)
410                         actual = tbuf->count;
411                 
412                 if (actual == tbuf->count) {
413                         if (debuglevel >= DEBUG_LEVEL_INFO)     
414                                 printk("%s(%d)frame %p completed\n",
415                                         __FILE__,__LINE__,tbuf);
416                                         
417                         /* free current transmit buffer */
418                         n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf);
419                         
420                         /* this tx buffer is done */
421                         n_hdlc->tbuf = NULL;
422                         
423                         /* wait up sleeping writers */
424                         wake_up_interruptible(&tty->write_wait);
425         
426                         /* get next pending transmit buffer */
427                         tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
428                 } else {
429                         if (debuglevel >= DEBUG_LEVEL_INFO)     
430                                 printk("%s(%d)frame %p pending\n",
431                                         __FILE__,__LINE__,tbuf);
432                                         
433                         /* buffer not accepted by driver */
434                         /* set this buffer as pending buffer */
435                         n_hdlc->tbuf = tbuf;
436                         break;
437                 }
438         }
439         
440         if (!tbuf)
441                 tty->flags  &= ~(1 << TTY_DO_WRITE_WAKEUP);
442         
443         /* Clear the re-entry flag */
444         spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
445         n_hdlc->tbusy = 0;
446         spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags); 
447         
448         if (n_hdlc->woke_up)
449           goto check_again;
450
451         if (debuglevel >= DEBUG_LEVEL_INFO)     
452                 printk("%s(%d)n_hdlc_send_frames() exit\n",__FILE__,__LINE__);
453                 
454 }       /* end of n_hdlc_send_frames() */
455
456 /**
457  * n_hdlc_tty_wakeup - Callback for transmit wakeup
458  * @tty - pointer to associated tty instance data
459  *
460  * Called when low level device driver can accept more send data.
461  */
462 static void n_hdlc_tty_wakeup(struct tty_struct *tty)
463 {
464         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
465
466         if (debuglevel >= DEBUG_LEVEL_INFO)     
467                 printk("%s(%d)n_hdlc_tty_wakeup() called\n",__FILE__,__LINE__);
468                 
469         if (!n_hdlc)
470                 return;
471
472         if (tty != n_hdlc->tty) {
473                 tty->flags &= ~(1 << TTY_DO_WRITE_WAKEUP);
474                 return;
475         }
476
477         n_hdlc_send_frames (n_hdlc, tty);
478                 
479 }       /* end of n_hdlc_tty_wakeup() */
480
481 /**
482  * n_hdlc_tty_room - Return the amount of space left in the receiver's buffer
483  * @tty - pointer to associated tty instance data
484  *
485  * Callback function from tty driver. Return the amount of space left in the
486  * receiver's buffer to decide if remote transmitter is to be throttled.
487  */
488 static int n_hdlc_tty_room(struct tty_struct *tty)
489 {
490         if (debuglevel >= DEBUG_LEVEL_INFO)     
491                 printk("%s(%d)n_hdlc_tty_room() called\n",__FILE__,__LINE__);
492         /* always return a larger number to prevent */
493         /* throttling of remote transmitter. */
494         return 65536;
495 }       /* end of n_hdlc_tty_root() */
496
497 /**
498  * n_hdlc_tty_receive - Called by tty driver when receive data is available
499  * @tty - pointer to tty instance data
500  * @data - pointer to received data
501  * @flags - pointer to flags for data
502  * @count - count of received data in bytes
503  *
504  * Called by tty low level driver when receive data is available. Data is
505  * interpreted as one HDLC frame.
506  */
507 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
508                                char *flags, int count)
509 {
510         register struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
511         register struct n_hdlc_buf *buf;
512
513         if (debuglevel >= DEBUG_LEVEL_INFO)     
514                 printk("%s(%d)n_hdlc_tty_receive() called count=%d\n",
515                         __FILE__,__LINE__, count);
516                 
517         /* This can happen if stuff comes in on the backup tty */
518         if (n_hdlc == 0 || tty != n_hdlc->tty)
519                 return;
520                 
521         /* verify line is using HDLC discipline */
522         if (n_hdlc->magic != HDLC_MAGIC) {
523                 printk("%s(%d) line not using HDLC discipline\n",
524                         __FILE__,__LINE__);
525                 return;
526         }
527         
528         if ( count>maxframe ) {
529                 if (debuglevel >= DEBUG_LEVEL_INFO)     
530                         printk("%s(%d) rx count>maxframesize, data discarded\n",
531                                __FILE__,__LINE__);
532                 return;
533         }
534
535         /* get a free HDLC buffer */    
536         buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
537         if (!buf) {
538                 /* no buffers in free list, attempt to allocate another rx buffer */
539                 /* unless the maximum count has been reached */
540                 if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT)
541                         buf = kmalloc(N_HDLC_BUF_SIZE, GFP_ATOMIC);
542         }
543         
544         if (!buf) {
545                 if (debuglevel >= DEBUG_LEVEL_INFO)     
546                         printk("%s(%d) no more rx buffers, data discarded\n",
547                                __FILE__,__LINE__);
548                 return;
549         }
550                 
551         /* copy received data to HDLC buffer */
552         memcpy(buf->buf,data,count);
553         buf->count=count;
554
555         /* add HDLC buffer to list of received frames */
556         n_hdlc_buf_put(&n_hdlc->rx_buf_list, buf);
557         
558         /* wake up any blocked reads and perform async signalling */
559         wake_up_interruptible (&tty->read_wait);
560         if (n_hdlc->tty->fasync != NULL)
561                 kill_fasync (&n_hdlc->tty->fasync, SIGIO, POLL_IN);
562
563 }       /* end of n_hdlc_tty_receive() */
564
565 /**
566  * n_hdlc_tty_read - Called to retreive one frame of data (if available)
567  * @tty - pointer to tty instance data
568  * @file - pointer to open file object
569  * @buf - pointer to returned data buffer
570  * @nr - size of returned data buffer
571  *      
572  * Returns the number of bytes returned or error code.
573  */
574 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
575                            __u8 __user *buf, size_t nr)
576 {
577         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
578         int ret;
579         struct n_hdlc_buf *rbuf;
580
581         if (debuglevel >= DEBUG_LEVEL_INFO)     
582                 printk("%s(%d)n_hdlc_tty_read() called\n",__FILE__,__LINE__);
583                 
584         /* Validate the pointers */
585         if (!n_hdlc)
586                 return -EIO;
587
588         /* verify user access to buffer */
589         if (!access_ok(VERIFY_WRITE, buf, nr)) {
590                 printk(KERN_WARNING "%s(%d) n_hdlc_tty_read() can't verify user "
591                 "buffer\n", __FILE__, __LINE__);
592                 return -EFAULT;
593         }
594
595         for (;;) {
596                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
597                         return -EIO;
598
599                 n_hdlc = tty2n_hdlc (tty);
600                 if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC ||
601                          tty != n_hdlc->tty)
602                         return 0;
603
604                 rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
605                 if (rbuf)
606                         break;
607                         
608                 /* no data */
609                 if (file->f_flags & O_NONBLOCK)
610                         return -EAGAIN;
611                         
612                 interruptible_sleep_on (&tty->read_wait);
613                 if (signal_pending(current))
614                         return -EINTR;
615         }
616                 
617         if (rbuf->count > nr)
618                 /* frame too large for caller's buffer (discard frame) */
619                 ret = -EOVERFLOW;
620         else {
621                 /* Copy the data to the caller's buffer */
622                 if (copy_to_user(buf, rbuf->buf, rbuf->count))
623                         ret = -EFAULT;
624                 else
625                         ret = rbuf->count;
626         }
627         
628         /* return HDLC buffer to free list unless the free list */
629         /* count has exceeded the default value, in which case the */
630         /* buffer is freed back to the OS to conserve memory */
631         if (n_hdlc->rx_free_buf_list.count > DEFAULT_RX_BUF_COUNT)
632                 kfree(rbuf);
633         else    
634                 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,rbuf);
635         
636         return ret;
637         
638 }       /* end of n_hdlc_tty_read() */
639
640 /**
641  * n_hdlc_tty_write - write a single frame of data to device
642  * @tty - pointer to associated tty device instance data
643  * @file - pointer to file object data
644  * @data - pointer to transmit data (one frame)
645  * @count - size of transmit frame in bytes
646  *              
647  * Returns the number of bytes written (or error code).
648  */
649 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
650                             const unsigned char *data, size_t count)
651 {
652         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
653         int error = 0;
654         DECLARE_WAITQUEUE(wait, current);
655         struct n_hdlc_buf *tbuf;
656
657         if (debuglevel >= DEBUG_LEVEL_INFO)     
658                 printk("%s(%d)n_hdlc_tty_write() called count=%Zd\n",
659                         __FILE__,__LINE__,count);
660                 
661         /* Verify pointers */
662         if (!n_hdlc)
663                 return -EIO;
664
665         if (n_hdlc->magic != HDLC_MAGIC)
666                 return -EIO;
667
668         /* verify frame size */
669         if (count > maxframe ) {
670                 if (debuglevel & DEBUG_LEVEL_INFO)
671                         printk (KERN_WARNING
672                                 "n_hdlc_tty_write: truncating user packet "
673                                 "from %lu to %d\n", (unsigned long) count,
674                                 maxframe );
675                 count = maxframe;
676         }
677         
678         add_wait_queue(&tty->write_wait, &wait);
679         set_current_state(TASK_INTERRUPTIBLE);
680         
681         /* Allocate transmit buffer */
682         /* sleep until transmit buffer available */             
683         while (!(tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list))) {
684                 schedule();
685                         
686                 n_hdlc = tty2n_hdlc (tty);
687                 if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC || 
688                     tty != n_hdlc->tty) {
689                         printk("n_hdlc_tty_write: %p invalid after wait!\n", n_hdlc);
690                         error = -EIO;
691                         break;
692                 }
693                         
694                 if (signal_pending(current)) {
695                         error = -EINTR;
696                         break;
697                 }
698         }
699
700         set_current_state(TASK_RUNNING);
701         remove_wait_queue(&tty->write_wait, &wait);
702
703         if (!error) {           
704                 /* Retrieve the user's buffer */
705                 memcpy(tbuf->buf, data, count);
706
707                 /* Send the data */
708                 tbuf->count = error = count;
709                 n_hdlc_buf_put(&n_hdlc->tx_buf_list,tbuf);
710                 n_hdlc_send_frames(n_hdlc,tty);
711         }
712
713         return error;
714         
715 }       /* end of n_hdlc_tty_write() */
716
717 /**
718  * n_hdlc_tty_ioctl - process IOCTL system call for the tty device.
719  * @tty - pointer to tty instance data
720  * @file - pointer to open file object for device
721  * @cmd - IOCTL command code
722  * @arg - argument for IOCTL call (cmd dependent)
723  *
724  * Returns command dependent result.
725  */
726 static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
727                             unsigned int cmd, unsigned long arg)
728 {
729         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
730         int error = 0;
731         int count;
732         unsigned long flags;
733         
734         if (debuglevel >= DEBUG_LEVEL_INFO)     
735                 printk("%s(%d)n_hdlc_tty_ioctl() called %d\n",
736                         __FILE__,__LINE__,cmd);
737                 
738         /* Verify the status of the device */
739         if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC)
740                 return -EBADF;
741
742         switch (cmd) {
743         case FIONREAD:
744                 /* report count of read data available */
745                 /* in next available frame (if any) */
746                 spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock,flags);
747                 if (n_hdlc->rx_buf_list.head)
748                         count = n_hdlc->rx_buf_list.head->count;
749                 else
750                         count = 0;
751                 spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock,flags);
752                 error = put_user(count, (int __user *)arg);
753                 break;
754
755         case TIOCOUTQ:
756                 /* get the pending tx byte count in the driver */
757                 count = tty->driver->chars_in_buffer ?
758                                 tty->driver->chars_in_buffer(tty) : 0;
759                 /* add size of next output frame in queue */
760                 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock,flags);
761                 if (n_hdlc->tx_buf_list.head)
762                         count += n_hdlc->tx_buf_list.head->count;
763                 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock,flags);
764                 error = put_user(count, (int __user *)arg);
765                 break;
766
767         default:
768                 error = n_tty_ioctl (tty, file, cmd, arg);
769                 break;
770         }
771         return error;
772         
773 }       /* end of n_hdlc_tty_ioctl() */
774
775 /**
776  * n_hdlc_tty_poll - TTY callback for poll system call
777  * @tty - pointer to tty instance data
778  * @filp - pointer to open file object for device
779  * @poll_table - wait queue for operations
780  * 
781  * Determine which operations (read/write) will not block and return info
782  * to caller.
783  * Returns a bit mask containing info on which ops will not block.
784  */
785 static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
786                                     poll_table *wait)
787 {
788         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
789         unsigned int mask = 0;
790
791         if (debuglevel >= DEBUG_LEVEL_INFO)     
792                 printk("%s(%d)n_hdlc_tty_poll() called\n",__FILE__,__LINE__);
793                 
794         if (n_hdlc && n_hdlc->magic == HDLC_MAGIC && tty == n_hdlc->tty) {
795                 /* queue current process into any wait queue that */
796                 /* may awaken in the future (read and write) */
797
798                 poll_wait(filp, &tty->read_wait, wait);
799                 poll_wait(filp, &tty->write_wait, wait);
800
801                 /* set bits for operations that won't block */
802                 if(n_hdlc->rx_buf_list.head)
803                         mask |= POLLIN | POLLRDNORM;    /* readable */
804                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
805                         mask |= POLLHUP;
806                 if(tty_hung_up_p(filp))
807                         mask |= POLLHUP;
808                 if(n_hdlc->tx_free_buf_list.head)
809                         mask |= POLLOUT | POLLWRNORM;   /* writable */
810         }
811         return mask;
812 }       /* end of n_hdlc_tty_poll() */
813
814 /**
815  * n_hdlc_alloc - allocate an n_hdlc instance data structure
816  *
817  * Returns a pointer to newly created structure if success, otherwise %NULL
818  */
819 static struct n_hdlc *n_hdlc_alloc(void)
820 {
821         struct n_hdlc_buf *buf;
822         int i;
823         struct n_hdlc *n_hdlc = kmalloc(sizeof(*n_hdlc), GFP_KERNEL);
824
825         if (!n_hdlc)
826                 return NULL;
827
828         memset(n_hdlc, 0, sizeof(*n_hdlc));
829
830         n_hdlc_buf_list_init(&n_hdlc->rx_free_buf_list);
831         n_hdlc_buf_list_init(&n_hdlc->tx_free_buf_list);
832         n_hdlc_buf_list_init(&n_hdlc->rx_buf_list);
833         n_hdlc_buf_list_init(&n_hdlc->tx_buf_list);
834         
835         /* allocate free rx buffer list */
836         for(i=0;i<DEFAULT_RX_BUF_COUNT;i++) {
837                 buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
838                 if (buf)
839                         n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,buf);
840                 else if (debuglevel >= DEBUG_LEVEL_INFO)        
841                         printk("%s(%d)n_hdlc_alloc(), kalloc() failed for rx buffer %d\n",__FILE__,__LINE__, i);
842         }
843         
844         /* allocate free tx buffer list */
845         for(i=0;i<DEFAULT_TX_BUF_COUNT;i++) {
846                 buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
847                 if (buf)
848                         n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,buf);
849                 else if (debuglevel >= DEBUG_LEVEL_INFO)        
850                         printk("%s(%d)n_hdlc_alloc(), kalloc() failed for tx buffer %d\n",__FILE__,__LINE__, i);
851         }
852         
853         /* Initialize the control block */
854         n_hdlc->magic  = HDLC_MAGIC;
855         n_hdlc->flags  = 0;
856         
857         return n_hdlc;
858         
859 }       /* end of n_hdlc_alloc() */
860
861 /**
862  * n_hdlc_buf_list_init - initialize specified HDLC buffer list
863  * @list - pointer to buffer list
864  */
865 static void n_hdlc_buf_list_init(struct n_hdlc_buf_list *list)
866 {
867         memset(list, 0, sizeof(*list));
868         spin_lock_init(&list->spinlock);
869 }       /* end of n_hdlc_buf_list_init() */
870
871 /**
872  * n_hdlc_buf_put - add specified HDLC buffer to tail of specified list
873  * @list - pointer to buffer list
874  * @buf - pointer to buffer
875  */
876 static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
877                            struct n_hdlc_buf *buf)
878 {
879         unsigned long flags;
880         spin_lock_irqsave(&list->spinlock,flags);
881         
882         buf->link=NULL;
883         if(list->tail)
884                 list->tail->link = buf;
885         else
886                 list->head = buf;
887         list->tail = buf;
888         (list->count)++;
889         
890         spin_unlock_irqrestore(&list->spinlock,flags);
891         
892 }       /* end of n_hdlc_buf_put() */
893
894 /**
895  * n_hdlc_buf_get - remove and return an HDLC buffer from list
896  * @list - pointer to HDLC buffer list
897  * 
898  * Remove and return an HDLC buffer from the head of the specified HDLC buffer
899  * list.
900  * Returns a pointer to HDLC buffer if available, otherwise %NULL.
901  */
902 static struct n_hdlc_buf* n_hdlc_buf_get(struct n_hdlc_buf_list *list)
903 {
904         unsigned long flags;
905         struct n_hdlc_buf *buf;
906         spin_lock_irqsave(&list->spinlock,flags);
907         
908         buf = list->head;
909         if (buf) {
910                 list->head = buf->link;
911                 (list->count)--;
912         }
913         if (!list->head)
914                 list->tail = NULL;
915         
916         spin_unlock_irqrestore(&list->spinlock,flags);
917         return buf;
918         
919 }       /* end of n_hdlc_buf_get() */
920
921 static char hdlc_banner[] __initdata =
922         KERN_INFO "HDLC line discipline: version " HDLC_VERSION
923         ", maxframe=%u\n";
924 static char hdlc_register_ok[] __initdata =
925         KERN_INFO "N_HDLC line discipline registered.\n";
926 static char hdlc_register_fail[] __initdata =
927         KERN_ERR "error registering line discipline: %d\n";
928 static char hdlc_init_fail[] __initdata =
929         KERN_INFO "N_HDLC: init failure %d\n";
930
931 static int __init n_hdlc_init(void)
932 {
933         int status;
934
935         /* range check maxframe arg */
936         if (maxframe < 4096)
937                 maxframe = 4096;
938         else if (maxframe > 65535)
939                 maxframe = 65535;
940
941         printk(hdlc_banner, maxframe);
942
943         status = tty_register_ldisc(N_HDLC, &n_hdlc_ldisc);
944         if (!status)
945                 printk(hdlc_register_ok);
946         else
947                 printk(hdlc_register_fail, status);
948
949         if (status)
950                 printk(hdlc_init_fail, status);
951         return status;
952         
953 }       /* end of init_module() */
954
955 static char hdlc_unregister_ok[] __exitdata =
956         KERN_INFO "N_HDLC: line discipline unregistered\n";
957 static char hdlc_unregister_fail[] __exitdata =
958         KERN_ERR "N_HDLC: can't unregister line discipline (err = %d)\n";
959
960 static void __exit n_hdlc_exit(void)
961 {
962         /* Release tty registration of line discipline */
963         int status = tty_unregister_ldisc(N_HDLC);
964
965         if (status)
966                 printk(hdlc_unregister_fail, status);
967         else
968                 printk(hdlc_unregister_ok);
969 }
970
971 module_init(n_hdlc_init);
972 module_exit(n_hdlc_exit);
973
974 MODULE_LICENSE("GPL");
975 MODULE_AUTHOR("Paul Fulghum paulkf@microgate.com");
976 module_param(debuglevel, int, 0);
977 module_param(maxframe, int, 0);
978 MODULE_ALIAS_LDISC(N_HDLC);