tty: n_hdlc: get rid of racy n_hdlc.tbuf
[pandora-kernel.git] / drivers / tty / 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  *
14  * This code is released under the GNU General Public License (GPL)
15  *
16  * This module implements the tty line discipline N_HDLC for use with
17  * tty device drivers that support bit-synchronous HDLC communications.
18  *
19  * All HDLC data is frame oriented which means:
20  *
21  * 1. tty write calls represent one complete transmit frame of data
22  *    The device driver should accept the complete frame or none of 
23  *    the frame (busy) in the write method. Each write call should have
24  *    a byte count in the range of 2-65535 bytes (2 is min HDLC frame
25  *    with 1 addr byte and 1 ctrl byte). The max byte count of 65535
26  *    should include any crc bytes required. For example, when using
27  *    CCITT CRC32, 4 crc bytes are required, so the maximum size frame
28  *    the application may transmit is limited to 65531 bytes. For CCITT
29  *    CRC16, the maximum application frame size would be 65533.
30  *
31  *
32  * 2. receive callbacks from the device driver represents
33  *    one received frame. The device driver should bypass
34  *    the tty flip buffer and call the line discipline receive
35  *    callback directly to avoid fragmenting or concatenating
36  *    multiple frames into a single receive callback.
37  *
38  *    The HDLC line discipline queues the receive frames in separate
39  *    buffers so complete receive frames can be returned by the
40  *    tty read calls.
41  *
42  * 3. tty read calls returns an entire frame of data or nothing.
43  *    
44  * 4. all send and receive data is considered raw. No processing
45  *    or translation is performed by the line discipline, regardless
46  *    of the tty flags
47  *
48  * 5. When line discipline is queried for the amount of receive
49  *    data available (FIOC), 0 is returned if no data available,
50  *    otherwise the count of the next available frame is returned.
51  *    (instead of the sum of all received frame counts).
52  *
53  * These conventions allow the standard tty programming interface
54  * to be used for synchronous HDLC applications when used with
55  * this line discipline (or another line discipline that is frame
56  * oriented such as N_PPP).
57  *
58  * The SyncLink driver (synclink.c) implements both asynchronous
59  * (using standard line discipline N_TTY) and synchronous HDLC
60  * (using N_HDLC) communications, with the latter using the above
61  * conventions.
62  *
63  * This implementation is very basic and does not maintain
64  * any statistics. The main point is to enforce the raw data
65  * and frame orientation of HDLC communications.
66  *
67  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
68  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
69  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
70  * DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
71  * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
72  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
73  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
74  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
75  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
76  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
77  * OF THE POSSIBILITY OF SUCH DAMAGE.
78  */
79
80 #define HDLC_MAGIC 0x239e
81
82 #include <linux/module.h>
83 #include <linux/init.h>
84 #include <linux/kernel.h>
85 #include <linux/sched.h>
86 #include <linux/types.h>
87 #include <linux/fcntl.h>
88 #include <linux/interrupt.h>
89 #include <linux/ptrace.h>
90
91 #undef VERSION
92 #define VERSION(major,minor,patch) (((((major)<<8)+(minor))<<8)+(patch))
93
94 #include <linux/poll.h>
95 #include <linux/in.h>
96 #include <linux/ioctl.h>
97 #include <linux/slab.h>
98 #include <linux/tty.h>
99 #include <linux/errno.h>
100 #include <linux/string.h>       /* used in new tty drivers */
101 #include <linux/signal.h>       /* used in new tty drivers */
102 #include <linux/if.h>
103 #include <linux/bitops.h>
104
105 #include <asm/system.h>
106 #include <asm/termios.h>
107 #include <asm/uaccess.h>
108
109 /*
110  * Buffers for individual HDLC frames
111  */
112 #define MAX_HDLC_FRAME_SIZE 65535 
113 #define DEFAULT_RX_BUF_COUNT 10
114 #define MAX_RX_BUF_COUNT 60
115 #define DEFAULT_TX_BUF_COUNT 3
116
117 struct n_hdlc_buf {
118         struct list_head  list_item;
119         int               count;
120         char              buf[1];
121 };
122
123 #define N_HDLC_BUF_SIZE (sizeof(struct n_hdlc_buf) + maxframe)
124
125 struct n_hdlc_buf_list {
126         struct list_head  list;
127         int               count;
128         spinlock_t        spinlock;
129 };
130
131 /**
132  * struct n_hdlc - per device instance data structure
133  * @magic - magic value for structure
134  * @flags - miscellaneous control flags
135  * @tty - ptr to TTY structure
136  * @backup_tty - TTY to use if tty gets closed
137  * @tbusy - reentrancy flag for tx wakeup code
138  * @woke_up - FIXME: describe this field
139  * @tx_buf_list - list of pending transmit frame buffers
140  * @rx_buf_list - list of received frame buffers
141  * @tx_free_buf_list - list unused transmit frame buffers
142  * @rx_free_buf_list - list unused received frame buffers
143  */
144 struct n_hdlc {
145         int                     magic;
146         __u32                   flags;
147         struct tty_struct       *tty;
148         struct tty_struct       *backup_tty;
149         int                     tbusy;
150         int                     woke_up;
151         struct n_hdlc_buf_list  tx_buf_list;
152         struct n_hdlc_buf_list  rx_buf_list;
153         struct n_hdlc_buf_list  tx_free_buf_list;
154         struct n_hdlc_buf_list  rx_free_buf_list;
155 };
156
157 /*
158  * HDLC buffer list manipulation functions
159  */
160 static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
161                                                 struct n_hdlc_buf *buf);
162 static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
163                            struct n_hdlc_buf *buf);
164 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
165
166 /* Local functions */
167
168 static struct n_hdlc *n_hdlc_alloc (void);
169
170 /* debug level can be set by insmod for debugging purposes */
171 #define DEBUG_LEVEL_INFO        1
172 static int debuglevel;
173
174 /* max frame size for memory allocations */
175 static int maxframe = 4096;
176
177 /* TTY callbacks */
178
179 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
180                            __u8 __user *buf, size_t nr);
181 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
182                             const unsigned char *buf, size_t nr);
183 static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
184                             unsigned int cmd, unsigned long arg);
185 static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
186                                     poll_table *wait);
187 static int n_hdlc_tty_open(struct tty_struct *tty);
188 static void n_hdlc_tty_close(struct tty_struct *tty);
189 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *cp,
190                                char *fp, int count);
191 static void n_hdlc_tty_wakeup(struct tty_struct *tty);
192
193 #define bset(p,b)       ((p)[(b) >> 5] |= (1 << ((b) & 0x1f)))
194
195 #define tty2n_hdlc(tty) ((struct n_hdlc *) ((tty)->disc_data))
196 #define n_hdlc2tty(n_hdlc)      ((n_hdlc)->tty)
197
198 static void flush_rx_queue(struct tty_struct *tty)
199 {
200         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
201         struct n_hdlc_buf *buf;
202
203         while ((buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list)))
204                 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, buf);
205 }
206
207 static void flush_tx_queue(struct tty_struct *tty)
208 {
209         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
210         struct n_hdlc_buf *buf;
211
212         while ((buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list)))
213                 n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, buf);
214 }
215
216 static struct tty_ldisc_ops n_hdlc_ldisc = {
217         .owner          = THIS_MODULE,
218         .magic          = TTY_LDISC_MAGIC,
219         .name           = "hdlc",
220         .open           = n_hdlc_tty_open,
221         .close          = n_hdlc_tty_close,
222         .read           = n_hdlc_tty_read,
223         .write          = n_hdlc_tty_write,
224         .ioctl          = n_hdlc_tty_ioctl,
225         .poll           = n_hdlc_tty_poll,
226         .receive_buf    = n_hdlc_tty_receive,
227         .write_wakeup   = n_hdlc_tty_wakeup,
228         .flush_buffer   = flush_rx_queue,
229 };
230
231 /**
232  * n_hdlc_release - release an n_hdlc per device line discipline info structure
233  * @n_hdlc - per device line discipline info structure
234  */
235 static void n_hdlc_release(struct n_hdlc *n_hdlc)
236 {
237         struct tty_struct *tty = n_hdlc2tty (n_hdlc);
238         struct n_hdlc_buf *buf;
239         
240         if (debuglevel >= DEBUG_LEVEL_INFO)     
241                 printk("%s(%d)n_hdlc_release() called\n",__FILE__,__LINE__);
242                 
243         /* Ensure that the n_hdlcd process is not hanging on select()/poll() */
244         wake_up_interruptible (&tty->read_wait);
245         wake_up_interruptible (&tty->write_wait);
246
247         if (tty->disc_data == n_hdlc)
248                 tty->disc_data = NULL;  /* Break the tty->n_hdlc link */
249
250         /* Release transmit and receive buffers */
251         for(;;) {
252                 buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
253                 if (buf) {
254                         kfree(buf);
255                 } else
256                         break;
257         }
258         for(;;) {
259                 buf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
260                 if (buf) {
261                         kfree(buf);
262                 } else
263                         break;
264         }
265         for(;;) {
266                 buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
267                 if (buf) {
268                         kfree(buf);
269                 } else
270                         break;
271         }
272         for(;;) {
273                 buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
274                 if (buf) {
275                         kfree(buf);
276                 } else
277                         break;
278         }
279         kfree(n_hdlc);
280         
281 }       /* end of n_hdlc_release() */
282
283 /**
284  * n_hdlc_tty_close - line discipline close
285  * @tty - pointer to tty info structure
286  *
287  * Called when the line discipline is changed to something
288  * else, the tty is closed, or the tty detects a hangup.
289  */
290 static void n_hdlc_tty_close(struct tty_struct *tty)
291 {
292         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
293
294         if (debuglevel >= DEBUG_LEVEL_INFO)     
295                 printk("%s(%d)n_hdlc_tty_close() called\n",__FILE__,__LINE__);
296                 
297         if (n_hdlc != NULL) {
298                 if (n_hdlc->magic != HDLC_MAGIC) {
299                         printk (KERN_WARNING"n_hdlc: trying to close unopened tty!\n");
300                         return;
301                 }
302 #if defined(TTY_NO_WRITE_SPLIT)
303                 clear_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
304 #endif
305                 tty->disc_data = NULL;
306                 if (tty == n_hdlc->backup_tty)
307                         n_hdlc->backup_tty = NULL;
308                 if (tty != n_hdlc->tty)
309                         return;
310                 if (n_hdlc->backup_tty) {
311                         n_hdlc->tty = n_hdlc->backup_tty;
312                 } else {
313                         n_hdlc_release (n_hdlc);
314                 }
315         }
316         
317         if (debuglevel >= DEBUG_LEVEL_INFO)     
318                 printk("%s(%d)n_hdlc_tty_close() success\n",__FILE__,__LINE__);
319                 
320 }       /* end of n_hdlc_tty_close() */
321
322 /**
323  * n_hdlc_tty_open - called when line discipline changed to n_hdlc
324  * @tty - pointer to tty info structure
325  *
326  * Returns 0 if success, otherwise error code
327  */
328 static int n_hdlc_tty_open (struct tty_struct *tty)
329 {
330         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
331
332         if (debuglevel >= DEBUG_LEVEL_INFO)     
333                 printk("%s(%d)n_hdlc_tty_open() called (device=%s)\n",
334                 __FILE__,__LINE__,
335                 tty->name);
336                 
337         /* There should not be an existing table for this slot. */
338         if (n_hdlc) {
339                 printk (KERN_ERR"n_hdlc_tty_open:tty already associated!\n" );
340                 return -EEXIST;
341         }
342         
343         n_hdlc = n_hdlc_alloc();
344         if (!n_hdlc) {
345                 printk (KERN_ERR "n_hdlc_alloc failed\n");
346                 return -ENFILE;
347         }
348                 
349         tty->disc_data = n_hdlc;
350         n_hdlc->tty    = tty;
351         tty->receive_room = 65536;
352         
353 #if defined(TTY_NO_WRITE_SPLIT)
354         /* change tty_io write() to not split large writes into 8K chunks */
355         set_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
356 #endif
357         
358         /* flush receive data from driver */
359         tty_driver_flush_buffer(tty);
360                 
361         if (debuglevel >= DEBUG_LEVEL_INFO)     
362                 printk("%s(%d)n_hdlc_tty_open() success\n",__FILE__,__LINE__);
363                 
364         return 0;
365         
366 }       /* end of n_tty_hdlc_open() */
367
368 /**
369  * n_hdlc_send_frames - send frames on pending send buffer list
370  * @n_hdlc - pointer to ldisc instance data
371  * @tty - pointer to tty instance data
372  *
373  * Send frames on pending send buffer list until the driver does not accept a
374  * frame (busy) this function is called after adding a frame to the send buffer
375  * list and by the tty wakeup callback.
376  */
377 static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
378 {
379         register int actual;
380         unsigned long flags;
381         struct n_hdlc_buf *tbuf;
382
383         if (debuglevel >= DEBUG_LEVEL_INFO)     
384                 printk("%s(%d)n_hdlc_send_frames() called\n",__FILE__,__LINE__);
385  check_again:
386                 
387         spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
388         if (n_hdlc->tbusy) {
389                 n_hdlc->woke_up = 1;
390                 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
391                 return;
392         }
393         n_hdlc->tbusy = 1;
394         n_hdlc->woke_up = 0;
395         spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
396
397         tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
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->ops->write(tty, tbuf->buf, tbuf->count);
406
407                 /* rollback was possible and has been done */
408                 if (actual == -ERESTARTSYS) {
409                         n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
410                         break;
411                 }
412                 /* if transmit error, throw frame away by */
413                 /* pretending it was accepted by driver */
414                 if (actual < 0)
415                         actual = tbuf->count;
416                 
417                 if (actual == tbuf->count) {
418                         if (debuglevel >= DEBUG_LEVEL_INFO)     
419                                 printk("%s(%d)frame %p completed\n",
420                                         __FILE__,__LINE__,tbuf);
421                                         
422                         /* free current transmit buffer */
423                         n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf);
424
425                         /* wait up sleeping writers */
426                         wake_up_interruptible(&tty->write_wait);
427         
428                         /* get next pending transmit buffer */
429                         tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
430                 } else {
431                         if (debuglevel >= DEBUG_LEVEL_INFO)     
432                                 printk("%s(%d)frame %p pending\n",
433                                         __FILE__,__LINE__,tbuf);
434
435                         /*
436                          * the buffer was not accepted by driver,
437                          * return it back into tx queue
438                          */
439                         n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
440                         break;
441                 }
442         }
443         
444         if (!tbuf)
445                 tty->flags  &= ~(1 << TTY_DO_WRITE_WAKEUP);
446         
447         /* Clear the re-entry flag */
448         spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
449         n_hdlc->tbusy = 0;
450         spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags); 
451         
452         if (n_hdlc->woke_up)
453           goto check_again;
454
455         if (debuglevel >= DEBUG_LEVEL_INFO)     
456                 printk("%s(%d)n_hdlc_send_frames() exit\n",__FILE__,__LINE__);
457                 
458 }       /* end of n_hdlc_send_frames() */
459
460 /**
461  * n_hdlc_tty_wakeup - Callback for transmit wakeup
462  * @tty - pointer to associated tty instance data
463  *
464  * Called when low level device driver can accept more send data.
465  */
466 static void n_hdlc_tty_wakeup(struct tty_struct *tty)
467 {
468         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
469
470         if (debuglevel >= DEBUG_LEVEL_INFO)     
471                 printk("%s(%d)n_hdlc_tty_wakeup() called\n",__FILE__,__LINE__);
472                 
473         if (!n_hdlc)
474                 return;
475
476         if (tty != n_hdlc->tty) {
477                 tty->flags &= ~(1 << TTY_DO_WRITE_WAKEUP);
478                 return;
479         }
480
481         n_hdlc_send_frames (n_hdlc, tty);
482                 
483 }       /* end of n_hdlc_tty_wakeup() */
484
485 /**
486  * n_hdlc_tty_receive - Called by tty driver when receive data is available
487  * @tty - pointer to tty instance data
488  * @data - pointer to received data
489  * @flags - pointer to flags for data
490  * @count - count of received data in bytes
491  *
492  * Called by tty low level driver when receive data is available. Data is
493  * interpreted as one HDLC frame.
494  */
495 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
496                                char *flags, int count)
497 {
498         register struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
499         register struct n_hdlc_buf *buf;
500
501         if (debuglevel >= DEBUG_LEVEL_INFO)     
502                 printk("%s(%d)n_hdlc_tty_receive() called count=%d\n",
503                         __FILE__,__LINE__, count);
504                 
505         /* This can happen if stuff comes in on the backup tty */
506         if (!n_hdlc || tty != n_hdlc->tty)
507                 return;
508                 
509         /* verify line is using HDLC discipline */
510         if (n_hdlc->magic != HDLC_MAGIC) {
511                 printk("%s(%d) line not using HDLC discipline\n",
512                         __FILE__,__LINE__);
513                 return;
514         }
515         
516         if ( count>maxframe ) {
517                 if (debuglevel >= DEBUG_LEVEL_INFO)     
518                         printk("%s(%d) rx count>maxframesize, data discarded\n",
519                                __FILE__,__LINE__);
520                 return;
521         }
522
523         /* get a free HDLC buffer */    
524         buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
525         if (!buf) {
526                 /* no buffers in free list, attempt to allocate another rx buffer */
527                 /* unless the maximum count has been reached */
528                 if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT)
529                         buf = kmalloc(N_HDLC_BUF_SIZE, GFP_ATOMIC);
530         }
531         
532         if (!buf) {
533                 if (debuglevel >= DEBUG_LEVEL_INFO)     
534                         printk("%s(%d) no more rx buffers, data discarded\n",
535                                __FILE__,__LINE__);
536                 return;
537         }
538                 
539         /* copy received data to HDLC buffer */
540         memcpy(buf->buf,data,count);
541         buf->count=count;
542
543         /* add HDLC buffer to list of received frames */
544         n_hdlc_buf_put(&n_hdlc->rx_buf_list, buf);
545         
546         /* wake up any blocked reads and perform async signalling */
547         wake_up_interruptible (&tty->read_wait);
548         if (n_hdlc->tty->fasync != NULL)
549                 kill_fasync (&n_hdlc->tty->fasync, SIGIO, POLL_IN);
550
551 }       /* end of n_hdlc_tty_receive() */
552
553 /**
554  * n_hdlc_tty_read - Called to retrieve one frame of data (if available)
555  * @tty - pointer to tty instance data
556  * @file - pointer to open file object
557  * @buf - pointer to returned data buffer
558  * @nr - size of returned data buffer
559  *      
560  * Returns the number of bytes returned or error code.
561  */
562 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
563                            __u8 __user *buf, size_t nr)
564 {
565         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
566         int ret = 0;
567         struct n_hdlc_buf *rbuf;
568         DECLARE_WAITQUEUE(wait, current);
569
570         if (debuglevel >= DEBUG_LEVEL_INFO)     
571                 printk("%s(%d)n_hdlc_tty_read() called\n",__FILE__,__LINE__);
572                 
573         /* Validate the pointers */
574         if (!n_hdlc)
575                 return -EIO;
576
577         /* verify user access to buffer */
578         if (!access_ok(VERIFY_WRITE, buf, nr)) {
579                 printk(KERN_WARNING "%s(%d) n_hdlc_tty_read() can't verify user "
580                 "buffer\n", __FILE__, __LINE__);
581                 return -EFAULT;
582         }
583
584         add_wait_queue(&tty->read_wait, &wait);
585
586         for (;;) {
587                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
588                         ret = -EIO;
589                         break;
590                 }
591                 if (tty_hung_up_p(file))
592                         break;
593
594                 set_current_state(TASK_INTERRUPTIBLE);
595
596                 rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
597                 if (rbuf) {
598                         if (rbuf->count > nr) {
599                                 /* too large for caller's buffer */
600                                 ret = -EOVERFLOW;
601                         } else {
602                                 if (copy_to_user(buf, rbuf->buf, rbuf->count))
603                                         ret = -EFAULT;
604                                 else
605                                         ret = rbuf->count;
606                         }
607
608                         if (n_hdlc->rx_free_buf_list.count >
609                             DEFAULT_RX_BUF_COUNT)
610                                 kfree(rbuf);
611                         else
612                                 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
613                         break;
614                 }
615                         
616                 /* no data */
617                 if (file->f_flags & O_NONBLOCK) {
618                         ret = -EAGAIN;
619                         break;
620                 }
621
622                 schedule();
623
624                 if (signal_pending(current)) {
625                         ret = -EINTR;
626                         break;
627                 }
628         }
629
630         remove_wait_queue(&tty->read_wait, &wait);
631         __set_current_state(TASK_RUNNING);
632
633         return ret;
634         
635 }       /* end of n_hdlc_tty_read() */
636
637 /**
638  * n_hdlc_tty_write - write a single frame of data to device
639  * @tty - pointer to associated tty device instance data
640  * @file - pointer to file object data
641  * @data - pointer to transmit data (one frame)
642  * @count - size of transmit frame in bytes
643  *              
644  * Returns the number of bytes written (or error code).
645  */
646 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
647                             const unsigned char *data, size_t count)
648 {
649         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
650         int error = 0;
651         DECLARE_WAITQUEUE(wait, current);
652         struct n_hdlc_buf *tbuf;
653
654         if (debuglevel >= DEBUG_LEVEL_INFO)     
655                 printk("%s(%d)n_hdlc_tty_write() called count=%Zd\n",
656                         __FILE__,__LINE__,count);
657                 
658         /* Verify pointers */
659         if (!n_hdlc)
660                 return -EIO;
661
662         if (n_hdlc->magic != HDLC_MAGIC)
663                 return -EIO;
664
665         /* verify frame size */
666         if (count > maxframe ) {
667                 if (debuglevel & DEBUG_LEVEL_INFO)
668                         printk (KERN_WARNING
669                                 "n_hdlc_tty_write: truncating user packet "
670                                 "from %lu to %d\n", (unsigned long) count,
671                                 maxframe );
672                 count = maxframe;
673         }
674         
675         add_wait_queue(&tty->write_wait, &wait);
676
677         for (;;) {
678                 set_current_state(TASK_INTERRUPTIBLE);
679         
680                 tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
681                 if (tbuf)
682                         break;
683
684                 if (file->f_flags & O_NONBLOCK) {
685                         error = -EAGAIN;
686                         break;
687                 }
688                 schedule();
689                         
690                 n_hdlc = tty2n_hdlc (tty);
691                 if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC || 
692                     tty != n_hdlc->tty) {
693                         printk("n_hdlc_tty_write: %p invalid after wait!\n", n_hdlc);
694                         error = -EIO;
695                         break;
696                 }
697                         
698                 if (signal_pending(current)) {
699                         error = -EINTR;
700                         break;
701                 }
702         }
703
704         __set_current_state(TASK_RUNNING);
705         remove_wait_queue(&tty->write_wait, &wait);
706
707         if (!error) {           
708                 /* Retrieve the user's buffer */
709                 memcpy(tbuf->buf, data, count);
710
711                 /* Send the data */
712                 tbuf->count = error = count;
713                 n_hdlc_buf_put(&n_hdlc->tx_buf_list,tbuf);
714                 n_hdlc_send_frames(n_hdlc,tty);
715         }
716
717         return error;
718         
719 }       /* end of n_hdlc_tty_write() */
720
721 /**
722  * n_hdlc_tty_ioctl - process IOCTL system call for the tty device.
723  * @tty - pointer to tty instance data
724  * @file - pointer to open file object for device
725  * @cmd - IOCTL command code
726  * @arg - argument for IOCTL call (cmd dependent)
727  *
728  * Returns command dependent result.
729  */
730 static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
731                             unsigned int cmd, unsigned long arg)
732 {
733         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
734         int error = 0;
735         int count;
736         unsigned long flags;
737         struct n_hdlc_buf *buf = NULL;
738
739         if (debuglevel >= DEBUG_LEVEL_INFO)     
740                 printk("%s(%d)n_hdlc_tty_ioctl() called %d\n",
741                         __FILE__,__LINE__,cmd);
742                 
743         /* Verify the status of the device */
744         if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC)
745                 return -EBADF;
746
747         switch (cmd) {
748         case FIONREAD:
749                 /* report count of read data available */
750                 /* in next available frame (if any) */
751                 spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock,flags);
752                 buf = list_first_entry_or_null(&n_hdlc->rx_buf_list.list,
753                                                 struct n_hdlc_buf, list_item);
754                 if (buf)
755                         count = buf->count;
756                 else
757                         count = 0;
758                 spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock,flags);
759                 error = put_user(count, (int __user *)arg);
760                 break;
761
762         case TIOCOUTQ:
763                 /* get the pending tx byte count in the driver */
764                 count = tty_chars_in_buffer(tty);
765                 /* add size of next output frame in queue */
766                 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock,flags);
767                 buf = list_first_entry_or_null(&n_hdlc->tx_buf_list.list,
768                                                 struct n_hdlc_buf, list_item);
769                 if (buf)
770                         count += buf->count;
771                 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock,flags);
772                 error = put_user(count, (int __user *)arg);
773                 break;
774
775         case TCFLSH:
776                 switch (arg) {
777                 case TCIOFLUSH:
778                 case TCOFLUSH:
779                         flush_tx_queue(tty);
780                 }
781                 /* fall through to default */
782
783         default:
784                 error = n_tty_ioctl_helper(tty, file, cmd, arg);
785                 break;
786         }
787         return error;
788         
789 }       /* end of n_hdlc_tty_ioctl() */
790
791 /**
792  * n_hdlc_tty_poll - TTY callback for poll system call
793  * @tty - pointer to tty instance data
794  * @filp - pointer to open file object for device
795  * @poll_table - wait queue for operations
796  * 
797  * Determine which operations (read/write) will not block and return info
798  * to caller.
799  * Returns a bit mask containing info on which ops will not block.
800  */
801 static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
802                                     poll_table *wait)
803 {
804         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
805         unsigned int mask = 0;
806
807         if (debuglevel >= DEBUG_LEVEL_INFO)     
808                 printk("%s(%d)n_hdlc_tty_poll() called\n",__FILE__,__LINE__);
809                 
810         if (n_hdlc && n_hdlc->magic == HDLC_MAGIC && tty == n_hdlc->tty) {
811                 /* queue current process into any wait queue that */
812                 /* may awaken in the future (read and write) */
813
814                 poll_wait(filp, &tty->read_wait, wait);
815                 poll_wait(filp, &tty->write_wait, wait);
816
817                 /* set bits for operations that won't block */
818                 if (!list_empty(&n_hdlc->rx_buf_list.list))
819                         mask |= POLLIN | POLLRDNORM;    /* readable */
820                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
821                         mask |= POLLHUP;
822                 if (tty_hung_up_p(filp))
823                         mask |= POLLHUP;
824                 if (!tty_is_writelocked(tty) &&
825                                 !list_empty(&n_hdlc->tx_free_buf_list.list))
826                         mask |= POLLOUT | POLLWRNORM;   /* writable */
827         }
828         return mask;
829 }       /* end of n_hdlc_tty_poll() */
830
831 /**
832  * n_hdlc_alloc - allocate an n_hdlc instance data structure
833  *
834  * Returns a pointer to newly created structure if success, otherwise %NULL
835  */
836 static struct n_hdlc *n_hdlc_alloc(void)
837 {
838         struct n_hdlc_buf *buf;
839         int i;
840         struct n_hdlc *n_hdlc = kmalloc(sizeof(*n_hdlc), GFP_KERNEL);
841
842         if (!n_hdlc)
843                 return NULL;
844
845         memset(n_hdlc, 0, sizeof(*n_hdlc));
846
847         spin_lock_init(&n_hdlc->rx_free_buf_list.spinlock);
848         spin_lock_init(&n_hdlc->tx_free_buf_list.spinlock);
849         spin_lock_init(&n_hdlc->rx_buf_list.spinlock);
850         spin_lock_init(&n_hdlc->tx_buf_list.spinlock);
851
852         INIT_LIST_HEAD(&n_hdlc->rx_free_buf_list.list);
853         INIT_LIST_HEAD(&n_hdlc->tx_free_buf_list.list);
854         INIT_LIST_HEAD(&n_hdlc->rx_buf_list.list);
855         INIT_LIST_HEAD(&n_hdlc->tx_buf_list.list);
856
857         /* allocate free rx buffer list */
858         for(i=0;i<DEFAULT_RX_BUF_COUNT;i++) {
859                 buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
860                 if (buf)
861                         n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,buf);
862                 else if (debuglevel >= DEBUG_LEVEL_INFO)        
863                         printk("%s(%d)n_hdlc_alloc(), kalloc() failed for rx buffer %d\n",__FILE__,__LINE__, i);
864         }
865         
866         /* allocate free tx buffer list */
867         for(i=0;i<DEFAULT_TX_BUF_COUNT;i++) {
868                 buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
869                 if (buf)
870                         n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,buf);
871                 else if (debuglevel >= DEBUG_LEVEL_INFO)        
872                         printk("%s(%d)n_hdlc_alloc(), kalloc() failed for tx buffer %d\n",__FILE__,__LINE__, i);
873         }
874         
875         /* Initialize the control block */
876         n_hdlc->magic  = HDLC_MAGIC;
877         n_hdlc->flags  = 0;
878         
879         return n_hdlc;
880         
881 }       /* end of n_hdlc_alloc() */
882
883 /**
884  * n_hdlc_buf_return - put the HDLC buffer after the head of the specified list
885  * @buf_list - pointer to the buffer list
886  * @buf - pointer to the buffer
887  */
888 static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
889                                                 struct n_hdlc_buf *buf)
890 {
891         unsigned long flags;
892
893         spin_lock_irqsave(&buf_list->spinlock, flags);
894
895         list_add(&buf->list_item, &buf_list->list);
896         buf_list->count++;
897
898         spin_unlock_irqrestore(&buf_list->spinlock, flags);
899 }
900
901 /**
902  * n_hdlc_buf_put - add specified HDLC buffer to tail of specified list
903  * @buf_list - pointer to buffer list
904  * @buf - pointer to buffer
905  */
906 static void n_hdlc_buf_put(struct n_hdlc_buf_list *buf_list,
907                            struct n_hdlc_buf *buf)
908 {
909         unsigned long flags;
910
911         spin_lock_irqsave(&buf_list->spinlock, flags);
912
913         list_add_tail(&buf->list_item, &buf_list->list);
914         buf_list->count++;
915
916         spin_unlock_irqrestore(&buf_list->spinlock, flags);
917 }       /* end of n_hdlc_buf_put() */
918
919 /**
920  * n_hdlc_buf_get - remove and return an HDLC buffer from list
921  * @buf_list - pointer to HDLC buffer list
922  * 
923  * Remove and return an HDLC buffer from the head of the specified HDLC buffer
924  * list.
925  * Returns a pointer to HDLC buffer if available, otherwise %NULL.
926  */
927 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *buf_list)
928 {
929         unsigned long flags;
930         struct n_hdlc_buf *buf;
931
932         spin_lock_irqsave(&buf_list->spinlock, flags);
933
934         buf = list_first_entry_or_null(&buf_list->list,
935                                                 struct n_hdlc_buf, list_item);
936         if (buf) {
937                 list_del(&buf->list_item);
938                 buf_list->count--;
939         }
940
941         spin_unlock_irqrestore(&buf_list->spinlock, flags);
942         return buf;
943 }       /* end of n_hdlc_buf_get() */
944
945 static char hdlc_banner[] __initdata =
946         KERN_INFO "HDLC line discipline maxframe=%u\n";
947 static char hdlc_register_ok[] __initdata =
948         KERN_INFO "N_HDLC line discipline registered.\n";
949 static char hdlc_register_fail[] __initdata =
950         KERN_ERR "error registering line discipline: %d\n";
951 static char hdlc_init_fail[] __initdata =
952         KERN_INFO "N_HDLC: init failure %d\n";
953
954 static int __init n_hdlc_init(void)
955 {
956         int status;
957
958         /* range check maxframe arg */
959         if (maxframe < 4096)
960                 maxframe = 4096;
961         else if (maxframe > 65535)
962                 maxframe = 65535;
963
964         printk(hdlc_banner, maxframe);
965
966         status = tty_register_ldisc(N_HDLC, &n_hdlc_ldisc);
967         if (!status)
968                 printk(hdlc_register_ok);
969         else
970                 printk(hdlc_register_fail, status);
971
972         if (status)
973                 printk(hdlc_init_fail, status);
974         return status;
975         
976 }       /* end of init_module() */
977
978 static char hdlc_unregister_ok[] __exitdata =
979         KERN_INFO "N_HDLC: line discipline unregistered\n";
980 static char hdlc_unregister_fail[] __exitdata =
981         KERN_ERR "N_HDLC: can't unregister line discipline (err = %d)\n";
982
983 static void __exit n_hdlc_exit(void)
984 {
985         /* Release tty registration of line discipline */
986         int status = tty_unregister_ldisc(N_HDLC);
987
988         if (status)
989                 printk(hdlc_unregister_fail, status);
990         else
991                 printk(hdlc_unregister_ok);
992 }
993
994 module_init(n_hdlc_init);
995 module_exit(n_hdlc_exit);
996
997 MODULE_LICENSE("GPL");
998 MODULE_AUTHOR("Paul Fulghum paulkf@microgate.com");
999 module_param(debuglevel, int, 0);
1000 module_param(maxframe, int, 0);
1001 MODULE_ALIAS_LDISC(N_HDLC);