1 // SPDX-License-Identifier: GPL-1.0+
2 /* generic HDLC line discipline for Linux
3 *
4 * Written by Paul Fulghum paulkf@microgate.com
5 * for Microgate Corporation
6 *
7 * Microgate and SyncLink are registered trademarks of Microgate Corporation
8 *
9 * Adapted from ppp.c, written by Michael Callahan <callahan@maths.ox.ac.uk>,
10 * Al Longyear <longyear@netcom.com>,
11 * Paul Mackerras <Paul.Mackerras@cs.anu.edu.au>
12 *
13 * Original release 01/11/99
14 *
15 * This module implements the tty line discipline N_HDLC for use with
16 * tty device drivers that support bit-synchronous HDLC communications.
17 *
18 * All HDLC data is frame oriented which means:
19 *
20 * 1. tty write calls represent one complete transmit frame of data
21 * The device driver should accept the complete frame or none of
22 * the frame (busy) in the write method. Each write call should have
23 * a byte count in the range of 2-65535 bytes (2 is min HDLC frame
24 * with 1 addr byte and 1 ctrl byte). The max byte count of 65535
25 * should include any crc bytes required. For example, when using
26 * CCITT CRC32, 4 crc bytes are required, so the maximum size frame
27 * the application may transmit is limited to 65531 bytes. For CCITT
28 * CRC16, the maximum application frame size would be 65533.
29 *
30 *
31 * 2. receive callbacks from the device driver represents
32 * one received frame. The device driver should bypass
33 * the tty flip buffer and call the line discipline receive
34 * callback directly to avoid fragmenting or concatenating
35 * multiple frames into a single receive callback.
36 *
37 * The HDLC line discipline queues the receive frames in separate
38 * buffers so complete receive frames can be returned by the
39 * tty read calls.
40 *
41 * 3. tty read calls returns an entire frame of data or nothing.
42 *
43 * 4. all send and receive data is considered raw. No processing
44 * or translation is performed by the line discipline, regardless
45 * of the tty flags
46 *
47 * 5. When line discipline is queried for the amount of receive
48 * data available (FIOC), 0 is returned if no data available,
49 * otherwise the count of the next available frame is returned.
50 * (instead of the sum of all received frame counts).
51 *
52 * These conventions allow the standard tty programming interface
53 * to be used for synchronous HDLC applications when used with
54 * this line discipline (or another line discipline that is frame
55 * oriented such as N_PPP).
56 *
57 * The SyncLink driver (synclink.c) implements both asynchronous
58 * (using standard line discipline N_TTY) and synchronous HDLC
59 * (using N_HDLC) communications, with the latter using the above
60 * conventions.
61 *
62 * This implementation is very basic and does not maintain
63 * any statistics. The main point is to enforce the raw data
64 * and frame orientation of HDLC communications.
65 *
66 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
67 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
68 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
69 * DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
70 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
71 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
72 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
73 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
74 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
75 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
76 * OF THE POSSIBILITY OF SUCH DAMAGE.
77 */
78
79 #include <linux/module.h>
80 #include <linux/init.h>
81 #include <linux/kernel.h>
82 #include <linux/sched.h>
83 #include <linux/types.h>
84 #include <linux/fcntl.h>
85 #include <linux/interrupt.h>
86 #include <linux/ptrace.h>
87
88 #include <linux/poll.h>
89 #include <linux/in.h>
90 #include <linux/ioctl.h>
91 #include <linux/slab.h>
92 #include <linux/tty.h>
93 #include <linux/errno.h>
94 #include <linux/string.h> /* used in new tty drivers */
95 #include <linux/signal.h> /* used in new tty drivers */
96 #include <linux/if.h>
97 #include <linux/bitops.h>
98
99 #include <linux/uaccess.h>
100 #include "tty.h"
101
102 /*
103 * Buffers for individual HDLC frames
104 */
105 #define MAX_HDLC_FRAME_SIZE 65535
106 #define DEFAULT_RX_BUF_COUNT 10
107 #define MAX_RX_BUF_COUNT 60
108 #define DEFAULT_TX_BUF_COUNT 3
109
110 struct n_hdlc_buf {
111 struct list_head list_item;
112 int count;
113 char buf[];
114 };
115
116 struct n_hdlc_buf_list {
117 struct list_head list;
118 int count;
119 spinlock_t spinlock;
120 };
121
122 /**
123 * struct n_hdlc - per device instance data structure
124 * @tbusy: reentrancy flag for tx wakeup code
125 * @woke_up: tx wakeup needs to be run again as it was called while @tbusy
126 * @tx_buf_list: list of pending transmit frame buffers
127 * @rx_buf_list: list of received frame buffers
128 * @tx_free_buf_list: list unused transmit frame buffers
129 * @rx_free_buf_list: list unused received frame buffers
130 */
131 struct n_hdlc {
132 bool tbusy;
133 bool woke_up;
134 struct n_hdlc_buf_list tx_buf_list;
135 struct n_hdlc_buf_list rx_buf_list;
136 struct n_hdlc_buf_list tx_free_buf_list;
137 struct n_hdlc_buf_list rx_free_buf_list;
138 struct work_struct write_work;
139 struct tty_struct *tty_for_write_work;
140 };
141
142 /*
143 * HDLC buffer list manipulation functions
144 */
145 static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
146 struct n_hdlc_buf *buf);
147 static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
148 struct n_hdlc_buf *buf);
149 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
150
151 /* Local functions */
152
153 static struct n_hdlc *n_hdlc_alloc(void);
154 static void n_hdlc_tty_write_work(struct work_struct *work);
155
156 /* max frame size for memory allocations */
157 static int maxframe = 4096;
158
flush_rx_queue(struct tty_struct * tty)159 static void flush_rx_queue(struct tty_struct *tty)
160 {
161 struct n_hdlc *n_hdlc = tty->disc_data;
162 struct n_hdlc_buf *buf;
163
164 while ((buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list)))
165 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, buf);
166 }
167
flush_tx_queue(struct tty_struct * tty)168 static void flush_tx_queue(struct tty_struct *tty)
169 {
170 struct n_hdlc *n_hdlc = tty->disc_data;
171 struct n_hdlc_buf *buf;
172
173 while ((buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list)))
174 n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, buf);
175 }
176
n_hdlc_free_buf_list(struct n_hdlc_buf_list * list)177 static void n_hdlc_free_buf_list(struct n_hdlc_buf_list *list)
178 {
179 struct n_hdlc_buf *buf;
180
181 do {
182 buf = n_hdlc_buf_get(list);
183 kfree(buf);
184 } while (buf);
185 }
186
187 /**
188 * n_hdlc_tty_close - line discipline close
189 * @tty: pointer to tty info structure
190 *
191 * Called when the line discipline is changed to something
192 * else, the tty is closed, or the tty detects a hangup.
193 */
n_hdlc_tty_close(struct tty_struct * tty)194 static void n_hdlc_tty_close(struct tty_struct *tty)
195 {
196 struct n_hdlc *n_hdlc = tty->disc_data;
197
198 #if defined(TTY_NO_WRITE_SPLIT)
199 clear_bit(TTY_NO_WRITE_SPLIT, &tty->flags);
200 #endif
201 tty->disc_data = NULL;
202
203 /* Ensure that the n_hdlcd process is not hanging on select()/poll() */
204 wake_up_interruptible(&tty->read_wait);
205 wake_up_interruptible(&tty->write_wait);
206
207 cancel_work_sync(&n_hdlc->write_work);
208
209 n_hdlc_free_buf_list(&n_hdlc->rx_free_buf_list);
210 n_hdlc_free_buf_list(&n_hdlc->tx_free_buf_list);
211 n_hdlc_free_buf_list(&n_hdlc->rx_buf_list);
212 n_hdlc_free_buf_list(&n_hdlc->tx_buf_list);
213 kfree(n_hdlc);
214 } /* end of n_hdlc_tty_close() */
215
216 /**
217 * n_hdlc_tty_open - called when line discipline changed to n_hdlc
218 * @tty: pointer to tty info structure
219 *
220 * Returns 0 if success, otherwise error code
221 */
n_hdlc_tty_open(struct tty_struct * tty)222 static int n_hdlc_tty_open(struct tty_struct *tty)
223 {
224 struct n_hdlc *n_hdlc = tty->disc_data;
225
226 pr_debug("%s() called (device=%s)\n", __func__, tty->name);
227
228 /* There should not be an existing table for this slot. */
229 if (n_hdlc) {
230 pr_err("%s: tty already associated!\n", __func__);
231 return -EEXIST;
232 }
233
234 n_hdlc = n_hdlc_alloc();
235 if (!n_hdlc) {
236 pr_err("%s: n_hdlc_alloc failed\n", __func__);
237 return -ENFILE;
238 }
239
240 INIT_WORK(&n_hdlc->write_work, n_hdlc_tty_write_work);
241 n_hdlc->tty_for_write_work = tty;
242 tty->disc_data = n_hdlc;
243 tty->receive_room = 65536;
244
245 /* change tty_io write() to not split large writes into 8K chunks */
246 set_bit(TTY_NO_WRITE_SPLIT, &tty->flags);
247
248 /* flush receive data from driver */
249 tty_driver_flush_buffer(tty);
250
251 return 0;
252
253 } /* end of n_tty_hdlc_open() */
254
255 /**
256 * n_hdlc_send_frames - send frames on pending send buffer list
257 * @n_hdlc: pointer to ldisc instance data
258 * @tty: pointer to tty instance data
259 *
260 * Send frames on pending send buffer list until the driver does not accept a
261 * frame (busy) this function is called after adding a frame to the send buffer
262 * list and by the tty wakeup callback.
263 */
n_hdlc_send_frames(struct n_hdlc * n_hdlc,struct tty_struct * tty)264 static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
265 {
266 register int actual;
267 unsigned long flags;
268 struct n_hdlc_buf *tbuf;
269
270 check_again:
271
272 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
273 if (n_hdlc->tbusy) {
274 n_hdlc->woke_up = true;
275 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
276 return;
277 }
278 n_hdlc->tbusy = true;
279 n_hdlc->woke_up = false;
280 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
281
282 tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
283 while (tbuf) {
284 pr_debug("sending frame %p, count=%d\n", tbuf, tbuf->count);
285
286 /* Send the next block of data to device */
287 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
288 actual = tty->ops->write(tty, tbuf->buf, tbuf->count);
289
290 /* rollback was possible and has been done */
291 if (actual == -ERESTARTSYS) {
292 n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
293 break;
294 }
295 /* if transmit error, throw frame away by */
296 /* pretending it was accepted by driver */
297 if (actual < 0)
298 actual = tbuf->count;
299
300 if (actual == tbuf->count) {
301 pr_debug("frame %p completed\n", tbuf);
302
303 /* free current transmit buffer */
304 n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf);
305
306 /* wait up sleeping writers */
307 wake_up_interruptible(&tty->write_wait);
308
309 /* get next pending transmit buffer */
310 tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
311 } else {
312 pr_debug("frame %p pending\n", tbuf);
313
314 /*
315 * the buffer was not accepted by driver,
316 * return it back into tx queue
317 */
318 n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
319 break;
320 }
321 }
322
323 if (!tbuf)
324 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
325
326 /* Clear the re-entry flag */
327 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
328 n_hdlc->tbusy = false;
329 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
330
331 if (n_hdlc->woke_up)
332 goto check_again;
333 } /* end of n_hdlc_send_frames() */
334
335 /**
336 * n_hdlc_tty_write_work - Asynchronous callback for transmit wakeup
337 * @work: pointer to work_struct
338 *
339 * Called when low level device driver can accept more send data.
340 */
n_hdlc_tty_write_work(struct work_struct * work)341 static void n_hdlc_tty_write_work(struct work_struct *work)
342 {
343 struct n_hdlc *n_hdlc = container_of(work, struct n_hdlc, write_work);
344 struct tty_struct *tty = n_hdlc->tty_for_write_work;
345
346 n_hdlc_send_frames(n_hdlc, tty);
347 } /* end of n_hdlc_tty_write_work() */
348
349 /**
350 * n_hdlc_tty_wakeup - Callback for transmit wakeup
351 * @tty: pointer to associated tty instance data
352 *
353 * Called when low level device driver can accept more send data.
354 */
n_hdlc_tty_wakeup(struct tty_struct * tty)355 static void n_hdlc_tty_wakeup(struct tty_struct *tty)
356 {
357 struct n_hdlc *n_hdlc = tty->disc_data;
358
359 schedule_work(&n_hdlc->write_work);
360 } /* end of n_hdlc_tty_wakeup() */
361
362 /**
363 * n_hdlc_tty_receive - Called by tty driver when receive data is available
364 * @tty: pointer to tty instance data
365 * @data: pointer to received data
366 * @flags: pointer to flags for data
367 * @count: count of received data in bytes
368 *
369 * Called by tty low level driver when receive data is available. Data is
370 * interpreted as one HDLC frame.
371 */
n_hdlc_tty_receive(struct tty_struct * tty,const __u8 * data,const char * flags,int count)372 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
373 const char *flags, int count)
374 {
375 register struct n_hdlc *n_hdlc = tty->disc_data;
376 register struct n_hdlc_buf *buf;
377
378 pr_debug("%s() called count=%d\n", __func__, count);
379
380 if (count > maxframe) {
381 pr_debug("rx count>maxframesize, data discarded\n");
382 return;
383 }
384
385 /* get a free HDLC buffer */
386 buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
387 if (!buf) {
388 /*
389 * no buffers in free list, attempt to allocate another rx
390 * buffer unless the maximum count has been reached
391 */
392 if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT)
393 buf = kmalloc(struct_size(buf, buf, maxframe),
394 GFP_ATOMIC);
395 }
396
397 if (!buf) {
398 pr_debug("no more rx buffers, data discarded\n");
399 return;
400 }
401
402 /* copy received data to HDLC buffer */
403 memcpy(buf->buf, data, count);
404 buf->count = count;
405
406 /* add HDLC buffer to list of received frames */
407 n_hdlc_buf_put(&n_hdlc->rx_buf_list, buf);
408
409 /* wake up any blocked reads and perform async signalling */
410 wake_up_interruptible(&tty->read_wait);
411 if (tty->fasync != NULL)
412 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
413
414 } /* end of n_hdlc_tty_receive() */
415
416 /**
417 * n_hdlc_tty_read - Called to retrieve one frame of data (if available)
418 * @tty: pointer to tty instance data
419 * @file: pointer to open file object
420 * @kbuf: pointer to returned data buffer
421 * @nr: size of returned data buffer
422 * @cookie: stored rbuf from previous run
423 * @offset: offset into the data buffer
424 *
425 * Returns the number of bytes returned or error code.
426 */
n_hdlc_tty_read(struct tty_struct * tty,struct file * file,__u8 * kbuf,size_t nr,void ** cookie,unsigned long offset)427 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
428 __u8 *kbuf, size_t nr,
429 void **cookie, unsigned long offset)
430 {
431 struct n_hdlc *n_hdlc = tty->disc_data;
432 int ret = 0;
433 struct n_hdlc_buf *rbuf;
434 DECLARE_WAITQUEUE(wait, current);
435
436 /* Is this a repeated call for an rbuf we already found earlier? */
437 rbuf = *cookie;
438 if (rbuf)
439 goto have_rbuf;
440
441 add_wait_queue(&tty->read_wait, &wait);
442
443 for (;;) {
444 if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
445 ret = -EIO;
446 break;
447 }
448 if (tty_hung_up_p(file))
449 break;
450
451 set_current_state(TASK_INTERRUPTIBLE);
452
453 rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
454 if (rbuf)
455 break;
456
457 /* no data */
458 if (tty_io_nonblock(tty, file)) {
459 ret = -EAGAIN;
460 break;
461 }
462
463 schedule();
464
465 if (signal_pending(current)) {
466 ret = -EINTR;
467 break;
468 }
469 }
470
471 remove_wait_queue(&tty->read_wait, &wait);
472 __set_current_state(TASK_RUNNING);
473
474 if (!rbuf)
475 return ret;
476 *cookie = rbuf;
477
478 have_rbuf:
479 /* Have we used it up entirely? */
480 if (offset >= rbuf->count)
481 goto done_with_rbuf;
482
483 /* More data to go, but can't copy any more? EOVERFLOW */
484 ret = -EOVERFLOW;
485 if (!nr)
486 goto done_with_rbuf;
487
488 /* Copy as much data as possible */
489 ret = rbuf->count - offset;
490 if (ret > nr)
491 ret = nr;
492 memcpy(kbuf, rbuf->buf+offset, ret);
493 offset += ret;
494
495 /* If we still have data left, we leave the rbuf in the cookie */
496 if (offset < rbuf->count)
497 return ret;
498
499 done_with_rbuf:
500 *cookie = NULL;
501
502 if (n_hdlc->rx_free_buf_list.count > DEFAULT_RX_BUF_COUNT)
503 kfree(rbuf);
504 else
505 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
506
507 return ret;
508
509 } /* end of n_hdlc_tty_read() */
510
511 /**
512 * n_hdlc_tty_write - write a single frame of data to device
513 * @tty: pointer to associated tty device instance data
514 * @file: pointer to file object data
515 * @data: pointer to transmit data (one frame)
516 * @count: size of transmit frame in bytes
517 *
518 * Returns the number of bytes written (or error code).
519 */
n_hdlc_tty_write(struct tty_struct * tty,struct file * file,const unsigned char * data,size_t count)520 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
521 const unsigned char *data, size_t count)
522 {
523 struct n_hdlc *n_hdlc = tty->disc_data;
524 int error = 0;
525 DECLARE_WAITQUEUE(wait, current);
526 struct n_hdlc_buf *tbuf;
527
528 pr_debug("%s() called count=%zd\n", __func__, count);
529
530 /* verify frame size */
531 if (count > maxframe) {
532 pr_debug("%s: truncating user packet from %zu to %d\n",
533 __func__, count, maxframe);
534 count = maxframe;
535 }
536
537 add_wait_queue(&tty->write_wait, &wait);
538
539 for (;;) {
540 set_current_state(TASK_INTERRUPTIBLE);
541
542 tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
543 if (tbuf)
544 break;
545
546 if (tty_io_nonblock(tty, file)) {
547 error = -EAGAIN;
548 break;
549 }
550 schedule();
551
552 if (signal_pending(current)) {
553 error = -EINTR;
554 break;
555 }
556 }
557
558 __set_current_state(TASK_RUNNING);
559 remove_wait_queue(&tty->write_wait, &wait);
560
561 if (!error) {
562 /* Retrieve the user's buffer */
563 memcpy(tbuf->buf, data, count);
564
565 /* Send the data */
566 tbuf->count = error = count;
567 n_hdlc_buf_put(&n_hdlc->tx_buf_list, tbuf);
568 n_hdlc_send_frames(n_hdlc, tty);
569 }
570
571 return error;
572
573 } /* end of n_hdlc_tty_write() */
574
575 /**
576 * n_hdlc_tty_ioctl - process IOCTL system call for the tty device.
577 * @tty: pointer to tty instance data
578 * @cmd: IOCTL command code
579 * @arg: argument for IOCTL call (cmd dependent)
580 *
581 * Returns command dependent result.
582 */
n_hdlc_tty_ioctl(struct tty_struct * tty,unsigned int cmd,unsigned long arg)583 static int n_hdlc_tty_ioctl(struct tty_struct *tty, unsigned int cmd,
584 unsigned long arg)
585 {
586 struct n_hdlc *n_hdlc = tty->disc_data;
587 int error = 0;
588 int count;
589 unsigned long flags;
590 struct n_hdlc_buf *buf = NULL;
591
592 pr_debug("%s() called %d\n", __func__, cmd);
593
594 switch (cmd) {
595 case FIONREAD:
596 /* report count of read data available */
597 /* in next available frame (if any) */
598 spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock, flags);
599 buf = list_first_entry_or_null(&n_hdlc->rx_buf_list.list,
600 struct n_hdlc_buf, list_item);
601 if (buf)
602 count = buf->count;
603 else
604 count = 0;
605 spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock, flags);
606 error = put_user(count, (int __user *)arg);
607 break;
608
609 case TIOCOUTQ:
610 /* get the pending tx byte count in the driver */
611 count = tty_chars_in_buffer(tty);
612 /* add size of next output frame in queue */
613 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
614 buf = list_first_entry_or_null(&n_hdlc->tx_buf_list.list,
615 struct n_hdlc_buf, list_item);
616 if (buf)
617 count += buf->count;
618 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
619 error = put_user(count, (int __user *)arg);
620 break;
621
622 case TCFLSH:
623 switch (arg) {
624 case TCIOFLUSH:
625 case TCOFLUSH:
626 flush_tx_queue(tty);
627 }
628 fallthrough; /* to default */
629
630 default:
631 error = n_tty_ioctl_helper(tty, cmd, arg);
632 break;
633 }
634 return error;
635
636 } /* end of n_hdlc_tty_ioctl() */
637
638 /**
639 * n_hdlc_tty_poll - TTY callback for poll system call
640 * @tty: pointer to tty instance data
641 * @filp: pointer to open file object for device
642 * @wait: wait queue for operations
643 *
644 * Determine which operations (read/write) will not block and return info
645 * to caller.
646 * Returns a bit mask containing info on which ops will not block.
647 */
n_hdlc_tty_poll(struct tty_struct * tty,struct file * filp,poll_table * wait)648 static __poll_t n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
649 poll_table *wait)
650 {
651 struct n_hdlc *n_hdlc = tty->disc_data;
652 __poll_t mask = 0;
653
654 /*
655 * queue the current process into any wait queue that may awaken in the
656 * future (read and write)
657 */
658 poll_wait(filp, &tty->read_wait, wait);
659 poll_wait(filp, &tty->write_wait, wait);
660
661 /* set bits for operations that won't block */
662 if (!list_empty(&n_hdlc->rx_buf_list.list))
663 mask |= EPOLLIN | EPOLLRDNORM; /* readable */
664 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
665 mask |= EPOLLHUP;
666 if (tty_hung_up_p(filp))
667 mask |= EPOLLHUP;
668 if (!tty_is_writelocked(tty) &&
669 !list_empty(&n_hdlc->tx_free_buf_list.list))
670 mask |= EPOLLOUT | EPOLLWRNORM; /* writable */
671
672 return mask;
673 } /* end of n_hdlc_tty_poll() */
674
n_hdlc_alloc_buf(struct n_hdlc_buf_list * list,unsigned int count,const char * name)675 static void n_hdlc_alloc_buf(struct n_hdlc_buf_list *list, unsigned int count,
676 const char *name)
677 {
678 struct n_hdlc_buf *buf;
679 unsigned int i;
680
681 for (i = 0; i < count; i++) {
682 buf = kmalloc(struct_size(buf, buf, maxframe), GFP_KERNEL);
683 if (!buf) {
684 pr_debug("%s(), kmalloc() failed for %s buffer %u\n",
685 __func__, name, i);
686 return;
687 }
688 n_hdlc_buf_put(list, buf);
689 }
690 }
691
692 /**
693 * n_hdlc_alloc - allocate an n_hdlc instance data structure
694 *
695 * Returns a pointer to newly created structure if success, otherwise %NULL
696 */
n_hdlc_alloc(void)697 static struct n_hdlc *n_hdlc_alloc(void)
698 {
699 struct n_hdlc *n_hdlc = kzalloc(sizeof(*n_hdlc), GFP_KERNEL);
700
701 if (!n_hdlc)
702 return NULL;
703
704 spin_lock_init(&n_hdlc->rx_free_buf_list.spinlock);
705 spin_lock_init(&n_hdlc->tx_free_buf_list.spinlock);
706 spin_lock_init(&n_hdlc->rx_buf_list.spinlock);
707 spin_lock_init(&n_hdlc->tx_buf_list.spinlock);
708
709 INIT_LIST_HEAD(&n_hdlc->rx_free_buf_list.list);
710 INIT_LIST_HEAD(&n_hdlc->tx_free_buf_list.list);
711 INIT_LIST_HEAD(&n_hdlc->rx_buf_list.list);
712 INIT_LIST_HEAD(&n_hdlc->tx_buf_list.list);
713
714 n_hdlc_alloc_buf(&n_hdlc->rx_free_buf_list, DEFAULT_RX_BUF_COUNT, "rx");
715 n_hdlc_alloc_buf(&n_hdlc->tx_free_buf_list, DEFAULT_TX_BUF_COUNT, "tx");
716
717 return n_hdlc;
718
719 } /* end of n_hdlc_alloc() */
720
721 /**
722 * n_hdlc_buf_return - put the HDLC buffer after the head of the specified list
723 * @buf_list: pointer to the buffer list
724 * @buf: pointer to the buffer
725 */
n_hdlc_buf_return(struct n_hdlc_buf_list * buf_list,struct n_hdlc_buf * buf)726 static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
727 struct n_hdlc_buf *buf)
728 {
729 unsigned long flags;
730
731 spin_lock_irqsave(&buf_list->spinlock, flags);
732
733 list_add(&buf->list_item, &buf_list->list);
734 buf_list->count++;
735
736 spin_unlock_irqrestore(&buf_list->spinlock, flags);
737 }
738
739 /**
740 * n_hdlc_buf_put - add specified HDLC buffer to tail of specified list
741 * @buf_list: pointer to buffer list
742 * @buf: pointer to buffer
743 */
n_hdlc_buf_put(struct n_hdlc_buf_list * buf_list,struct n_hdlc_buf * buf)744 static void n_hdlc_buf_put(struct n_hdlc_buf_list *buf_list,
745 struct n_hdlc_buf *buf)
746 {
747 unsigned long flags;
748
749 spin_lock_irqsave(&buf_list->spinlock, flags);
750
751 list_add_tail(&buf->list_item, &buf_list->list);
752 buf_list->count++;
753
754 spin_unlock_irqrestore(&buf_list->spinlock, flags);
755 } /* end of n_hdlc_buf_put() */
756
757 /**
758 * n_hdlc_buf_get - remove and return an HDLC buffer from list
759 * @buf_list: pointer to HDLC buffer list
760 *
761 * Remove and return an HDLC buffer from the head of the specified HDLC buffer
762 * list.
763 * Returns a pointer to HDLC buffer if available, otherwise %NULL.
764 */
n_hdlc_buf_get(struct n_hdlc_buf_list * buf_list)765 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *buf_list)
766 {
767 unsigned long flags;
768 struct n_hdlc_buf *buf;
769
770 spin_lock_irqsave(&buf_list->spinlock, flags);
771
772 buf = list_first_entry_or_null(&buf_list->list,
773 struct n_hdlc_buf, list_item);
774 if (buf) {
775 list_del(&buf->list_item);
776 buf_list->count--;
777 }
778
779 spin_unlock_irqrestore(&buf_list->spinlock, flags);
780 return buf;
781 } /* end of n_hdlc_buf_get() */
782
783 static struct tty_ldisc_ops n_hdlc_ldisc = {
784 .owner = THIS_MODULE,
785 .num = N_HDLC,
786 .name = "hdlc",
787 .open = n_hdlc_tty_open,
788 .close = n_hdlc_tty_close,
789 .read = n_hdlc_tty_read,
790 .write = n_hdlc_tty_write,
791 .ioctl = n_hdlc_tty_ioctl,
792 .poll = n_hdlc_tty_poll,
793 .receive_buf = n_hdlc_tty_receive,
794 .write_wakeup = n_hdlc_tty_wakeup,
795 .flush_buffer = flush_rx_queue,
796 };
797
n_hdlc_init(void)798 static int __init n_hdlc_init(void)
799 {
800 int status;
801
802 /* range check maxframe arg */
803 maxframe = clamp(maxframe, 4096, MAX_HDLC_FRAME_SIZE);
804
805 status = tty_register_ldisc(&n_hdlc_ldisc);
806 if (!status)
807 pr_info("N_HDLC line discipline registered with maxframe=%d\n",
808 maxframe);
809 else
810 pr_err("N_HDLC: error registering line discipline: %d\n",
811 status);
812
813 return status;
814
815 } /* end of init_module() */
816
n_hdlc_exit(void)817 static void __exit n_hdlc_exit(void)
818 {
819 tty_unregister_ldisc(&n_hdlc_ldisc);
820 }
821
822 module_init(n_hdlc_init);
823 module_exit(n_hdlc_exit);
824
825 MODULE_LICENSE("GPL");
826 MODULE_AUTHOR("Paul Fulghum paulkf@microgate.com");
827 module_param(maxframe, int, 0);
828 MODULE_ALIAS_LDISC(N_HDLC);
829