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 #define HDLC_MAGIC 0x239e
80
81 #include <linux/module.h>
82 #include <linux/init.h>
83 #include <linux/kernel.h>
84 #include <linux/sched.h>
85 #include <linux/types.h>
86 #include <linux/fcntl.h>
87 #include <linux/interrupt.h>
88 #include <linux/ptrace.h>
89
90 #include <linux/poll.h>
91 #include <linux/in.h>
92 #include <linux/ioctl.h>
93 #include <linux/slab.h>
94 #include <linux/tty.h>
95 #include <linux/errno.h>
96 #include <linux/string.h> /* used in new tty drivers */
97 #include <linux/signal.h> /* used in new tty drivers */
98 #include <linux/if.h>
99 #include <linux/bitops.h>
100
101 #include <asm/termios.h>
102 #include <linux/uaccess.h>
103 #include "tty.h"
104
105 /*
106 * Buffers for individual HDLC frames
107 */
108 #define MAX_HDLC_FRAME_SIZE 65535
109 #define DEFAULT_RX_BUF_COUNT 10
110 #define MAX_RX_BUF_COUNT 60
111 #define DEFAULT_TX_BUF_COUNT 3
112
113 struct n_hdlc_buf {
114 struct list_head list_item;
115 int count;
116 char buf[];
117 };
118
119 struct n_hdlc_buf_list {
120 struct list_head list;
121 int count;
122 spinlock_t spinlock;
123 };
124
125 /**
126 * struct n_hdlc - per device instance data structure
127 * @magic: magic value for structure
128 * @tbusy: reentrancy flag for tx wakeup code
129 * @woke_up: tx wakeup needs to be run again as it was called while @tbusy
130 * @tx_buf_list: list of pending transmit frame buffers
131 * @rx_buf_list: list of received frame buffers
132 * @tx_free_buf_list: list unused transmit frame buffers
133 * @rx_free_buf_list: list unused received frame buffers
134 */
135 struct n_hdlc {
136 int magic;
137 bool tbusy;
138 bool woke_up;
139 struct n_hdlc_buf_list tx_buf_list;
140 struct n_hdlc_buf_list rx_buf_list;
141 struct n_hdlc_buf_list tx_free_buf_list;
142 struct n_hdlc_buf_list rx_free_buf_list;
143 struct work_struct write_work;
144 struct tty_struct *tty_for_write_work;
145 };
146
147 /*
148 * HDLC buffer list manipulation functions
149 */
150 static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
151 struct n_hdlc_buf *buf);
152 static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
153 struct n_hdlc_buf *buf);
154 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
155
156 /* Local functions */
157
158 static struct n_hdlc *n_hdlc_alloc(void);
159 static void n_hdlc_tty_write_work(struct work_struct *work);
160
161 /* max frame size for memory allocations */
162 static int maxframe = 4096;
163
flush_rx_queue(struct tty_struct *tty)164 static void flush_rx_queue(struct tty_struct *tty)
165 {
166 struct n_hdlc *n_hdlc = tty->disc_data;
167 struct n_hdlc_buf *buf;
168
169 while ((buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list)))
170 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, buf);
171 }
172
flush_tx_queue(struct tty_struct *tty)173 static void flush_tx_queue(struct tty_struct *tty)
174 {
175 struct n_hdlc *n_hdlc = tty->disc_data;
176 struct n_hdlc_buf *buf;
177
178 while ((buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list)))
179 n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, buf);
180 }
181
n_hdlc_free_buf_list(struct n_hdlc_buf_list *list)182 static void n_hdlc_free_buf_list(struct n_hdlc_buf_list *list)
183 {
184 struct n_hdlc_buf *buf;
185
186 do {
187 buf = n_hdlc_buf_get(list);
188 kfree(buf);
189 } while (buf);
190 }
191
192 /**
193 * n_hdlc_tty_close - line discipline close
194 * @tty: pointer to tty info structure
195 *
196 * Called when the line discipline is changed to something
197 * else, the tty is closed, or the tty detects a hangup.
198 */
n_hdlc_tty_close(struct tty_struct *tty)199 static void n_hdlc_tty_close(struct tty_struct *tty)
200 {
201 struct n_hdlc *n_hdlc = tty->disc_data;
202
203 if (n_hdlc->magic != HDLC_MAGIC) {
204 pr_warn("n_hdlc: trying to close unopened tty!\n");
205 return;
206 }
207 #if defined(TTY_NO_WRITE_SPLIT)
208 clear_bit(TTY_NO_WRITE_SPLIT, &tty->flags);
209 #endif
210 tty->disc_data = NULL;
211
212 /* Ensure that the n_hdlcd process is not hanging on select()/poll() */
213 wake_up_interruptible(&tty->read_wait);
214 wake_up_interruptible(&tty->write_wait);
215
216 cancel_work_sync(&n_hdlc->write_work);
217
218 n_hdlc_free_buf_list(&n_hdlc->rx_free_buf_list);
219 n_hdlc_free_buf_list(&n_hdlc->tx_free_buf_list);
220 n_hdlc_free_buf_list(&n_hdlc->rx_buf_list);
221 n_hdlc_free_buf_list(&n_hdlc->tx_buf_list);
222 kfree(n_hdlc);
223 } /* end of n_hdlc_tty_close() */
224
225 /**
226 * n_hdlc_tty_open - called when line discipline changed to n_hdlc
227 * @tty: pointer to tty info structure
228 *
229 * Returns 0 if success, otherwise error code
230 */
n_hdlc_tty_open(struct tty_struct *tty)231 static int n_hdlc_tty_open(struct tty_struct *tty)
232 {
233 struct n_hdlc *n_hdlc = tty->disc_data;
234
235 pr_debug("%s() called (device=%s)\n", __func__, tty->name);
236
237 /* There should not be an existing table for this slot. */
238 if (n_hdlc) {
239 pr_err("%s: tty already associated!\n", __func__);
240 return -EEXIST;
241 }
242
243 n_hdlc = n_hdlc_alloc();
244 if (!n_hdlc) {
245 pr_err("%s: n_hdlc_alloc failed\n", __func__);
246 return -ENFILE;
247 }
248
249 INIT_WORK(&n_hdlc->write_work, n_hdlc_tty_write_work);
250 n_hdlc->tty_for_write_work = tty;
251 tty->disc_data = n_hdlc;
252 tty->receive_room = 65536;
253
254 /* change tty_io write() to not split large writes into 8K chunks */
255 set_bit(TTY_NO_WRITE_SPLIT, &tty->flags);
256
257 /* flush receive data from driver */
258 tty_driver_flush_buffer(tty);
259
260 return 0;
261
262 } /* end of n_tty_hdlc_open() */
263
264 /**
265 * n_hdlc_send_frames - send frames on pending send buffer list
266 * @n_hdlc: pointer to ldisc instance data
267 * @tty: pointer to tty instance data
268 *
269 * Send frames on pending send buffer list until the driver does not accept a
270 * frame (busy) this function is called after adding a frame to the send buffer
271 * list and by the tty wakeup callback.
272 */
n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)273 static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
274 {
275 register int actual;
276 unsigned long flags;
277 struct n_hdlc_buf *tbuf;
278
279 check_again:
280
281 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
282 if (n_hdlc->tbusy) {
283 n_hdlc->woke_up = true;
284 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
285 return;
286 }
287 n_hdlc->tbusy = true;
288 n_hdlc->woke_up = false;
289 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
290
291 tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
292 while (tbuf) {
293 pr_debug("sending frame %p, count=%d\n", tbuf, tbuf->count);
294
295 /* Send the next block of data to device */
296 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
297 actual = tty->ops->write(tty, tbuf->buf, tbuf->count);
298
299 /* rollback was possible and has been done */
300 if (actual == -ERESTARTSYS) {
301 n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
302 break;
303 }
304 /* if transmit error, throw frame away by */
305 /* pretending it was accepted by driver */
306 if (actual < 0)
307 actual = tbuf->count;
308
309 if (actual == tbuf->count) {
310 pr_debug("frame %p completed\n", tbuf);
311
312 /* free current transmit buffer */
313 n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf);
314
315 /* wait up sleeping writers */
316 wake_up_interruptible(&tty->write_wait);
317
318 /* get next pending transmit buffer */
319 tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
320 } else {
321 pr_debug("frame %p pending\n", tbuf);
322
323 /*
324 * the buffer was not accepted by driver,
325 * return it back into tx queue
326 */
327 n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
328 break;
329 }
330 }
331
332 if (!tbuf)
333 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
334
335 /* Clear the re-entry flag */
336 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
337 n_hdlc->tbusy = false;
338 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
339
340 if (n_hdlc->woke_up)
341 goto check_again;
342 } /* end of n_hdlc_send_frames() */
343
344 /**
345 * n_hdlc_tty_write_work - Asynchronous callback for transmit wakeup
346 * @work: pointer to work_struct
347 *
348 * Called when low level device driver can accept more send data.
349 */
n_hdlc_tty_write_work(struct work_struct *work)350 static void n_hdlc_tty_write_work(struct work_struct *work)
351 {
352 struct n_hdlc *n_hdlc = container_of(work, struct n_hdlc, write_work);
353 struct tty_struct *tty = n_hdlc->tty_for_write_work;
354
355 n_hdlc_send_frames(n_hdlc, tty);
356 } /* end of n_hdlc_tty_write_work() */
357
358 /**
359 * n_hdlc_tty_wakeup - Callback for transmit wakeup
360 * @tty: pointer to associated tty instance data
361 *
362 * Called when low level device driver can accept more send data.
363 */
n_hdlc_tty_wakeup(struct tty_struct *tty)364 static void n_hdlc_tty_wakeup(struct tty_struct *tty)
365 {
366 struct n_hdlc *n_hdlc = tty->disc_data;
367
368 schedule_work(&n_hdlc->write_work);
369 } /* end of n_hdlc_tty_wakeup() */
370
371 /**
372 * n_hdlc_tty_receive - Called by tty driver when receive data is available
373 * @tty: pointer to tty instance data
374 * @data: pointer to received data
375 * @flags: pointer to flags for data
376 * @count: count of received data in bytes
377 *
378 * Called by tty low level driver when receive data is available. Data is
379 * interpreted as one HDLC frame.
380 */
n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data, char *flags, int count)381 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
382 char *flags, int count)
383 {
384 register struct n_hdlc *n_hdlc = tty->disc_data;
385 register struct n_hdlc_buf *buf;
386
387 pr_debug("%s() called count=%d\n", __func__, count);
388
389 /* verify line is using HDLC discipline */
390 if (n_hdlc->magic != HDLC_MAGIC) {
391 pr_err("line not using HDLC discipline\n");
392 return;
393 }
394
395 if (count > maxframe) {
396 pr_debug("rx count>maxframesize, data discarded\n");
397 return;
398 }
399
400 /* get a free HDLC buffer */
401 buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
402 if (!buf) {
403 /*
404 * no buffers in free list, attempt to allocate another rx
405 * buffer unless the maximum count has been reached
406 */
407 if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT)
408 buf = kmalloc(struct_size(buf, buf, maxframe),
409 GFP_ATOMIC);
410 }
411
412 if (!buf) {
413 pr_debug("no more rx buffers, data discarded\n");
414 return;
415 }
416
417 /* copy received data to HDLC buffer */
418 memcpy(buf->buf, data, count);
419 buf->count = count;
420
421 /* add HDLC buffer to list of received frames */
422 n_hdlc_buf_put(&n_hdlc->rx_buf_list, buf);
423
424 /* wake up any blocked reads and perform async signalling */
425 wake_up_interruptible(&tty->read_wait);
426 if (tty->fasync != NULL)
427 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
428
429 } /* end of n_hdlc_tty_receive() */
430
431 /**
432 * n_hdlc_tty_read - Called to retrieve one frame of data (if available)
433 * @tty: pointer to tty instance data
434 * @file: pointer to open file object
435 * @buf: pointer to returned data buffer
436 * @nr: size of returned data buffer
437 *
438 * Returns the number of bytes returned or error code.
439 */
n_hdlc_tty_read(struct tty_struct *tty, struct file *file, __u8 *kbuf, size_t nr, void **cookie, unsigned long offset)440 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
441 __u8 *kbuf, size_t nr,
442 void **cookie, unsigned long offset)
443 {
444 struct n_hdlc *n_hdlc = tty->disc_data;
445 int ret = 0;
446 struct n_hdlc_buf *rbuf;
447 DECLARE_WAITQUEUE(wait, current);
448
449 /* Is this a repeated call for an rbuf we already found earlier? */
450 rbuf = *cookie;
451 if (rbuf)
452 goto have_rbuf;
453
454 add_wait_queue(&tty->read_wait, &wait);
455
456 for (;;) {
457 if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
458 ret = -EIO;
459 break;
460 }
461 if (tty_hung_up_p(file))
462 break;
463
464 set_current_state(TASK_INTERRUPTIBLE);
465
466 rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
467 if (rbuf)
468 break;
469
470 /* no data */
471 if (tty_io_nonblock(tty, file)) {
472 ret = -EAGAIN;
473 break;
474 }
475
476 schedule();
477
478 if (signal_pending(current)) {
479 ret = -EINTR;
480 break;
481 }
482 }
483
484 remove_wait_queue(&tty->read_wait, &wait);
485 __set_current_state(TASK_RUNNING);
486
487 if (!rbuf)
488 return ret;
489 *cookie = rbuf;
490
491 have_rbuf:
492 /* Have we used it up entirely? */
493 if (offset >= rbuf->count)
494 goto done_with_rbuf;
495
496 /* More data to go, but can't copy any more? EOVERFLOW */
497 ret = -EOVERFLOW;
498 if (!nr)
499 goto done_with_rbuf;
500
501 /* Copy as much data as possible */
502 ret = rbuf->count - offset;
503 if (ret > nr)
504 ret = nr;
505 memcpy(kbuf, rbuf->buf+offset, ret);
506 offset += ret;
507
508 /* If we still have data left, we leave the rbuf in the cookie */
509 if (offset < rbuf->count)
510 return ret;
511
512 done_with_rbuf:
513 *cookie = NULL;
514
515 if (n_hdlc->rx_free_buf_list.count > DEFAULT_RX_BUF_COUNT)
516 kfree(rbuf);
517 else
518 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
519
520 return ret;
521
522 } /* end of n_hdlc_tty_read() */
523
524 /**
525 * n_hdlc_tty_write - write a single frame of data to device
526 * @tty: pointer to associated tty device instance data
527 * @file: pointer to file object data
528 * @data: pointer to transmit data (one frame)
529 * @count: size of transmit frame in bytes
530 *
531 * Returns the number of bytes written (or error code).
532 */
n_hdlc_tty_write(struct tty_struct *tty, struct file *file, const unsigned char *data, size_t count)533 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
534 const unsigned char *data, size_t count)
535 {
536 struct n_hdlc *n_hdlc = tty->disc_data;
537 int error = 0;
538 DECLARE_WAITQUEUE(wait, current);
539 struct n_hdlc_buf *tbuf;
540
541 pr_debug("%s() called count=%zd\n", __func__, count);
542
543 if (n_hdlc->magic != HDLC_MAGIC)
544 return -EIO;
545
546 /* verify frame size */
547 if (count > maxframe) {
548 pr_debug("%s: truncating user packet from %zu to %d\n",
549 __func__, count, maxframe);
550 count = maxframe;
551 }
552
553 add_wait_queue(&tty->write_wait, &wait);
554
555 for (;;) {
556 set_current_state(TASK_INTERRUPTIBLE);
557
558 tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
559 if (tbuf)
560 break;
561
562 if (tty_io_nonblock(tty, file)) {
563 error = -EAGAIN;
564 break;
565 }
566 schedule();
567
568 if (signal_pending(current)) {
569 error = -EINTR;
570 break;
571 }
572 }
573
574 __set_current_state(TASK_RUNNING);
575 remove_wait_queue(&tty->write_wait, &wait);
576
577 if (!error) {
578 /* Retrieve the user's buffer */
579 memcpy(tbuf->buf, data, count);
580
581 /* Send the data */
582 tbuf->count = error = count;
583 n_hdlc_buf_put(&n_hdlc->tx_buf_list, tbuf);
584 n_hdlc_send_frames(n_hdlc, tty);
585 }
586
587 return error;
588
589 } /* end of n_hdlc_tty_write() */
590
591 /**
592 * n_hdlc_tty_ioctl - process IOCTL system call for the tty device.
593 * @tty: pointer to tty instance data
594 * @file: pointer to open file object for device
595 * @cmd: IOCTL command code
596 * @arg: argument for IOCTL call (cmd dependent)
597 *
598 * Returns command dependent result.
599 */
n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file, unsigned int cmd, unsigned long arg)600 static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
601 unsigned int cmd, unsigned long arg)
602 {
603 struct n_hdlc *n_hdlc = tty->disc_data;
604 int error = 0;
605 int count;
606 unsigned long flags;
607 struct n_hdlc_buf *buf = NULL;
608
609 pr_debug("%s() called %d\n", __func__, cmd);
610
611 /* Verify the status of the device */
612 if (n_hdlc->magic != HDLC_MAGIC)
613 return -EBADF;
614
615 switch (cmd) {
616 case FIONREAD:
617 /* report count of read data available */
618 /* in next available frame (if any) */
619 spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock, flags);
620 buf = list_first_entry_or_null(&n_hdlc->rx_buf_list.list,
621 struct n_hdlc_buf, list_item);
622 if (buf)
623 count = buf->count;
624 else
625 count = 0;
626 spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock, flags);
627 error = put_user(count, (int __user *)arg);
628 break;
629
630 case TIOCOUTQ:
631 /* get the pending tx byte count in the driver */
632 count = tty_chars_in_buffer(tty);
633 /* add size of next output frame in queue */
634 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
635 buf = list_first_entry_or_null(&n_hdlc->tx_buf_list.list,
636 struct n_hdlc_buf, list_item);
637 if (buf)
638 count += buf->count;
639 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
640 error = put_user(count, (int __user *)arg);
641 break;
642
643 case TCFLSH:
644 switch (arg) {
645 case TCIOFLUSH:
646 case TCOFLUSH:
647 flush_tx_queue(tty);
648 }
649 fallthrough; /* to default */
650
651 default:
652 error = n_tty_ioctl_helper(tty, file, cmd, arg);
653 break;
654 }
655 return error;
656
657 } /* end of n_hdlc_tty_ioctl() */
658
659 /**
660 * n_hdlc_tty_poll - TTY callback for poll system call
661 * @tty: pointer to tty instance data
662 * @filp: pointer to open file object for device
663 * @wait: wait queue for operations
664 *
665 * Determine which operations (read/write) will not block and return info
666 * to caller.
667 * Returns a bit mask containing info on which ops will not block.
668 */
n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp, poll_table *wait)669 static __poll_t n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
670 poll_table *wait)
671 {
672 struct n_hdlc *n_hdlc = tty->disc_data;
673 __poll_t mask = 0;
674
675 if (n_hdlc->magic != HDLC_MAGIC)
676 return 0;
677
678 /*
679 * queue the current process into any wait queue that may awaken in the
680 * future (read and write)
681 */
682 poll_wait(filp, &tty->read_wait, wait);
683 poll_wait(filp, &tty->write_wait, wait);
684
685 /* set bits for operations that won't block */
686 if (!list_empty(&n_hdlc->rx_buf_list.list))
687 mask |= EPOLLIN | EPOLLRDNORM; /* readable */
688 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
689 mask |= EPOLLHUP;
690 if (tty_hung_up_p(filp))
691 mask |= EPOLLHUP;
692 if (!tty_is_writelocked(tty) &&
693 !list_empty(&n_hdlc->tx_free_buf_list.list))
694 mask |= EPOLLOUT | EPOLLWRNORM; /* writable */
695
696 return mask;
697 } /* end of n_hdlc_tty_poll() */
698
n_hdlc_alloc_buf(struct n_hdlc_buf_list *list, unsigned int count, const char *name)699 static void n_hdlc_alloc_buf(struct n_hdlc_buf_list *list, unsigned int count,
700 const char *name)
701 {
702 struct n_hdlc_buf *buf;
703 unsigned int i;
704
705 for (i = 0; i < count; i++) {
706 buf = kmalloc(struct_size(buf, buf, maxframe), GFP_KERNEL);
707 if (!buf) {
708 pr_debug("%s(), kmalloc() failed for %s buffer %u\n",
709 __func__, name, i);
710 return;
711 }
712 n_hdlc_buf_put(list, buf);
713 }
714 }
715
716 /**
717 * n_hdlc_alloc - allocate an n_hdlc instance data structure
718 *
719 * Returns a pointer to newly created structure if success, otherwise %NULL
720 */
n_hdlc_alloc(void)721 static struct n_hdlc *n_hdlc_alloc(void)
722 {
723 struct n_hdlc *n_hdlc = kzalloc(sizeof(*n_hdlc), GFP_KERNEL);
724
725 if (!n_hdlc)
726 return NULL;
727
728 spin_lock_init(&n_hdlc->rx_free_buf_list.spinlock);
729 spin_lock_init(&n_hdlc->tx_free_buf_list.spinlock);
730 spin_lock_init(&n_hdlc->rx_buf_list.spinlock);
731 spin_lock_init(&n_hdlc->tx_buf_list.spinlock);
732
733 INIT_LIST_HEAD(&n_hdlc->rx_free_buf_list.list);
734 INIT_LIST_HEAD(&n_hdlc->tx_free_buf_list.list);
735 INIT_LIST_HEAD(&n_hdlc->rx_buf_list.list);
736 INIT_LIST_HEAD(&n_hdlc->tx_buf_list.list);
737
738 n_hdlc_alloc_buf(&n_hdlc->rx_free_buf_list, DEFAULT_RX_BUF_COUNT, "rx");
739 n_hdlc_alloc_buf(&n_hdlc->tx_free_buf_list, DEFAULT_TX_BUF_COUNT, "tx");
740
741 /* Initialize the control block */
742 n_hdlc->magic = HDLC_MAGIC;
743
744 return n_hdlc;
745
746 } /* end of n_hdlc_alloc() */
747
748 /**
749 * n_hdlc_buf_return - put the HDLC buffer after the head of the specified list
750 * @buf_list: pointer to the buffer list
751 * @buf: pointer to the buffer
752 */
n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list, struct n_hdlc_buf *buf)753 static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
754 struct n_hdlc_buf *buf)
755 {
756 unsigned long flags;
757
758 spin_lock_irqsave(&buf_list->spinlock, flags);
759
760 list_add(&buf->list_item, &buf_list->list);
761 buf_list->count++;
762
763 spin_unlock_irqrestore(&buf_list->spinlock, flags);
764 }
765
766 /**
767 * n_hdlc_buf_put - add specified HDLC buffer to tail of specified list
768 * @buf_list: pointer to buffer list
769 * @buf: pointer to buffer
770 */
n_hdlc_buf_put(struct n_hdlc_buf_list *buf_list, struct n_hdlc_buf *buf)771 static void n_hdlc_buf_put(struct n_hdlc_buf_list *buf_list,
772 struct n_hdlc_buf *buf)
773 {
774 unsigned long flags;
775
776 spin_lock_irqsave(&buf_list->spinlock, flags);
777
778 list_add_tail(&buf->list_item, &buf_list->list);
779 buf_list->count++;
780
781 spin_unlock_irqrestore(&buf_list->spinlock, flags);
782 } /* end of n_hdlc_buf_put() */
783
784 /**
785 * n_hdlc_buf_get - remove and return an HDLC buffer from list
786 * @buf_list: pointer to HDLC buffer list
787 *
788 * Remove and return an HDLC buffer from the head of the specified HDLC buffer
789 * list.
790 * Returns a pointer to HDLC buffer if available, otherwise %NULL.
791 */
n_hdlc_buf_get(struct n_hdlc_buf_list *buf_list)792 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *buf_list)
793 {
794 unsigned long flags;
795 struct n_hdlc_buf *buf;
796
797 spin_lock_irqsave(&buf_list->spinlock, flags);
798
799 buf = list_first_entry_or_null(&buf_list->list,
800 struct n_hdlc_buf, list_item);
801 if (buf) {
802 list_del(&buf->list_item);
803 buf_list->count--;
804 }
805
806 spin_unlock_irqrestore(&buf_list->spinlock, flags);
807 return buf;
808 } /* end of n_hdlc_buf_get() */
809
810 static struct tty_ldisc_ops n_hdlc_ldisc = {
811 .owner = THIS_MODULE,
812 .magic = TTY_LDISC_MAGIC,
813 .name = "hdlc",
814 .open = n_hdlc_tty_open,
815 .close = n_hdlc_tty_close,
816 .read = n_hdlc_tty_read,
817 .write = n_hdlc_tty_write,
818 .ioctl = n_hdlc_tty_ioctl,
819 .poll = n_hdlc_tty_poll,
820 .receive_buf = n_hdlc_tty_receive,
821 .write_wakeup = n_hdlc_tty_wakeup,
822 .flush_buffer = flush_rx_queue,
823 };
824
n_hdlc_init(void)825 static int __init n_hdlc_init(void)
826 {
827 int status;
828
829 /* range check maxframe arg */
830 maxframe = clamp(maxframe, 4096, MAX_HDLC_FRAME_SIZE);
831
832 status = tty_register_ldisc(N_HDLC, &n_hdlc_ldisc);
833 if (!status)
834 pr_info("N_HDLC line discipline registered with maxframe=%d\n",
835 maxframe);
836 else
837 pr_err("N_HDLC: error registering line discipline: %d\n",
838 status);
839
840 return status;
841
842 } /* end of init_module() */
843
n_hdlc_exit(void)844 static void __exit n_hdlc_exit(void)
845 {
846 /* Release tty registration of line discipline */
847 int status = tty_unregister_ldisc(N_HDLC);
848
849 if (status)
850 pr_err("N_HDLC: can't unregister line discipline (err = %d)\n",
851 status);
852 else
853 pr_info("N_HDLC: line discipline unregistered\n");
854 }
855
856 module_init(n_hdlc_init);
857 module_exit(n_hdlc_exit);
858
859 MODULE_LICENSE("GPL");
860 MODULE_AUTHOR("Paul Fulghum paulkf@microgate.com");
861 module_param(maxframe, int, 0);
862 MODULE_ALIAS_LDISC(N_HDLC);
863