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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
110struct n_hdlc_buf {
111 struct list_head list_item;
112 size_t count;
113 u8 buf[];
114};
115
116struct 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 */
131struct 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 */
145static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
146 struct n_hdlc_buf *buf);
147static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
148 struct n_hdlc_buf *buf);
149static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
150
151/* Local functions */
152
153static struct n_hdlc *n_hdlc_alloc(void);
154static void n_hdlc_tty_write_work(struct work_struct *work);
155
156/* max frame size for memory allocations */
157static int maxframe = 4096;
158
159static 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
168static 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
177static 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 */
194static 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 */
222static 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 */
264static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
265{
266 unsigned long flags;
267 struct n_hdlc_buf *tbuf;
268 ssize_t actual;
269
270check_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=%zu\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 */
341static 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 */
355static 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 */
372static void n_hdlc_tty_receive(struct tty_struct *tty, const u8 *data,
373 const u8 *flags, size_t 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=%zu\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 */
427static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
428 u8 *kbuf, size_t nr, void **cookie,
429 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
478have_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
499done_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 */
520static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
521 const u8 *data, size_t count)
522{
523 struct n_hdlc *n_hdlc = tty->disc_data;
524 DECLARE_WAITQUEUE(wait, current);
525 struct n_hdlc_buf *tbuf;
526 ssize_t error = 0;
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 */
583static 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 */
648static __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
675static 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 */
697static 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 */
726static 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 */
744static 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 */
765static 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
783static 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
798static 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
817static void __exit n_hdlc_exit(void)
818{
819 tty_unregister_ldisc(&n_hdlc_ldisc);
820}
821
822module_init(n_hdlc_init);
823module_exit(n_hdlc_exit);
824
825MODULE_LICENSE("GPL");
826MODULE_AUTHOR("Paul Fulghum paulkf@microgate.com");
827module_param(maxframe, int, 0);
828MODULE_ALIAS_LDISC(N_HDLC);
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
113struct n_hdlc_buf {
114 struct list_head list_item;
115 int count;
116 char buf[];
117};
118
119struct 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 */
135struct 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};
144
145/*
146 * HDLC buffer list manipulation functions
147 */
148static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
149 struct n_hdlc_buf *buf);
150static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
151 struct n_hdlc_buf *buf);
152static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
153
154/* Local functions */
155
156static struct n_hdlc *n_hdlc_alloc(void);
157
158/* max frame size for memory allocations */
159static int maxframe = 4096;
160
161static void flush_rx_queue(struct tty_struct *tty)
162{
163 struct n_hdlc *n_hdlc = tty->disc_data;
164 struct n_hdlc_buf *buf;
165
166 while ((buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list)))
167 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, buf);
168}
169
170static void flush_tx_queue(struct tty_struct *tty)
171{
172 struct n_hdlc *n_hdlc = tty->disc_data;
173 struct n_hdlc_buf *buf;
174
175 while ((buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list)))
176 n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, buf);
177}
178
179static void n_hdlc_free_buf_list(struct n_hdlc_buf_list *list)
180{
181 struct n_hdlc_buf *buf;
182
183 do {
184 buf = n_hdlc_buf_get(list);
185 kfree(buf);
186 } while (buf);
187}
188
189/**
190 * n_hdlc_tty_close - line discipline close
191 * @tty: pointer to tty info structure
192 *
193 * Called when the line discipline is changed to something
194 * else, the tty is closed, or the tty detects a hangup.
195 */
196static void n_hdlc_tty_close(struct tty_struct *tty)
197{
198 struct n_hdlc *n_hdlc = tty->disc_data;
199
200 if (n_hdlc->magic != HDLC_MAGIC) {
201 pr_warn("n_hdlc: trying to close unopened tty!\n");
202 return;
203 }
204#if defined(TTY_NO_WRITE_SPLIT)
205 clear_bit(TTY_NO_WRITE_SPLIT, &tty->flags);
206#endif
207 tty->disc_data = NULL;
208
209 /* Ensure that the n_hdlcd process is not hanging on select()/poll() */
210 wake_up_interruptible(&tty->read_wait);
211 wake_up_interruptible(&tty->write_wait);
212
213 n_hdlc_free_buf_list(&n_hdlc->rx_free_buf_list);
214 n_hdlc_free_buf_list(&n_hdlc->tx_free_buf_list);
215 n_hdlc_free_buf_list(&n_hdlc->rx_buf_list);
216 n_hdlc_free_buf_list(&n_hdlc->tx_buf_list);
217 kfree(n_hdlc);
218} /* end of n_hdlc_tty_close() */
219
220/**
221 * n_hdlc_tty_open - called when line discipline changed to n_hdlc
222 * @tty: pointer to tty info structure
223 *
224 * Returns 0 if success, otherwise error code
225 */
226static int n_hdlc_tty_open(struct tty_struct *tty)
227{
228 struct n_hdlc *n_hdlc = tty->disc_data;
229
230 pr_debug("%s() called (device=%s)\n", __func__, tty->name);
231
232 /* There should not be an existing table for this slot. */
233 if (n_hdlc) {
234 pr_err("%s: tty already associated!\n", __func__);
235 return -EEXIST;
236 }
237
238 n_hdlc = n_hdlc_alloc();
239 if (!n_hdlc) {
240 pr_err("%s: n_hdlc_alloc failed\n", __func__);
241 return -ENFILE;
242 }
243
244 tty->disc_data = n_hdlc;
245 tty->receive_room = 65536;
246
247 /* change tty_io write() to not split large writes into 8K chunks */
248 set_bit(TTY_NO_WRITE_SPLIT, &tty->flags);
249
250 /* flush receive data from driver */
251 tty_driver_flush_buffer(tty);
252
253 return 0;
254
255} /* end of n_tty_hdlc_open() */
256
257/**
258 * n_hdlc_send_frames - send frames on pending send buffer list
259 * @n_hdlc: pointer to ldisc instance data
260 * @tty: pointer to tty instance data
261 *
262 * Send frames on pending send buffer list until the driver does not accept a
263 * frame (busy) this function is called after adding a frame to the send buffer
264 * list and by the tty wakeup callback.
265 */
266static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
267{
268 register int actual;
269 unsigned long flags;
270 struct n_hdlc_buf *tbuf;
271
272check_again:
273
274 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
275 if (n_hdlc->tbusy) {
276 n_hdlc->woke_up = true;
277 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
278 return;
279 }
280 n_hdlc->tbusy = true;
281 n_hdlc->woke_up = false;
282 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
283
284 tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
285 while (tbuf) {
286 pr_debug("sending frame %p, count=%d\n", tbuf, tbuf->count);
287
288 /* Send the next block of data to device */
289 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
290 actual = tty->ops->write(tty, tbuf->buf, tbuf->count);
291
292 /* rollback was possible and has been done */
293 if (actual == -ERESTARTSYS) {
294 n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
295 break;
296 }
297 /* if transmit error, throw frame away by */
298 /* pretending it was accepted by driver */
299 if (actual < 0)
300 actual = tbuf->count;
301
302 if (actual == tbuf->count) {
303 pr_debug("frame %p completed\n", tbuf);
304
305 /* free current transmit buffer */
306 n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf);
307
308 /* wait up sleeping writers */
309 wake_up_interruptible(&tty->write_wait);
310
311 /* get next pending transmit buffer */
312 tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
313 } else {
314 pr_debug("frame %p pending\n", tbuf);
315
316 /*
317 * the buffer was not accepted by driver,
318 * return it back into tx queue
319 */
320 n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
321 break;
322 }
323 }
324
325 if (!tbuf)
326 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
327
328 /* Clear the re-entry flag */
329 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
330 n_hdlc->tbusy = false;
331 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
332
333 if (n_hdlc->woke_up)
334 goto check_again;
335} /* end of n_hdlc_send_frames() */
336
337/**
338 * n_hdlc_tty_wakeup - Callback for transmit wakeup
339 * @tty: pointer to associated tty instance data
340 *
341 * Called when low level device driver can accept more send data.
342 */
343static void n_hdlc_tty_wakeup(struct tty_struct *tty)
344{
345 struct n_hdlc *n_hdlc = tty->disc_data;
346
347 n_hdlc_send_frames(n_hdlc, tty);
348} /* end of n_hdlc_tty_wakeup() */
349
350/**
351 * n_hdlc_tty_receive - Called by tty driver when receive data is available
352 * @tty: pointer to tty instance data
353 * @data: pointer to received data
354 * @flags: pointer to flags for data
355 * @count: count of received data in bytes
356 *
357 * Called by tty low level driver when receive data is available. Data is
358 * interpreted as one HDLC frame.
359 */
360static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
361 const char *flags, int count)
362{
363 register struct n_hdlc *n_hdlc = tty->disc_data;
364 register struct n_hdlc_buf *buf;
365
366 pr_debug("%s() called count=%d\n", __func__, count);
367
368 /* verify line is using HDLC discipline */
369 if (n_hdlc->magic != HDLC_MAGIC) {
370 pr_err("line not using HDLC discipline\n");
371 return;
372 }
373
374 if (count > maxframe) {
375 pr_debug("rx count>maxframesize, data discarded\n");
376 return;
377 }
378
379 /* get a free HDLC buffer */
380 buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
381 if (!buf) {
382 /*
383 * no buffers in free list, attempt to allocate another rx
384 * buffer unless the maximum count has been reached
385 */
386 if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT)
387 buf = kmalloc(struct_size(buf, buf, maxframe),
388 GFP_ATOMIC);
389 }
390
391 if (!buf) {
392 pr_debug("no more rx buffers, data discarded\n");
393 return;
394 }
395
396 /* copy received data to HDLC buffer */
397 memcpy(buf->buf, data, count);
398 buf->count = count;
399
400 /* add HDLC buffer to list of received frames */
401 n_hdlc_buf_put(&n_hdlc->rx_buf_list, buf);
402
403 /* wake up any blocked reads and perform async signalling */
404 wake_up_interruptible(&tty->read_wait);
405 if (tty->fasync != NULL)
406 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
407
408} /* end of n_hdlc_tty_receive() */
409
410/**
411 * n_hdlc_tty_read - Called to retrieve one frame of data (if available)
412 * @tty: pointer to tty instance data
413 * @file: pointer to open file object
414 * @kbuf: pointer to returned data buffer
415 * @nr: size of returned data buffer
416 * @cookie: stored rbuf from previous run
417 * @offset: offset into the data buffer
418 *
419 * Returns the number of bytes returned or error code.
420 */
421static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
422 __u8 *kbuf, size_t nr,
423 void **cookie, unsigned long offset)
424{
425 struct n_hdlc *n_hdlc = tty->disc_data;
426 int ret = 0;
427 struct n_hdlc_buf *rbuf;
428 DECLARE_WAITQUEUE(wait, current);
429
430 /* Is this a repeated call for an rbuf we already found earlier? */
431 rbuf = *cookie;
432 if (rbuf)
433 goto have_rbuf;
434
435 add_wait_queue(&tty->read_wait, &wait);
436
437 for (;;) {
438 if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
439 ret = -EIO;
440 break;
441 }
442 if (tty_hung_up_p(file))
443 break;
444
445 set_current_state(TASK_INTERRUPTIBLE);
446
447 rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
448 if (rbuf)
449 break;
450
451 /* no data */
452 if (tty_io_nonblock(tty, file)) {
453 ret = -EAGAIN;
454 break;
455 }
456
457 schedule();
458
459 if (signal_pending(current)) {
460 ret = -EINTR;
461 break;
462 }
463 }
464
465 remove_wait_queue(&tty->read_wait, &wait);
466 __set_current_state(TASK_RUNNING);
467
468 if (!rbuf)
469 return ret;
470 *cookie = rbuf;
471
472have_rbuf:
473 /* Have we used it up entirely? */
474 if (offset >= rbuf->count)
475 goto done_with_rbuf;
476
477 /* More data to go, but can't copy any more? EOVERFLOW */
478 ret = -EOVERFLOW;
479 if (!nr)
480 goto done_with_rbuf;
481
482 /* Copy as much data as possible */
483 ret = rbuf->count - offset;
484 if (ret > nr)
485 ret = nr;
486 memcpy(kbuf, rbuf->buf+offset, ret);
487 offset += ret;
488
489 /* If we still have data left, we leave the rbuf in the cookie */
490 if (offset < rbuf->count)
491 return ret;
492
493done_with_rbuf:
494 *cookie = NULL;
495
496 if (n_hdlc->rx_free_buf_list.count > DEFAULT_RX_BUF_COUNT)
497 kfree(rbuf);
498 else
499 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
500
501 return ret;
502
503} /* end of n_hdlc_tty_read() */
504
505/**
506 * n_hdlc_tty_write - write a single frame of data to device
507 * @tty: pointer to associated tty device instance data
508 * @file: pointer to file object data
509 * @data: pointer to transmit data (one frame)
510 * @count: size of transmit frame in bytes
511 *
512 * Returns the number of bytes written (or error code).
513 */
514static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
515 const unsigned char *data, size_t count)
516{
517 struct n_hdlc *n_hdlc = tty->disc_data;
518 int error = 0;
519 DECLARE_WAITQUEUE(wait, current);
520 struct n_hdlc_buf *tbuf;
521
522 pr_debug("%s() called count=%zd\n", __func__, count);
523
524 if (n_hdlc->magic != HDLC_MAGIC)
525 return -EIO;
526
527 /* verify frame size */
528 if (count > maxframe) {
529 pr_debug("%s: truncating user packet from %zu to %d\n",
530 __func__, count, maxframe);
531 count = maxframe;
532 }
533
534 add_wait_queue(&tty->write_wait, &wait);
535
536 for (;;) {
537 set_current_state(TASK_INTERRUPTIBLE);
538
539 tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
540 if (tbuf)
541 break;
542
543 if (tty_io_nonblock(tty, file)) {
544 error = -EAGAIN;
545 break;
546 }
547 schedule();
548
549 if (signal_pending(current)) {
550 error = -EINTR;
551 break;
552 }
553 }
554
555 __set_current_state(TASK_RUNNING);
556 remove_wait_queue(&tty->write_wait, &wait);
557
558 if (!error) {
559 /* Retrieve the user's buffer */
560 memcpy(tbuf->buf, data, count);
561
562 /* Send the data */
563 tbuf->count = error = count;
564 n_hdlc_buf_put(&n_hdlc->tx_buf_list, tbuf);
565 n_hdlc_send_frames(n_hdlc, tty);
566 }
567
568 return error;
569
570} /* end of n_hdlc_tty_write() */
571
572/**
573 * n_hdlc_tty_ioctl - process IOCTL system call for the tty device.
574 * @tty: pointer to tty instance data
575 * @file: pointer to open file object for device
576 * @cmd: IOCTL command code
577 * @arg: argument for IOCTL call (cmd dependent)
578 *
579 * Returns command dependent result.
580 */
581static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
582 unsigned int cmd, unsigned long arg)
583{
584 struct n_hdlc *n_hdlc = tty->disc_data;
585 int error = 0;
586 int count;
587 unsigned long flags;
588 struct n_hdlc_buf *buf = NULL;
589
590 pr_debug("%s() called %d\n", __func__, cmd);
591
592 /* Verify the status of the device */
593 if (n_hdlc->magic != HDLC_MAGIC)
594 return -EBADF;
595
596 switch (cmd) {
597 case FIONREAD:
598 /* report count of read data available */
599 /* in next available frame (if any) */
600 spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock, flags);
601 buf = list_first_entry_or_null(&n_hdlc->rx_buf_list.list,
602 struct n_hdlc_buf, list_item);
603 if (buf)
604 count = buf->count;
605 else
606 count = 0;
607 spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock, flags);
608 error = put_user(count, (int __user *)arg);
609 break;
610
611 case TIOCOUTQ:
612 /* get the pending tx byte count in the driver */
613 count = tty_chars_in_buffer(tty);
614 /* add size of next output frame in queue */
615 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
616 buf = list_first_entry_or_null(&n_hdlc->tx_buf_list.list,
617 struct n_hdlc_buf, list_item);
618 if (buf)
619 count += buf->count;
620 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
621 error = put_user(count, (int __user *)arg);
622 break;
623
624 case TCFLSH:
625 switch (arg) {
626 case TCIOFLUSH:
627 case TCOFLUSH:
628 flush_tx_queue(tty);
629 }
630 fallthrough; /* to default */
631
632 default:
633 error = n_tty_ioctl_helper(tty, file, cmd, arg);
634 break;
635 }
636 return error;
637
638} /* end of n_hdlc_tty_ioctl() */
639
640/**
641 * n_hdlc_tty_poll - TTY callback for poll system call
642 * @tty: pointer to tty instance data
643 * @filp: pointer to open file object for device
644 * @wait: wait queue for operations
645 *
646 * Determine which operations (read/write) will not block and return info
647 * to caller.
648 * Returns a bit mask containing info on which ops will not block.
649 */
650static __poll_t n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
651 poll_table *wait)
652{
653 struct n_hdlc *n_hdlc = tty->disc_data;
654 __poll_t mask = 0;
655
656 if (n_hdlc->magic != HDLC_MAGIC)
657 return 0;
658
659 /*
660 * queue the current process into any wait queue that may awaken in the
661 * future (read and write)
662 */
663 poll_wait(filp, &tty->read_wait, wait);
664 poll_wait(filp, &tty->write_wait, wait);
665
666 /* set bits for operations that won't block */
667 if (!list_empty(&n_hdlc->rx_buf_list.list))
668 mask |= EPOLLIN | EPOLLRDNORM; /* readable */
669 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
670 mask |= EPOLLHUP;
671 if (tty_hung_up_p(filp))
672 mask |= EPOLLHUP;
673 if (!tty_is_writelocked(tty) &&
674 !list_empty(&n_hdlc->tx_free_buf_list.list))
675 mask |= EPOLLOUT | EPOLLWRNORM; /* writable */
676
677 return mask;
678} /* end of n_hdlc_tty_poll() */
679
680static void n_hdlc_alloc_buf(struct n_hdlc_buf_list *list, unsigned int count,
681 const char *name)
682{
683 struct n_hdlc_buf *buf;
684 unsigned int i;
685
686 for (i = 0; i < count; i++) {
687 buf = kmalloc(struct_size(buf, buf, maxframe), GFP_KERNEL);
688 if (!buf) {
689 pr_debug("%s(), kmalloc() failed for %s buffer %u\n",
690 __func__, name, i);
691 return;
692 }
693 n_hdlc_buf_put(list, buf);
694 }
695}
696
697/**
698 * n_hdlc_alloc - allocate an n_hdlc instance data structure
699 *
700 * Returns a pointer to newly created structure if success, otherwise %NULL
701 */
702static struct n_hdlc *n_hdlc_alloc(void)
703{
704 struct n_hdlc *n_hdlc = kzalloc(sizeof(*n_hdlc), GFP_KERNEL);
705
706 if (!n_hdlc)
707 return NULL;
708
709 spin_lock_init(&n_hdlc->rx_free_buf_list.spinlock);
710 spin_lock_init(&n_hdlc->tx_free_buf_list.spinlock);
711 spin_lock_init(&n_hdlc->rx_buf_list.spinlock);
712 spin_lock_init(&n_hdlc->tx_buf_list.spinlock);
713
714 INIT_LIST_HEAD(&n_hdlc->rx_free_buf_list.list);
715 INIT_LIST_HEAD(&n_hdlc->tx_free_buf_list.list);
716 INIT_LIST_HEAD(&n_hdlc->rx_buf_list.list);
717 INIT_LIST_HEAD(&n_hdlc->tx_buf_list.list);
718
719 n_hdlc_alloc_buf(&n_hdlc->rx_free_buf_list, DEFAULT_RX_BUF_COUNT, "rx");
720 n_hdlc_alloc_buf(&n_hdlc->tx_free_buf_list, DEFAULT_TX_BUF_COUNT, "tx");
721
722 /* Initialize the control block */
723 n_hdlc->magic = HDLC_MAGIC;
724
725 return n_hdlc;
726
727} /* end of n_hdlc_alloc() */
728
729/**
730 * n_hdlc_buf_return - put the HDLC buffer after the head of the specified list
731 * @buf_list: pointer to the buffer list
732 * @buf: pointer to the buffer
733 */
734static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
735 struct n_hdlc_buf *buf)
736{
737 unsigned long flags;
738
739 spin_lock_irqsave(&buf_list->spinlock, flags);
740
741 list_add(&buf->list_item, &buf_list->list);
742 buf_list->count++;
743
744 spin_unlock_irqrestore(&buf_list->spinlock, flags);
745}
746
747/**
748 * n_hdlc_buf_put - add specified HDLC buffer to tail of specified list
749 * @buf_list: pointer to buffer list
750 * @buf: pointer to buffer
751 */
752static void n_hdlc_buf_put(struct n_hdlc_buf_list *buf_list,
753 struct n_hdlc_buf *buf)
754{
755 unsigned long flags;
756
757 spin_lock_irqsave(&buf_list->spinlock, flags);
758
759 list_add_tail(&buf->list_item, &buf_list->list);
760 buf_list->count++;
761
762 spin_unlock_irqrestore(&buf_list->spinlock, flags);
763} /* end of n_hdlc_buf_put() */
764
765/**
766 * n_hdlc_buf_get - remove and return an HDLC buffer from list
767 * @buf_list: pointer to HDLC buffer list
768 *
769 * Remove and return an HDLC buffer from the head of the specified HDLC buffer
770 * list.
771 * Returns a pointer to HDLC buffer if available, otherwise %NULL.
772 */
773static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *buf_list)
774{
775 unsigned long flags;
776 struct n_hdlc_buf *buf;
777
778 spin_lock_irqsave(&buf_list->spinlock, flags);
779
780 buf = list_first_entry_or_null(&buf_list->list,
781 struct n_hdlc_buf, list_item);
782 if (buf) {
783 list_del(&buf->list_item);
784 buf_list->count--;
785 }
786
787 spin_unlock_irqrestore(&buf_list->spinlock, flags);
788 return buf;
789} /* end of n_hdlc_buf_get() */
790
791static struct tty_ldisc_ops n_hdlc_ldisc = {
792 .owner = THIS_MODULE,
793 .num = N_HDLC,
794 .name = "hdlc",
795 .open = n_hdlc_tty_open,
796 .close = n_hdlc_tty_close,
797 .read = n_hdlc_tty_read,
798 .write = n_hdlc_tty_write,
799 .ioctl = n_hdlc_tty_ioctl,
800 .poll = n_hdlc_tty_poll,
801 .receive_buf = n_hdlc_tty_receive,
802 .write_wakeup = n_hdlc_tty_wakeup,
803 .flush_buffer = flush_rx_queue,
804};
805
806static int __init n_hdlc_init(void)
807{
808 int status;
809
810 /* range check maxframe arg */
811 maxframe = clamp(maxframe, 4096, MAX_HDLC_FRAME_SIZE);
812
813 status = tty_register_ldisc(&n_hdlc_ldisc);
814 if (!status)
815 pr_info("N_HDLC line discipline registered with maxframe=%d\n",
816 maxframe);
817 else
818 pr_err("N_HDLC: error registering line discipline: %d\n",
819 status);
820
821 return status;
822
823} /* end of init_module() */
824
825static void __exit n_hdlc_exit(void)
826{
827 tty_unregister_ldisc(&n_hdlc_ldisc);
828}
829
830module_init(n_hdlc_init);
831module_exit(n_hdlc_exit);
832
833MODULE_LICENSE("GPL");
834MODULE_AUTHOR("Paul Fulghum paulkf@microgate.com");
835module_param(maxframe, int, 0);
836MODULE_ALIAS_LDISC(N_HDLC);