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 size_t count;
113 u8 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 * @write_work: work struct for deferred frame transmission
131 * @tty_for_write_work: pointer to tty instance used by the @write_work
132 */
133 struct n_hdlc {
134 bool tbusy;
135 bool woke_up;
136 struct n_hdlc_buf_list tx_buf_list;
137 struct n_hdlc_buf_list rx_buf_list;
138 struct n_hdlc_buf_list tx_free_buf_list;
139 struct n_hdlc_buf_list rx_free_buf_list;
140 struct work_struct write_work;
141 struct tty_struct *tty_for_write_work;
142 };
143
144 /*
145 * HDLC buffer list manipulation functions
146 */
147 static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
148 struct n_hdlc_buf *buf);
149 static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
150 struct n_hdlc_buf *buf);
151 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
152
153 /* Local functions */
154
155 static struct n_hdlc *n_hdlc_alloc(void);
156 static void n_hdlc_tty_write_work(struct work_struct *work);
157
158 /* max frame size for memory allocations */
159 static int maxframe = 4096;
160
flush_rx_queue(struct tty_struct * tty)161 static 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
flush_tx_queue(struct tty_struct * tty)170 static 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
n_hdlc_free_buf_list(struct n_hdlc_buf_list * list)179 static 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 */
n_hdlc_tty_close(struct tty_struct * tty)196 static void n_hdlc_tty_close(struct tty_struct *tty)
197 {
198 struct n_hdlc *n_hdlc = tty->disc_data;
199
200 #if defined(TTY_NO_WRITE_SPLIT)
201 clear_bit(TTY_NO_WRITE_SPLIT, &tty->flags);
202 #endif
203 tty->disc_data = NULL;
204
205 /* Ensure that the n_hdlcd process is not hanging on select()/poll() */
206 wake_up_interruptible(&tty->read_wait);
207 wake_up_interruptible(&tty->write_wait);
208
209 cancel_work_sync(&n_hdlc->write_work);
210
211 n_hdlc_free_buf_list(&n_hdlc->rx_free_buf_list);
212 n_hdlc_free_buf_list(&n_hdlc->tx_free_buf_list);
213 n_hdlc_free_buf_list(&n_hdlc->rx_buf_list);
214 n_hdlc_free_buf_list(&n_hdlc->tx_buf_list);
215 kfree(n_hdlc);
216 } /* end of n_hdlc_tty_close() */
217
218 /**
219 * n_hdlc_tty_open - called when line discipline changed to n_hdlc
220 * @tty: pointer to tty info structure
221 *
222 * Returns 0 if success, otherwise error code
223 */
n_hdlc_tty_open(struct tty_struct * tty)224 static int n_hdlc_tty_open(struct tty_struct *tty)
225 {
226 struct n_hdlc *n_hdlc = tty->disc_data;
227
228 pr_debug("%s() called (device=%s)\n", __func__, tty->name);
229
230 /* There should not be an existing table for this slot. */
231 if (n_hdlc) {
232 pr_err("%s: tty already associated!\n", __func__);
233 return -EEXIST;
234 }
235
236 n_hdlc = n_hdlc_alloc();
237 if (!n_hdlc) {
238 pr_err("%s: n_hdlc_alloc failed\n", __func__);
239 return -ENFILE;
240 }
241
242 INIT_WORK(&n_hdlc->write_work, n_hdlc_tty_write_work);
243 n_hdlc->tty_for_write_work = tty;
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 */
n_hdlc_send_frames(struct n_hdlc * n_hdlc,struct tty_struct * tty)266 static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
267 {
268 struct n_hdlc_buf *tbuf;
269 ssize_t actual;
270
271 check_again:
272 scoped_guard(spinlock_irqsave, &n_hdlc->tx_buf_list.spinlock) {
273 if (n_hdlc->tbusy) {
274 n_hdlc->woke_up = true;
275 return;
276 }
277 n_hdlc->tbusy = true;
278 n_hdlc->woke_up = false;
279 }
280
281 tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
282 while (tbuf) {
283 pr_debug("sending frame %p, count=%zu\n", tbuf, tbuf->count);
284
285 /* Send the next block of data to device */
286 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
287 actual = tty->ops->write(tty, tbuf->buf, tbuf->count);
288
289 /* rollback was possible and has been done */
290 if (actual == -ERESTARTSYS) {
291 n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
292 break;
293 }
294 /* if transmit error, throw frame away by */
295 /* pretending it was accepted by driver */
296 if (actual < 0)
297 actual = tbuf->count;
298
299 if (actual == tbuf->count) {
300 pr_debug("frame %p completed\n", tbuf);
301
302 /* free current transmit buffer */
303 n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf);
304
305 /* wait up sleeping writers */
306 wake_up_interruptible(&tty->write_wait);
307
308 /* get next pending transmit buffer */
309 tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
310 } else {
311 pr_debug("frame %p pending\n", tbuf);
312
313 /*
314 * the buffer was not accepted by driver,
315 * return it back into tx queue
316 */
317 n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
318 break;
319 }
320 }
321
322 if (!tbuf)
323 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
324
325 /* Clear the re-entry flag */
326 scoped_guard(spinlock_irqsave, &n_hdlc->tx_buf_list.spinlock)
327 n_hdlc->tbusy = false;
328
329 if (n_hdlc->woke_up)
330 goto check_again;
331 } /* end of n_hdlc_send_frames() */
332
333 /**
334 * n_hdlc_tty_write_work - Asynchronous callback for transmit wakeup
335 * @work: pointer to work_struct
336 *
337 * Called when low level device driver can accept more send data.
338 */
n_hdlc_tty_write_work(struct work_struct * work)339 static void n_hdlc_tty_write_work(struct work_struct *work)
340 {
341 struct n_hdlc *n_hdlc = container_of(work, struct n_hdlc, write_work);
342 struct tty_struct *tty = n_hdlc->tty_for_write_work;
343
344 n_hdlc_send_frames(n_hdlc, tty);
345 } /* end of n_hdlc_tty_write_work() */
346
347 /**
348 * n_hdlc_tty_wakeup - Callback for transmit wakeup
349 * @tty: pointer to associated tty instance data
350 *
351 * Called when low level device driver can accept more send data.
352 */
n_hdlc_tty_wakeup(struct tty_struct * tty)353 static void n_hdlc_tty_wakeup(struct tty_struct *tty)
354 {
355 struct n_hdlc *n_hdlc = tty->disc_data;
356
357 schedule_work(&n_hdlc->write_work);
358 } /* end of n_hdlc_tty_wakeup() */
359
360 /**
361 * n_hdlc_tty_receive - Called by tty driver when receive data is available
362 * @tty: pointer to tty instance data
363 * @data: pointer to received data
364 * @flags: pointer to flags for data
365 * @count: count of received data in bytes
366 *
367 * Called by tty low level driver when receive data is available. Data is
368 * interpreted as one HDLC frame.
369 */
n_hdlc_tty_receive(struct tty_struct * tty,const u8 * data,const u8 * flags,size_t count)370 static void n_hdlc_tty_receive(struct tty_struct *tty, const u8 *data,
371 const u8 *flags, size_t count)
372 {
373 register struct n_hdlc *n_hdlc = tty->disc_data;
374 register struct n_hdlc_buf *buf;
375
376 pr_debug("%s() called count=%zu\n", __func__, count);
377
378 if (count > maxframe) {
379 pr_debug("rx count>maxframesize, data discarded\n");
380 return;
381 }
382
383 /* get a free HDLC buffer */
384 buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
385 if (!buf) {
386 /*
387 * no buffers in free list, attempt to allocate another rx
388 * buffer unless the maximum count has been reached
389 */
390 if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT)
391 buf = kmalloc_flex(*buf, buf, maxframe, GFP_ATOMIC);
392 }
393
394 if (!buf) {
395 pr_debug("no more rx buffers, data discarded\n");
396 return;
397 }
398
399 /* copy received data to HDLC buffer */
400 memcpy(buf->buf, data, count);
401 buf->count = count;
402
403 /* add HDLC buffer to list of received frames */
404 n_hdlc_buf_put(&n_hdlc->rx_buf_list, buf);
405
406 /* wake up any blocked reads and perform async signalling */
407 wake_up_interruptible(&tty->read_wait);
408 if (tty->fasync != NULL)
409 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
410
411 } /* end of n_hdlc_tty_receive() */
412
413 /**
414 * n_hdlc_tty_read - Called to retrieve one frame of data (if available)
415 * @tty: pointer to tty instance data
416 * @file: pointer to open file object
417 * @kbuf: pointer to returned data buffer
418 * @nr: size of returned data buffer
419 * @cookie: stored rbuf from previous run
420 * @offset: offset into the data buffer
421 *
422 * Returns the number of bytes returned or error code.
423 */
n_hdlc_tty_read(struct tty_struct * tty,struct file * file,u8 * kbuf,size_t nr,void ** cookie,unsigned long offset)424 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
425 u8 *kbuf, size_t nr, void **cookie,
426 unsigned long offset)
427 {
428 struct n_hdlc *n_hdlc = tty->disc_data;
429 int ret = 0;
430 struct n_hdlc_buf *rbuf;
431 DECLARE_WAITQUEUE(wait, current);
432
433 /* Is this a repeated call for an rbuf we already found earlier? */
434 rbuf = *cookie;
435 if (rbuf)
436 goto have_rbuf;
437
438 add_wait_queue(&tty->read_wait, &wait);
439
440 for (;;) {
441 if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
442 ret = -EIO;
443 break;
444 }
445 if (tty_hung_up_p(file))
446 break;
447
448 set_current_state(TASK_INTERRUPTIBLE);
449
450 rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
451 if (rbuf)
452 break;
453
454 /* no data */
455 if (tty_io_nonblock(tty, file)) {
456 ret = -EAGAIN;
457 break;
458 }
459
460 schedule();
461
462 if (signal_pending(current)) {
463 ret = -EINTR;
464 break;
465 }
466 }
467
468 remove_wait_queue(&tty->read_wait, &wait);
469 __set_current_state(TASK_RUNNING);
470
471 if (!rbuf)
472 return ret;
473 *cookie = rbuf;
474
475 have_rbuf:
476 /* Have we used it up entirely? */
477 if (offset >= rbuf->count)
478 goto done_with_rbuf;
479
480 /* More data to go, but can't copy any more? EOVERFLOW */
481 ret = -EOVERFLOW;
482 if (!nr)
483 goto done_with_rbuf;
484
485 /* Copy as much data as possible */
486 ret = rbuf->count - offset;
487 if (ret > nr)
488 ret = nr;
489 memcpy(kbuf, rbuf->buf+offset, ret);
490 offset += ret;
491
492 /* If we still have data left, we leave the rbuf in the cookie */
493 if (offset < rbuf->count)
494 return ret;
495
496 done_with_rbuf:
497 *cookie = NULL;
498
499 if (n_hdlc->rx_free_buf_list.count > DEFAULT_RX_BUF_COUNT)
500 kfree(rbuf);
501 else
502 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
503
504 return ret;
505
506 } /* end of n_hdlc_tty_read() */
507
508 /**
509 * n_hdlc_tty_write - write a single frame of data to device
510 * @tty: pointer to associated tty device instance data
511 * @file: pointer to file object data
512 * @data: pointer to transmit data (one frame)
513 * @count: size of transmit frame in bytes
514 *
515 * Returns the number of bytes written (or error code).
516 */
n_hdlc_tty_write(struct tty_struct * tty,struct file * file,const u8 * data,size_t count)517 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
518 const u8 *data, size_t count)
519 {
520 struct n_hdlc *n_hdlc = tty->disc_data;
521 DECLARE_WAITQUEUE(wait, current);
522 struct n_hdlc_buf *tbuf;
523 ssize_t error = 0;
524
525 pr_debug("%s() called count=%zd\n", __func__, count);
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 * @cmd: IOCTL command code
576 * @arg: argument for IOCTL call (cmd dependent)
577 *
578 * Returns command dependent result.
579 */
n_hdlc_tty_ioctl(struct tty_struct * tty,unsigned int cmd,unsigned long arg)580 static int n_hdlc_tty_ioctl(struct tty_struct *tty, unsigned int cmd,
581 unsigned long arg)
582 {
583 struct n_hdlc *n_hdlc = tty->disc_data;
584 int count;
585 struct n_hdlc_buf *buf = NULL;
586
587 pr_debug("%s() called %d\n", __func__, cmd);
588
589 switch (cmd) {
590 case FIONREAD:
591 /* report count of read data available */
592 /* in next available frame (if any) */
593 scoped_guard(spinlock_irqsave, &n_hdlc->rx_buf_list.spinlock) {
594 buf = list_first_entry_or_null(&n_hdlc->rx_buf_list.list,
595 struct n_hdlc_buf, list_item);
596 if (buf)
597 count = buf->count;
598 else
599 count = 0;
600 }
601 return put_user(count, (int __user *)arg);
602
603 case TIOCOUTQ:
604 /* get the pending tx byte count in the driver */
605 count = tty_chars_in_buffer(tty);
606 /* add size of next output frame in queue */
607 scoped_guard(spinlock_irqsave, &n_hdlc->tx_buf_list.spinlock) {
608 buf = list_first_entry_or_null(&n_hdlc->tx_buf_list.list,
609 struct n_hdlc_buf, list_item);
610 if (buf)
611 count += buf->count;
612 }
613 return put_user(count, (int __user *)arg);
614
615 case TCFLSH:
616 switch (arg) {
617 case TCIOFLUSH:
618 case TCOFLUSH:
619 flush_tx_queue(tty);
620 }
621 fallthrough; /* to default */
622
623 default:
624 return n_tty_ioctl_helper(tty, cmd, arg);
625 }
626 } /* end of n_hdlc_tty_ioctl() */
627
628 /**
629 * n_hdlc_tty_poll - TTY callback for poll system call
630 * @tty: pointer to tty instance data
631 * @filp: pointer to open file object for device
632 * @wait: wait queue for operations
633 *
634 * Determine which operations (read/write) will not block and return info
635 * to caller.
636 * Returns a bit mask containing info on which ops will not block.
637 */
n_hdlc_tty_poll(struct tty_struct * tty,struct file * filp,poll_table * wait)638 static __poll_t n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
639 poll_table *wait)
640 {
641 struct n_hdlc *n_hdlc = tty->disc_data;
642 __poll_t mask = 0;
643
644 /*
645 * queue the current process into any wait queue that may awaken in the
646 * future (read and write)
647 */
648 poll_wait(filp, &tty->read_wait, wait);
649 poll_wait(filp, &tty->write_wait, wait);
650
651 /* set bits for operations that won't block */
652 if (!list_empty(&n_hdlc->rx_buf_list.list))
653 mask |= EPOLLIN | EPOLLRDNORM; /* readable */
654 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
655 mask |= EPOLLHUP;
656 if (tty_hung_up_p(filp))
657 mask |= EPOLLHUP;
658 if (!tty_is_writelocked(tty) &&
659 !list_empty(&n_hdlc->tx_free_buf_list.list))
660 mask |= EPOLLOUT | EPOLLWRNORM; /* writable */
661
662 return mask;
663 } /* end of n_hdlc_tty_poll() */
664
n_hdlc_alloc_buf(struct n_hdlc_buf_list * list,unsigned int count,const char * name)665 static void n_hdlc_alloc_buf(struct n_hdlc_buf_list *list, unsigned int count,
666 const char *name)
667 {
668 struct n_hdlc_buf *buf;
669 unsigned int i;
670
671 for (i = 0; i < count; i++) {
672 buf = kmalloc_flex(*buf, buf, maxframe);
673 if (!buf) {
674 pr_debug("%s(), kmalloc() failed for %s buffer %u\n",
675 __func__, name, i);
676 return;
677 }
678 n_hdlc_buf_put(list, buf);
679 }
680 }
681
682 /**
683 * n_hdlc_alloc - allocate an n_hdlc instance data structure
684 *
685 * Returns a pointer to newly created structure if success, otherwise %NULL
686 */
n_hdlc_alloc(void)687 static struct n_hdlc *n_hdlc_alloc(void)
688 {
689 struct n_hdlc *n_hdlc = kzalloc_obj(*n_hdlc);
690
691 if (!n_hdlc)
692 return NULL;
693
694 spin_lock_init(&n_hdlc->rx_free_buf_list.spinlock);
695 spin_lock_init(&n_hdlc->tx_free_buf_list.spinlock);
696 spin_lock_init(&n_hdlc->rx_buf_list.spinlock);
697 spin_lock_init(&n_hdlc->tx_buf_list.spinlock);
698
699 INIT_LIST_HEAD(&n_hdlc->rx_free_buf_list.list);
700 INIT_LIST_HEAD(&n_hdlc->tx_free_buf_list.list);
701 INIT_LIST_HEAD(&n_hdlc->rx_buf_list.list);
702 INIT_LIST_HEAD(&n_hdlc->tx_buf_list.list);
703
704 n_hdlc_alloc_buf(&n_hdlc->rx_free_buf_list, DEFAULT_RX_BUF_COUNT, "rx");
705 n_hdlc_alloc_buf(&n_hdlc->tx_free_buf_list, DEFAULT_TX_BUF_COUNT, "tx");
706
707 return n_hdlc;
708
709 } /* end of n_hdlc_alloc() */
710
711 /**
712 * n_hdlc_buf_return - put the HDLC buffer after the head of the specified list
713 * @buf_list: pointer to the buffer list
714 * @buf: pointer to the buffer
715 */
n_hdlc_buf_return(struct n_hdlc_buf_list * buf_list,struct n_hdlc_buf * buf)716 static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
717 struct n_hdlc_buf *buf)
718 {
719 guard(spinlock_irqsave)(&buf_list->spinlock);
720
721 list_add(&buf->list_item, &buf_list->list);
722 buf_list->count++;
723 }
724
725 /**
726 * n_hdlc_buf_put - add specified HDLC buffer to tail of specified list
727 * @buf_list: pointer to buffer list
728 * @buf: pointer to buffer
729 */
n_hdlc_buf_put(struct n_hdlc_buf_list * buf_list,struct n_hdlc_buf * buf)730 static void n_hdlc_buf_put(struct n_hdlc_buf_list *buf_list,
731 struct n_hdlc_buf *buf)
732 {
733 guard(spinlock_irqsave)(&buf_list->spinlock);
734
735 list_add_tail(&buf->list_item, &buf_list->list);
736 buf_list->count++;
737 } /* end of n_hdlc_buf_put() */
738
739 /**
740 * n_hdlc_buf_get - remove and return an HDLC buffer from list
741 * @buf_list: pointer to HDLC buffer list
742 *
743 * Remove and return an HDLC buffer from the head of the specified HDLC buffer
744 * list.
745 * Returns a pointer to HDLC buffer if available, otherwise %NULL.
746 */
n_hdlc_buf_get(struct n_hdlc_buf_list * buf_list)747 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *buf_list)
748 {
749 struct n_hdlc_buf *buf;
750
751 guard(spinlock_irqsave)(&buf_list->spinlock);
752
753 buf = list_first_entry_or_null(&buf_list->list,
754 struct n_hdlc_buf, list_item);
755 if (buf) {
756 list_del(&buf->list_item);
757 buf_list->count--;
758 }
759
760 return buf;
761 } /* end of n_hdlc_buf_get() */
762
763 static struct tty_ldisc_ops n_hdlc_ldisc = {
764 .owner = THIS_MODULE,
765 .num = N_HDLC,
766 .name = "hdlc",
767 .open = n_hdlc_tty_open,
768 .close = n_hdlc_tty_close,
769 .read = n_hdlc_tty_read,
770 .write = n_hdlc_tty_write,
771 .ioctl = n_hdlc_tty_ioctl,
772 .poll = n_hdlc_tty_poll,
773 .receive_buf = n_hdlc_tty_receive,
774 .write_wakeup = n_hdlc_tty_wakeup,
775 .flush_buffer = flush_rx_queue,
776 };
777
n_hdlc_init(void)778 static int __init n_hdlc_init(void)
779 {
780 int status;
781
782 /* range check maxframe arg */
783 maxframe = clamp(maxframe, 4096, MAX_HDLC_FRAME_SIZE);
784
785 status = tty_register_ldisc(&n_hdlc_ldisc);
786 if (!status)
787 pr_info("N_HDLC line discipline registered with maxframe=%d\n",
788 maxframe);
789 else
790 pr_err("N_HDLC: error registering line discipline: %d\n",
791 status);
792
793 return status;
794
795 } /* end of init_module() */
796
n_hdlc_exit(void)797 static void __exit n_hdlc_exit(void)
798 {
799 tty_unregister_ldisc(&n_hdlc_ldisc);
800 }
801
802 module_init(n_hdlc_init);
803 module_exit(n_hdlc_exit);
804
805 MODULE_DESCRIPTION("HDLC line discipline support");
806 MODULE_LICENSE("GPL");
807 MODULE_AUTHOR("Paul Fulghum paulkf@microgate.com");
808 module_param(maxframe, int, 0);
809 MODULE_ALIAS_LDISC(N_HDLC);
810