1 // SPDX-License-Identifier: GPL-1.0+
2 /* generic HDLC line discipline for Linux
4 * Written by Paul Fulghum paulkf@microgate.com
5 * for Microgate Corporation
7 * Microgate and SyncLink are registered trademarks of Microgate Corporation
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>
13 * Original release 01/11/99
15 * This module implements the tty line discipline N_HDLC for use with
16 * tty device drivers that support bit-synchronous HDLC communications.
18 * All HDLC data is frame oriented which means:
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.
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.
37 * The HDLC line discipline queues the receive frames in separate
38 * buffers so complete receive frames can be returned by the
41 * 3. tty read calls returns an entire frame of data or nothing.
43 * 4. all send and receive data is considered raw. No processing
44 * or translation is performed by the line discipline, regardless
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).
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).
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
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.
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.
79 #define HDLC_MAGIC 0x239e
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>
90 #include <linux/poll.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 */
99 #include <linux/bitops.h>
101 #include <asm/termios.h>
102 #include <linux/uaccess.h>
105 * Buffers for individual HDLC frames
107 #define MAX_HDLC_FRAME_SIZE 65535
108 #define DEFAULT_RX_BUF_COUNT 10
109 #define MAX_RX_BUF_COUNT 60
110 #define DEFAULT_TX_BUF_COUNT 3
113 struct list_head list_item;
118 struct n_hdlc_buf_list {
119 struct list_head list;
125 * struct n_hdlc - per device instance data structure
126 * @magic: magic value for structure
127 * @tbusy: reentrancy flag for tx wakeup code
128 * @woke_up: tx wakeup needs to be run again as it was called while @tbusy
129 * @tx_buf_list: list of pending transmit frame buffers
130 * @rx_buf_list: list of received frame buffers
131 * @tx_free_buf_list: list unused transmit frame buffers
132 * @rx_free_buf_list: list unused received frame buffers
138 struct n_hdlc_buf_list tx_buf_list;
139 struct n_hdlc_buf_list rx_buf_list;
140 struct n_hdlc_buf_list tx_free_buf_list;
141 struct n_hdlc_buf_list rx_free_buf_list;
142 struct work_struct write_work;
143 struct tty_struct *tty_for_write_work;
147 * HDLC buffer list manipulation functions
149 static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
150 struct n_hdlc_buf *buf);
151 static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
152 struct n_hdlc_buf *buf);
153 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
155 /* Local functions */
157 static struct n_hdlc *n_hdlc_alloc(void);
158 static void n_hdlc_tty_write_work(struct work_struct *work);
160 /* max frame size for memory allocations */
161 static int maxframe = 4096;
163 static void flush_rx_queue(struct tty_struct *tty)
165 struct n_hdlc *n_hdlc = tty->disc_data;
166 struct n_hdlc_buf *buf;
168 while ((buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list)))
169 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, buf);
172 static void flush_tx_queue(struct tty_struct *tty)
174 struct n_hdlc *n_hdlc = tty->disc_data;
175 struct n_hdlc_buf *buf;
177 while ((buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list)))
178 n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, buf);
181 static void n_hdlc_free_buf_list(struct n_hdlc_buf_list *list)
183 struct n_hdlc_buf *buf;
186 buf = n_hdlc_buf_get(list);
192 * n_hdlc_tty_close - line discipline close
193 * @tty: pointer to tty info structure
195 * Called when the line discipline is changed to something
196 * else, the tty is closed, or the tty detects a hangup.
198 static void n_hdlc_tty_close(struct tty_struct *tty)
200 struct n_hdlc *n_hdlc = tty->disc_data;
202 if (n_hdlc->magic != HDLC_MAGIC) {
203 pr_warn("n_hdlc: trying to close unopened tty!\n");
206 #if defined(TTY_NO_WRITE_SPLIT)
207 clear_bit(TTY_NO_WRITE_SPLIT, &tty->flags);
209 tty->disc_data = NULL;
211 /* Ensure that the n_hdlcd process is not hanging on select()/poll() */
212 wake_up_interruptible(&tty->read_wait);
213 wake_up_interruptible(&tty->write_wait);
215 cancel_work_sync(&n_hdlc->write_work);
217 n_hdlc_free_buf_list(&n_hdlc->rx_free_buf_list);
218 n_hdlc_free_buf_list(&n_hdlc->tx_free_buf_list);
219 n_hdlc_free_buf_list(&n_hdlc->rx_buf_list);
220 n_hdlc_free_buf_list(&n_hdlc->tx_buf_list);
222 } /* end of n_hdlc_tty_close() */
225 * n_hdlc_tty_open - called when line discipline changed to n_hdlc
226 * @tty: pointer to tty info structure
228 * Returns 0 if success, otherwise error code
230 static int n_hdlc_tty_open(struct tty_struct *tty)
232 struct n_hdlc *n_hdlc = tty->disc_data;
234 pr_debug("%s() called (device=%s)\n", __func__, tty->name);
236 /* There should not be an existing table for this slot. */
238 pr_err("%s: tty already associated!\n", __func__);
242 n_hdlc = n_hdlc_alloc();
244 pr_err("%s: n_hdlc_alloc failed\n", __func__);
248 INIT_WORK(&n_hdlc->write_work, n_hdlc_tty_write_work);
249 n_hdlc->tty_for_write_work = tty;
250 tty->disc_data = n_hdlc;
251 tty->receive_room = 65536;
253 /* change tty_io write() to not split large writes into 8K chunks */
254 set_bit(TTY_NO_WRITE_SPLIT, &tty->flags);
256 /* flush receive data from driver */
257 tty_driver_flush_buffer(tty);
261 } /* end of n_tty_hdlc_open() */
264 * n_hdlc_send_frames - send frames on pending send buffer list
265 * @n_hdlc: pointer to ldisc instance data
266 * @tty: pointer to tty instance data
268 * Send frames on pending send buffer list until the driver does not accept a
269 * frame (busy) this function is called after adding a frame to the send buffer
270 * list and by the tty wakeup callback.
272 static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
276 struct n_hdlc_buf *tbuf;
280 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
282 n_hdlc->woke_up = true;
283 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
286 n_hdlc->tbusy = true;
287 n_hdlc->woke_up = false;
288 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
290 tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
292 pr_debug("sending frame %p, count=%d\n", tbuf, tbuf->count);
294 /* Send the next block of data to device */
295 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
296 actual = tty->ops->write(tty, tbuf->buf, tbuf->count);
298 /* rollback was possible and has been done */
299 if (actual == -ERESTARTSYS) {
300 n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
303 /* if transmit error, throw frame away by */
304 /* pretending it was accepted by driver */
306 actual = tbuf->count;
308 if (actual == tbuf->count) {
309 pr_debug("frame %p completed\n", tbuf);
311 /* free current transmit buffer */
312 n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf);
314 /* wait up sleeping writers */
315 wake_up_interruptible(&tty->write_wait);
317 /* get next pending transmit buffer */
318 tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
320 pr_debug("frame %p pending\n", tbuf);
323 * the buffer was not accepted by driver,
324 * return it back into tx queue
326 n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
332 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
334 /* Clear the re-entry flag */
335 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
336 n_hdlc->tbusy = false;
337 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
341 } /* end of n_hdlc_send_frames() */
344 * n_hdlc_tty_write_work - Asynchronous callback for transmit wakeup
345 * @work: pointer to work_struct
347 * Called when low level device driver can accept more send data.
349 static void n_hdlc_tty_write_work(struct work_struct *work)
351 struct n_hdlc *n_hdlc = container_of(work, struct n_hdlc, write_work);
352 struct tty_struct *tty = n_hdlc->tty_for_write_work;
354 n_hdlc_send_frames(n_hdlc, tty);
355 } /* end of n_hdlc_tty_write_work() */
358 * n_hdlc_tty_wakeup - Callback for transmit wakeup
359 * @tty: pointer to associated tty instance data
361 * Called when low level device driver can accept more send data.
363 static void n_hdlc_tty_wakeup(struct tty_struct *tty)
365 struct n_hdlc *n_hdlc = tty->disc_data;
367 schedule_work(&n_hdlc->write_work);
368 } /* end of n_hdlc_tty_wakeup() */
371 * n_hdlc_tty_receive - Called by tty driver when receive data is available
372 * @tty: pointer to tty instance data
373 * @data: pointer to received data
374 * @flags: pointer to flags for data
375 * @count: count of received data in bytes
377 * Called by tty low level driver when receive data is available. Data is
378 * interpreted as one HDLC frame.
380 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
381 char *flags, int count)
383 register struct n_hdlc *n_hdlc = tty->disc_data;
384 register struct n_hdlc_buf *buf;
386 pr_debug("%s() called count=%d\n", __func__, count);
388 /* verify line is using HDLC discipline */
389 if (n_hdlc->magic != HDLC_MAGIC) {
390 pr_err("line not using HDLC discipline\n");
394 if (count > maxframe) {
395 pr_debug("rx count>maxframesize, data discarded\n");
399 /* get a free HDLC buffer */
400 buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
403 * no buffers in free list, attempt to allocate another rx
404 * buffer unless the maximum count has been reached
406 if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT)
407 buf = kmalloc(struct_size(buf, buf, maxframe),
412 pr_debug("no more rx buffers, data discarded\n");
416 /* copy received data to HDLC buffer */
417 memcpy(buf->buf, data, count);
420 /* add HDLC buffer to list of received frames */
421 n_hdlc_buf_put(&n_hdlc->rx_buf_list, buf);
423 /* wake up any blocked reads and perform async signalling */
424 wake_up_interruptible(&tty->read_wait);
425 if (tty->fasync != NULL)
426 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
428 } /* end of n_hdlc_tty_receive() */
431 * n_hdlc_tty_read - Called to retrieve one frame of data (if available)
432 * @tty: pointer to tty instance data
433 * @file: pointer to open file object
434 * @buf: pointer to returned data buffer
435 * @nr: size of returned data buffer
437 * Returns the number of bytes returned or error code.
439 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
440 __u8 *kbuf, size_t nr,
441 void **cookie, unsigned long offset)
443 struct n_hdlc *n_hdlc = tty->disc_data;
445 struct n_hdlc_buf *rbuf;
446 DECLARE_WAITQUEUE(wait, current);
448 /* Is this a repeated call for an rbuf we already found earlier? */
453 add_wait_queue(&tty->read_wait, &wait);
456 if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
460 if (tty_hung_up_p(file))
463 set_current_state(TASK_INTERRUPTIBLE);
465 rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
470 if (tty_io_nonblock(tty, file)) {
477 if (signal_pending(current)) {
483 remove_wait_queue(&tty->read_wait, &wait);
484 __set_current_state(TASK_RUNNING);
491 /* Have we used it up entirely? */
492 if (offset >= rbuf->count)
495 /* More data to go, but can't copy any more? EOVERFLOW */
500 /* Copy as much data as possible */
501 ret = rbuf->count - offset;
504 memcpy(kbuf, rbuf->buf+offset, ret);
507 /* If we still have data left, we leave the rbuf in the cookie */
508 if (offset < rbuf->count)
514 if (n_hdlc->rx_free_buf_list.count > DEFAULT_RX_BUF_COUNT)
517 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
521 } /* end of n_hdlc_tty_read() */
524 * n_hdlc_tty_write - write a single frame of data to device
525 * @tty: pointer to associated tty device instance data
526 * @file: pointer to file object data
527 * @data: pointer to transmit data (one frame)
528 * @count: size of transmit frame in bytes
530 * Returns the number of bytes written (or error code).
532 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
533 const unsigned char *data, size_t count)
535 struct n_hdlc *n_hdlc = tty->disc_data;
537 DECLARE_WAITQUEUE(wait, current);
538 struct n_hdlc_buf *tbuf;
540 pr_debug("%s() called count=%zd\n", __func__, count);
542 if (n_hdlc->magic != HDLC_MAGIC)
545 /* verify frame size */
546 if (count > maxframe) {
547 pr_debug("%s: truncating user packet from %zu to %d\n",
548 __func__, count, maxframe);
552 add_wait_queue(&tty->write_wait, &wait);
555 set_current_state(TASK_INTERRUPTIBLE);
557 tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
561 if (tty_io_nonblock(tty, file)) {
567 if (signal_pending(current)) {
573 __set_current_state(TASK_RUNNING);
574 remove_wait_queue(&tty->write_wait, &wait);
577 /* Retrieve the user's buffer */
578 memcpy(tbuf->buf, data, count);
581 tbuf->count = error = count;
582 n_hdlc_buf_put(&n_hdlc->tx_buf_list, tbuf);
583 n_hdlc_send_frames(n_hdlc, tty);
588 } /* end of n_hdlc_tty_write() */
591 * n_hdlc_tty_ioctl - process IOCTL system call for the tty device.
592 * @tty: pointer to tty instance data
593 * @file: pointer to open file object for device
594 * @cmd: IOCTL command code
595 * @arg: argument for IOCTL call (cmd dependent)
597 * Returns command dependent result.
599 static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
600 unsigned int cmd, unsigned long arg)
602 struct n_hdlc *n_hdlc = tty->disc_data;
606 struct n_hdlc_buf *buf = NULL;
608 pr_debug("%s() called %d\n", __func__, cmd);
610 /* Verify the status of the device */
611 if (n_hdlc->magic != HDLC_MAGIC)
616 /* report count of read data available */
617 /* in next available frame (if any) */
618 spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock, flags);
619 buf = list_first_entry_or_null(&n_hdlc->rx_buf_list.list,
620 struct n_hdlc_buf, list_item);
625 spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock, flags);
626 error = put_user(count, (int __user *)arg);
630 /* get the pending tx byte count in the driver */
631 count = tty_chars_in_buffer(tty);
632 /* add size of next output frame in queue */
633 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
634 buf = list_first_entry_or_null(&n_hdlc->tx_buf_list.list,
635 struct n_hdlc_buf, list_item);
638 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
639 error = put_user(count, (int __user *)arg);
648 fallthrough; /* to default */
651 error = n_tty_ioctl_helper(tty, file, cmd, arg);
656 } /* end of n_hdlc_tty_ioctl() */
659 * n_hdlc_tty_poll - TTY callback for poll system call
660 * @tty: pointer to tty instance data
661 * @filp: pointer to open file object for device
662 * @wait: wait queue for operations
664 * Determine which operations (read/write) will not block and return info
666 * Returns a bit mask containing info on which ops will not block.
668 static __poll_t n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
671 struct n_hdlc *n_hdlc = tty->disc_data;
674 if (n_hdlc->magic != HDLC_MAGIC)
678 * queue the current process into any wait queue that may awaken in the
679 * future (read and write)
681 poll_wait(filp, &tty->read_wait, wait);
682 poll_wait(filp, &tty->write_wait, wait);
684 /* set bits for operations that won't block */
685 if (!list_empty(&n_hdlc->rx_buf_list.list))
686 mask |= EPOLLIN | EPOLLRDNORM; /* readable */
687 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
689 if (tty_hung_up_p(filp))
691 if (!tty_is_writelocked(tty) &&
692 !list_empty(&n_hdlc->tx_free_buf_list.list))
693 mask |= EPOLLOUT | EPOLLWRNORM; /* writable */
696 } /* end of n_hdlc_tty_poll() */
698 static void n_hdlc_alloc_buf(struct n_hdlc_buf_list *list, unsigned int count,
701 struct n_hdlc_buf *buf;
704 for (i = 0; i < count; i++) {
705 buf = kmalloc(struct_size(buf, buf, maxframe), GFP_KERNEL);
707 pr_debug("%s(), kmalloc() failed for %s buffer %u\n",
711 n_hdlc_buf_put(list, buf);
716 * n_hdlc_alloc - allocate an n_hdlc instance data structure
718 * Returns a pointer to newly created structure if success, otherwise %NULL
720 static struct n_hdlc *n_hdlc_alloc(void)
722 struct n_hdlc *n_hdlc = kzalloc(sizeof(*n_hdlc), GFP_KERNEL);
727 spin_lock_init(&n_hdlc->rx_free_buf_list.spinlock);
728 spin_lock_init(&n_hdlc->tx_free_buf_list.spinlock);
729 spin_lock_init(&n_hdlc->rx_buf_list.spinlock);
730 spin_lock_init(&n_hdlc->tx_buf_list.spinlock);
732 INIT_LIST_HEAD(&n_hdlc->rx_free_buf_list.list);
733 INIT_LIST_HEAD(&n_hdlc->tx_free_buf_list.list);
734 INIT_LIST_HEAD(&n_hdlc->rx_buf_list.list);
735 INIT_LIST_HEAD(&n_hdlc->tx_buf_list.list);
737 n_hdlc_alloc_buf(&n_hdlc->rx_free_buf_list, DEFAULT_RX_BUF_COUNT, "rx");
738 n_hdlc_alloc_buf(&n_hdlc->tx_free_buf_list, DEFAULT_TX_BUF_COUNT, "tx");
740 /* Initialize the control block */
741 n_hdlc->magic = HDLC_MAGIC;
745 } /* end of n_hdlc_alloc() */
748 * n_hdlc_buf_return - put the HDLC buffer after the head of the specified list
749 * @buf_list: pointer to the buffer list
750 * @buf: pointer to the buffer
752 static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
753 struct n_hdlc_buf *buf)
757 spin_lock_irqsave(&buf_list->spinlock, flags);
759 list_add(&buf->list_item, &buf_list->list);
762 spin_unlock_irqrestore(&buf_list->spinlock, flags);
766 * n_hdlc_buf_put - add specified HDLC buffer to tail of specified list
767 * @buf_list: pointer to buffer list
768 * @buf: pointer to buffer
770 static void n_hdlc_buf_put(struct n_hdlc_buf_list *buf_list,
771 struct n_hdlc_buf *buf)
775 spin_lock_irqsave(&buf_list->spinlock, flags);
777 list_add_tail(&buf->list_item, &buf_list->list);
780 spin_unlock_irqrestore(&buf_list->spinlock, flags);
781 } /* end of n_hdlc_buf_put() */
784 * n_hdlc_buf_get - remove and return an HDLC buffer from list
785 * @buf_list: pointer to HDLC buffer list
787 * Remove and return an HDLC buffer from the head of the specified HDLC buffer
789 * Returns a pointer to HDLC buffer if available, otherwise %NULL.
791 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *buf_list)
794 struct n_hdlc_buf *buf;
796 spin_lock_irqsave(&buf_list->spinlock, flags);
798 buf = list_first_entry_or_null(&buf_list->list,
799 struct n_hdlc_buf, list_item);
801 list_del(&buf->list_item);
805 spin_unlock_irqrestore(&buf_list->spinlock, flags);
807 } /* end of n_hdlc_buf_get() */
809 static struct tty_ldisc_ops n_hdlc_ldisc = {
810 .owner = THIS_MODULE,
811 .magic = TTY_LDISC_MAGIC,
813 .open = n_hdlc_tty_open,
814 .close = n_hdlc_tty_close,
815 .read = n_hdlc_tty_read,
816 .write = n_hdlc_tty_write,
817 .ioctl = n_hdlc_tty_ioctl,
818 .poll = n_hdlc_tty_poll,
819 .receive_buf = n_hdlc_tty_receive,
820 .write_wakeup = n_hdlc_tty_wakeup,
821 .flush_buffer = flush_rx_queue,
824 static int __init n_hdlc_init(void)
828 /* range check maxframe arg */
829 maxframe = clamp(maxframe, 4096, MAX_HDLC_FRAME_SIZE);
831 status = tty_register_ldisc(N_HDLC, &n_hdlc_ldisc);
833 pr_info("N_HDLC line discipline registered with maxframe=%d\n",
836 pr_err("N_HDLC: error registering line discipline: %d\n",
841 } /* end of init_module() */
843 static void __exit n_hdlc_exit(void)
845 /* Release tty registration of line discipline */
846 int status = tty_unregister_ldisc(N_HDLC);
849 pr_err("N_HDLC: can't unregister line discipline (err = %d)\n",
852 pr_info("N_HDLC: line discipline unregistered\n");
855 module_init(n_hdlc_init);
856 module_exit(n_hdlc_exit);
858 MODULE_LICENSE("GPL");
859 MODULE_AUTHOR("Paul Fulghum paulkf@microgate.com");
860 module_param(maxframe, int, 0);
861 MODULE_ALIAS_LDISC(N_HDLC);