drivers/tty/n_hdlc.c

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