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  * @flags - miscellaneous control flags
 128  * @tty - ptr to TTY structure
 129  * @backup_tty - TTY to use if tty gets closed
 130  * @tbusy - reentrancy flag for tx wakeup code
 131  * @woke_up - FIXME: describe this field
 132  * @tx_buf_list - list of pending transmit frame buffers
 133  * @rx_buf_list - list of received frame buffers
 134  * @tx_free_buf_list - list unused transmit frame buffers
 135  * @rx_free_buf_list - list unused received frame buffers
 136  */
 137 struct n_hdlc {
 138         int                     magic;
 139         __u32                   flags;
 140         struct tty_struct       *tty;
 141         struct tty_struct       *backup_tty;
 142         int                     tbusy;
 143         int                     woke_up;
 144         struct n_hdlc_buf_list  tx_buf_list;
 145         struct n_hdlc_buf_list  rx_buf_list;
 146         struct n_hdlc_buf_list  tx_free_buf_list;
 147         struct n_hdlc_buf_list  rx_free_buf_list;
 148 };
 149
 150 /*
 151  * HDLC buffer list manipulation functions
 152  */
 153 static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
 154                                                 struct n_hdlc_buf *buf);
 155 static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
 156                            struct n_hdlc_buf *buf);
 157 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
 158
 159 /* Local functions */
 160
 161 static struct n_hdlc *n_hdlc_alloc (void);
 162
 163 /* max frame size for memory allocations */
 164 static int maxframe = 4096;
 165
 166 /* TTY callbacks */
 167
 168 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 169                            __u8 __user *buf, size_t nr);
 170 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 171                             const unsigned char *buf, size_t nr);
 172 static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
 173                             unsigned int cmd, unsigned long arg);
 174 static __poll_t n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
 175                                     poll_table *wait);
 176 static int n_hdlc_tty_open(struct tty_struct *tty);
 177 static void n_hdlc_tty_close(struct tty_struct *tty);
 178 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *cp,
 179                                char *fp, int count);
 180 static void n_hdlc_tty_wakeup(struct tty_struct *tty);
 181
 182 #define tty2n_hdlc(tty) ((struct n_hdlc *) ((tty)->disc_data))
 183 #define n_hdlc2tty(n_hdlc)      ((n_hdlc)->tty)
 184
 185 static void flush_rx_queue(struct tty_struct *tty)
 186 {
 187         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 188         struct n_hdlc_buf *buf;
 189
 190         while ((buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list)))
 191                 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, buf);
 192 }
 193
 194 static void flush_tx_queue(struct tty_struct *tty)
 195 {
 196         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 197         struct n_hdlc_buf *buf;
 198
 199         while ((buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list)))
 200                 n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, buf);
 201 }
 202
 203 static struct tty_ldisc_ops n_hdlc_ldisc = {
 204         .owner          = THIS_MODULE,
 205         .magic          = TTY_LDISC_MAGIC,
 206         .name           = "hdlc",
 207         .open           = n_hdlc_tty_open,
 208         .close          = n_hdlc_tty_close,
 209         .read           = n_hdlc_tty_read,
 210         .write          = n_hdlc_tty_write,
 211         .ioctl          = n_hdlc_tty_ioctl,
 212         .poll           = n_hdlc_tty_poll,
 213         .receive_buf    = n_hdlc_tty_receive,
 214         .write_wakeup   = n_hdlc_tty_wakeup,
 215         .flush_buffer   = flush_rx_queue,
 216 };
 217
 218 /**
 219  * n_hdlc_release - release an n_hdlc per device line discipline info structure
 220  * @n_hdlc - per device line discipline info structure
 221  */
 222 static void n_hdlc_release(struct n_hdlc *n_hdlc)
 223 {
 224         struct tty_struct *tty = n_hdlc2tty (n_hdlc);
 225         struct n_hdlc_buf *buf;
 226
 227         /* Ensure that the n_hdlcd process is not hanging on select()/poll() */
 228         wake_up_interruptible (&tty->read_wait);
 229         wake_up_interruptible (&tty->write_wait);
 230
 231         if (tty->disc_data == n_hdlc)
 232                 tty->disc_data = NULL;  /* Break the tty->n_hdlc link */
 233
 234         /* Release transmit and receive buffers */
 235         for(;;) {
 236                 buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
 237                 if (buf) {
 238                         kfree(buf);
 239                 } else
 240                         break;
 241         }
 242         for(;;) {
 243                 buf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
 244                 if (buf) {
 245                         kfree(buf);
 246                 } else
 247                         break;
 248         }
 249         for(;;) {
 250                 buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
 251                 if (buf) {
 252                         kfree(buf);
 253                 } else
 254                         break;
 255         }
 256         for(;;) {
 257                 buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 258                 if (buf) {
 259                         kfree(buf);
 260                 } else
 261                         break;
 262         }
 263         kfree(n_hdlc);
 264
 265 }       /* end of n_hdlc_release() */
 266
 267 /**
 268  * n_hdlc_tty_close - line discipline close
 269  * @tty - pointer to tty info structure
 270  *
 271  * Called when the line discipline is changed to something
 272  * else, the tty is closed, or the tty detects a hangup.
 273  */
 274 static void n_hdlc_tty_close(struct tty_struct *tty)
 275 {
 276         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 277
 278         if (n_hdlc != NULL) {
 279                 if (n_hdlc->magic != HDLC_MAGIC) {
 280                         printk (KERN_WARNING"n_hdlc: trying to close unopened tty!\n");
 281                         return;
 282                 }
 283 #if defined(TTY_NO_WRITE_SPLIT)
 284                 clear_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
 285 #endif
 286                 tty->disc_data = NULL;
 287                 if (tty == n_hdlc->backup_tty)
 288                         n_hdlc->backup_tty = NULL;
 289                 if (tty != n_hdlc->tty)
 290                         return;
 291                 if (n_hdlc->backup_tty) {
 292                         n_hdlc->tty = n_hdlc->backup_tty;
 293                 } else {
 294                         n_hdlc_release (n_hdlc);
 295                 }
 296         }
 297 }       /* end of n_hdlc_tty_close() */
 298
 299 /**
 300  * n_hdlc_tty_open - called when line discipline changed to n_hdlc
 301  * @tty - pointer to tty info structure
 302  *
 303  * Returns 0 if success, otherwise error code
 304  */
 305 static int n_hdlc_tty_open (struct tty_struct *tty)
 306 {
 307         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 308
 309         pr_debug("%s(%d)%s() called (device=%s)\n",
 310                         __FILE__, __LINE__, __func__, tty->name);
 311
 312         /* There should not be an existing table for this slot. */
 313         if (n_hdlc) {
 314                 printk (KERN_ERR"n_hdlc_tty_open:tty already associated!\n" );
 315                 return -EEXIST;
 316         }
 317
 318         n_hdlc = n_hdlc_alloc();
 319         if (!n_hdlc) {
 320                 printk (KERN_ERR "n_hdlc_alloc failed\n");
 321                 return -ENFILE;
 322         }
 323
 324         tty->disc_data = n_hdlc;
 325         n_hdlc->tty    = tty;
 326         tty->receive_room = 65536;
 327
 328 #if defined(TTY_NO_WRITE_SPLIT)
 329         /* change tty_io write() to not split large writes into 8K chunks */
 330         set_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
 331 #endif
 332
 333         /* flush receive data from driver */
 334         tty_driver_flush_buffer(tty);
 335
 336         return 0;
 337
 338 }       /* end of n_tty_hdlc_open() */
 339
 340 /**
 341  * n_hdlc_send_frames - send frames on pending send buffer list
 342  * @n_hdlc - pointer to ldisc instance data
 343  * @tty - pointer to tty instance data
 344  *
 345  * Send frames on pending send buffer list until the driver does not accept a
 346  * frame (busy) this function is called after adding a frame to the send buffer
 347  * list and by the tty wakeup callback.
 348  */
 349 static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
 350 {
 351         register int actual;
 352         unsigned long flags;
 353         struct n_hdlc_buf *tbuf;
 354
 355  check_again:
 356
 357         spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
 358         if (n_hdlc->tbusy) {
 359                 n_hdlc->woke_up = 1;
 360                 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 361                 return;
 362         }
 363         n_hdlc->tbusy = 1;
 364         n_hdlc->woke_up = 0;
 365         spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 366
 367         tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 368         while (tbuf) {
 369                 pr_debug("%s(%d)sending frame %p, count=%d\n",
 370                                 __FILE__, __LINE__, tbuf, tbuf->count);
 371
 372                 /* Send the next block of data to device */
 373                 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 374                 actual = tty->ops->write(tty, tbuf->buf, tbuf->count);
 375
 376                 /* rollback was possible and has been done */
 377                 if (actual == -ERESTARTSYS) {
 378                         n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
 379                         break;
 380                 }
 381                 /* if transmit error, throw frame away by */
 382                 /* pretending it was accepted by driver */
 383                 if (actual < 0)
 384                         actual = tbuf->count;
 385
 386                 if (actual == tbuf->count) {
 387                         pr_debug("%s(%d)frame %p completed\n",
 388                                         __FILE__, __LINE__, tbuf);
 389
 390                         /* free current transmit buffer */
 391                         n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf);
 392
 393                         /* wait up sleeping writers */
 394                         wake_up_interruptible(&tty->write_wait);
 395
 396                         /* get next pending transmit buffer */
 397                         tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 398                 } else {
 399                         pr_debug("%s(%d)frame %p pending\n",
 400                                         __FILE__, __LINE__, tbuf);
 401
 402                         /*
 403                          * the buffer was not accepted by driver,
 404                          * return it back into tx queue
 405                          */
 406                         n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
 407                         break;
 408                 }
 409         }
 410
 411         if (!tbuf)
 412                 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 413
 414         /* Clear the re-entry flag */
 415         spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
 416         n_hdlc->tbusy = 0;
 417         spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 418
 419         if (n_hdlc->woke_up)
 420           goto check_again;
 421 }       /* end of n_hdlc_send_frames() */
 422
 423 /**
 424  * n_hdlc_tty_wakeup - Callback for transmit wakeup
 425  * @tty - pointer to associated tty instance data
 426  *
 427  * Called when low level device driver can accept more send data.
 428  */
 429 static void n_hdlc_tty_wakeup(struct tty_struct *tty)
 430 {
 431         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 432
 433         if (!n_hdlc)
 434                 return;
 435
 436         if (tty != n_hdlc->tty) {
 437                 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 438                 return;
 439         }
 440
 441         n_hdlc_send_frames (n_hdlc, tty);
 442
 443 }       /* end of n_hdlc_tty_wakeup() */
 444
 445 /**
 446  * n_hdlc_tty_receive - Called by tty driver when receive data is available
 447  * @tty - pointer to tty instance data
 448  * @data - pointer to received data
 449  * @flags - pointer to flags for data
 450  * @count - count of received data in bytes
 451  *
 452  * Called by tty low level driver when receive data is available. Data is
 453  * interpreted as one HDLC frame.
 454  */
 455 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
 456                                char *flags, int count)
 457 {
 458         register struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 459         register struct n_hdlc_buf *buf;
 460
 461         pr_debug("%s(%d)%s() called count=%d\n",
 462                         __FILE__, __LINE__, __func__, count);
 463
 464         /* This can happen if stuff comes in on the backup tty */
 465         if (!n_hdlc || tty != n_hdlc->tty)
 466                 return;
 467
 468         /* verify line is using HDLC discipline */
 469         if (n_hdlc->magic != HDLC_MAGIC) {
 470                 printk("%s(%d) line not using HDLC discipline\n",
 471                         __FILE__,__LINE__);
 472                 return;
 473         }
 474
 475         if ( count>maxframe ) {
 476                 pr_debug("%s(%d) rx count>maxframesize, data discarded\n",
 477                                 __FILE__, __LINE__);
 478                 return;
 479         }
 480
 481         /* get a free HDLC buffer */
 482         buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
 483         if (!buf) {
 484                 /* no buffers in free list, attempt to allocate another rx buffer */
 485                 /* unless the maximum count has been reached */
 486                 if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT)
 487                         buf = kmalloc(struct_size(buf, buf, maxframe),
 488                                       GFP_ATOMIC);
 489         }
 490
 491         if (!buf) {
 492                 pr_debug("%s(%d) no more rx buffers, data discarded\n",
 493                                 __FILE__, __LINE__);
 494                 return;
 495         }
 496
 497         /* copy received data to HDLC buffer */
 498         memcpy(buf->buf,data,count);
 499         buf->count=count;
 500
 501         /* add HDLC buffer to list of received frames */
 502         n_hdlc_buf_put(&n_hdlc->rx_buf_list, buf);
 503
 504         /* wake up any blocked reads and perform async signalling */
 505         wake_up_interruptible (&tty->read_wait);
 506         if (n_hdlc->tty->fasync != NULL)
 507                 kill_fasync (&n_hdlc->tty->fasync, SIGIO, POLL_IN);
 508
 509 }       /* end of n_hdlc_tty_receive() */
 510
 511 /**
 512  * n_hdlc_tty_read - Called to retrieve one frame of data (if available)
 513  * @tty - pointer to tty instance data
 514  * @file - pointer to open file object
 515  * @buf - pointer to returned data buffer
 516  * @nr - size of returned data buffer
 517  *
 518  * Returns the number of bytes returned or error code.
 519  */
 520 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 521                            __u8 __user *buf, size_t nr)
 522 {
 523         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 524         int ret = 0;
 525         struct n_hdlc_buf *rbuf;
 526         DECLARE_WAITQUEUE(wait, current);
 527
 528         /* Validate the pointers */
 529         if (!n_hdlc)
 530                 return -EIO;
 531
 532         /* verify user access to buffer */
 533         if (!access_ok(buf, nr)) {
 534                 printk(KERN_WARNING "%s(%d) n_hdlc_tty_read() can't verify user "
 535                 "buffer\n", __FILE__, __LINE__);
 536                 return -EFAULT;
 537         }
 538
 539         add_wait_queue(&tty->read_wait, &wait);
 540
 541         for (;;) {
 542                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
 543                         ret = -EIO;
 544                         break;
 545                 }
 546                 if (tty_hung_up_p(file))
 547                         break;
 548
 549                 set_current_state(TASK_INTERRUPTIBLE);
 550
 551                 rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
 552                 if (rbuf) {
 553                         if (rbuf->count > nr) {
 554                                 /* too large for caller's buffer */
 555                                 ret = -EOVERFLOW;
 556                         } else {
 557                                 __set_current_state(TASK_RUNNING);
 558                                 if (copy_to_user(buf, rbuf->buf, rbuf->count))
 559                                         ret = -EFAULT;
 560                                 else
 561                                         ret = rbuf->count;
 562                         }
 563
 564                         if (n_hdlc->rx_free_buf_list.count >
 565                             DEFAULT_RX_BUF_COUNT)
 566                                 kfree(rbuf);
 567                         else
 568                                 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
 569                         break;
 570                 }
 571
 572                 /* no data */
 573                 if (tty_io_nonblock(tty, file)) {
 574                         ret = -EAGAIN;
 575                         break;
 576                 }
 577
 578                 schedule();
 579
 580                 if (signal_pending(current)) {
 581                         ret = -EINTR;
 582                         break;
 583                 }
 584         }
 585
 586         remove_wait_queue(&tty->read_wait, &wait);
 587         __set_current_state(TASK_RUNNING);
 588
 589         return ret;
 590
 591 }       /* end of n_hdlc_tty_read() */
 592
 593 /**
 594  * n_hdlc_tty_write - write a single frame of data to device
 595  * @tty - pointer to associated tty device instance data
 596  * @file - pointer to file object data
 597  * @data - pointer to transmit data (one frame)
 598  * @count - size of transmit frame in bytes
 599  *
 600  * Returns the number of bytes written (or error code).
 601  */
 602 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 603                             const unsigned char *data, size_t count)
 604 {
 605         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 606         int error = 0;
 607         DECLARE_WAITQUEUE(wait, current);
 608         struct n_hdlc_buf *tbuf;
 609
 610         pr_debug("%s(%d)%s() called count=%zd\n", __FILE__, __LINE__, __func__,
 611                         count);
 612
 613         /* Verify pointers */
 614         if (!n_hdlc)
 615                 return -EIO;
 616
 617         if (n_hdlc->magic != HDLC_MAGIC)
 618                 return -EIO;
 619
 620         /* verify frame size */
 621         if (count > maxframe ) {
 622                 pr_debug("%s: truncating user packet from %zu to %d\n",
 623                                 __func__, count, maxframe);
 624                 count = maxframe;
 625         }
 626
 627         add_wait_queue(&tty->write_wait, &wait);
 628
 629         for (;;) {
 630                 set_current_state(TASK_INTERRUPTIBLE);
 631
 632                 tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
 633                 if (tbuf)
 634                         break;
 635
 636                 if (tty_io_nonblock(tty, file)) {
 637                         error = -EAGAIN;
 638                         break;
 639                 }
 640                 schedule();
 641
 642                 n_hdlc = tty2n_hdlc (tty);
 643                 if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC ||
 644                     tty != n_hdlc->tty) {
 645                         printk("n_hdlc_tty_write: %p invalid after wait!\n", n_hdlc);
 646                         error = -EIO;
 647                         break;
 648                 }
 649
 650                 if (signal_pending(current)) {
 651                         error = -EINTR;
 652                         break;
 653                 }
 654         }
 655
 656         __set_current_state(TASK_RUNNING);
 657         remove_wait_queue(&tty->write_wait, &wait);
 658
 659         if (!error) {
 660                 /* Retrieve the user's buffer */
 661                 memcpy(tbuf->buf, data, count);
 662
 663                 /* Send the data */
 664                 tbuf->count = error = count;
 665                 n_hdlc_buf_put(&n_hdlc->tx_buf_list,tbuf);
 666                 n_hdlc_send_frames(n_hdlc,tty);
 667         }
 668
 669         return error;
 670
 671 }       /* end of n_hdlc_tty_write() */
 672
 673 /**
 674  * n_hdlc_tty_ioctl - process IOCTL system call for the tty device.
 675  * @tty - pointer to tty instance data
 676  * @file - pointer to open file object for device
 677  * @cmd - IOCTL command code
 678  * @arg - argument for IOCTL call (cmd dependent)
 679  *
 680  * Returns command dependent result.
 681  */
 682 static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
 683                             unsigned int cmd, unsigned long arg)
 684 {
 685         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 686         int error = 0;
 687         int count;
 688         unsigned long flags;
 689         struct n_hdlc_buf *buf = NULL;
 690
 691         pr_debug("%s(%d)%s() called %d\n", __FILE__, __LINE__, __func__, cmd);
 692
 693         /* Verify the status of the device */
 694         if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC)
 695                 return -EBADF;
 696
 697         switch (cmd) {
 698         case FIONREAD:
 699                 /* report count of read data available */
 700                 /* in next available frame (if any) */
 701                 spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock,flags);
 702                 buf = list_first_entry_or_null(&n_hdlc->rx_buf_list.list,
 703                                                 struct n_hdlc_buf, list_item);
 704                 if (buf)
 705                         count = buf->count;
 706                 else
 707                         count = 0;
 708                 spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock,flags);
 709                 error = put_user(count, (int __user *)arg);
 710                 break;
 711
 712         case TIOCOUTQ:
 713                 /* get the pending tx byte count in the driver */
 714                 count = tty_chars_in_buffer(tty);
 715                 /* add size of next output frame in queue */
 716                 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock,flags);
 717                 buf = list_first_entry_or_null(&n_hdlc->tx_buf_list.list,
 718                                                 struct n_hdlc_buf, list_item);
 719                 if (buf)
 720                         count += buf->count;
 721                 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock,flags);
 722                 error = put_user(count, (int __user *)arg);
 723                 break;
 724
 725         case TCFLSH:
 726                 switch (arg) {
 727                 case TCIOFLUSH:
 728                 case TCOFLUSH:
 729                         flush_tx_queue(tty);
 730                 }
 731                 /* fall through - to default */
 732
 733         default:
 734                 error = n_tty_ioctl_helper(tty, file, cmd, arg);
 735                 break;
 736         }
 737         return error;
 738
 739 }       /* end of n_hdlc_tty_ioctl() */
 740
 741 /**
 742  * n_hdlc_tty_poll - TTY callback for poll system call
 743  * @tty - pointer to tty instance data
 744  * @filp - pointer to open file object for device
 745  * @poll_table - wait queue for operations
 746  *
 747  * Determine which operations (read/write) will not block and return info
 748  * to caller.
 749  * Returns a bit mask containing info on which ops will not block.
 750  */
 751 static __poll_t n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
 752                                     poll_table *wait)
 753 {
 754         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 755         __poll_t mask = 0;
 756
 757         if (n_hdlc && n_hdlc->magic == HDLC_MAGIC && tty == n_hdlc->tty) {
 758                 /* queue current process into any wait queue that */
 759                 /* may awaken in the future (read and write) */
 760
 761                 poll_wait(filp, &tty->read_wait, wait);
 762                 poll_wait(filp, &tty->write_wait, wait);
 763
 764                 /* set bits for operations that won't block */
 765                 if (!list_empty(&n_hdlc->rx_buf_list.list))
 766                         mask |= EPOLLIN | EPOLLRDNORM;  /* readable */
 767                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 768                         mask |= EPOLLHUP;
 769                 if (tty_hung_up_p(filp))
 770                         mask |= EPOLLHUP;
 771                 if (!tty_is_writelocked(tty) &&
 772                                 !list_empty(&n_hdlc->tx_free_buf_list.list))
 773                         mask |= EPOLLOUT | EPOLLWRNORM; /* writable */
 774         }
 775         return mask;
 776 }       /* end of n_hdlc_tty_poll() */
 777
 778 /**
 779  * n_hdlc_alloc - allocate an n_hdlc instance data structure
 780  *
 781  * Returns a pointer to newly created structure if success, otherwise %NULL
 782  */
 783 static struct n_hdlc *n_hdlc_alloc(void)
 784 {
 785         struct n_hdlc_buf *buf;
 786         int i;
 787         struct n_hdlc *n_hdlc = kzalloc(sizeof(*n_hdlc), GFP_KERNEL);
 788
 789         if (!n_hdlc)
 790                 return NULL;
 791
 792         spin_lock_init(&n_hdlc->rx_free_buf_list.spinlock);
 793         spin_lock_init(&n_hdlc->tx_free_buf_list.spinlock);
 794         spin_lock_init(&n_hdlc->rx_buf_list.spinlock);
 795         spin_lock_init(&n_hdlc->tx_buf_list.spinlock);
 796
 797         INIT_LIST_HEAD(&n_hdlc->rx_free_buf_list.list);
 798         INIT_LIST_HEAD(&n_hdlc->tx_free_buf_list.list);
 799         INIT_LIST_HEAD(&n_hdlc->rx_buf_list.list);
 800         INIT_LIST_HEAD(&n_hdlc->tx_buf_list.list);
 801
 802         /* allocate free rx buffer list */
 803         for(i=0;i<DEFAULT_RX_BUF_COUNT;i++) {
 804                 buf = kmalloc(struct_size(buf, buf, maxframe), GFP_KERNEL);
 805                 if (buf)
 806                         n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,buf);
 807                 else
 808                         pr_debug("%s(%d)%s(), kmalloc() failed for rx buffer %d\n",
 809                                         __FILE__, __LINE__, __func__, i);
 810         }
 811
 812         /* allocate free tx buffer list */
 813         for(i=0;i<DEFAULT_TX_BUF_COUNT;i++) {
 814                 buf = kmalloc(struct_size(buf, buf, maxframe), GFP_KERNEL);
 815                 if (buf)
 816                         n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,buf);
 817                 else
 818                         pr_debug("%s(%d)%s(), kmalloc() failed for tx buffer %d\n",
 819                                         __FILE__, __LINE__, __func__, i);
 820         }
 821
 822         /* Initialize the control block */
 823         n_hdlc->magic  = HDLC_MAGIC;
 824         n_hdlc->flags  = 0;
 825
 826         return n_hdlc;
 827
 828 }       /* end of n_hdlc_alloc() */
 829
 830 /**
 831  * n_hdlc_buf_return - put the HDLC buffer after the head of the specified list
 832  * @buf_list - pointer to the buffer list
 833  * @buf - pointer to the buffer
 834  */
 835 static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
 836                                                 struct n_hdlc_buf *buf)
 837 {
 838         unsigned long flags;
 839
 840         spin_lock_irqsave(&buf_list->spinlock, flags);
 841
 842         list_add(&buf->list_item, &buf_list->list);
 843         buf_list->count++;
 844
 845         spin_unlock_irqrestore(&buf_list->spinlock, flags);
 846 }
 847
 848 /**
 849  * n_hdlc_buf_put - add specified HDLC buffer to tail of specified list
 850  * @buf_list - pointer to buffer list
 851  * @buf - pointer to buffer
 852  */
 853 static void n_hdlc_buf_put(struct n_hdlc_buf_list *buf_list,
 854                            struct n_hdlc_buf *buf)
 855 {
 856         unsigned long flags;
 857
 858         spin_lock_irqsave(&buf_list->spinlock, flags);
 859
 860         list_add_tail(&buf->list_item, &buf_list->list);
 861         buf_list->count++;
 862
 863         spin_unlock_irqrestore(&buf_list->spinlock, flags);
 864 }       /* end of n_hdlc_buf_put() */
 865
 866 /**
 867  * n_hdlc_buf_get - remove and return an HDLC buffer from list
 868  * @buf_list - pointer to HDLC buffer list
 869  *
 870  * Remove and return an HDLC buffer from the head of the specified HDLC buffer
 871  * list.
 872  * Returns a pointer to HDLC buffer if available, otherwise %NULL.
 873  */
 874 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *buf_list)
 875 {
 876         unsigned long flags;
 877         struct n_hdlc_buf *buf;
 878
 879         spin_lock_irqsave(&buf_list->spinlock, flags);
 880
 881         buf = list_first_entry_or_null(&buf_list->list,
 882                                                 struct n_hdlc_buf, list_item);
 883         if (buf) {
 884                 list_del(&buf->list_item);
 885                 buf_list->count--;
 886         }
 887
 888         spin_unlock_irqrestore(&buf_list->spinlock, flags);
 889         return buf;
 890 }       /* end of n_hdlc_buf_get() */
 891
 892 static int __init n_hdlc_init(void)
 893 {
 894         int status;
 895
 896         /* range check maxframe arg */
 897         if (maxframe < 4096)
 898                 maxframe = 4096;
 899         else if (maxframe > 65535)
 900                 maxframe = 65535;
 901
 902         status = tty_register_ldisc(N_HDLC, &n_hdlc_ldisc);
 903         if (!status)
 904                 pr_info("N_HDLC line discipline registered with maxframe=%d\n",
 905                                 maxframe);
 906         else
 907                 pr_err("N_HDLC: error registering line discipline: %d\n",
 908                                 status);
 909
 910         return status;
 911
 912 }       /* end of init_module() */
 913
 914 static void __exit n_hdlc_exit(void)
 915 {
 916         /* Release tty registration of line discipline */
 917         int status = tty_unregister_ldisc(N_HDLC);
 918
 919         if (status)
 920                 pr_err("N_HDLC: can't unregister line discipline (err = %d)\n",
 921                                 status);
 922         else
 923                 pr_info("N_HDLC: line discipline unregistered\n");
 924 }
 925
 926 module_init(n_hdlc_init);
 927 module_exit(n_hdlc_exit);
 928
 929 MODULE_LICENSE("GPL");
 930 MODULE_AUTHOR("Paul Fulghum paulkf@microgate.com");
 931 module_param(maxframe, int, 0);
 932 MODULE_ALIAS_LDISC(N_HDLC);