git.oblomov.eu Git - linux-2.6/blob - drivers/char/n_hdlc.c

   1 /* generic HDLC line discipline for Linux
   2  *
   3  * Written by Paul Fulghum paulkf@microgate.com
   4  * for Microgate Corporation
   5  *
   6  * Microgate and SyncLink are registered trademarks of Microgate Corporation
   7  *
   8  * Adapted from ppp.c, written by Michael Callahan <callahan@maths.ox.ac.uk>,
   9  *      Al Longyear <longyear@netcom.com>,
  10  *      Paul Mackerras <Paul.Mackerras@cs.anu.edu.au>
  11  *
  12  * Original release 01/11/99
  13  * $Id: n_hdlc.c,v 4.8 2003/05/06 21:18:51 paulkf Exp $
  14  *
  15  * This code is released under the GNU General Public License (GPL)
  16  *
  17  * This module implements the tty line discipline N_HDLC for use with
  18  * tty device drivers that support bit-synchronous HDLC communications.
  19  *
  20  * All HDLC data is frame oriented which means:
  21  *
  22  * 1. tty write calls represent one complete transmit frame of data
  23  *    The device driver should accept the complete frame or none of
  24  *    the frame (busy) in the write method. Each write call should have
  25  *    a byte count in the range of 2-65535 bytes (2 is min HDLC frame
  26  *    with 1 addr byte and 1 ctrl byte). The max byte count of 65535
  27  *    should include any crc bytes required. For example, when using
  28  *    CCITT CRC32, 4 crc bytes are required, so the maximum size frame
  29  *    the application may transmit is limited to 65531 bytes. For CCITT
  30  *    CRC16, the maximum application frame size would be 65533.
  31  *
  32  *
  33  * 2. receive callbacks from the device driver represents
  34  *    one received frame. The device driver should bypass
  35  *    the tty flip buffer and call the line discipline receive
  36  *    callback directly to avoid fragmenting or concatenating
  37  *    multiple frames into a single receive callback.
  38  *
  39  *    The HDLC line discipline queues the receive frames in separate
  40  *    buffers so complete receive frames can be returned by the
  41  *    tty read calls.
  42  *
  43  * 3. tty read calls returns an entire frame of data or nothing.
  44  *
  45  * 4. all send and receive data is considered raw. No processing
  46  *    or translation is performed by the line discipline, regardless
  47  *    of the tty flags
  48  *
  49  * 5. When line discipline is queried for the amount of receive
  50  *    data available (FIOC), 0 is returned if no data available,
  51  *    otherwise the count of the next available frame is returned.
  52  *    (instead of the sum of all received frame counts).
  53  *
  54  * These conventions allow the standard tty programming interface
  55  * to be used for synchronous HDLC applications when used with
  56  * this line discipline (or another line discipline that is frame
  57  * oriented such as N_PPP).
  58  *
  59  * The SyncLink driver (synclink.c) implements both asynchronous
  60  * (using standard line discipline N_TTY) and synchronous HDLC
  61  * (using N_HDLC) communications, with the latter using the above
  62  * conventions.
  63  *
  64  * This implementation is very basic and does not maintain
  65  * any statistics. The main point is to enforce the raw data
  66  * and frame orientation of HDLC communications.
  67  *
  68  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
  69  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  70  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  71  * DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
  72  * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  73  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  74  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  75  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  76  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  77  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
  78  * OF THE POSSIBILITY OF SUCH DAMAGE.
  79  */
  80
  81 #define HDLC_MAGIC 0x239e
  82 #define HDLC_VERSION "$Revision: 4.8 $"
  83
  84 #include <linux/config.h>
  85 #include <linux/module.h>
  86 #include <linux/init.h>
  87 #include <linux/kernel.h>
  88 #include <linux/sched.h>
  89 #include <linux/types.h>
  90 #include <linux/fcntl.h>
  91 #include <linux/interrupt.h>
  92 #include <linux/ptrace.h>
  93
  94 #undef VERSION
  95 #define VERSION(major,minor,patch) (((((major)<<8)+(minor))<<8)+(patch))
  96
  97 #include <linux/poll.h>
  98 #include <linux/in.h>
  99 #include <linux/ioctl.h>
 100 #include <linux/slab.h>
 101 #include <linux/tty.h>
 102 #include <linux/errno.h>
 103 #include <linux/string.h>       /* used in new tty drivers */
 104 #include <linux/signal.h>       /* used in new tty drivers */
 105 #include <linux/if.h>
 106 #include <linux/bitops.h>
 107
 108 #include <asm/system.h>
 109 #include <asm/termios.h>
 110 #include <asm/uaccess.h>
 111
 112 /*
 113  * Buffers for individual HDLC frames
 114  */
 115 #define MAX_HDLC_FRAME_SIZE 65535
 116 #define DEFAULT_RX_BUF_COUNT 10
 117 #define MAX_RX_BUF_COUNT 60
 118 #define DEFAULT_TX_BUF_COUNT 1
 119
 120 struct n_hdlc_buf {
 121         struct n_hdlc_buf *link;
 122         int               count;
 123         char              buf[1];
 124 };
 125
 126 #define N_HDLC_BUF_SIZE (sizeof(struct n_hdlc_buf) + maxframe)
 127
 128 struct n_hdlc_buf_list {
 129         struct n_hdlc_buf *head;
 130         struct n_hdlc_buf *tail;
 131         int               count;
 132         spinlock_t        spinlock;
 133 };
 134
 135 /**
 136  * struct n_hdlc - per device instance data structure
 137  * @magic - magic value for structure
 138  * @flags - miscellaneous control flags
 139  * @tty - ptr to TTY structure
 140  * @backup_tty - TTY to use if tty gets closed
 141  * @tbusy - reentrancy flag for tx wakeup code
 142  * @woke_up - FIXME: describe this field
 143  * @tbuf - currently transmitting tx buffer
 144  * @tx_buf_list - list of pending transmit frame buffers
 145  * @rx_buf_list - list of received frame buffers
 146  * @tx_free_buf_list - list unused transmit frame buffers
 147  * @rx_free_buf_list - list unused received frame buffers
 148  */
 149 struct n_hdlc {
 150         int                     magic;
 151         __u32                   flags;
 152         struct tty_struct       *tty;
 153         struct tty_struct       *backup_tty;
 154         int                     tbusy;
 155         int                     woke_up;
 156         struct n_hdlc_buf       *tbuf;
 157         struct n_hdlc_buf_list  tx_buf_list;
 158         struct n_hdlc_buf_list  rx_buf_list;
 159         struct n_hdlc_buf_list  tx_free_buf_list;
 160         struct n_hdlc_buf_list  rx_free_buf_list;
 161 };
 162
 163 /*
 164  * HDLC buffer list manipulation functions
 165  */
 166 static void n_hdlc_buf_list_init(struct n_hdlc_buf_list *list);
 167 static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
 168                            struct n_hdlc_buf *buf);
 169 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
 170
 171 /* Local functions */
 172
 173 static struct n_hdlc *n_hdlc_alloc (void);
 174
 175 /* debug level can be set by insmod for debugging purposes */
 176 #define DEBUG_LEVEL_INFO        1
 177 static int debuglevel;
 178
 179 /* max frame size for memory allocations */
 180 static int maxframe = 4096;
 181
 182 /* TTY callbacks */
 183
 184 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 185                            __u8 __user *buf, size_t nr);
 186 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 187                             const unsigned char *buf, size_t nr);
 188 static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
 189                             unsigned int cmd, unsigned long arg);
 190 static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
 191                                     poll_table *wait);
 192 static int n_hdlc_tty_open(struct tty_struct *tty);
 193 static void n_hdlc_tty_close(struct tty_struct *tty);
 194 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *cp,
 195                                char *fp, int count);
 196 static void n_hdlc_tty_wakeup(struct tty_struct *tty);
 197
 198 #define bset(p,b)       ((p)[(b) >> 5] |= (1 << ((b) & 0x1f)))
 199
 200 #define tty2n_hdlc(tty) ((struct n_hdlc *) ((tty)->disc_data))
 201 #define n_hdlc2tty(n_hdlc)      ((n_hdlc)->tty)
 202
 203 static struct tty_ldisc 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 };
 216
 217 /**
 218  * n_hdlc_release - release an n_hdlc per device line discipline info structure
 219  * @n_hdlc - per device line discipline info structure
 220  */
 221 static void n_hdlc_release(struct n_hdlc *n_hdlc)
 222 {
 223         struct tty_struct *tty = n_hdlc2tty (n_hdlc);
 224         struct n_hdlc_buf *buf;
 225
 226         if (debuglevel >= DEBUG_LEVEL_INFO)
 227                 printk("%s(%d)n_hdlc_release() called\n",__FILE__,__LINE__);
 228
 229         /* Ensure that the n_hdlcd process is not hanging on select()/poll() */
 230         wake_up_interruptible (&tty->read_wait);
 231         wake_up_interruptible (&tty->write_wait);
 232
 233         if (tty != NULL && tty->disc_data == n_hdlc)
 234                 tty->disc_data = NULL;  /* Break the tty->n_hdlc link */
 235
 236         /* Release transmit and receive buffers */
 237         for(;;) {
 238                 buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
 239                 if (buf) {
 240                         kfree(buf);
 241                 } else
 242                         break;
 243         }
 244         for(;;) {
 245                 buf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
 246                 if (buf) {
 247                         kfree(buf);
 248                 } else
 249                         break;
 250         }
 251         for(;;) {
 252                 buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
 253                 if (buf) {
 254                         kfree(buf);
 255                 } else
 256                         break;
 257         }
 258         for(;;) {
 259                 buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 260                 if (buf) {
 261                         kfree(buf);
 262                 } else
 263                         break;
 264         }
 265         kfree(n_hdlc->tbuf);
 266         kfree(n_hdlc);
 267
 268 }       /* end of n_hdlc_release() */
 269
 270 /**
 271  * n_hdlc_tty_close - line discipline close
 272  * @tty - pointer to tty info structure
 273  *
 274  * Called when the line discipline is changed to something
 275  * else, the tty is closed, or the tty detects a hangup.
 276  */
 277 static void n_hdlc_tty_close(struct tty_struct *tty)
 278 {
 279         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 280
 281         if (debuglevel >= DEBUG_LEVEL_INFO)
 282                 printk("%s(%d)n_hdlc_tty_close() called\n",__FILE__,__LINE__);
 283
 284         if (n_hdlc != NULL) {
 285                 if (n_hdlc->magic != HDLC_MAGIC) {
 286                         printk (KERN_WARNING"n_hdlc: trying to close unopened tty!\n");
 287                         return;
 288                 }
 289 #if defined(TTY_NO_WRITE_SPLIT)
 290                 clear_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
 291 #endif
 292                 tty->disc_data = NULL;
 293                 if (tty == n_hdlc->backup_tty)
 294                         n_hdlc->backup_tty = NULL;
 295                 if (tty != n_hdlc->tty)
 296                         return;
 297                 if (n_hdlc->backup_tty) {
 298                         n_hdlc->tty = n_hdlc->backup_tty;
 299                 } else {
 300                         n_hdlc_release (n_hdlc);
 301                 }
 302         }
 303
 304         if (debuglevel >= DEBUG_LEVEL_INFO)
 305                 printk("%s(%d)n_hdlc_tty_close() success\n",__FILE__,__LINE__);
 306
 307 }       /* end of n_hdlc_tty_close() */
 308
 309 /**
 310  * n_hdlc_tty_open - called when line discipline changed to n_hdlc
 311  * @tty - pointer to tty info structure
 312  *
 313  * Returns 0 if success, otherwise error code
 314  */
 315 static int n_hdlc_tty_open (struct tty_struct *tty)
 316 {
 317         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 318
 319         if (debuglevel >= DEBUG_LEVEL_INFO)
 320                 printk("%s(%d)n_hdlc_tty_open() called (device=%s)\n",
 321                 __FILE__,__LINE__,
 322                 tty->name);
 323
 324         /* There should not be an existing table for this slot. */
 325         if (n_hdlc) {
 326                 printk (KERN_ERR"n_hdlc_tty_open:tty already associated!\n" );
 327                 return -EEXIST;
 328         }
 329
 330         n_hdlc = n_hdlc_alloc();
 331         if (!n_hdlc) {
 332                 printk (KERN_ERR "n_hdlc_alloc failed\n");
 333                 return -ENFILE;
 334         }
 335
 336         tty->disc_data = n_hdlc;
 337         n_hdlc->tty    = tty;
 338         tty->receive_room = 65536;
 339
 340 #if defined(TTY_NO_WRITE_SPLIT)
 341         /* change tty_io write() to not split large writes into 8K chunks */
 342         set_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
 343 #endif
 344
 345         /* Flush any pending characters in the driver and discipline. */
 346
 347         if (tty->ldisc.flush_buffer)
 348                 tty->ldisc.flush_buffer (tty);
 349
 350         if (tty->driver->flush_buffer)
 351                 tty->driver->flush_buffer (tty);
 352
 353         if (debuglevel >= DEBUG_LEVEL_INFO)
 354                 printk("%s(%d)n_hdlc_tty_open() success\n",__FILE__,__LINE__);
 355
 356         return 0;
 357
 358 }       /* end of n_tty_hdlc_open() */
 359
 360 /**
 361  * n_hdlc_send_frames - send frames on pending send buffer list
 362  * @n_hdlc - pointer to ldisc instance data
 363  * @tty - pointer to tty instance data
 364  *
 365  * Send frames on pending send buffer list until the driver does not accept a
 366  * frame (busy) this function is called after adding a frame to the send buffer
 367  * list and by the tty wakeup callback.
 368  */
 369 static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
 370 {
 371         register int actual;
 372         unsigned long flags;
 373         struct n_hdlc_buf *tbuf;
 374
 375         if (debuglevel >= DEBUG_LEVEL_INFO)
 376                 printk("%s(%d)n_hdlc_send_frames() called\n",__FILE__,__LINE__);
 377  check_again:
 378
 379         spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
 380         if (n_hdlc->tbusy) {
 381                 n_hdlc->woke_up = 1;
 382                 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 383                 return;
 384         }
 385         n_hdlc->tbusy = 1;
 386         n_hdlc->woke_up = 0;
 387         spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 388
 389         /* get current transmit buffer or get new transmit */
 390         /* buffer from list of pending transmit buffers */
 391
 392         tbuf = n_hdlc->tbuf;
 393         if (!tbuf)
 394                 tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 395
 396         while (tbuf) {
 397                 if (debuglevel >= DEBUG_LEVEL_INFO)
 398                         printk("%s(%d)sending frame %p, count=%d\n",
 399                                 __FILE__,__LINE__,tbuf,tbuf->count);
 400
 401                 /* Send the next block of data to device */
 402                 tty->flags |= (1 << TTY_DO_WRITE_WAKEUP);
 403                 actual = tty->driver->write(tty, tbuf->buf, tbuf->count);
 404
 405                 /* if transmit error, throw frame away by */
 406                 /* pretending it was accepted by driver */
 407                 if (actual < 0)
 408                         actual = tbuf->count;
 409
 410                 if (actual == tbuf->count) {
 411                         if (debuglevel >= DEBUG_LEVEL_INFO)
 412                                 printk("%s(%d)frame %p completed\n",
 413                                         __FILE__,__LINE__,tbuf);
 414
 415                         /* free current transmit buffer */
 416                         n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf);
 417
 418                         /* this tx buffer is done */
 419                         n_hdlc->tbuf = NULL;
 420
 421                         /* wait up sleeping writers */
 422                         wake_up_interruptible(&tty->write_wait);
 423
 424                         /* get next pending transmit buffer */
 425                         tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 426                 } else {
 427                         if (debuglevel >= DEBUG_LEVEL_INFO)
 428                                 printk("%s(%d)frame %p pending\n",
 429                                         __FILE__,__LINE__,tbuf);
 430
 431                         /* buffer not accepted by driver */
 432                         /* set this buffer as pending buffer */
 433                         n_hdlc->tbuf = tbuf;
 434                         break;
 435                 }
 436         }
 437
 438         if (!tbuf)
 439                 tty->flags  &= ~(1 << TTY_DO_WRITE_WAKEUP);
 440
 441         /* Clear the re-entry flag */
 442         spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
 443         n_hdlc->tbusy = 0;
 444         spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 445
 446         if (n_hdlc->woke_up)
 447           goto check_again;
 448
 449         if (debuglevel >= DEBUG_LEVEL_INFO)
 450                 printk("%s(%d)n_hdlc_send_frames() exit\n",__FILE__,__LINE__);
 451
 452 }       /* end of n_hdlc_send_frames() */
 453
 454 /**
 455  * n_hdlc_tty_wakeup - Callback for transmit wakeup
 456  * @tty - pointer to associated tty instance data
 457  *
 458  * Called when low level device driver can accept more send data.
 459  */
 460 static void n_hdlc_tty_wakeup(struct tty_struct *tty)
 461 {
 462         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 463
 464         if (debuglevel >= DEBUG_LEVEL_INFO)
 465                 printk("%s(%d)n_hdlc_tty_wakeup() called\n",__FILE__,__LINE__);
 466
 467         if (!n_hdlc)
 468                 return;
 469
 470         if (tty != n_hdlc->tty) {
 471                 tty->flags &= ~(1 << TTY_DO_WRITE_WAKEUP);
 472                 return;
 473         }
 474
 475         n_hdlc_send_frames (n_hdlc, tty);
 476
 477 }       /* end of n_hdlc_tty_wakeup() */
 478
 479 /**
 480  * n_hdlc_tty_receive - Called by tty driver when receive data is available
 481  * @tty - pointer to tty instance data
 482  * @data - pointer to received data
 483  * @flags - pointer to flags for data
 484  * @count - count of received data in bytes
 485  *
 486  * Called by tty low level driver when receive data is available. Data is
 487  * interpreted as one HDLC frame.
 488  */
 489 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
 490                                char *flags, int count)
 491 {
 492         register struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 493         register struct n_hdlc_buf *buf;
 494
 495         if (debuglevel >= DEBUG_LEVEL_INFO)
 496                 printk("%s(%d)n_hdlc_tty_receive() called count=%d\n",
 497                         __FILE__,__LINE__, count);
 498
 499         /* This can happen if stuff comes in on the backup tty */
 500         if (n_hdlc == 0 || tty != n_hdlc->tty)
 501                 return;
 502
 503         /* verify line is using HDLC discipline */
 504         if (n_hdlc->magic != HDLC_MAGIC) {
 505                 printk("%s(%d) line not using HDLC discipline\n",
 506                         __FILE__,__LINE__);
 507                 return;
 508         }
 509
 510         if ( count>maxframe ) {
 511                 if (debuglevel >= DEBUG_LEVEL_INFO)
 512                         printk("%s(%d) rx count>maxframesize, data discarded\n",
 513                                __FILE__,__LINE__);
 514                 return;
 515         }
 516
 517         /* get a free HDLC buffer */
 518         buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
 519         if (!buf) {
 520                 /* no buffers in free list, attempt to allocate another rx buffer */
 521                 /* unless the maximum count has been reached */
 522                 if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT)
 523                         buf = kmalloc(N_HDLC_BUF_SIZE, GFP_ATOMIC);
 524         }
 525
 526         if (!buf) {
 527                 if (debuglevel >= DEBUG_LEVEL_INFO)
 528                         printk("%s(%d) no more rx buffers, data discarded\n",
 529                                __FILE__,__LINE__);
 530                 return;
 531         }
 532
 533         /* copy received data to HDLC buffer */
 534         memcpy(buf->buf,data,count);
 535         buf->count=count;
 536
 537         /* add HDLC buffer to list of received frames */
 538         n_hdlc_buf_put(&n_hdlc->rx_buf_list, buf);
 539
 540         /* wake up any blocked reads and perform async signalling */
 541         wake_up_interruptible (&tty->read_wait);
 542         if (n_hdlc->tty->fasync != NULL)
 543                 kill_fasync (&n_hdlc->tty->fasync, SIGIO, POLL_IN);
 544
 545 }       /* end of n_hdlc_tty_receive() */
 546
 547 /**
 548  * n_hdlc_tty_read - Called to retrieve one frame of data (if available)
 549  * @tty - pointer to tty instance data
 550  * @file - pointer to open file object
 551  * @buf - pointer to returned data buffer
 552  * @nr - size of returned data buffer
 553  *
 554  * Returns the number of bytes returned or error code.
 555  */
 556 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 557                            __u8 __user *buf, size_t nr)
 558 {
 559         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 560         int ret;
 561         struct n_hdlc_buf *rbuf;
 562
 563         if (debuglevel >= DEBUG_LEVEL_INFO)
 564                 printk("%s(%d)n_hdlc_tty_read() called\n",__FILE__,__LINE__);
 565
 566         /* Validate the pointers */
 567         if (!n_hdlc)
 568                 return -EIO;
 569
 570         /* verify user access to buffer */
 571         if (!access_ok(VERIFY_WRITE, buf, nr)) {
 572                 printk(KERN_WARNING "%s(%d) n_hdlc_tty_read() can't verify user "
 573                 "buffer\n", __FILE__, __LINE__);
 574                 return -EFAULT;
 575         }
 576
 577         for (;;) {
 578                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 579                         return -EIO;
 580
 581                 n_hdlc = tty2n_hdlc (tty);
 582                 if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC ||
 583                          tty != n_hdlc->tty)
 584                         return 0;
 585
 586                 rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
 587                 if (rbuf)
 588                         break;
 589
 590                 /* no data */
 591                 if (file->f_flags & O_NONBLOCK)
 592                         return -EAGAIN;
 593
 594                 interruptible_sleep_on (&tty->read_wait);
 595                 if (signal_pending(current))
 596                         return -EINTR;
 597         }
 598
 599         if (rbuf->count > nr)
 600                 /* frame too large for caller's buffer (discard frame) */
 601                 ret = -EOVERFLOW;
 602         else {
 603                 /* Copy the data to the caller's buffer */
 604                 if (copy_to_user(buf, rbuf->buf, rbuf->count))
 605                         ret = -EFAULT;
 606                 else
 607                         ret = rbuf->count;
 608         }
 609
 610         /* return HDLC buffer to free list unless the free list */
 611         /* count has exceeded the default value, in which case the */
 612         /* buffer is freed back to the OS to conserve memory */
 613         if (n_hdlc->rx_free_buf_list.count > DEFAULT_RX_BUF_COUNT)
 614                 kfree(rbuf);
 615         else
 616                 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,rbuf);
 617
 618         return ret;
 619
 620 }       /* end of n_hdlc_tty_read() */
 621
 622 /**
 623  * n_hdlc_tty_write - write a single frame of data to device
 624  * @tty - pointer to associated tty device instance data
 625  * @file - pointer to file object data
 626  * @data - pointer to transmit data (one frame)
 627  * @count - size of transmit frame in bytes
 628  *
 629  * Returns the number of bytes written (or error code).
 630  */
 631 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 632                             const unsigned char *data, size_t count)
 633 {
 634         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 635         int error = 0;
 636         DECLARE_WAITQUEUE(wait, current);
 637         struct n_hdlc_buf *tbuf;
 638
 639         if (debuglevel >= DEBUG_LEVEL_INFO)
 640                 printk("%s(%d)n_hdlc_tty_write() called count=%Zd\n",
 641                         __FILE__,__LINE__,count);
 642
 643         /* Verify pointers */
 644         if (!n_hdlc)
 645                 return -EIO;
 646
 647         if (n_hdlc->magic != HDLC_MAGIC)
 648                 return -EIO;
 649
 650         /* verify frame size */
 651         if (count > maxframe ) {
 652                 if (debuglevel & DEBUG_LEVEL_INFO)
 653                         printk (KERN_WARNING
 654                                 "n_hdlc_tty_write: truncating user packet "
 655                                 "from %lu to %d\n", (unsigned long) count,
 656                                 maxframe );
 657                 count = maxframe;
 658         }
 659
 660         add_wait_queue(&tty->write_wait, &wait);
 661         set_current_state(TASK_INTERRUPTIBLE);
 662
 663         /* Allocate transmit buffer */
 664         /* sleep until transmit buffer available */
 665         while (!(tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list))) {
 666                 schedule();
 667
 668                 n_hdlc = tty2n_hdlc (tty);
 669                 if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC ||
 670                     tty != n_hdlc->tty) {
 671                         printk("n_hdlc_tty_write: %p invalid after wait!\n", n_hdlc);
 672                         error = -EIO;
 673                         break;
 674                 }
 675
 676                 if (signal_pending(current)) {
 677                         error = -EINTR;
 678                         break;
 679                 }
 680         }
 681
 682         set_current_state(TASK_RUNNING);
 683         remove_wait_queue(&tty->write_wait, &wait);
 684
 685         if (!error) {
 686                 /* Retrieve the user's buffer */
 687                 memcpy(tbuf->buf, data, count);
 688
 689                 /* Send the data */
 690                 tbuf->count = error = count;
 691                 n_hdlc_buf_put(&n_hdlc->tx_buf_list,tbuf);
 692                 n_hdlc_send_frames(n_hdlc,tty);
 693         }
 694
 695         return error;
 696
 697 }       /* end of n_hdlc_tty_write() */
 698
 699 /**
 700  * n_hdlc_tty_ioctl - process IOCTL system call for the tty device.
 701  * @tty - pointer to tty instance data
 702  * @file - pointer to open file object for device
 703  * @cmd - IOCTL command code
 704  * @arg - argument for IOCTL call (cmd dependent)
 705  *
 706  * Returns command dependent result.
 707  */
 708 static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
 709                             unsigned int cmd, unsigned long arg)
 710 {
 711         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 712         int error = 0;
 713         int count;
 714         unsigned long flags;
 715
 716         if (debuglevel >= DEBUG_LEVEL_INFO)
 717                 printk("%s(%d)n_hdlc_tty_ioctl() called %d\n",
 718                         __FILE__,__LINE__,cmd);
 719
 720         /* Verify the status of the device */
 721         if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC)
 722                 return -EBADF;
 723
 724         switch (cmd) {
 725         case FIONREAD:
 726                 /* report count of read data available */
 727                 /* in next available frame (if any) */
 728                 spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock,flags);
 729                 if (n_hdlc->rx_buf_list.head)
 730                         count = n_hdlc->rx_buf_list.head->count;
 731                 else
 732                         count = 0;
 733                 spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock,flags);
 734                 error = put_user(count, (int __user *)arg);
 735                 break;
 736
 737         case TIOCOUTQ:
 738                 /* get the pending tx byte count in the driver */
 739                 count = tty->driver->chars_in_buffer ?
 740                                 tty->driver->chars_in_buffer(tty) : 0;
 741                 /* add size of next output frame in queue */
 742                 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock,flags);
 743                 if (n_hdlc->tx_buf_list.head)
 744                         count += n_hdlc->tx_buf_list.head->count;
 745                 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock,flags);
 746                 error = put_user(count, (int __user *)arg);
 747                 break;
 748
 749         default:
 750                 error = n_tty_ioctl (tty, file, cmd, arg);
 751                 break;
 752         }
 753         return error;
 754
 755 }       /* end of n_hdlc_tty_ioctl() */
 756
 757 /**
 758  * n_hdlc_tty_poll - TTY callback for poll system call
 759  * @tty - pointer to tty instance data
 760  * @filp - pointer to open file object for device
 761  * @poll_table - wait queue for operations
 762  *
 763  * Determine which operations (read/write) will not block and return info
 764  * to caller.
 765  * Returns a bit mask containing info on which ops will not block.
 766  */
 767 static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
 768                                     poll_table *wait)
 769 {
 770         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 771         unsigned int mask = 0;
 772
 773         if (debuglevel >= DEBUG_LEVEL_INFO)
 774                 printk("%s(%d)n_hdlc_tty_poll() called\n",__FILE__,__LINE__);
 775
 776         if (n_hdlc && n_hdlc->magic == HDLC_MAGIC && tty == n_hdlc->tty) {
 777                 /* queue current process into any wait queue that */
 778                 /* may awaken in the future (read and write) */
 779
 780                 poll_wait(filp, &tty->read_wait, wait);
 781                 poll_wait(filp, &tty->write_wait, wait);
 782
 783                 /* set bits for operations that won't block */
 784                 if(n_hdlc->rx_buf_list.head)
 785                         mask |= POLLIN | POLLRDNORM;    /* readable */
 786                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 787                         mask |= POLLHUP;
 788                 if(tty_hung_up_p(filp))
 789                         mask |= POLLHUP;
 790                 if(n_hdlc->tx_free_buf_list.head)
 791                         mask |= POLLOUT | POLLWRNORM;   /* writable */
 792         }
 793         return mask;
 794 }       /* end of n_hdlc_tty_poll() */
 795
 796 /**
 797  * n_hdlc_alloc - allocate an n_hdlc instance data structure
 798  *
 799  * Returns a pointer to newly created structure if success, otherwise %NULL
 800  */
 801 static struct n_hdlc *n_hdlc_alloc(void)
 802 {
 803         struct n_hdlc_buf *buf;
 804         int i;
 805         struct n_hdlc *n_hdlc = kmalloc(sizeof(*n_hdlc), GFP_KERNEL);
 806
 807         if (!n_hdlc)
 808                 return NULL;
 809
 810         memset(n_hdlc, 0, sizeof(*n_hdlc));
 811
 812         n_hdlc_buf_list_init(&n_hdlc->rx_free_buf_list);
 813         n_hdlc_buf_list_init(&n_hdlc->tx_free_buf_list);
 814         n_hdlc_buf_list_init(&n_hdlc->rx_buf_list);
 815         n_hdlc_buf_list_init(&n_hdlc->tx_buf_list);
 816
 817         /* allocate free rx buffer list */
 818         for(i=0;i<DEFAULT_RX_BUF_COUNT;i++) {
 819                 buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
 820                 if (buf)
 821                         n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,buf);
 822                 else if (debuglevel >= DEBUG_LEVEL_INFO)
 823                         printk("%s(%d)n_hdlc_alloc(), kalloc() failed for rx buffer %d\n",__FILE__,__LINE__, i);
 824         }
 825
 826         /* allocate free tx buffer list */
 827         for(i=0;i<DEFAULT_TX_BUF_COUNT;i++) {
 828                 buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
 829                 if (buf)
 830                         n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,buf);
 831                 else if (debuglevel >= DEBUG_LEVEL_INFO)
 832                         printk("%s(%d)n_hdlc_alloc(), kalloc() failed for tx buffer %d\n",__FILE__,__LINE__, i);
 833         }
 834
 835         /* Initialize the control block */
 836         n_hdlc->magic  = HDLC_MAGIC;
 837         n_hdlc->flags  = 0;
 838
 839         return n_hdlc;
 840
 841 }       /* end of n_hdlc_alloc() */
 842
 843 /**
 844  * n_hdlc_buf_list_init - initialize specified HDLC buffer list
 845  * @list - pointer to buffer list
 846  */
 847 static void n_hdlc_buf_list_init(struct n_hdlc_buf_list *list)
 848 {
 849         memset(list, 0, sizeof(*list));
 850         spin_lock_init(&list->spinlock);
 851 }       /* end of n_hdlc_buf_list_init() */
 852
 853 /**
 854  * n_hdlc_buf_put - add specified HDLC buffer to tail of specified list
 855  * @list - pointer to buffer list
 856  * @buf - pointer to buffer
 857  */
 858 static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
 859                            struct n_hdlc_buf *buf)
 860 {
 861         unsigned long flags;
 862         spin_lock_irqsave(&list->spinlock,flags);
 863
 864         buf->link=NULL;
 865         if(list->tail)
 866                 list->tail->link = buf;
 867         else
 868                 list->head = buf;
 869         list->tail = buf;
 870         (list->count)++;
 871
 872         spin_unlock_irqrestore(&list->spinlock,flags);
 873
 874 }       /* end of n_hdlc_buf_put() */
 875
 876 /**
 877  * n_hdlc_buf_get - remove and return an HDLC buffer from list
 878  * @list - pointer to HDLC buffer list
 879  *
 880  * Remove and return an HDLC buffer from the head of the specified HDLC buffer
 881  * list.
 882  * Returns a pointer to HDLC buffer if available, otherwise %NULL.
 883  */
 884 static struct n_hdlc_buf* n_hdlc_buf_get(struct n_hdlc_buf_list *list)
 885 {
 886         unsigned long flags;
 887         struct n_hdlc_buf *buf;
 888         spin_lock_irqsave(&list->spinlock,flags);
 889
 890         buf = list->head;
 891         if (buf) {
 892                 list->head = buf->link;
 893                 (list->count)--;
 894         }
 895         if (!list->head)
 896                 list->tail = NULL;
 897
 898         spin_unlock_irqrestore(&list->spinlock,flags);
 899         return buf;
 900
 901 }       /* end of n_hdlc_buf_get() */
 902
 903 static char hdlc_banner[] __initdata =
 904         KERN_INFO "HDLC line discipline: version " HDLC_VERSION
 905         ", maxframe=%u\n";
 906 static char hdlc_register_ok[] __initdata =
 907         KERN_INFO "N_HDLC line discipline registered.\n";
 908 static char hdlc_register_fail[] __initdata =
 909         KERN_ERR "error registering line discipline: %d\n";
 910 static char hdlc_init_fail[] __initdata =
 911         KERN_INFO "N_HDLC: init failure %d\n";
 912
 913 static int __init n_hdlc_init(void)
 914 {
 915         int status;
 916
 917         /* range check maxframe arg */
 918         if (maxframe < 4096)
 919                 maxframe = 4096;
 920         else if (maxframe > 65535)
 921                 maxframe = 65535;
 922
 923         printk(hdlc_banner, maxframe);
 924
 925         status = tty_register_ldisc(N_HDLC, &n_hdlc_ldisc);
 926         if (!status)
 927                 printk(hdlc_register_ok);
 928         else
 929                 printk(hdlc_register_fail, status);
 930
 931         if (status)
 932                 printk(hdlc_init_fail, status);
 933         return status;
 934
 935 }       /* end of init_module() */
 936
 937 static char hdlc_unregister_ok[] __exitdata =
 938         KERN_INFO "N_HDLC: line discipline unregistered\n";
 939 static char hdlc_unregister_fail[] __exitdata =
 940         KERN_ERR "N_HDLC: can't unregister line discipline (err = %d)\n";
 941
 942 static void __exit n_hdlc_exit(void)
 943 {
 944         /* Release tty registration of line discipline */
 945         int status = tty_unregister_ldisc(N_HDLC);
 946
 947         if (status)
 948                 printk(hdlc_unregister_fail, status);
 949         else
 950                 printk(hdlc_unregister_ok);
 951 }
 952
 953 module_init(n_hdlc_init);
 954 module_exit(n_hdlc_exit);
 955
 956 MODULE_LICENSE("GPL");
 957 MODULE_AUTHOR("Paul Fulghum paulkf@microgate.com");
 958 module_param(debuglevel, int, 0);
 959 module_param(maxframe, int, 0);
 960 MODULE_ALIAS_LDISC(N_HDLC);