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   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 int n_hdlc_tty_room(struct tty_struct *tty);
 195 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *cp,
 196                                char *fp, int count);
 197 static void n_hdlc_tty_wakeup(struct tty_struct *tty);
 198
 199 #define bset(p,b)       ((p)[(b) >> 5] |= (1 << ((b) & 0x1f)))
 200
 201 #define tty2n_hdlc(tty) ((struct n_hdlc *) ((tty)->disc_data))
 202 #define n_hdlc2tty(n_hdlc)      ((n_hdlc)->tty)
 203
 204 static struct tty_ldisc n_hdlc_ldisc = {
 205         .owner          = THIS_MODULE,
 206         .magic          = TTY_LDISC_MAGIC,
 207         .name           = "hdlc",
 208         .open           = n_hdlc_tty_open,
 209         .close          = n_hdlc_tty_close,
 210         .read           = n_hdlc_tty_read,
 211         .write          = n_hdlc_tty_write,
 212         .ioctl          = n_hdlc_tty_ioctl,
 213         .poll           = n_hdlc_tty_poll,
 214         .receive_buf    = n_hdlc_tty_receive,
 215         .receive_room   = n_hdlc_tty_room,
 216         .write_wakeup   = n_hdlc_tty_wakeup,
 217 };
 218
 219 /**
 220  * n_hdlc_release - release an n_hdlc per device line discipline info structure
 221  * @n_hdlc - per device line discipline info structure
 222  */
 223 static void n_hdlc_release(struct n_hdlc *n_hdlc)
 224 {
 225         struct tty_struct *tty = n_hdlc2tty (n_hdlc);
 226         struct n_hdlc_buf *buf;
 227
 228         if (debuglevel >= DEBUG_LEVEL_INFO)
 229                 printk("%s(%d)n_hdlc_release() called\n",__FILE__,__LINE__);
 230
 231         /* Ensure that the n_hdlcd process is not hanging on select()/poll() */
 232         wake_up_interruptible (&tty->read_wait);
 233         wake_up_interruptible (&tty->write_wait);
 234
 235         if (tty != NULL && tty->disc_data == n_hdlc)
 236                 tty->disc_data = NULL;  /* Break the tty->n_hdlc link */
 237
 238         /* Release transmit and receive buffers */
 239         for(;;) {
 240                 buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
 241                 if (buf) {
 242                         kfree(buf);
 243                 } else
 244                         break;
 245         }
 246         for(;;) {
 247                 buf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
 248                 if (buf) {
 249                         kfree(buf);
 250                 } else
 251                         break;
 252         }
 253         for(;;) {
 254                 buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
 255                 if (buf) {
 256                         kfree(buf);
 257                 } else
 258                         break;
 259         }
 260         for(;;) {
 261                 buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 262                 if (buf) {
 263                         kfree(buf);
 264                 } else
 265                         break;
 266         }
 267         kfree(n_hdlc->tbuf);
 268         kfree(n_hdlc);
 269
 270 }       /* end of n_hdlc_release() */
 271
 272 /**
 273  * n_hdlc_tty_close - line discipline close
 274  * @tty - pointer to tty info structure
 275  *
 276  * Called when the line discipline is changed to something
 277  * else, the tty is closed, or the tty detects a hangup.
 278  */
 279 static void n_hdlc_tty_close(struct tty_struct *tty)
 280 {
 281         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 282
 283         if (debuglevel >= DEBUG_LEVEL_INFO)
 284                 printk("%s(%d)n_hdlc_tty_close() called\n",__FILE__,__LINE__);
 285
 286         if (n_hdlc != NULL) {
 287                 if (n_hdlc->magic != HDLC_MAGIC) {
 288                         printk (KERN_WARNING"n_hdlc: trying to close unopened tty!\n");
 289                         return;
 290                 }
 291 #if defined(TTY_NO_WRITE_SPLIT)
 292                 clear_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
 293 #endif
 294                 tty->disc_data = NULL;
 295                 if (tty == n_hdlc->backup_tty)
 296                         n_hdlc->backup_tty = NULL;
 297                 if (tty != n_hdlc->tty)
 298                         return;
 299                 if (n_hdlc->backup_tty) {
 300                         n_hdlc->tty = n_hdlc->backup_tty;
 301                 } else {
 302                         n_hdlc_release (n_hdlc);
 303                 }
 304         }
 305
 306         if (debuglevel >= DEBUG_LEVEL_INFO)
 307                 printk("%s(%d)n_hdlc_tty_close() success\n",__FILE__,__LINE__);
 308
 309 }       /* end of n_hdlc_tty_close() */
 310
 311 /**
 312  * n_hdlc_tty_open - called when line discipline changed to n_hdlc
 313  * @tty - pointer to tty info structure
 314  *
 315  * Returns 0 if success, otherwise error code
 316  */
 317 static int n_hdlc_tty_open (struct tty_struct *tty)
 318 {
 319         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 320
 321         if (debuglevel >= DEBUG_LEVEL_INFO)
 322                 printk("%s(%d)n_hdlc_tty_open() called (device=%s)\n",
 323                 __FILE__,__LINE__,
 324                 tty->name);
 325
 326         /* There should not be an existing table for this slot. */
 327         if (n_hdlc) {
 328                 printk (KERN_ERR"n_hdlc_tty_open:tty already associated!\n" );
 329                 return -EEXIST;
 330         }
 331
 332         n_hdlc = n_hdlc_alloc();
 333         if (!n_hdlc) {
 334                 printk (KERN_ERR "n_hdlc_alloc failed\n");
 335                 return -ENFILE;
 336         }
 337
 338         tty->disc_data = n_hdlc;
 339         n_hdlc->tty    = tty;
 340
 341 #if defined(TTY_NO_WRITE_SPLIT)
 342         /* change tty_io write() to not split large writes into 8K chunks */
 343         set_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
 344 #endif
 345
 346         /* Flush any pending characters in the driver and discipline. */
 347
 348         if (tty->ldisc.flush_buffer)
 349                 tty->ldisc.flush_buffer (tty);
 350
 351         if (tty->driver->flush_buffer)
 352                 tty->driver->flush_buffer (tty);
 353
 354         if (debuglevel >= DEBUG_LEVEL_INFO)
 355                 printk("%s(%d)n_hdlc_tty_open() success\n",__FILE__,__LINE__);
 356
 357         return 0;
 358
 359 }       /* end of n_tty_hdlc_open() */
 360
 361 /**
 362  * n_hdlc_send_frames - send frames on pending send buffer list
 363  * @n_hdlc - pointer to ldisc instance data
 364  * @tty - pointer to tty instance data
 365  *
 366  * Send frames on pending send buffer list until the driver does not accept a
 367  * frame (busy) this function is called after adding a frame to the send buffer
 368  * list and by the tty wakeup callback.
 369  */
 370 static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
 371 {
 372         register int actual;
 373         unsigned long flags;
 374         struct n_hdlc_buf *tbuf;
 375
 376         if (debuglevel >= DEBUG_LEVEL_INFO)
 377                 printk("%s(%d)n_hdlc_send_frames() called\n",__FILE__,__LINE__);
 378  check_again:
 379
 380         spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
 381         if (n_hdlc->tbusy) {
 382                 n_hdlc->woke_up = 1;
 383                 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 384                 return;
 385         }
 386         n_hdlc->tbusy = 1;
 387         n_hdlc->woke_up = 0;
 388         spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 389
 390         /* get current transmit buffer or get new transmit */
 391         /* buffer from list of pending transmit buffers */
 392
 393         tbuf = n_hdlc->tbuf;
 394         if (!tbuf)
 395                 tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 396
 397         while (tbuf) {
 398                 if (debuglevel >= DEBUG_LEVEL_INFO)
 399                         printk("%s(%d)sending frame %p, count=%d\n",
 400                                 __FILE__,__LINE__,tbuf,tbuf->count);
 401
 402                 /* Send the next block of data to device */
 403                 tty->flags |= (1 << TTY_DO_WRITE_WAKEUP);
 404                 actual = tty->driver->write(tty, tbuf->buf, tbuf->count);
 405
 406                 /* if transmit error, throw frame away by */
 407                 /* pretending it was accepted by driver */
 408                 if (actual < 0)
 409                         actual = tbuf->count;
 410
 411                 if (actual == tbuf->count) {
 412                         if (debuglevel >= DEBUG_LEVEL_INFO)
 413                                 printk("%s(%d)frame %p completed\n",
 414                                         __FILE__,__LINE__,tbuf);
 415
 416                         /* free current transmit buffer */
 417                         n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf);
 418
 419                         /* this tx buffer is done */
 420                         n_hdlc->tbuf = NULL;
 421
 422                         /* wait up sleeping writers */
 423                         wake_up_interruptible(&tty->write_wait);
 424
 425                         /* get next pending transmit buffer */
 426                         tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 427                 } else {
 428                         if (debuglevel >= DEBUG_LEVEL_INFO)
 429                                 printk("%s(%d)frame %p pending\n",
 430                                         __FILE__,__LINE__,tbuf);
 431
 432                         /* buffer not accepted by driver */
 433                         /* set this buffer as pending buffer */
 434                         n_hdlc->tbuf = tbuf;
 435                         break;
 436                 }
 437         }
 438
 439         if (!tbuf)
 440                 tty->flags  &= ~(1 << TTY_DO_WRITE_WAKEUP);
 441
 442         /* Clear the re-entry flag */
 443         spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
 444         n_hdlc->tbusy = 0;
 445         spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 446
 447         if (n_hdlc->woke_up)
 448           goto check_again;
 449
 450         if (debuglevel >= DEBUG_LEVEL_INFO)
 451                 printk("%s(%d)n_hdlc_send_frames() exit\n",__FILE__,__LINE__);
 452
 453 }       /* end of n_hdlc_send_frames() */
 454
 455 /**
 456  * n_hdlc_tty_wakeup - Callback for transmit wakeup
 457  * @tty - pointer to associated tty instance data
 458  *
 459  * Called when low level device driver can accept more send data.
 460  */
 461 static void n_hdlc_tty_wakeup(struct tty_struct *tty)
 462 {
 463         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 464
 465         if (debuglevel >= DEBUG_LEVEL_INFO)
 466                 printk("%s(%d)n_hdlc_tty_wakeup() called\n",__FILE__,__LINE__);
 467
 468         if (!n_hdlc)
 469                 return;
 470
 471         if (tty != n_hdlc->tty) {
 472                 tty->flags &= ~(1 << TTY_DO_WRITE_WAKEUP);
 473                 return;
 474         }
 475
 476         n_hdlc_send_frames (n_hdlc, tty);
 477
 478 }       /* end of n_hdlc_tty_wakeup() */
 479
 480 /**
 481  * n_hdlc_tty_room - Return the amount of space left in the receiver's buffer
 482  * @tty - pointer to associated tty instance data
 483  *
 484  * Callback function from tty driver. Return the amount of space left in the
 485  * receiver's buffer to decide if remote transmitter is to be throttled.
 486  */
 487 static int n_hdlc_tty_room(struct tty_struct *tty)
 488 {
 489         if (debuglevel >= DEBUG_LEVEL_INFO)
 490                 printk("%s(%d)n_hdlc_tty_room() called\n",__FILE__,__LINE__);
 491         /* always return a larger number to prevent */
 492         /* throttling of remote transmitter. */
 493         return 65536;
 494 }       /* end of n_hdlc_tty_root() */
 495
 496 /**
 497  * n_hdlc_tty_receive - Called by tty driver when receive data is available
 498  * @tty - pointer to tty instance data
 499  * @data - pointer to received data
 500  * @flags - pointer to flags for data
 501  * @count - count of received data in bytes
 502  *
 503  * Called by tty low level driver when receive data is available. Data is
 504  * interpreted as one HDLC frame.
 505  */
 506 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
 507                                char *flags, int count)
 508 {
 509         register struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 510         register struct n_hdlc_buf *buf;
 511
 512         if (debuglevel >= DEBUG_LEVEL_INFO)
 513                 printk("%s(%d)n_hdlc_tty_receive() called count=%d\n",
 514                         __FILE__,__LINE__, count);
 515
 516         /* This can happen if stuff comes in on the backup tty */
 517         if (n_hdlc == 0 || tty != n_hdlc->tty)
 518                 return;
 519
 520         /* verify line is using HDLC discipline */
 521         if (n_hdlc->magic != HDLC_MAGIC) {
 522                 printk("%s(%d) line not using HDLC discipline\n",
 523                         __FILE__,__LINE__);
 524                 return;
 525         }
 526
 527         if ( count>maxframe ) {
 528                 if (debuglevel >= DEBUG_LEVEL_INFO)
 529                         printk("%s(%d) rx count>maxframesize, data discarded\n",
 530                                __FILE__,__LINE__);
 531                 return;
 532         }
 533
 534         /* get a free HDLC buffer */
 535         buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
 536         if (!buf) {
 537                 /* no buffers in free list, attempt to allocate another rx buffer */
 538                 /* unless the maximum count has been reached */
 539                 if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT)
 540                         buf = kmalloc(N_HDLC_BUF_SIZE, GFP_ATOMIC);
 541         }
 542
 543         if (!buf) {
 544                 if (debuglevel >= DEBUG_LEVEL_INFO)
 545                         printk("%s(%d) no more rx buffers, data discarded\n",
 546                                __FILE__,__LINE__);
 547                 return;
 548         }
 549
 550         /* copy received data to HDLC buffer */
 551         memcpy(buf->buf,data,count);
 552         buf->count=count;
 553
 554         /* add HDLC buffer to list of received frames */
 555         n_hdlc_buf_put(&n_hdlc->rx_buf_list, buf);
 556
 557         /* wake up any blocked reads and perform async signalling */
 558         wake_up_interruptible (&tty->read_wait);
 559         if (n_hdlc->tty->fasync != NULL)
 560                 kill_fasync (&n_hdlc->tty->fasync, SIGIO, POLL_IN);
 561
 562 }       /* end of n_hdlc_tty_receive() */
 563
 564 /**
 565  * n_hdlc_tty_read - Called to retrieve one frame of data (if available)
 566  * @tty - pointer to tty instance data
 567  * @file - pointer to open file object
 568  * @buf - pointer to returned data buffer
 569  * @nr - size of returned data buffer
 570  *
 571  * Returns the number of bytes returned or error code.
 572  */
 573 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 574                            __u8 __user *buf, size_t nr)
 575 {
 576         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 577         int ret;
 578         struct n_hdlc_buf *rbuf;
 579
 580         if (debuglevel >= DEBUG_LEVEL_INFO)
 581                 printk("%s(%d)n_hdlc_tty_read() called\n",__FILE__,__LINE__);
 582
 583         /* Validate the pointers */
 584         if (!n_hdlc)
 585                 return -EIO;
 586
 587         /* verify user access to buffer */
 588         if (!access_ok(VERIFY_WRITE, buf, nr)) {
 589                 printk(KERN_WARNING "%s(%d) n_hdlc_tty_read() can't verify user "
 590                 "buffer\n", __FILE__, __LINE__);
 591                 return -EFAULT;
 592         }
 593
 594         for (;;) {
 595                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 596                         return -EIO;
 597
 598                 n_hdlc = tty2n_hdlc (tty);
 599                 if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC ||
 600                          tty != n_hdlc->tty)
 601                         return 0;
 602
 603                 rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
 604                 if (rbuf)
 605                         break;
 606
 607                 /* no data */
 608                 if (file->f_flags & O_NONBLOCK)
 609                         return -EAGAIN;
 610
 611                 interruptible_sleep_on (&tty->read_wait);
 612                 if (signal_pending(current))
 613                         return -EINTR;
 614         }
 615
 616         if (rbuf->count > nr)
 617                 /* frame too large for caller's buffer (discard frame) */
 618                 ret = -EOVERFLOW;
 619         else {
 620                 /* Copy the data to the caller's buffer */
 621                 if (copy_to_user(buf, rbuf->buf, rbuf->count))
 622                         ret = -EFAULT;
 623                 else
 624                         ret = rbuf->count;
 625         }
 626
 627         /* return HDLC buffer to free list unless the free list */
 628         /* count has exceeded the default value, in which case the */
 629         /* buffer is freed back to the OS to conserve memory */
 630         if (n_hdlc->rx_free_buf_list.count > DEFAULT_RX_BUF_COUNT)
 631                 kfree(rbuf);
 632         else
 633                 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,rbuf);
 634
 635         return ret;
 636
 637 }       /* end of n_hdlc_tty_read() */
 638
 639 /**
 640  * n_hdlc_tty_write - write a single frame of data to device
 641  * @tty - pointer to associated tty device instance data
 642  * @file - pointer to file object data
 643  * @data - pointer to transmit data (one frame)
 644  * @count - size of transmit frame in bytes
 645  *
 646  * Returns the number of bytes written (or error code).
 647  */
 648 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 649                             const unsigned char *data, size_t count)
 650 {
 651         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 652         int error = 0;
 653         DECLARE_WAITQUEUE(wait, current);
 654         struct n_hdlc_buf *tbuf;
 655
 656         if (debuglevel >= DEBUG_LEVEL_INFO)
 657                 printk("%s(%d)n_hdlc_tty_write() called count=%Zd\n",
 658                         __FILE__,__LINE__,count);
 659
 660         /* Verify pointers */
 661         if (!n_hdlc)
 662                 return -EIO;
 663
 664         if (n_hdlc->magic != HDLC_MAGIC)
 665                 return -EIO;
 666
 667         /* verify frame size */
 668         if (count > maxframe ) {
 669                 if (debuglevel & DEBUG_LEVEL_INFO)
 670                         printk (KERN_WARNING
 671                                 "n_hdlc_tty_write: truncating user packet "
 672                                 "from %lu to %d\n", (unsigned long) count,
 673                                 maxframe );
 674                 count = maxframe;
 675         }
 676
 677         add_wait_queue(&tty->write_wait, &wait);
 678         set_current_state(TASK_INTERRUPTIBLE);
 679
 680         /* Allocate transmit buffer */
 681         /* sleep until transmit buffer available */
 682         while (!(tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list))) {
 683                 schedule();
 684
 685                 n_hdlc = tty2n_hdlc (tty);
 686                 if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC ||
 687                     tty != n_hdlc->tty) {
 688                         printk("n_hdlc_tty_write: %p invalid after wait!\n", n_hdlc);
 689                         error = -EIO;
 690                         break;
 691                 }
 692
 693                 if (signal_pending(current)) {
 694                         error = -EINTR;
 695                         break;
 696                 }
 697         }
 698
 699         set_current_state(TASK_RUNNING);
 700         remove_wait_queue(&tty->write_wait, &wait);
 701
 702         if (!error) {
 703                 /* Retrieve the user's buffer */
 704                 memcpy(tbuf->buf, data, count);
 705
 706                 /* Send the data */
 707                 tbuf->count = error = count;
 708                 n_hdlc_buf_put(&n_hdlc->tx_buf_list,tbuf);
 709                 n_hdlc_send_frames(n_hdlc,tty);
 710         }
 711
 712         return error;
 713
 714 }       /* end of n_hdlc_tty_write() */
 715
 716 /**
 717  * n_hdlc_tty_ioctl - process IOCTL system call for the tty device.
 718  * @tty - pointer to tty instance data
 719  * @file - pointer to open file object for device
 720  * @cmd - IOCTL command code
 721  * @arg - argument for IOCTL call (cmd dependent)
 722  *
 723  * Returns command dependent result.
 724  */
 725 static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
 726                             unsigned int cmd, unsigned long arg)
 727 {
 728         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 729         int error = 0;
 730         int count;
 731         unsigned long flags;
 732
 733         if (debuglevel >= DEBUG_LEVEL_INFO)
 734                 printk("%s(%d)n_hdlc_tty_ioctl() called %d\n",
 735                         __FILE__,__LINE__,cmd);
 736
 737         /* Verify the status of the device */
 738         if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC)
 739                 return -EBADF;
 740
 741         switch (cmd) {
 742         case FIONREAD:
 743                 /* report count of read data available */
 744                 /* in next available frame (if any) */
 745                 spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock,flags);
 746                 if (n_hdlc->rx_buf_list.head)
 747                         count = n_hdlc->rx_buf_list.head->count;
 748                 else
 749                         count = 0;
 750                 spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock,flags);
 751                 error = put_user(count, (int __user *)arg);
 752                 break;
 753
 754         case TIOCOUTQ:
 755                 /* get the pending tx byte count in the driver */
 756                 count = tty->driver->chars_in_buffer ?
 757                                 tty->driver->chars_in_buffer(tty) : 0;
 758                 /* add size of next output frame in queue */
 759                 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock,flags);
 760                 if (n_hdlc->tx_buf_list.head)
 761                         count += n_hdlc->tx_buf_list.head->count;
 762                 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock,flags);
 763                 error = put_user(count, (int __user *)arg);
 764                 break;
 765
 766         default:
 767                 error = n_tty_ioctl (tty, file, cmd, arg);
 768                 break;
 769         }
 770         return error;
 771
 772 }       /* end of n_hdlc_tty_ioctl() */
 773
 774 /**
 775  * n_hdlc_tty_poll - TTY callback for poll system call
 776  * @tty - pointer to tty instance data
 777  * @filp - pointer to open file object for device
 778  * @poll_table - wait queue for operations
 779  *
 780  * Determine which operations (read/write) will not block and return info
 781  * to caller.
 782  * Returns a bit mask containing info on which ops will not block.
 783  */
 784 static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
 785                                     poll_table *wait)
 786 {
 787         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 788         unsigned int mask = 0;
 789
 790         if (debuglevel >= DEBUG_LEVEL_INFO)
 791                 printk("%s(%d)n_hdlc_tty_poll() called\n",__FILE__,__LINE__);
 792
 793         if (n_hdlc && n_hdlc->magic == HDLC_MAGIC && tty == n_hdlc->tty) {
 794                 /* queue current process into any wait queue that */
 795                 /* may awaken in the future (read and write) */
 796
 797                 poll_wait(filp, &tty->read_wait, wait);
 798                 poll_wait(filp, &tty->write_wait, wait);
 799
 800                 /* set bits for operations that won't block */
 801                 if(n_hdlc->rx_buf_list.head)
 802                         mask |= POLLIN | POLLRDNORM;    /* readable */
 803                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 804                         mask |= POLLHUP;
 805                 if(tty_hung_up_p(filp))
 806                         mask |= POLLHUP;
 807                 if(n_hdlc->tx_free_buf_list.head)
 808                         mask |= POLLOUT | POLLWRNORM;   /* writable */
 809         }
 810         return mask;
 811 }       /* end of n_hdlc_tty_poll() */
 812
 813 /**
 814  * n_hdlc_alloc - allocate an n_hdlc instance data structure
 815  *
 816  * Returns a pointer to newly created structure if success, otherwise %NULL
 817  */
 818 static struct n_hdlc *n_hdlc_alloc(void)
 819 {
 820         struct n_hdlc_buf *buf;
 821         int i;
 822         struct n_hdlc *n_hdlc = kmalloc(sizeof(*n_hdlc), GFP_KERNEL);
 823
 824         if (!n_hdlc)
 825                 return NULL;
 826
 827         memset(n_hdlc, 0, sizeof(*n_hdlc));
 828
 829         n_hdlc_buf_list_init(&n_hdlc->rx_free_buf_list);
 830         n_hdlc_buf_list_init(&n_hdlc->tx_free_buf_list);
 831         n_hdlc_buf_list_init(&n_hdlc->rx_buf_list);
 832         n_hdlc_buf_list_init(&n_hdlc->tx_buf_list);
 833
 834         /* allocate free rx buffer list */
 835         for(i=0;i<DEFAULT_RX_BUF_COUNT;i++) {
 836                 buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
 837                 if (buf)
 838                         n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,buf);
 839                 else if (debuglevel >= DEBUG_LEVEL_INFO)
 840                         printk("%s(%d)n_hdlc_alloc(), kalloc() failed for rx buffer %d\n",__FILE__,__LINE__, i);
 841         }
 842
 843         /* allocate free tx buffer list */
 844         for(i=0;i<DEFAULT_TX_BUF_COUNT;i++) {
 845                 buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
 846                 if (buf)
 847                         n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,buf);
 848                 else if (debuglevel >= DEBUG_LEVEL_INFO)
 849                         printk("%s(%d)n_hdlc_alloc(), kalloc() failed for tx buffer %d\n",__FILE__,__LINE__, i);
 850         }
 851
 852         /* Initialize the control block */
 853         n_hdlc->magic  = HDLC_MAGIC;
 854         n_hdlc->flags  = 0;
 855
 856         return n_hdlc;
 857
 858 }       /* end of n_hdlc_alloc() */
 859
 860 /**
 861  * n_hdlc_buf_list_init - initialize specified HDLC buffer list
 862  * @list - pointer to buffer list
 863  */
 864 static void n_hdlc_buf_list_init(struct n_hdlc_buf_list *list)
 865 {
 866         memset(list, 0, sizeof(*list));
 867         spin_lock_init(&list->spinlock);
 868 }       /* end of n_hdlc_buf_list_init() */
 869
 870 /**
 871  * n_hdlc_buf_put - add specified HDLC buffer to tail of specified list
 872  * @list - pointer to buffer list
 873  * @buf - pointer to buffer
 874  */
 875 static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
 876                            struct n_hdlc_buf *buf)
 877 {
 878         unsigned long flags;
 879         spin_lock_irqsave(&list->spinlock,flags);
 880
 881         buf->link=NULL;
 882         if(list->tail)
 883                 list->tail->link = buf;
 884         else
 885                 list->head = buf;
 886         list->tail = buf;
 887         (list->count)++;
 888
 889         spin_unlock_irqrestore(&list->spinlock,flags);
 890
 891 }       /* end of n_hdlc_buf_put() */
 892
 893 /**
 894  * n_hdlc_buf_get - remove and return an HDLC buffer from list
 895  * @list - pointer to HDLC buffer list
 896  *
 897  * Remove and return an HDLC buffer from the head of the specified HDLC buffer
 898  * list.
 899  * Returns a pointer to HDLC buffer if available, otherwise %NULL.
 900  */
 901 static struct n_hdlc_buf* n_hdlc_buf_get(struct n_hdlc_buf_list *list)
 902 {
 903         unsigned long flags;
 904         struct n_hdlc_buf *buf;
 905         spin_lock_irqsave(&list->spinlock,flags);
 906
 907         buf = list->head;
 908         if (buf) {
 909                 list->head = buf->link;
 910                 (list->count)--;
 911         }
 912         if (!list->head)
 913                 list->tail = NULL;
 914
 915         spin_unlock_irqrestore(&list->spinlock,flags);
 916         return buf;
 917
 918 }       /* end of n_hdlc_buf_get() */
 919
 920 static char hdlc_banner[] __initdata =
 921         KERN_INFO "HDLC line discipline: version " HDLC_VERSION
 922         ", maxframe=%u\n";
 923 static char hdlc_register_ok[] __initdata =
 924         KERN_INFO "N_HDLC line discipline registered.\n";
 925 static char hdlc_register_fail[] __initdata =
 926         KERN_ERR "error registering line discipline: %d\n";
 927 static char hdlc_init_fail[] __initdata =
 928         KERN_INFO "N_HDLC: init failure %d\n";
 929
 930 static int __init n_hdlc_init(void)
 931 {
 932         int status;
 933
 934         /* range check maxframe arg */
 935         if (maxframe < 4096)
 936                 maxframe = 4096;
 937         else if (maxframe > 65535)
 938                 maxframe = 65535;
 939
 940         printk(hdlc_banner, maxframe);
 941
 942         status = tty_register_ldisc(N_HDLC, &n_hdlc_ldisc);
 943         if (!status)
 944                 printk(hdlc_register_ok);
 945         else
 946                 printk(hdlc_register_fail, status);
 947
 948         if (status)
 949                 printk(hdlc_init_fail, status);
 950         return status;
 951
 952 }       /* end of init_module() */
 953
 954 static char hdlc_unregister_ok[] __exitdata =
 955         KERN_INFO "N_HDLC: line discipline unregistered\n";
 956 static char hdlc_unregister_fail[] __exitdata =
 957         KERN_ERR "N_HDLC: can't unregister line discipline (err = %d)\n";
 958
 959 static void __exit n_hdlc_exit(void)
 960 {
 961         /* Release tty registration of line discipline */
 962         int status = tty_unregister_ldisc(N_HDLC);
 963
 964         if (status)
 965                 printk(hdlc_unregister_fail, status);
 966         else
 967                 printk(hdlc_unregister_ok);
 968 }
 969
 970 module_init(n_hdlc_init);
 971 module_exit(n_hdlc_exit);
 972
 973 MODULE_LICENSE("GPL");
 974 MODULE_AUTHOR("Paul Fulghum paulkf@microgate.com");
 975 module_param(debuglevel, int, 0);
 976 module_param(maxframe, int, 0);
 977 MODULE_ALIAS_LDISC(N_HDLC);