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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/module.h>
  85 #include <linux/init.h>
  86 #include <linux/kernel.h>
  87 #include <linux/sched.h>
  88 #include <linux/types.h>
  89 #include <linux/fcntl.h>
  90 #include <linux/interrupt.h>
  91 #include <linux/ptrace.h>
  92
  93 #undef VERSION
  94 #define VERSION(major,minor,patch) (((((major)<<8)+(minor))<<8)+(patch))
  95
  96 #include <linux/poll.h>
  97 #include <linux/in.h>
  98 #include <linux/ioctl.h>
  99 #include <linux/slab.h>
 100 #include <linux/tty.h>
 101 #include <linux/errno.h>
 102 #include <linux/string.h>       /* used in new tty drivers */
 103 #include <linux/signal.h>       /* used in new tty drivers */
 104 #include <linux/if.h>
 105 #include <linux/bitops.h>
 106
 107 #include <asm/system.h>
 108 #include <asm/termios.h>
 109 #include <asm/uaccess.h>
 110
 111 /*
 112  * Buffers for individual HDLC frames
 113  */
 114 #define MAX_HDLC_FRAME_SIZE 65535
 115 #define DEFAULT_RX_BUF_COUNT 10
 116 #define MAX_RX_BUF_COUNT 60
 117 #define DEFAULT_TX_BUF_COUNT 1
 118
 119 struct n_hdlc_buf {
 120         struct n_hdlc_buf *link;
 121         int               count;
 122         char              buf[1];
 123 };
 124
 125 #define N_HDLC_BUF_SIZE (sizeof(struct n_hdlc_buf) + maxframe)
 126
 127 struct n_hdlc_buf_list {
 128         struct n_hdlc_buf *head;
 129         struct n_hdlc_buf *tail;
 130         int               count;
 131         spinlock_t        spinlock;
 132 };
 133
 134 /**
 135  * struct n_hdlc - per device instance data structure
 136  * @magic - magic value for structure
 137  * @flags - miscellaneous control flags
 138  * @tty - ptr to TTY structure
 139  * @backup_tty - TTY to use if tty gets closed
 140  * @tbusy - reentrancy flag for tx wakeup code
 141  * @woke_up - FIXME: describe this field
 142  * @tbuf - currently transmitting tx buffer
 143  * @tx_buf_list - list of pending transmit frame buffers
 144  * @rx_buf_list - list of received frame buffers
 145  * @tx_free_buf_list - list unused transmit frame buffers
 146  * @rx_free_buf_list - list unused received frame buffers
 147  */
 148 struct n_hdlc {
 149         int                     magic;
 150         __u32                   flags;
 151         struct tty_struct       *tty;
 152         struct tty_struct       *backup_tty;
 153         int                     tbusy;
 154         int                     woke_up;
 155         struct n_hdlc_buf       *tbuf;
 156         struct n_hdlc_buf_list  tx_buf_list;
 157         struct n_hdlc_buf_list  rx_buf_list;
 158         struct n_hdlc_buf_list  tx_free_buf_list;
 159         struct n_hdlc_buf_list  rx_free_buf_list;
 160 };
 161
 162 /*
 163  * HDLC buffer list manipulation functions
 164  */
 165 static void n_hdlc_buf_list_init(struct n_hdlc_buf_list *list);
 166 static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
 167                            struct n_hdlc_buf *buf);
 168 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
 169
 170 /* Local functions */
 171
 172 static struct n_hdlc *n_hdlc_alloc (void);
 173
 174 /* debug level can be set by insmod for debugging purposes */
 175 #define DEBUG_LEVEL_INFO        1
 176 static int debuglevel;
 177
 178 /* max frame size for memory allocations */
 179 static int maxframe = 4096;
 180
 181 /* TTY callbacks */
 182
 183 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 184                            __u8 __user *buf, size_t nr);
 185 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 186                             const unsigned char *buf, size_t nr);
 187 static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
 188                             unsigned int cmd, unsigned long arg);
 189 static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
 190                                     poll_table *wait);
 191 static int n_hdlc_tty_open(struct tty_struct *tty);
 192 static void n_hdlc_tty_close(struct tty_struct *tty);
 193 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *cp,
 194                                char *fp, int count);
 195 static void n_hdlc_tty_wakeup(struct tty_struct *tty);
 196
 197 #define bset(p,b)       ((p)[(b) >> 5] |= (1 << ((b) & 0x1f)))
 198
 199 #define tty2n_hdlc(tty) ((struct n_hdlc *) ((tty)->disc_data))
 200 #define n_hdlc2tty(n_hdlc)      ((n_hdlc)->tty)
 201
 202 static struct tty_ldisc n_hdlc_ldisc = {
 203         .owner          = THIS_MODULE,
 204         .magic          = TTY_LDISC_MAGIC,
 205         .name           = "hdlc",
 206         .open           = n_hdlc_tty_open,
 207         .close          = n_hdlc_tty_close,
 208         .read           = n_hdlc_tty_read,
 209         .write          = n_hdlc_tty_write,
 210         .ioctl          = n_hdlc_tty_ioctl,
 211         .poll           = n_hdlc_tty_poll,
 212         .receive_buf    = n_hdlc_tty_receive,
 213         .write_wakeup   = n_hdlc_tty_wakeup,
 214 };
 215
 216 /**
 217  * n_hdlc_release - release an n_hdlc per device line discipline info structure
 218  * @n_hdlc - per device line discipline info structure
 219  */
 220 static void n_hdlc_release(struct n_hdlc *n_hdlc)
 221 {
 222         struct tty_struct *tty = n_hdlc2tty (n_hdlc);
 223         struct n_hdlc_buf *buf;
 224
 225         if (debuglevel >= DEBUG_LEVEL_INFO)
 226                 printk("%s(%d)n_hdlc_release() called\n",__FILE__,__LINE__);
 227
 228         /* Ensure that the n_hdlcd process is not hanging on select()/poll() */
 229         wake_up_interruptible (&tty->read_wait);
 230         wake_up_interruptible (&tty->write_wait);
 231
 232         if (tty->disc_data == n_hdlc)
 233                 tty->disc_data = NULL;  /* Break the tty->n_hdlc link */
 234
 235         /* Release transmit and receive buffers */
 236         for(;;) {
 237                 buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
 238                 if (buf) {
 239                         kfree(buf);
 240                 } else
 241                         break;
 242         }
 243         for(;;) {
 244                 buf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
 245                 if (buf) {
 246                         kfree(buf);
 247                 } else
 248                         break;
 249         }
 250         for(;;) {
 251                 buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
 252                 if (buf) {
 253                         kfree(buf);
 254                 } else
 255                         break;
 256         }
 257         for(;;) {
 258                 buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 259                 if (buf) {
 260                         kfree(buf);
 261                 } else
 262                         break;
 263         }
 264         kfree(n_hdlc->tbuf);
 265         kfree(n_hdlc);
 266
 267 }       /* end of n_hdlc_release() */
 268
 269 /**
 270  * n_hdlc_tty_close - line discipline close
 271  * @tty - pointer to tty info structure
 272  *
 273  * Called when the line discipline is changed to something
 274  * else, the tty is closed, or the tty detects a hangup.
 275  */
 276 static void n_hdlc_tty_close(struct tty_struct *tty)
 277 {
 278         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 279
 280         if (debuglevel >= DEBUG_LEVEL_INFO)
 281                 printk("%s(%d)n_hdlc_tty_close() called\n",__FILE__,__LINE__);
 282
 283         if (n_hdlc != NULL) {
 284                 if (n_hdlc->magic != HDLC_MAGIC) {
 285                         printk (KERN_WARNING"n_hdlc: trying to close unopened tty!\n");
 286                         return;
 287                 }
 288 #if defined(TTY_NO_WRITE_SPLIT)
 289                 clear_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
 290 #endif
 291                 tty->disc_data = NULL;
 292                 if (tty == n_hdlc->backup_tty)
 293                         n_hdlc->backup_tty = NULL;
 294                 if (tty != n_hdlc->tty)
 295                         return;
 296                 if (n_hdlc->backup_tty) {
 297                         n_hdlc->tty = n_hdlc->backup_tty;
 298                 } else {
 299                         n_hdlc_release (n_hdlc);
 300                 }
 301         }
 302
 303         if (debuglevel >= DEBUG_LEVEL_INFO)
 304                 printk("%s(%d)n_hdlc_tty_close() success\n",__FILE__,__LINE__);
 305
 306 }       /* end of n_hdlc_tty_close() */
 307
 308 /**
 309  * n_hdlc_tty_open - called when line discipline changed to n_hdlc
 310  * @tty - pointer to tty info structure
 311  *
 312  * Returns 0 if success, otherwise error code
 313  */
 314 static int n_hdlc_tty_open (struct tty_struct *tty)
 315 {
 316         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 317
 318         if (debuglevel >= DEBUG_LEVEL_INFO)
 319                 printk("%s(%d)n_hdlc_tty_open() called (device=%s)\n",
 320                 __FILE__,__LINE__,
 321                 tty->name);
 322
 323         /* There should not be an existing table for this slot. */
 324         if (n_hdlc) {
 325                 printk (KERN_ERR"n_hdlc_tty_open:tty already associated!\n" );
 326                 return -EEXIST;
 327         }
 328
 329         n_hdlc = n_hdlc_alloc();
 330         if (!n_hdlc) {
 331                 printk (KERN_ERR "n_hdlc_alloc failed\n");
 332                 return -ENFILE;
 333         }
 334
 335         tty->disc_data = n_hdlc;
 336         n_hdlc->tty    = tty;
 337         tty->receive_room = 65536;
 338
 339 #if defined(TTY_NO_WRITE_SPLIT)
 340         /* change tty_io write() to not split large writes into 8K chunks */
 341         set_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
 342 #endif
 343
 344         /* Flush any pending characters in the driver and discipline. */
 345         if (tty->ldisc.flush_buffer)
 346                 tty->ldisc.flush_buffer(tty);
 347
 348         tty_driver_flush_buffer(tty);
 349
 350         if (debuglevel >= DEBUG_LEVEL_INFO)
 351                 printk("%s(%d)n_hdlc_tty_open() success\n",__FILE__,__LINE__);
 352
 353         return 0;
 354
 355 }       /* end of n_tty_hdlc_open() */
 356
 357 /**
 358  * n_hdlc_send_frames - send frames on pending send buffer list
 359  * @n_hdlc - pointer to ldisc instance data
 360  * @tty - pointer to tty instance data
 361  *
 362  * Send frames on pending send buffer list until the driver does not accept a
 363  * frame (busy) this function is called after adding a frame to the send buffer
 364  * list and by the tty wakeup callback.
 365  */
 366 static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
 367 {
 368         register int actual;
 369         unsigned long flags;
 370         struct n_hdlc_buf *tbuf;
 371
 372         if (debuglevel >= DEBUG_LEVEL_INFO)
 373                 printk("%s(%d)n_hdlc_send_frames() called\n",__FILE__,__LINE__);
 374  check_again:
 375
 376         spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
 377         if (n_hdlc->tbusy) {
 378                 n_hdlc->woke_up = 1;
 379                 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 380                 return;
 381         }
 382         n_hdlc->tbusy = 1;
 383         n_hdlc->woke_up = 0;
 384         spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 385
 386         /* get current transmit buffer or get new transmit */
 387         /* buffer from list of pending transmit buffers */
 388
 389         tbuf = n_hdlc->tbuf;
 390         if (!tbuf)
 391                 tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 392
 393         while (tbuf) {
 394                 if (debuglevel >= DEBUG_LEVEL_INFO)
 395                         printk("%s(%d)sending frame %p, count=%d\n",
 396                                 __FILE__,__LINE__,tbuf,tbuf->count);
 397
 398                 /* Send the next block of data to device */
 399                 tty->flags |= (1 << TTY_DO_WRITE_WAKEUP);
 400                 actual = tty->ops->write(tty, tbuf->buf, tbuf->count);
 401
 402                 /* rollback was possible and has been done */
 403                 if (actual == -ERESTARTSYS) {
 404                         n_hdlc->tbuf = tbuf;
 405                         break;
 406                 }
 407                 /* if transmit error, throw frame away by */
 408                 /* pretending it was accepted by driver */
 409                 if (actual < 0)
 410                         actual = tbuf->count;
 411
 412                 if (actual == tbuf->count) {
 413                         if (debuglevel >= DEBUG_LEVEL_INFO)
 414                                 printk("%s(%d)frame %p completed\n",
 415                                         __FILE__,__LINE__,tbuf);
 416
 417                         /* free current transmit buffer */
 418                         n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf);
 419
 420                         /* this tx buffer is done */
 421                         n_hdlc->tbuf = NULL;
 422
 423                         /* wait up sleeping writers */
 424                         wake_up_interruptible(&tty->write_wait);
 425
 426                         /* get next pending transmit buffer */
 427                         tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 428                 } else {
 429                         if (debuglevel >= DEBUG_LEVEL_INFO)
 430                                 printk("%s(%d)frame %p pending\n",
 431                                         __FILE__,__LINE__,tbuf);
 432
 433                         /* buffer not accepted by driver */
 434                         /* set this buffer as pending buffer */
 435                         n_hdlc->tbuf = tbuf;
 436                         break;
 437                 }
 438         }
 439
 440         if (!tbuf)
 441                 tty->flags  &= ~(1 << TTY_DO_WRITE_WAKEUP);
 442
 443         /* Clear the re-entry flag */
 444         spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
 445         n_hdlc->tbusy = 0;
 446         spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 447
 448         if (n_hdlc->woke_up)
 449           goto check_again;
 450
 451         if (debuglevel >= DEBUG_LEVEL_INFO)
 452                 printk("%s(%d)n_hdlc_send_frames() exit\n",__FILE__,__LINE__);
 453
 454 }       /* end of n_hdlc_send_frames() */
 455
 456 /**
 457  * n_hdlc_tty_wakeup - Callback for transmit wakeup
 458  * @tty - pointer to associated tty instance data
 459  *
 460  * Called when low level device driver can accept more send data.
 461  */
 462 static void n_hdlc_tty_wakeup(struct tty_struct *tty)
 463 {
 464         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 465
 466         if (debuglevel >= DEBUG_LEVEL_INFO)
 467                 printk("%s(%d)n_hdlc_tty_wakeup() called\n",__FILE__,__LINE__);
 468
 469         if (!n_hdlc)
 470                 return;
 471
 472         if (tty != n_hdlc->tty) {
 473                 tty->flags &= ~(1 << TTY_DO_WRITE_WAKEUP);
 474                 return;
 475         }
 476
 477         n_hdlc_send_frames (n_hdlc, tty);
 478
 479 }       /* end of n_hdlc_tty_wakeup() */
 480
 481 /**
 482  * n_hdlc_tty_receive - Called by tty driver when receive data is available
 483  * @tty - pointer to tty instance data
 484  * @data - pointer to received data
 485  * @flags - pointer to flags for data
 486  * @count - count of received data in bytes
 487  *
 488  * Called by tty low level driver when receive data is available. Data is
 489  * interpreted as one HDLC frame.
 490  */
 491 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
 492                                char *flags, int count)
 493 {
 494         register struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 495         register struct n_hdlc_buf *buf;
 496
 497         if (debuglevel >= DEBUG_LEVEL_INFO)
 498                 printk("%s(%d)n_hdlc_tty_receive() called count=%d\n",
 499                         __FILE__,__LINE__, count);
 500
 501         /* This can happen if stuff comes in on the backup tty */
 502         if (!n_hdlc || tty != n_hdlc->tty)
 503                 return;
 504
 505         /* verify line is using HDLC discipline */
 506         if (n_hdlc->magic != HDLC_MAGIC) {
 507                 printk("%s(%d) line not using HDLC discipline\n",
 508                         __FILE__,__LINE__);
 509                 return;
 510         }
 511
 512         if ( count>maxframe ) {
 513                 if (debuglevel >= DEBUG_LEVEL_INFO)
 514                         printk("%s(%d) rx count>maxframesize, data discarded\n",
 515                                __FILE__,__LINE__);
 516                 return;
 517         }
 518
 519         /* get a free HDLC buffer */
 520         buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
 521         if (!buf) {
 522                 /* no buffers in free list, attempt to allocate another rx buffer */
 523                 /* unless the maximum count has been reached */
 524                 if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT)
 525                         buf = kmalloc(N_HDLC_BUF_SIZE, GFP_ATOMIC);
 526         }
 527
 528         if (!buf) {
 529                 if (debuglevel >= DEBUG_LEVEL_INFO)
 530                         printk("%s(%d) no more rx buffers, data discarded\n",
 531                                __FILE__,__LINE__);
 532                 return;
 533         }
 534
 535         /* copy received data to HDLC buffer */
 536         memcpy(buf->buf,data,count);
 537         buf->count=count;
 538
 539         /* add HDLC buffer to list of received frames */
 540         n_hdlc_buf_put(&n_hdlc->rx_buf_list, buf);
 541
 542         /* wake up any blocked reads and perform async signalling */
 543         wake_up_interruptible (&tty->read_wait);
 544         if (n_hdlc->tty->fasync != NULL)
 545                 kill_fasync (&n_hdlc->tty->fasync, SIGIO, POLL_IN);
 546
 547 }       /* end of n_hdlc_tty_receive() */
 548
 549 /**
 550  * n_hdlc_tty_read - Called to retrieve one frame of data (if available)
 551  * @tty - pointer to tty instance data
 552  * @file - pointer to open file object
 553  * @buf - pointer to returned data buffer
 554  * @nr - size of returned data buffer
 555  *
 556  * Returns the number of bytes returned or error code.
 557  */
 558 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 559                            __u8 __user *buf, size_t nr)
 560 {
 561         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 562         int ret;
 563         struct n_hdlc_buf *rbuf;
 564
 565         if (debuglevel >= DEBUG_LEVEL_INFO)
 566                 printk("%s(%d)n_hdlc_tty_read() called\n",__FILE__,__LINE__);
 567
 568         /* Validate the pointers */
 569         if (!n_hdlc)
 570                 return -EIO;
 571
 572         /* verify user access to buffer */
 573         if (!access_ok(VERIFY_WRITE, buf, nr)) {
 574                 printk(KERN_WARNING "%s(%d) n_hdlc_tty_read() can't verify user "
 575                 "buffer\n", __FILE__, __LINE__);
 576                 return -EFAULT;
 577         }
 578
 579         lock_kernel();
 580
 581         for (;;) {
 582                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
 583                         unlock_kernel();
 584                         return -EIO;
 585                 }
 586
 587                 n_hdlc = tty2n_hdlc (tty);
 588                 if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC ||
 589                          tty != n_hdlc->tty) {
 590                         unlock_kernel();
 591                         return 0;
 592                 }
 593
 594                 rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
 595                 if (rbuf)
 596                         break;
 597
 598                 /* no data */
 599                 if (file->f_flags & O_NONBLOCK) {
 600                         unlock_kernel();
 601                         return -EAGAIN;
 602                 }
 603
 604                 interruptible_sleep_on (&tty->read_wait);
 605                 if (signal_pending(current)) {
 606                         unlock_kernel();
 607                         return -EINTR;
 608                 }
 609         }
 610
 611         if (rbuf->count > nr)
 612                 /* frame too large for caller's buffer (discard frame) */
 613                 ret = -EOVERFLOW;
 614         else {
 615                 /* Copy the data to the caller's buffer */
 616                 if (copy_to_user(buf, rbuf->buf, rbuf->count))
 617                         ret = -EFAULT;
 618                 else
 619                         ret = rbuf->count;
 620         }
 621
 622         /* return HDLC buffer to free list unless the free list */
 623         /* count has exceeded the default value, in which case the */
 624         /* buffer is freed back to the OS to conserve memory */
 625         if (n_hdlc->rx_free_buf_list.count > DEFAULT_RX_BUF_COUNT)
 626                 kfree(rbuf);
 627         else
 628                 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,rbuf);
 629         unlock_kernel();
 630         return ret;
 631
 632 }       /* end of n_hdlc_tty_read() */
 633
 634 /**
 635  * n_hdlc_tty_write - write a single frame of data to device
 636  * @tty - pointer to associated tty device instance data
 637  * @file - pointer to file object data
 638  * @data - pointer to transmit data (one frame)
 639  * @count - size of transmit frame in bytes
 640  *
 641  * Returns the number of bytes written (or error code).
 642  */
 643 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 644                             const unsigned char *data, size_t count)
 645 {
 646         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 647         int error = 0;
 648         DECLARE_WAITQUEUE(wait, current);
 649         struct n_hdlc_buf *tbuf;
 650
 651         if (debuglevel >= DEBUG_LEVEL_INFO)
 652                 printk("%s(%d)n_hdlc_tty_write() called count=%Zd\n",
 653                         __FILE__,__LINE__,count);
 654
 655         /* Verify pointers */
 656         if (!n_hdlc)
 657                 return -EIO;
 658
 659         if (n_hdlc->magic != HDLC_MAGIC)
 660                 return -EIO;
 661
 662         /* verify frame size */
 663         if (count > maxframe ) {
 664                 if (debuglevel & DEBUG_LEVEL_INFO)
 665                         printk (KERN_WARNING
 666                                 "n_hdlc_tty_write: truncating user packet "
 667                                 "from %lu to %d\n", (unsigned long) count,
 668                                 maxframe );
 669                 count = maxframe;
 670         }
 671
 672         lock_kernel();
 673
 674         add_wait_queue(&tty->write_wait, &wait);
 675         set_current_state(TASK_INTERRUPTIBLE);
 676
 677         /* Allocate transmit buffer */
 678         /* sleep until transmit buffer available */
 679         while (!(tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list))) {
 680                 schedule();
 681
 682                 n_hdlc = tty2n_hdlc (tty);
 683                 if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC ||
 684                     tty != n_hdlc->tty) {
 685                         printk("n_hdlc_tty_write: %p invalid after wait!\n", n_hdlc);
 686                         error = -EIO;
 687                         break;
 688                 }
 689
 690                 if (signal_pending(current)) {
 691                         error = -EINTR;
 692                         break;
 693                 }
 694         }
 695
 696         set_current_state(TASK_RUNNING);
 697         remove_wait_queue(&tty->write_wait, &wait);
 698
 699         if (!error) {
 700                 /* Retrieve the user's buffer */
 701                 memcpy(tbuf->buf, data, count);
 702
 703                 /* Send the data */
 704                 tbuf->count = error = count;
 705                 n_hdlc_buf_put(&n_hdlc->tx_buf_list,tbuf);
 706                 n_hdlc_send_frames(n_hdlc,tty);
 707         }
 708         unlock_kernel();
 709         return error;
 710
 711 }       /* end of n_hdlc_tty_write() */
 712
 713 /**
 714  * n_hdlc_tty_ioctl - process IOCTL system call for the tty device.
 715  * @tty - pointer to tty instance data
 716  * @file - pointer to open file object for device
 717  * @cmd - IOCTL command code
 718  * @arg - argument for IOCTL call (cmd dependent)
 719  *
 720  * Returns command dependent result.
 721  */
 722 static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
 723                             unsigned int cmd, unsigned long arg)
 724 {
 725         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 726         int error = 0;
 727         int count;
 728         unsigned long flags;
 729
 730         if (debuglevel >= DEBUG_LEVEL_INFO)
 731                 printk("%s(%d)n_hdlc_tty_ioctl() called %d\n",
 732                         __FILE__,__LINE__,cmd);
 733
 734         /* Verify the status of the device */
 735         if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC)
 736                 return -EBADF;
 737
 738         switch (cmd) {
 739         case FIONREAD:
 740                 /* report count of read data available */
 741                 /* in next available frame (if any) */
 742                 spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock,flags);
 743                 if (n_hdlc->rx_buf_list.head)
 744                         count = n_hdlc->rx_buf_list.head->count;
 745                 else
 746                         count = 0;
 747                 spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock,flags);
 748                 error = put_user(count, (int __user *)arg);
 749                 break;
 750
 751         case TIOCOUTQ:
 752                 /* get the pending tx byte count in the driver */
 753                 count = tty_chars_in_buffer(tty);
 754                 /* add size of next output frame in queue */
 755                 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock,flags);
 756                 if (n_hdlc->tx_buf_list.head)
 757                         count += n_hdlc->tx_buf_list.head->count;
 758                 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock,flags);
 759                 error = put_user(count, (int __user *)arg);
 760                 break;
 761
 762         default:
 763                 error = n_tty_ioctl (tty, file, cmd, arg);
 764                 break;
 765         }
 766         return error;
 767
 768 }       /* end of n_hdlc_tty_ioctl() */
 769
 770 /**
 771  * n_hdlc_tty_poll - TTY callback for poll system call
 772  * @tty - pointer to tty instance data
 773  * @filp - pointer to open file object for device
 774  * @poll_table - wait queue for operations
 775  *
 776  * Determine which operations (read/write) will not block and return info
 777  * to caller.
 778  * Returns a bit mask containing info on which ops will not block.
 779  */
 780 static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
 781                                     poll_table *wait)
 782 {
 783         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 784         unsigned int mask = 0;
 785
 786         if (debuglevel >= DEBUG_LEVEL_INFO)
 787                 printk("%s(%d)n_hdlc_tty_poll() called\n",__FILE__,__LINE__);
 788
 789         if (n_hdlc && n_hdlc->magic == HDLC_MAGIC && tty == n_hdlc->tty) {
 790                 /* queue current process into any wait queue that */
 791                 /* may awaken in the future (read and write) */
 792
 793                 poll_wait(filp, &tty->read_wait, wait);
 794                 poll_wait(filp, &tty->write_wait, wait);
 795
 796                 /* set bits for operations that won't block */
 797                 if (n_hdlc->rx_buf_list.head)
 798                         mask |= POLLIN | POLLRDNORM;    /* readable */
 799                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 800                         mask |= POLLHUP;
 801                 if (tty_hung_up_p(filp))
 802                         mask |= POLLHUP;
 803                 if (!tty_is_writelocked(tty) &&
 804                                 n_hdlc->tx_free_buf_list.head)
 805                         mask |= POLLOUT | POLLWRNORM;   /* writable */
 806         }
 807         return mask;
 808 }       /* end of n_hdlc_tty_poll() */
 809
 810 /**
 811  * n_hdlc_alloc - allocate an n_hdlc instance data structure
 812  *
 813  * Returns a pointer to newly created structure if success, otherwise %NULL
 814  */
 815 static struct n_hdlc *n_hdlc_alloc(void)
 816 {
 817         struct n_hdlc_buf *buf;
 818         int i;
 819         struct n_hdlc *n_hdlc = kmalloc(sizeof(*n_hdlc), GFP_KERNEL);
 820
 821         if (!n_hdlc)
 822                 return NULL;
 823
 824         memset(n_hdlc, 0, sizeof(*n_hdlc));
 825
 826         n_hdlc_buf_list_init(&n_hdlc->rx_free_buf_list);
 827         n_hdlc_buf_list_init(&n_hdlc->tx_free_buf_list);
 828         n_hdlc_buf_list_init(&n_hdlc->rx_buf_list);
 829         n_hdlc_buf_list_init(&n_hdlc->tx_buf_list);
 830
 831         /* allocate free rx buffer list */
 832         for(i=0;i<DEFAULT_RX_BUF_COUNT;i++) {
 833                 buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
 834                 if (buf)
 835                         n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,buf);
 836                 else if (debuglevel >= DEBUG_LEVEL_INFO)
 837                         printk("%s(%d)n_hdlc_alloc(), kalloc() failed for rx buffer %d\n",__FILE__,__LINE__, i);
 838         }
 839
 840         /* allocate free tx buffer list */
 841         for(i=0;i<DEFAULT_TX_BUF_COUNT;i++) {
 842                 buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
 843                 if (buf)
 844                         n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,buf);
 845                 else if (debuglevel >= DEBUG_LEVEL_INFO)
 846                         printk("%s(%d)n_hdlc_alloc(), kalloc() failed for tx buffer %d\n",__FILE__,__LINE__, i);
 847         }
 848
 849         /* Initialize the control block */
 850         n_hdlc->magic  = HDLC_MAGIC;
 851         n_hdlc->flags  = 0;
 852
 853         return n_hdlc;
 854
 855 }       /* end of n_hdlc_alloc() */
 856
 857 /**
 858  * n_hdlc_buf_list_init - initialize specified HDLC buffer list
 859  * @list - pointer to buffer list
 860  */
 861 static void n_hdlc_buf_list_init(struct n_hdlc_buf_list *list)
 862 {
 863         memset(list, 0, sizeof(*list));
 864         spin_lock_init(&list->spinlock);
 865 }       /* end of n_hdlc_buf_list_init() */
 866
 867 /**
 868  * n_hdlc_buf_put - add specified HDLC buffer to tail of specified list
 869  * @list - pointer to buffer list
 870  * @buf - pointer to buffer
 871  */
 872 static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
 873                            struct n_hdlc_buf *buf)
 874 {
 875         unsigned long flags;
 876         spin_lock_irqsave(&list->spinlock,flags);
 877
 878         buf->link=NULL;
 879         if (list->tail)
 880                 list->tail->link = buf;
 881         else
 882                 list->head = buf;
 883         list->tail = buf;
 884         (list->count)++;
 885
 886         spin_unlock_irqrestore(&list->spinlock,flags);
 887
 888 }       /* end of n_hdlc_buf_put() */
 889
 890 /**
 891  * n_hdlc_buf_get - remove and return an HDLC buffer from list
 892  * @list - pointer to HDLC buffer list
 893  *
 894  * Remove and return an HDLC buffer from the head of the specified HDLC buffer
 895  * list.
 896  * Returns a pointer to HDLC buffer if available, otherwise %NULL.
 897  */
 898 static struct n_hdlc_buf* n_hdlc_buf_get(struct n_hdlc_buf_list *list)
 899 {
 900         unsigned long flags;
 901         struct n_hdlc_buf *buf;
 902         spin_lock_irqsave(&list->spinlock,flags);
 903
 904         buf = list->head;
 905         if (buf) {
 906                 list->head = buf->link;
 907                 (list->count)--;
 908         }
 909         if (!list->head)
 910                 list->tail = NULL;
 911
 912         spin_unlock_irqrestore(&list->spinlock,flags);
 913         return buf;
 914
 915 }       /* end of n_hdlc_buf_get() */
 916
 917 static char hdlc_banner[] __initdata =
 918         KERN_INFO "HDLC line discipline: version " HDLC_VERSION
 919         ", maxframe=%u\n";
 920 static char hdlc_register_ok[] __initdata =
 921         KERN_INFO "N_HDLC line discipline registered.\n";
 922 static char hdlc_register_fail[] __initdata =
 923         KERN_ERR "error registering line discipline: %d\n";
 924 static char hdlc_init_fail[] __initdata =
 925         KERN_INFO "N_HDLC: init failure %d\n";
 926
 927 static int __init n_hdlc_init(void)
 928 {
 929         int status;
 930
 931         /* range check maxframe arg */
 932         if (maxframe < 4096)
 933                 maxframe = 4096;
 934         else if (maxframe > 65535)
 935                 maxframe = 65535;
 936
 937         printk(hdlc_banner, maxframe);
 938
 939         status = tty_register_ldisc(N_HDLC, &n_hdlc_ldisc);
 940         if (!status)
 941                 printk(hdlc_register_ok);
 942         else
 943                 printk(hdlc_register_fail, status);
 944
 945         if (status)
 946                 printk(hdlc_init_fail, status);
 947         return status;
 948
 949 }       /* end of init_module() */
 950
 951 static char hdlc_unregister_ok[] __exitdata =
 952         KERN_INFO "N_HDLC: line discipline unregistered\n";
 953 static char hdlc_unregister_fail[] __exitdata =
 954         KERN_ERR "N_HDLC: can't unregister line discipline (err = %d)\n";
 955
 956 static void __exit n_hdlc_exit(void)
 957 {
 958         /* Release tty registration of line discipline */
 959         int status = tty_unregister_ldisc(N_HDLC);
 960
 961         if (status)
 962                 printk(hdlc_unregister_fail, status);
 963         else
 964                 printk(hdlc_unregister_ok);
 965 }
 966
 967 module_init(n_hdlc_init);
 968 module_exit(n_hdlc_exit);
 969
 970 MODULE_LICENSE("GPL");
 971 MODULE_AUTHOR("Paul Fulghum paulkf@microgate.com");
 972 module_param(debuglevel, int, 0);
 973 module_param(maxframe, int, 0);
 974 MODULE_ALIAS_LDISC(N_HDLC);