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
 107 #include <asm/system.h>
 108 #include <asm/bitops.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 ssize_t maxframe = 4096;
 181
 182 /* TTY callbacks */
 183
 184 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 185                            __u8 *buf, size_t nr);
 186 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 187                             const __u8 *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         if (n_hdlc->tbuf)
 268                 kfree(n_hdlc->tbuf);
 269         kfree(n_hdlc);
 270
 271 }       /* end of n_hdlc_release() */
 272
 273 /**
 274  * n_hdlc_tty_close - line discipline close
 275  * @tty - pointer to tty info structure
 276  *
 277  * Called when the line discipline is changed to something
 278  * else, the tty is closed, or the tty detects a hangup.
 279  */
 280 static void n_hdlc_tty_close(struct tty_struct *tty)
 281 {
 282         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 283
 284         if (debuglevel >= DEBUG_LEVEL_INFO)
 285                 printk("%s(%d)n_hdlc_tty_close() called\n",__FILE__,__LINE__);
 286
 287         if (n_hdlc != NULL) {
 288                 if (n_hdlc->magic != HDLC_MAGIC) {
 289                         printk (KERN_WARNING"n_hdlc: trying to close unopened tty!\n");
 290                         return;
 291                 }
 292 #if defined(TTY_NO_WRITE_SPLIT)
 293                 clear_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
 294 #endif
 295                 tty->disc_data = NULL;
 296                 if (tty == n_hdlc->backup_tty)
 297                         n_hdlc->backup_tty = 0;
 298                 if (tty != n_hdlc->tty)
 299                         return;
 300                 if (n_hdlc->backup_tty) {
 301                         n_hdlc->tty = n_hdlc->backup_tty;
 302                 } else {
 303                         n_hdlc_release (n_hdlc);
 304                 }
 305         }
 306
 307         if (debuglevel >= DEBUG_LEVEL_INFO)
 308                 printk("%s(%d)n_hdlc_tty_close() success\n",__FILE__,__LINE__);
 309
 310 }       /* end of n_hdlc_tty_close() */
 311
 312 /**
 313  * n_hdlc_tty_open - called when line discipline changed to n_hdlc
 314  * @tty - pointer to tty info structure
 315  *
 316  * Returns 0 if success, otherwise error code
 317  */
 318 static int n_hdlc_tty_open (struct tty_struct *tty)
 319 {
 320         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 321
 322         if (debuglevel >= DEBUG_LEVEL_INFO)
 323                 printk("%s(%d)n_hdlc_tty_open() called (device=%s)\n",
 324                 __FILE__,__LINE__,
 325                 tty->name);
 326
 327         /* There should not be an existing table for this slot. */
 328         if (n_hdlc) {
 329                 printk (KERN_ERR"n_hdlc_tty_open:tty already associated!\n" );
 330                 return -EEXIST;
 331         }
 332
 333         n_hdlc = n_hdlc_alloc();
 334         if (!n_hdlc) {
 335                 printk (KERN_ERR "n_hdlc_alloc failed\n");
 336                 return -ENFILE;
 337         }
 338
 339         tty->disc_data = n_hdlc;
 340         n_hdlc->tty    = tty;
 341
 342 #if defined(TTY_NO_WRITE_SPLIT)
 343         /* change tty_io write() to not split large writes into 8K chunks */
 344         set_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
 345 #endif
 346
 347         /* Flush any pending characters in the driver and discipline. */
 348
 349         if (tty->ldisc.flush_buffer)
 350                 tty->ldisc.flush_buffer (tty);
 351
 352         if (tty->driver->flush_buffer)
 353                 tty->driver->flush_buffer (tty);
 354
 355         if (debuglevel >= DEBUG_LEVEL_INFO)
 356                 printk("%s(%d)n_hdlc_tty_open() success\n",__FILE__,__LINE__);
 357
 358         return 0;
 359
 360 }       /* end of n_tty_hdlc_open() */
 361
 362 /**
 363  * n_hdlc_send_frames - send frames on pending send buffer list
 364  * @n_hdlc - pointer to ldisc instance data
 365  * @tty - pointer to tty instance data
 366  *
 367  * Send frames on pending send buffer list until the driver does not accept a
 368  * frame (busy) this function is called after adding a frame to the send buffer
 369  * list and by the tty wakeup callback.
 370  */
 371 static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
 372 {
 373         register int actual;
 374         unsigned long flags;
 375         struct n_hdlc_buf *tbuf;
 376
 377         if (debuglevel >= DEBUG_LEVEL_INFO)
 378                 printk("%s(%d)n_hdlc_send_frames() called\n",__FILE__,__LINE__);
 379  check_again:
 380
 381         spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
 382         if (n_hdlc->tbusy) {
 383                 n_hdlc->woke_up = 1;
 384                 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 385                 return;
 386         }
 387         n_hdlc->tbusy = 1;
 388         n_hdlc->woke_up = 0;
 389         spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 390
 391         /* get current transmit buffer or get new transmit */
 392         /* buffer from list of pending transmit buffers */
 393
 394         tbuf = n_hdlc->tbuf;
 395         if (!tbuf)
 396                 tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 397
 398         while (tbuf) {
 399                 if (debuglevel >= DEBUG_LEVEL_INFO)
 400                         printk("%s(%d)sending frame %p, count=%d\n",
 401                                 __FILE__,__LINE__,tbuf,tbuf->count);
 402
 403                 /* Send the next block of data to device */
 404                 tty->flags |= (1 << TTY_DO_WRITE_WAKEUP);
 405                 actual = tty->driver->write(tty, 0, tbuf->buf, tbuf->count);
 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_room - Return the amount of space left in the receiver's buffer
 483  * @tty - pointer to associated tty instance data
 484  *
 485  * Callback function from tty driver. Return the amount of space left in the
 486  * receiver's buffer to decide if remote transmitter is to be throttled.
 487  */
 488 static int n_hdlc_tty_room(struct tty_struct *tty)
 489 {
 490         if (debuglevel >= DEBUG_LEVEL_INFO)
 491                 printk("%s(%d)n_hdlc_tty_room() called\n",__FILE__,__LINE__);
 492         /* always return a larger number to prevent */
 493         /* throttling of remote transmitter. */
 494         return 65536;
 495 }       /* end of n_hdlc_tty_root() */
 496
 497 /**
 498  * n_hdlc_tty_receive - Called by tty driver when receive data is available
 499  * @tty - pointer to tty instance data
 500  * @data - pointer to received data
 501  * @flags - pointer to flags for data
 502  * @count - count of received data in bytes
 503  *
 504  * Called by tty low level driver when receive data is available. Data is
 505  * interpreted as one HDLC frame.
 506  */
 507 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
 508                                char *flags, int count)
 509 {
 510         register struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 511         register struct n_hdlc_buf *buf;
 512
 513         if (debuglevel >= DEBUG_LEVEL_INFO)
 514                 printk("%s(%d)n_hdlc_tty_receive() called count=%d\n",
 515                         __FILE__,__LINE__, count);
 516
 517         /* This can happen if stuff comes in on the backup tty */
 518         if (n_hdlc == 0 || tty != n_hdlc->tty)
 519                 return;
 520
 521         /* verify line is using HDLC discipline */
 522         if (n_hdlc->magic != HDLC_MAGIC) {
 523                 printk("%s(%d) line not using HDLC discipline\n",
 524                         __FILE__,__LINE__);
 525                 return;
 526         }
 527
 528         if ( count>maxframe ) {
 529                 if (debuglevel >= DEBUG_LEVEL_INFO)
 530                         printk("%s(%d) rx count>maxframesize, data discarded\n",
 531                                __FILE__,__LINE__);
 532                 return;
 533         }
 534
 535         /* get a free HDLC buffer */
 536         buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
 537         if (!buf) {
 538                 /* no buffers in free list, attempt to allocate another rx buffer */
 539                 /* unless the maximum count has been reached */
 540                 if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT)
 541                         buf = kmalloc(N_HDLC_BUF_SIZE, GFP_ATOMIC);
 542         }
 543
 544         if (!buf) {
 545                 if (debuglevel >= DEBUG_LEVEL_INFO)
 546                         printk("%s(%d) no more rx buffers, data discarded\n",
 547                                __FILE__,__LINE__);
 548                 return;
 549         }
 550
 551         /* copy received data to HDLC buffer */
 552         memcpy(buf->buf,data,count);
 553         buf->count=count;
 554
 555         /* add HDLC buffer to list of received frames */
 556         n_hdlc_buf_put(&n_hdlc->rx_buf_list, buf);
 557
 558         /* wake up any blocked reads and perform async signalling */
 559         wake_up_interruptible (&tty->read_wait);
 560         if (n_hdlc->tty->fasync != NULL)
 561                 kill_fasync (&n_hdlc->tty->fasync, SIGIO, POLL_IN);
 562
 563 }       /* end of n_hdlc_tty_receive() */
 564
 565 /**
 566  * n_hdlc_tty_read - Called to retreive one frame of data (if available)
 567  * @tty - pointer to tty instance data
 568  * @file - pointer to open file object
 569  * @buf - pointer to returned data buffer
 570  * @nr - size of returned data buffer
 571  *
 572  * Returns the number of bytes returned or error code.
 573  */
 574 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 575                            __u8 *buf, size_t nr)
 576 {
 577         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 578         int error;
 579         int ret;
 580         struct n_hdlc_buf *rbuf;
 581
 582         if (debuglevel >= DEBUG_LEVEL_INFO)
 583                 printk("%s(%d)n_hdlc_tty_read() called\n",__FILE__,__LINE__);
 584
 585         /* Validate the pointers */
 586         if (!n_hdlc)
 587                 return -EIO;
 588
 589         /* verify user access to buffer */
 590         error = verify_area (VERIFY_WRITE, buf, nr);
 591         if (error != 0) {
 592                 printk(KERN_WARNING"%s(%d) n_hdlc_tty_read() can't verify user "
 593                 "buffer\n",__FILE__,__LINE__);
 594                 return (error);
 595         }
 596
 597         for (;;) {
 598                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 599                         return -EIO;
 600
 601                 n_hdlc = tty2n_hdlc (tty);
 602                 if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC ||
 603                          tty != n_hdlc->tty)
 604                         return 0;
 605
 606                 rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
 607                 if (rbuf)
 608                         break;
 609
 610                 /* no data */
 611                 if (file->f_flags & O_NONBLOCK)
 612                         return -EAGAIN;
 613
 614                 interruptible_sleep_on (&tty->read_wait);
 615                 if (signal_pending(current))
 616                         return -EINTR;
 617         }
 618
 619         if (rbuf->count > nr)
 620                 /* frame too large for caller's buffer (discard frame) */
 621                 ret = -EOVERFLOW;
 622         else {
 623                 /* Copy the data to the caller's buffer */
 624                 if (copy_to_user(buf, rbuf->buf, rbuf->count))
 625                         ret = -EFAULT;
 626                 else
 627                         ret = rbuf->count;
 628         }
 629
 630         /* return HDLC buffer to free list unless the free list */
 631         /* count has exceeded the default value, in which case the */
 632         /* buffer is freed back to the OS to conserve memory */
 633         if (n_hdlc->rx_free_buf_list.count > DEFAULT_RX_BUF_COUNT)
 634                 kfree(rbuf);
 635         else
 636                 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,rbuf);
 637
 638         return ret;
 639
 640 }       /* end of n_hdlc_tty_read() */
 641
 642 /**
 643  * n_hdlc_tty_write - write a single frame of data to device
 644  * @tty - pointer to associated tty device instance data
 645  * @file - pointer to file object data
 646  * @data - pointer to transmit data (one frame)
 647  * @count - size of transmit frame in bytes
 648  *
 649  * Returns the number of bytes written (or error code).
 650  */
 651 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 652                             const __u8 *data, size_t count)
 653 {
 654         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 655         int error = 0;
 656         DECLARE_WAITQUEUE(wait, current);
 657         struct n_hdlc_buf *tbuf;
 658
 659         if (debuglevel >= DEBUG_LEVEL_INFO)
 660                 printk("%s(%d)n_hdlc_tty_write() called count=%Zd\n",
 661                         __FILE__,__LINE__,count);
 662
 663         /* Verify pointers */
 664         if (!n_hdlc)
 665                 return -EIO;
 666
 667         if (n_hdlc->magic != HDLC_MAGIC)
 668                 return -EIO;
 669
 670         /* verify frame size */
 671         if (count > maxframe ) {
 672                 if (debuglevel & DEBUG_LEVEL_INFO)
 673                         printk (KERN_WARNING
 674                                 "n_hdlc_tty_write: truncating user packet "
 675                                 "from %lu to %Zd\n", (unsigned long) count,
 676                                 maxframe );
 677                 count = maxframe;
 678         }
 679
 680         add_wait_queue(&tty->write_wait, &wait);
 681         set_current_state(TASK_INTERRUPTIBLE);
 682
 683         /* Allocate transmit buffer */
 684         /* sleep until transmit buffer available */
 685         while (!(tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list))) {
 686                 schedule();
 687
 688                 n_hdlc = tty2n_hdlc (tty);
 689                 if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC ||
 690                     tty != n_hdlc->tty) {
 691                         printk("n_hdlc_tty_write: %p invalid after wait!\n", n_hdlc);
 692                         error = -EIO;
 693                         break;
 694                 }
 695
 696                 if (signal_pending(current)) {
 697                         error = -EINTR;
 698                         break;
 699                 }
 700         }
 701
 702         set_current_state(TASK_RUNNING);
 703         remove_wait_queue(&tty->write_wait, &wait);
 704
 705         if (!error) {
 706                 /* Retrieve the user's buffer */
 707                 if (copy_from_user(tbuf->buf, data, count)) {
 708                         /* return tx buffer to free list */
 709                         n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,tbuf);
 710                         error = -EFAULT;
 711                 } else {
 712                         /* Send the data */
 713                         tbuf->count = error = count;
 714                         n_hdlc_buf_put(&n_hdlc->tx_buf_list,tbuf);
 715                         n_hdlc_send_frames(n_hdlc,tty);
 716                 }
 717         }
 718
 719         return error;
 720
 721 }       /* end of n_hdlc_tty_write() */
 722
 723 /**
 724  * n_hdlc_tty_ioctl - process IOCTL system call for the tty device.
 725  * @tty - pointer to tty instance data
 726  * @file - pointer to open file object for device
 727  * @cmd - IOCTL command code
 728  * @arg - argument for IOCTL call (cmd dependent)
 729  *
 730  * Returns command dependent result.
 731  */
 732 static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
 733                             unsigned int cmd, unsigned long arg)
 734 {
 735         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 736         int error = 0;
 737         int count;
 738         unsigned long flags;
 739
 740         if (debuglevel >= DEBUG_LEVEL_INFO)
 741                 printk("%s(%d)n_hdlc_tty_ioctl() called %d\n",
 742                         __FILE__,__LINE__,cmd);
 743
 744         /* Verify the status of the device */
 745         if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC)
 746                 return -EBADF;
 747
 748         switch (cmd) {
 749         case FIONREAD:
 750                 /* report count of read data available */
 751                 /* in next available frame (if any) */
 752                 spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock,flags);
 753                 if (n_hdlc->rx_buf_list.head)
 754                         count = n_hdlc->rx_buf_list.head->count;
 755                 else
 756                         count = 0;
 757                 spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock,flags);
 758                 error = put_user(count, (int *)arg);
 759                 break;
 760
 761         case TIOCOUTQ:
 762                 /* get the pending tx byte count in the driver */
 763                 count = tty->driver->chars_in_buffer ?
 764                                 tty->driver->chars_in_buffer(tty) : 0;
 765                 /* add size of next output frame in queue */
 766                 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock,flags);
 767                 if (n_hdlc->tx_buf_list.head)
 768                         count += n_hdlc->tx_buf_list.head->count;
 769                 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock,flags);
 770                 error = put_user(count, (int*)arg);
 771                 break;
 772
 773         default:
 774                 error = n_tty_ioctl (tty, file, cmd, arg);
 775                 break;
 776         }
 777         return error;
 778
 779 }       /* end of n_hdlc_tty_ioctl() */
 780
 781 /**
 782  * n_hdlc_tty_poll - TTY callback for poll system call
 783  * @tty - pointer to tty instance data
 784  * @filp - pointer to open file object for device
 785  * @poll_table - wait queue for operations
 786  *
 787  * Determine which operations (read/write) will not block and return info
 788  * to caller.
 789  * Returns a bit mask containing info on which ops will not block.
 790  */
 791 static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
 792                                     poll_table *wait)
 793 {
 794         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 795         unsigned int mask = 0;
 796
 797         if (debuglevel >= DEBUG_LEVEL_INFO)
 798                 printk("%s(%d)n_hdlc_tty_poll() called\n",__FILE__,__LINE__);
 799
 800         if (n_hdlc && n_hdlc->magic == HDLC_MAGIC && tty == n_hdlc->tty) {
 801                 /* queue current process into any wait queue that */
 802                 /* may awaken in the future (read and write) */
 803
 804                 poll_wait(filp, &tty->read_wait, wait);
 805                 poll_wait(filp, &tty->write_wait, wait);
 806
 807                 /* set bits for operations that won't block */
 808                 if(n_hdlc->rx_buf_list.head)
 809                         mask |= POLLIN | POLLRDNORM;    /* readable */
 810                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 811                         mask |= POLLHUP;
 812                 if(tty_hung_up_p(filp))
 813                         mask |= POLLHUP;
 814                 if(n_hdlc->tx_free_buf_list.head)
 815                         mask |= POLLOUT | POLLWRNORM;   /* writable */
 816         }
 817         return mask;
 818 }       /* end of n_hdlc_tty_poll() */
 819
 820 /**
 821  * n_hdlc_alloc - allocate an n_hdlc instance data structure
 822  *
 823  * Returns a pointer to newly created structure if success, otherwise %NULL
 824  */
 825 static struct n_hdlc *n_hdlc_alloc(void)
 826 {
 827         struct n_hdlc_buf *buf;
 828         int i;
 829         struct n_hdlc *n_hdlc = kmalloc(sizeof(*n_hdlc), GFP_KERNEL);
 830
 831         if (!n_hdlc)
 832                 return 0;
 833
 834         memset(n_hdlc, 0, sizeof(*n_hdlc));
 835
 836         n_hdlc_buf_list_init(&n_hdlc->rx_free_buf_list);
 837         n_hdlc_buf_list_init(&n_hdlc->tx_free_buf_list);
 838         n_hdlc_buf_list_init(&n_hdlc->rx_buf_list);
 839         n_hdlc_buf_list_init(&n_hdlc->tx_buf_list);
 840
 841         /* allocate free rx buffer list */
 842         for(i=0;i<DEFAULT_RX_BUF_COUNT;i++) {
 843                 buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
 844                 if (buf)
 845                         n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,buf);
 846                 else if (debuglevel >= DEBUG_LEVEL_INFO)
 847                         printk("%s(%d)n_hdlc_alloc(), kalloc() failed for rx buffer %d\n",__FILE__,__LINE__, i);
 848         }
 849
 850         /* allocate free tx buffer list */
 851         for(i=0;i<DEFAULT_TX_BUF_COUNT;i++) {
 852                 buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
 853                 if (buf)
 854                         n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,buf);
 855                 else if (debuglevel >= DEBUG_LEVEL_INFO)
 856                         printk("%s(%d)n_hdlc_alloc(), kalloc() failed for tx buffer %d\n",__FILE__,__LINE__, i);
 857         }
 858
 859         /* Initialize the control block */
 860         n_hdlc->magic  = HDLC_MAGIC;
 861         n_hdlc->flags  = 0;
 862
 863         return n_hdlc;
 864
 865 }       /* end of n_hdlc_alloc() */
 866
 867 /**
 868  * n_hdlc_buf_list_init - initialize specified HDLC buffer list
 869  * @list - pointer to buffer list
 870  */
 871 static void n_hdlc_buf_list_init(struct n_hdlc_buf_list *list)
 872 {
 873         memset(list, 0, sizeof(*list));
 874         spin_lock_init(&list->spinlock);
 875 }       /* end of n_hdlc_buf_list_init() */
 876
 877 /**
 878  * n_hdlc_buf_put - add specified HDLC buffer to tail of specified list
 879  * @list - pointer to buffer list
 880  * @buf - pointer to buffer
 881  */
 882 static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
 883                            struct n_hdlc_buf *buf)
 884 {
 885         unsigned long flags;
 886         spin_lock_irqsave(&list->spinlock,flags);
 887
 888         buf->link=NULL;
 889         if(list->tail)
 890                 list->tail->link = buf;
 891         else
 892                 list->head = buf;
 893         list->tail = buf;
 894         (list->count)++;
 895
 896         spin_unlock_irqrestore(&list->spinlock,flags);
 897
 898 }       /* end of n_hdlc_buf_put() */
 899
 900 /**
 901  * n_hdlc_buf_get - remove and return an HDLC buffer from list
 902  * @list - pointer to HDLC buffer list
 903  *
 904  * Remove and return an HDLC buffer from the head of the specified HDLC buffer
 905  * list.
 906  * Returns a pointer to HDLC buffer if available, otherwise %NULL.
 907  */
 908 static struct n_hdlc_buf* n_hdlc_buf_get(struct n_hdlc_buf_list *list)
 909 {
 910         unsigned long flags;
 911         struct n_hdlc_buf *buf;
 912         spin_lock_irqsave(&list->spinlock,flags);
 913
 914         buf = list->head;
 915         if (buf) {
 916                 list->head = buf->link;
 917                 (list->count)--;
 918         }
 919         if (!list->head)
 920                 list->tail = NULL;
 921
 922         spin_unlock_irqrestore(&list->spinlock,flags);
 923         return buf;
 924
 925 }       /* end of n_hdlc_buf_get() */
 926
 927 static char hdlc_banner[] __initdata =
 928         KERN_INFO "HDLC line discipline: version " HDLC_VERSION
 929         ", maxframe=%u\n";
 930 static char hdlc_register_ok[] __initdata =
 931         KERN_INFO "N_HDLC line discipline registered.\n";
 932 static char hdlc_register_fail[] __initdata =
 933         KERN_ERR "error registering line discipline: %d\n";
 934 static char hdlc_init_fail[] __initdata =
 935         KERN_INFO "N_HDLC: init failure %d\n";
 936
 937 static int __init n_hdlc_init(void)
 938 {
 939         int status;
 940
 941         /* range check maxframe arg */
 942         if (maxframe < 4096)
 943                 maxframe = 4096;
 944         else if (maxframe > 65535)
 945                 maxframe = 65535;
 946
 947         printk(hdlc_banner, maxframe);
 948
 949         status = tty_register_ldisc(N_HDLC, &n_hdlc_ldisc);
 950         if (!status)
 951                 printk(hdlc_register_ok);
 952         else
 953                 printk(hdlc_register_fail, status);
 954
 955         if (status)
 956                 printk(hdlc_init_fail, status);
 957         return status;
 958
 959 }       /* end of init_module() */
 960
 961 static char hdlc_unregister_ok[] __exitdata =
 962         KERN_INFO "N_HDLC: line discipline unregistered\n";
 963 static char hdlc_unregister_fail[] __exitdata =
 964         KERN_ERR "N_HDLC: can't unregister line discipline (err = %d)\n";
 965
 966 static void __exit n_hdlc_exit(void)
 967 {
 968         /* Release tty registration of line discipline */
 969         int status = tty_register_ldisc(N_HDLC, NULL);
 970
 971         if (status)
 972                 printk(hdlc_unregister_fail, status);
 973         else
 974                 printk(hdlc_unregister_ok);
 975 }
 976
 977 module_init(n_hdlc_init);
 978 module_exit(n_hdlc_exit);
 979
 980 MODULE_LICENSE("GPL");
 981 MODULE_AUTHOR("Paul Fulghum paulkf@microgate.com");
 982 MODULE_PARM(debuglevel, "i");
 983 MODULE_PARM(maxframe, "i");
 984 MODULE_ALIAS_LDISC(N_HDLC);