drivers/tty/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  *
  14  * This code is released under the GNU General Public License (GPL)
  15  *
  16  * This module implements the tty line discipline N_HDLC for use with
  17  * tty device drivers that support bit-synchronous HDLC communications.
  18  *
  19  * All HDLC data is frame oriented which means:
  20  *
  21  * 1. tty write calls represent one complete transmit frame of data
  22  *    The device driver should accept the complete frame or none of
  23  *    the frame (busy) in the write method. Each write call should have
  24  *    a byte count in the range of 2-65535 bytes (2 is min HDLC frame
  25  *    with 1 addr byte and 1 ctrl byte). The max byte count of 65535
  26  *    should include any crc bytes required. For example, when using
  27  *    CCITT CRC32, 4 crc bytes are required, so the maximum size frame
  28  *    the application may transmit is limited to 65531 bytes. For CCITT
  29  *    CRC16, the maximum application frame size would be 65533.
  30  *
  31  *
  32  * 2. receive callbacks from the device driver represents
  33  *    one received frame. The device driver should bypass
  34  *    the tty flip buffer and call the line discipline receive
  35  *    callback directly to avoid fragmenting or concatenating
  36  *    multiple frames into a single receive callback.
  37  *
  38  *    The HDLC line discipline queues the receive frames in separate
  39  *    buffers so complete receive frames can be returned by the
  40  *    tty read calls.
  41  *
  42  * 3. tty read calls returns an entire frame of data or nothing.
  43  *
  44  * 4. all send and receive data is considered raw. No processing
  45  *    or translation is performed by the line discipline, regardless
  46  *    of the tty flags
  47  *
  48  * 5. When line discipline is queried for the amount of receive
  49  *    data available (FIOC), 0 is returned if no data available,
  50  *    otherwise the count of the next available frame is returned.
  51  *    (instead of the sum of all received frame counts).
  52  *
  53  * These conventions allow the standard tty programming interface
  54  * to be used for synchronous HDLC applications when used with
  55  * this line discipline (or another line discipline that is frame
  56  * oriented such as N_PPP).
  57  *
  58  * The SyncLink driver (synclink.c) implements both asynchronous
  59  * (using standard line discipline N_TTY) and synchronous HDLC
  60  * (using N_HDLC) communications, with the latter using the above
  61  * conventions.
  62  *
  63  * This implementation is very basic and does not maintain
  64  * any statistics. The main point is to enforce the raw data
  65  * and frame orientation of HDLC communications.
  66  *
  67  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
  68  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  69  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  70  * DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
  71  * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  72  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  73  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  74  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  75  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  76  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
  77  * OF THE POSSIBILITY OF SUCH DAMAGE.
  78  */
  79
  80 #define HDLC_MAGIC 0x239e
  81
  82 #include <linux/module.h>
  83 #include <linux/init.h>
  84 #include <linux/kernel.h>
  85 #include <linux/sched.h>
  86 #include <linux/types.h>
  87 #include <linux/fcntl.h>
  88 #include <linux/interrupt.h>
  89 #include <linux/ptrace.h>
  90
  91 #undef VERSION
  92 #define VERSION(major,minor,patch) (((((major)<<8)+(minor))<<8)+(patch))
  93
  94 #include <linux/poll.h>
  95 #include <linux/in.h>
  96 #include <linux/ioctl.h>
  97 #include <linux/slab.h>
  98 #include <linux/tty.h>
  99 #include <linux/errno.h>
 100 #include <linux/string.h>       /* used in new tty drivers */
 101 #include <linux/signal.h>       /* used in new tty drivers */
 102 #include <linux/if.h>
 103 #include <linux/bitops.h>
 104
 105 #include <asm/termios.h>
 106 #include <linux/uaccess.h>
 107
 108 /*
 109  * Buffers for individual HDLC frames
 110  */
 111 #define MAX_HDLC_FRAME_SIZE 65535
 112 #define DEFAULT_RX_BUF_COUNT 10
 113 #define MAX_RX_BUF_COUNT 60
 114 #define DEFAULT_TX_BUF_COUNT 3
 115
 116 struct n_hdlc_buf {
 117         struct n_hdlc_buf *link;
 118         int               count;
 119         char              buf[1];
 120 };
 121
 122 #define N_HDLC_BUF_SIZE (sizeof(struct n_hdlc_buf) + maxframe)
 123
 124 struct n_hdlc_buf_list {
 125         struct n_hdlc_buf *head;
 126         struct n_hdlc_buf *tail;
 127         int               count;
 128         spinlock_t        spinlock;
 129 };
 130
 131 /**
 132  * struct n_hdlc - per device instance data structure
 133  * @magic - magic value for structure
 134  * @flags - miscellaneous control flags
 135  * @tty - ptr to TTY structure
 136  * @backup_tty - TTY to use if tty gets closed
 137  * @tbusy - reentrancy flag for tx wakeup code
 138  * @woke_up - FIXME: describe this field
 139  * @tbuf - currently transmitting tx buffer
 140  * @tx_buf_list - list of pending transmit frame buffers
 141  * @rx_buf_list - list of received frame buffers
 142  * @tx_free_buf_list - list unused transmit frame buffers
 143  * @rx_free_buf_list - list unused received frame buffers
 144  */
 145 struct n_hdlc {
 146         int                     magic;
 147         __u32                   flags;
 148         struct tty_struct       *tty;
 149         struct tty_struct       *backup_tty;
 150         int                     tbusy;
 151         int                     woke_up;
 152         struct n_hdlc_buf       *tbuf;
 153         struct n_hdlc_buf_list  tx_buf_list;
 154         struct n_hdlc_buf_list  rx_buf_list;
 155         struct n_hdlc_buf_list  tx_free_buf_list;
 156         struct n_hdlc_buf_list  rx_free_buf_list;
 157 };
 158
 159 /*
 160  * HDLC buffer list manipulation functions
 161  */
 162 static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
 163                            struct n_hdlc_buf *buf);
 164 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
 165
 166 /* Local functions */
 167
 168 static struct n_hdlc *n_hdlc_alloc (void);
 169
 170 /* debug level can be set by insmod for debugging purposes */
 171 #define DEBUG_LEVEL_INFO        1
 172 static int debuglevel;
 173
 174 /* max frame size for memory allocations */
 175 static int maxframe = 4096;
 176
 177 /* TTY callbacks */
 178
 179 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 180                            __u8 __user *buf, size_t nr);
 181 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 182                             const unsigned char *buf, size_t nr);
 183 static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
 184                             unsigned int cmd, unsigned long arg);
 185 static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
 186                                     poll_table *wait);
 187 static int n_hdlc_tty_open(struct tty_struct *tty);
 188 static void n_hdlc_tty_close(struct tty_struct *tty);
 189 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *cp,
 190                                char *fp, int count);
 191 static void n_hdlc_tty_wakeup(struct tty_struct *tty);
 192
 193 #define bset(p,b)       ((p)[(b) >> 5] |= (1 << ((b) & 0x1f)))
 194
 195 #define tty2n_hdlc(tty) ((struct n_hdlc *) ((tty)->disc_data))
 196 #define n_hdlc2tty(n_hdlc)      ((n_hdlc)->tty)
 197
 198 static void flush_rx_queue(struct tty_struct *tty)
 199 {
 200         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 201         struct n_hdlc_buf *buf;
 202
 203         while ((buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list)))
 204                 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, buf);
 205 }
 206
 207 static void flush_tx_queue(struct tty_struct *tty)
 208 {
 209         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 210         struct n_hdlc_buf *buf;
 211         unsigned long flags;
 212
 213         while ((buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list)))
 214                 n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, buf);
 215         spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
 216         if (n_hdlc->tbuf) {
 217                 n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, n_hdlc->tbuf);
 218                 n_hdlc->tbuf = NULL;
 219         }
 220         spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 221 }
 222
 223 static struct tty_ldisc_ops n_hdlc_ldisc = {
 224         .owner          = THIS_MODULE,
 225         .magic          = TTY_LDISC_MAGIC,
 226         .name           = "hdlc",
 227         .open           = n_hdlc_tty_open,
 228         .close          = n_hdlc_tty_close,
 229         .read           = n_hdlc_tty_read,
 230         .write          = n_hdlc_tty_write,
 231         .ioctl          = n_hdlc_tty_ioctl,
 232         .poll           = n_hdlc_tty_poll,
 233         .receive_buf    = n_hdlc_tty_receive,
 234         .write_wakeup   = n_hdlc_tty_wakeup,
 235         .flush_buffer   = flush_rx_queue,
 236 };
 237
 238 /**
 239  * n_hdlc_release - release an n_hdlc per device line discipline info structure
 240  * @n_hdlc - per device line discipline info structure
 241  */
 242 static void n_hdlc_release(struct n_hdlc *n_hdlc)
 243 {
 244         struct tty_struct *tty = n_hdlc2tty (n_hdlc);
 245         struct n_hdlc_buf *buf;
 246
 247         if (debuglevel >= DEBUG_LEVEL_INFO)
 248                 printk("%s(%d)n_hdlc_release() called\n",__FILE__,__LINE__);
 249
 250         /* Ensure that the n_hdlcd process is not hanging on select()/poll() */
 251         wake_up_interruptible (&tty->read_wait);
 252         wake_up_interruptible (&tty->write_wait);
 253
 254         if (tty->disc_data == n_hdlc)
 255                 tty->disc_data = NULL;  /* Break the tty->n_hdlc link */
 256
 257         /* Release transmit and receive buffers */
 258         for(;;) {
 259                 buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
 260                 if (buf) {
 261                         kfree(buf);
 262                 } else
 263                         break;
 264         }
 265         for(;;) {
 266                 buf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
 267                 if (buf) {
 268                         kfree(buf);
 269                 } else
 270                         break;
 271         }
 272         for(;;) {
 273                 buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
 274                 if (buf) {
 275                         kfree(buf);
 276                 } else
 277                         break;
 278         }
 279         for(;;) {
 280                 buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 281                 if (buf) {
 282                         kfree(buf);
 283                 } else
 284                         break;
 285         }
 286         kfree(n_hdlc->tbuf);
 287         kfree(n_hdlc);
 288
 289 }       /* end of n_hdlc_release() */
 290
 291 /**
 292  * n_hdlc_tty_close - line discipline close
 293  * @tty - pointer to tty info structure
 294  *
 295  * Called when the line discipline is changed to something
 296  * else, the tty is closed, or the tty detects a hangup.
 297  */
 298 static void n_hdlc_tty_close(struct tty_struct *tty)
 299 {
 300         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 301
 302         if (debuglevel >= DEBUG_LEVEL_INFO)
 303                 printk("%s(%d)n_hdlc_tty_close() called\n",__FILE__,__LINE__);
 304
 305         if (n_hdlc != NULL) {
 306                 if (n_hdlc->magic != HDLC_MAGIC) {
 307                         printk (KERN_WARNING"n_hdlc: trying to close unopened tty!\n");
 308                         return;
 309                 }
 310 #if defined(TTY_NO_WRITE_SPLIT)
 311                 clear_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
 312 #endif
 313                 tty->disc_data = NULL;
 314                 if (tty == n_hdlc->backup_tty)
 315                         n_hdlc->backup_tty = NULL;
 316                 if (tty != n_hdlc->tty)
 317                         return;
 318                 if (n_hdlc->backup_tty) {
 319                         n_hdlc->tty = n_hdlc->backup_tty;
 320                 } else {
 321                         n_hdlc_release (n_hdlc);
 322                 }
 323         }
 324
 325         if (debuglevel >= DEBUG_LEVEL_INFO)
 326                 printk("%s(%d)n_hdlc_tty_close() success\n",__FILE__,__LINE__);
 327
 328 }       /* end of n_hdlc_tty_close() */
 329
 330 /**
 331  * n_hdlc_tty_open - called when line discipline changed to n_hdlc
 332  * @tty - pointer to tty info structure
 333  *
 334  * Returns 0 if success, otherwise error code
 335  */
 336 static int n_hdlc_tty_open (struct tty_struct *tty)
 337 {
 338         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 339
 340         if (debuglevel >= DEBUG_LEVEL_INFO)
 341                 printk("%s(%d)n_hdlc_tty_open() called (device=%s)\n",
 342                 __FILE__,__LINE__,
 343                 tty->name);
 344
 345         /* There should not be an existing table for this slot. */
 346         if (n_hdlc) {
 347                 printk (KERN_ERR"n_hdlc_tty_open:tty already associated!\n" );
 348                 return -EEXIST;
 349         }
 350
 351         n_hdlc = n_hdlc_alloc();
 352         if (!n_hdlc) {
 353                 printk (KERN_ERR "n_hdlc_alloc failed\n");
 354                 return -ENFILE;
 355         }
 356
 357         tty->disc_data = n_hdlc;
 358         n_hdlc->tty    = tty;
 359         tty->receive_room = 65536;
 360
 361 #if defined(TTY_NO_WRITE_SPLIT)
 362         /* change tty_io write() to not split large writes into 8K chunks */
 363         set_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
 364 #endif
 365
 366         /* flush receive data from driver */
 367         tty_driver_flush_buffer(tty);
 368
 369         if (debuglevel >= DEBUG_LEVEL_INFO)
 370                 printk("%s(%d)n_hdlc_tty_open() success\n",__FILE__,__LINE__);
 371
 372         return 0;
 373
 374 }       /* end of n_tty_hdlc_open() */
 375
 376 /**
 377  * n_hdlc_send_frames - send frames on pending send buffer list
 378  * @n_hdlc - pointer to ldisc instance data
 379  * @tty - pointer to tty instance data
 380  *
 381  * Send frames on pending send buffer list until the driver does not accept a
 382  * frame (busy) this function is called after adding a frame to the send buffer
 383  * list and by the tty wakeup callback.
 384  */
 385 static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
 386 {
 387         register int actual;
 388         unsigned long flags;
 389         struct n_hdlc_buf *tbuf;
 390
 391         if (debuglevel >= DEBUG_LEVEL_INFO)
 392                 printk("%s(%d)n_hdlc_send_frames() called\n",__FILE__,__LINE__);
 393  check_again:
 394
 395         spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
 396         if (n_hdlc->tbusy) {
 397                 n_hdlc->woke_up = 1;
 398                 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 399                 return;
 400         }
 401         n_hdlc->tbusy = 1;
 402         n_hdlc->woke_up = 0;
 403         spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 404
 405         /* get current transmit buffer or get new transmit */
 406         /* buffer from list of pending transmit buffers */
 407
 408         tbuf = n_hdlc->tbuf;
 409         if (!tbuf)
 410                 tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 411
 412         while (tbuf) {
 413                 if (debuglevel >= DEBUG_LEVEL_INFO)
 414                         printk("%s(%d)sending frame %p, count=%d\n",
 415                                 __FILE__,__LINE__,tbuf,tbuf->count);
 416
 417                 /* Send the next block of data to device */
 418                 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 419                 actual = tty->ops->write(tty, tbuf->buf, tbuf->count);
 420
 421                 /* rollback was possible and has been done */
 422                 if (actual == -ERESTARTSYS) {
 423                         n_hdlc->tbuf = tbuf;
 424                         break;
 425                 }
 426                 /* if transmit error, throw frame away by */
 427                 /* pretending it was accepted by driver */
 428                 if (actual < 0)
 429                         actual = tbuf->count;
 430
 431                 if (actual == tbuf->count) {
 432                         if (debuglevel >= DEBUG_LEVEL_INFO)
 433                                 printk("%s(%d)frame %p completed\n",
 434                                         __FILE__,__LINE__,tbuf);
 435
 436                         /* free current transmit buffer */
 437                         n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf);
 438
 439                         /* this tx buffer is done */
 440                         n_hdlc->tbuf = NULL;
 441
 442                         /* wait up sleeping writers */
 443                         wake_up_interruptible(&tty->write_wait);
 444
 445                         /* get next pending transmit buffer */
 446                         tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 447                 } else {
 448                         if (debuglevel >= DEBUG_LEVEL_INFO)
 449                                 printk("%s(%d)frame %p pending\n",
 450                                         __FILE__,__LINE__,tbuf);
 451
 452                         /* buffer not accepted by driver */
 453                         /* set this buffer as pending buffer */
 454                         n_hdlc->tbuf = tbuf;
 455                         break;
 456                 }
 457         }
 458
 459         if (!tbuf)
 460                 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 461
 462         /* Clear the re-entry flag */
 463         spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
 464         n_hdlc->tbusy = 0;
 465         spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 466
 467         if (n_hdlc->woke_up)
 468           goto check_again;
 469
 470         if (debuglevel >= DEBUG_LEVEL_INFO)
 471                 printk("%s(%d)n_hdlc_send_frames() exit\n",__FILE__,__LINE__);
 472
 473 }       /* end of n_hdlc_send_frames() */
 474
 475 /**
 476  * n_hdlc_tty_wakeup - Callback for transmit wakeup
 477  * @tty - pointer to associated tty instance data
 478  *
 479  * Called when low level device driver can accept more send data.
 480  */
 481 static void n_hdlc_tty_wakeup(struct tty_struct *tty)
 482 {
 483         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 484
 485         if (debuglevel >= DEBUG_LEVEL_INFO)
 486                 printk("%s(%d)n_hdlc_tty_wakeup() called\n",__FILE__,__LINE__);
 487
 488         if (!n_hdlc)
 489                 return;
 490
 491         if (tty != n_hdlc->tty) {
 492                 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 493                 return;
 494         }
 495
 496         n_hdlc_send_frames (n_hdlc, tty);
 497
 498 }       /* end of n_hdlc_tty_wakeup() */
 499
 500 /**
 501  * n_hdlc_tty_receive - Called by tty driver when receive data is available
 502  * @tty - pointer to tty instance data
 503  * @data - pointer to received data
 504  * @flags - pointer to flags for data
 505  * @count - count of received data in bytes
 506  *
 507  * Called by tty low level driver when receive data is available. Data is
 508  * interpreted as one HDLC frame.
 509  */
 510 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
 511                                char *flags, int count)
 512 {
 513         register struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 514         register struct n_hdlc_buf *buf;
 515
 516         if (debuglevel >= DEBUG_LEVEL_INFO)
 517                 printk("%s(%d)n_hdlc_tty_receive() called count=%d\n",
 518                         __FILE__,__LINE__, count);
 519
 520         /* This can happen if stuff comes in on the backup tty */
 521         if (!n_hdlc || tty != n_hdlc->tty)
 522                 return;
 523
 524         /* verify line is using HDLC discipline */
 525         if (n_hdlc->magic != HDLC_MAGIC) {
 526                 printk("%s(%d) line not using HDLC discipline\n",
 527                         __FILE__,__LINE__);
 528                 return;
 529         }
 530
 531         if ( count>maxframe ) {
 532                 if (debuglevel >= DEBUG_LEVEL_INFO)
 533                         printk("%s(%d) rx count>maxframesize, data discarded\n",
 534                                __FILE__,__LINE__);
 535                 return;
 536         }
 537
 538         /* get a free HDLC buffer */
 539         buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
 540         if (!buf) {
 541                 /* no buffers in free list, attempt to allocate another rx buffer */
 542                 /* unless the maximum count has been reached */
 543                 if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT)
 544                         buf = kmalloc(N_HDLC_BUF_SIZE, GFP_ATOMIC);
 545         }
 546
 547         if (!buf) {
 548                 if (debuglevel >= DEBUG_LEVEL_INFO)
 549                         printk("%s(%d) no more rx buffers, data discarded\n",
 550                                __FILE__,__LINE__);
 551                 return;
 552         }
 553
 554         /* copy received data to HDLC buffer */
 555         memcpy(buf->buf,data,count);
 556         buf->count=count;
 557
 558         /* add HDLC buffer to list of received frames */
 559         n_hdlc_buf_put(&n_hdlc->rx_buf_list, buf);
 560
 561         /* wake up any blocked reads and perform async signalling */
 562         wake_up_interruptible (&tty->read_wait);
 563         if (n_hdlc->tty->fasync != NULL)
 564                 kill_fasync (&n_hdlc->tty->fasync, SIGIO, POLL_IN);
 565
 566 }       /* end of n_hdlc_tty_receive() */
 567
 568 /**
 569  * n_hdlc_tty_read - Called to retrieve one frame of data (if available)
 570  * @tty - pointer to tty instance data
 571  * @file - pointer to open file object
 572  * @buf - pointer to returned data buffer
 573  * @nr - size of returned data buffer
 574  *
 575  * Returns the number of bytes returned or error code.
 576  */
 577 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 578                            __u8 __user *buf, size_t nr)
 579 {
 580         struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 581         int ret = 0;
 582         struct n_hdlc_buf *rbuf;
 583         DECLARE_WAITQUEUE(wait, current);
 584
 585         if (debuglevel >= DEBUG_LEVEL_INFO)
 586                 printk("%s(%d)n_hdlc_tty_read() called\n",__FILE__,__LINE__);
 587
 588         /* Validate the pointers */
 589         if (!n_hdlc)
 590                 return -EIO;
 591
 592         /* verify user access to buffer */
 593         if (!access_ok(VERIFY_WRITE, buf, nr)) {
 594                 printk(KERN_WARNING "%s(%d) n_hdlc_tty_read() can't verify user "
 595                 "buffer\n", __FILE__, __LINE__);
 596                 return -EFAULT;
 597         }
 598
 599         add_wait_queue(&tty->read_wait, &wait);
 600
 601         for (;;) {
 602                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
 603                         ret = -EIO;
 604                         break;
 605                 }
 606                 if (tty_hung_up_p(file))
 607                         break;
 608
 609                 set_current_state(TASK_INTERRUPTIBLE);
 610
 611                 rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
 612                 if (rbuf) {
 613                         if (rbuf->count > nr) {
 614                                 /* too large for caller's buffer */
 615                                 ret = -EOVERFLOW;
 616                         } else {
 617                                 if (copy_to_user(buf, rbuf->buf, rbuf->count))
 618                                         ret = -EFAULT;
 619                                 else
 620                                         ret = rbuf->count;
 621                         }
 622
 623                         if (n_hdlc->rx_free_buf_list.count >
 624                             DEFAULT_RX_BUF_COUNT)
 625                                 kfree(rbuf);
 626                         else
 627                                 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
 628                         break;
 629                 }
 630
 631                 /* no data */
 632                 if (file->f_flags & O_NONBLOCK) {
 633                         ret = -EAGAIN;
 634                         break;
 635                 }
 636
 637                 schedule();
 638
 639                 if (signal_pending(current)) {
 640                         ret = -EINTR;
 641                         break;
 642                 }
 643         }
 644
 645         remove_wait_queue(&tty->read_wait, &wait);
 646         __set_current_state(TASK_RUNNING);
 647
 648         return ret;
 649
 650 }       /* end of n_hdlc_tty_read() */
 651
 652 /**
 653  * n_hdlc_tty_write - write a single frame of data to device
 654  * @tty - pointer to associated tty device instance data
 655  * @file - pointer to file object data
 656  * @data - pointer to transmit data (one frame)
 657  * @count - size of transmit frame in bytes
 658  *
 659  * Returns the number of bytes written (or error code).
 660  */
 661 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 662                             const unsigned char *data, size_t count)
 663 {
 664         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 665         int error = 0;
 666         DECLARE_WAITQUEUE(wait, current);
 667         struct n_hdlc_buf *tbuf;
 668
 669         if (debuglevel >= DEBUG_LEVEL_INFO)
 670                 printk("%s(%d)n_hdlc_tty_write() called count=%Zd\n",
 671                         __FILE__,__LINE__,count);
 672
 673         /* Verify pointers */
 674         if (!n_hdlc)
 675                 return -EIO;
 676
 677         if (n_hdlc->magic != HDLC_MAGIC)
 678                 return -EIO;
 679
 680         /* verify frame size */
 681         if (count > maxframe ) {
 682                 if (debuglevel & DEBUG_LEVEL_INFO)
 683                         printk (KERN_WARNING
 684                                 "n_hdlc_tty_write: truncating user packet "
 685                                 "from %lu to %d\n", (unsigned long) count,
 686                                 maxframe );
 687                 count = maxframe;
 688         }
 689
 690         add_wait_queue(&tty->write_wait, &wait);
 691
 692         for (;;) {
 693                 set_current_state(TASK_INTERRUPTIBLE);
 694
 695                 tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
 696                 if (tbuf)
 697                         break;
 698
 699                 if (file->f_flags & O_NONBLOCK) {
 700                         error = -EAGAIN;
 701                         break;
 702                 }
 703                 schedule();
 704
 705                 n_hdlc = tty2n_hdlc (tty);
 706                 if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC ||
 707                     tty != n_hdlc->tty) {
 708                         printk("n_hdlc_tty_write: %p invalid after wait!\n", n_hdlc);
 709                         error = -EIO;
 710                         break;
 711                 }
 712
 713                 if (signal_pending(current)) {
 714                         error = -EINTR;
 715                         break;
 716                 }
 717         }
 718
 719         __set_current_state(TASK_RUNNING);
 720         remove_wait_queue(&tty->write_wait, &wait);
 721
 722         if (!error) {
 723                 /* Retrieve the user's buffer */
 724                 memcpy(tbuf->buf, data, count);
 725
 726                 /* Send the data */
 727                 tbuf->count = error = count;
 728                 n_hdlc_buf_put(&n_hdlc->tx_buf_list,tbuf);
 729                 n_hdlc_send_frames(n_hdlc,tty);
 730         }
 731
 732         return error;
 733
 734 }       /* end of n_hdlc_tty_write() */
 735
 736 /**
 737  * n_hdlc_tty_ioctl - process IOCTL system call for the tty device.
 738  * @tty - pointer to tty instance data
 739  * @file - pointer to open file object for device
 740  * @cmd - IOCTL command code
 741  * @arg - argument for IOCTL call (cmd dependent)
 742  *
 743  * Returns command dependent result.
 744  */
 745 static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
 746                             unsigned int cmd, unsigned long arg)
 747 {
 748         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 749         int error = 0;
 750         int count;
 751         unsigned long flags;
 752
 753         if (debuglevel >= DEBUG_LEVEL_INFO)
 754                 printk("%s(%d)n_hdlc_tty_ioctl() called %d\n",
 755                         __FILE__,__LINE__,cmd);
 756
 757         /* Verify the status of the device */
 758         if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC)
 759                 return -EBADF;
 760
 761         switch (cmd) {
 762         case FIONREAD:
 763                 /* report count of read data available */
 764                 /* in next available frame (if any) */
 765                 spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock,flags);
 766                 if (n_hdlc->rx_buf_list.head)
 767                         count = n_hdlc->rx_buf_list.head->count;
 768                 else
 769                         count = 0;
 770                 spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock,flags);
 771                 error = put_user(count, (int __user *)arg);
 772                 break;
 773
 774         case TIOCOUTQ:
 775                 /* get the pending tx byte count in the driver */
 776                 count = tty_chars_in_buffer(tty);
 777                 /* add size of next output frame in queue */
 778                 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock,flags);
 779                 if (n_hdlc->tx_buf_list.head)
 780                         count += n_hdlc->tx_buf_list.head->count;
 781                 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock,flags);
 782                 error = put_user(count, (int __user *)arg);
 783                 break;
 784
 785         case TCFLSH:
 786                 switch (arg) {
 787                 case TCIOFLUSH:
 788                 case TCOFLUSH:
 789                         flush_tx_queue(tty);
 790                 }
 791                 /* fall through to default */
 792
 793         default:
 794                 error = n_tty_ioctl_helper(tty, file, cmd, arg);
 795                 break;
 796         }
 797         return error;
 798
 799 }       /* end of n_hdlc_tty_ioctl() */
 800
 801 /**
 802  * n_hdlc_tty_poll - TTY callback for poll system call
 803  * @tty - pointer to tty instance data
 804  * @filp - pointer to open file object for device
 805  * @poll_table - wait queue for operations
 806  *
 807  * Determine which operations (read/write) will not block and return info
 808  * to caller.
 809  * Returns a bit mask containing info on which ops will not block.
 810  */
 811 static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
 812                                     poll_table *wait)
 813 {
 814         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 815         unsigned int mask = 0;
 816
 817         if (debuglevel >= DEBUG_LEVEL_INFO)
 818                 printk("%s(%d)n_hdlc_tty_poll() called\n",__FILE__,__LINE__);
 819
 820         if (n_hdlc && n_hdlc->magic == HDLC_MAGIC && tty == n_hdlc->tty) {
 821                 /* queue current process into any wait queue that */
 822                 /* may awaken in the future (read and write) */
 823
 824                 poll_wait(filp, &tty->read_wait, wait);
 825                 poll_wait(filp, &tty->write_wait, wait);
 826
 827                 /* set bits for operations that won't block */
 828                 if (n_hdlc->rx_buf_list.head)
 829                         mask |= POLLIN | POLLRDNORM;    /* readable */
 830                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 831                         mask |= POLLHUP;
 832                 if (tty_hung_up_p(filp))
 833                         mask |= POLLHUP;
 834                 if (!tty_is_writelocked(tty) &&
 835                                 n_hdlc->tx_free_buf_list.head)
 836                         mask |= POLLOUT | POLLWRNORM;   /* writable */
 837         }
 838         return mask;
 839 }       /* end of n_hdlc_tty_poll() */
 840
 841 /**
 842  * n_hdlc_alloc - allocate an n_hdlc instance data structure
 843  *
 844  * Returns a pointer to newly created structure if success, otherwise %NULL
 845  */
 846 static struct n_hdlc *n_hdlc_alloc(void)
 847 {
 848         struct n_hdlc_buf *buf;
 849         int i;
 850         struct n_hdlc *n_hdlc = kzalloc(sizeof(*n_hdlc), GFP_KERNEL);
 851
 852         if (!n_hdlc)
 853                 return NULL;
 854
 855         spin_lock_init(&n_hdlc->rx_free_buf_list.spinlock);
 856         spin_lock_init(&n_hdlc->tx_free_buf_list.spinlock);
 857         spin_lock_init(&n_hdlc->rx_buf_list.spinlock);
 858         spin_lock_init(&n_hdlc->tx_buf_list.spinlock);
 859
 860         /* allocate free rx buffer list */
 861         for(i=0;i<DEFAULT_RX_BUF_COUNT;i++) {
 862                 buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
 863                 if (buf)
 864                         n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,buf);
 865                 else if (debuglevel >= DEBUG_LEVEL_INFO)
 866                         printk("%s(%d)n_hdlc_alloc(), kalloc() failed for rx buffer %d\n",__FILE__,__LINE__, i);
 867         }
 868
 869         /* allocate free tx buffer list */
 870         for(i=0;i<DEFAULT_TX_BUF_COUNT;i++) {
 871                 buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
 872                 if (buf)
 873                         n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,buf);
 874                 else if (debuglevel >= DEBUG_LEVEL_INFO)
 875                         printk("%s(%d)n_hdlc_alloc(), kalloc() failed for tx buffer %d\n",__FILE__,__LINE__, i);
 876         }
 877
 878         /* Initialize the control block */
 879         n_hdlc->magic  = HDLC_MAGIC;
 880         n_hdlc->flags  = 0;
 881
 882         return n_hdlc;
 883
 884 }       /* end of n_hdlc_alloc() */
 885
 886 /**
 887  * n_hdlc_buf_put - add specified HDLC buffer to tail of specified list
 888  * @list - pointer to buffer list
 889  * @buf - pointer to buffer
 890  */
 891 static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
 892                            struct n_hdlc_buf *buf)
 893 {
 894         unsigned long flags;
 895         spin_lock_irqsave(&list->spinlock,flags);
 896
 897         buf->link=NULL;
 898         if (list->tail)
 899                 list->tail->link = buf;
 900         else
 901                 list->head = buf;
 902         list->tail = buf;
 903         (list->count)++;
 904
 905         spin_unlock_irqrestore(&list->spinlock,flags);
 906
 907 }       /* end of n_hdlc_buf_put() */
 908
 909 /**
 910  * n_hdlc_buf_get - remove and return an HDLC buffer from list
 911  * @list - pointer to HDLC buffer list
 912  *
 913  * Remove and return an HDLC buffer from the head of the specified HDLC buffer
 914  * list.
 915  * Returns a pointer to HDLC buffer if available, otherwise %NULL.
 916  */
 917 static struct n_hdlc_buf* n_hdlc_buf_get(struct n_hdlc_buf_list *list)
 918 {
 919         unsigned long flags;
 920         struct n_hdlc_buf *buf;
 921         spin_lock_irqsave(&list->spinlock,flags);
 922
 923         buf = list->head;
 924         if (buf) {
 925                 list->head = buf->link;
 926                 (list->count)--;
 927         }
 928         if (!list->head)
 929                 list->tail = NULL;
 930
 931         spin_unlock_irqrestore(&list->spinlock,flags);
 932         return buf;
 933
 934 }       /* end of n_hdlc_buf_get() */
 935
 936 static char hdlc_banner[] __initdata =
 937         KERN_INFO "HDLC line discipline maxframe=%u\n";
 938 static char hdlc_register_ok[] __initdata =
 939         KERN_INFO "N_HDLC line discipline registered.\n";
 940 static char hdlc_register_fail[] __initdata =
 941         KERN_ERR "error registering line discipline: %d\n";
 942
 943 static int __init n_hdlc_init(void)
 944 {
 945         int status;
 946
 947         /* range check maxframe arg */
 948         if (maxframe < 4096)
 949                 maxframe = 4096;
 950         else if (maxframe > 65535)
 951                 maxframe = 65535;
 952
 953         printk(hdlc_banner, maxframe);
 954
 955         status = tty_register_ldisc(N_HDLC, &n_hdlc_ldisc);
 956         if (!status)
 957                 printk(hdlc_register_ok);
 958         else
 959                 printk(hdlc_register_fail, status);
 960
 961         return status;
 962
 963 }       /* end of init_module() */
 964
 965 static char hdlc_unregister_ok[] __exitdata =
 966         KERN_INFO "N_HDLC: line discipline unregistered\n";
 967 static char hdlc_unregister_fail[] __exitdata =
 968         KERN_ERR "N_HDLC: can't unregister line discipline (err = %d)\n";
 969
 970 static void __exit n_hdlc_exit(void)
 971 {
 972         /* Release tty registration of line discipline */
 973         int status = tty_unregister_ldisc(N_HDLC);
 974
 975         if (status)
 976                 printk(hdlc_unregister_fail, status);
 977         else
 978                 printk(hdlc_unregister_ok);
 979 }
 980
 981 module_init(n_hdlc_init);
 982 module_exit(n_hdlc_exit);
 983
 984 MODULE_LICENSE("GPL");
 985 MODULE_AUTHOR("Paul Fulghum paulkf@microgate.com");
 986 module_param(debuglevel, int, 0);
 987 module_param(maxframe, int, 0);
 988 MODULE_ALIAS_LDISC(N_HDLC);