linux/drivers/tty/n_hdlc.c
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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 *
  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 <asm/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
 116struct 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
 124struct 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 */
 145struct 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 */
 162static void n_hdlc_buf_list_init(struct n_hdlc_buf_list *list);
 163static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
 164                           struct n_hdlc_buf *buf);
 165static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
 166
 167/* Local functions */
 168
 169static struct n_hdlc *n_hdlc_alloc (void);
 170
 171/* debug level can be set by insmod for debugging purposes */
 172#define DEBUG_LEVEL_INFO        1
 173static int debuglevel;
 174
 175/* max frame size for memory allocations */
 176static int maxframe = 4096;
 177
 178/* TTY callbacks */
 179
 180static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 181                           __u8 __user *buf, size_t nr);
 182static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 183                            const unsigned char *buf, size_t nr);
 184static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
 185                            unsigned int cmd, unsigned long arg);
 186static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
 187                                    poll_table *wait);
 188static int n_hdlc_tty_open(struct tty_struct *tty);
 189static void n_hdlc_tty_close(struct tty_struct *tty);
 190static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *cp,
 191                               char *fp, int count);
 192static void n_hdlc_tty_wakeup(struct tty_struct *tty);
 193
 194#define bset(p,b)       ((p)[(b) >> 5] |= (1 << ((b) & 0x1f)))
 195
 196#define tty2n_hdlc(tty) ((struct n_hdlc *) ((tty)->disc_data))
 197#define n_hdlc2tty(n_hdlc)      ((n_hdlc)->tty)
 198
 199static void flush_rx_queue(struct tty_struct *tty)
 200{
 201        struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 202        struct n_hdlc_buf *buf;
 203
 204        while ((buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list)))
 205                n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, buf);
 206}
 207
 208static void flush_tx_queue(struct tty_struct *tty)
 209{
 210        struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 211        struct n_hdlc_buf *buf;
 212        unsigned long flags;
 213
 214        while ((buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list)))
 215                n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, buf);
 216        spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
 217        if (n_hdlc->tbuf) {
 218                n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, n_hdlc->tbuf);
 219                n_hdlc->tbuf = NULL;
 220        }
 221        spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 222}
 223
 224static struct tty_ldisc_ops n_hdlc_ldisc = {
 225        .owner          = THIS_MODULE,
 226        .magic          = TTY_LDISC_MAGIC,
 227        .name           = "hdlc",
 228        .open           = n_hdlc_tty_open,
 229        .close          = n_hdlc_tty_close,
 230        .read           = n_hdlc_tty_read,
 231        .write          = n_hdlc_tty_write,
 232        .ioctl          = n_hdlc_tty_ioctl,
 233        .poll           = n_hdlc_tty_poll,
 234        .receive_buf    = n_hdlc_tty_receive,
 235        .write_wakeup   = n_hdlc_tty_wakeup,
 236        .flush_buffer   = flush_rx_queue,
 237};
 238
 239/**
 240 * n_hdlc_release - release an n_hdlc per device line discipline info structure
 241 * @n_hdlc - per device line discipline info structure
 242 */
 243static void n_hdlc_release(struct n_hdlc *n_hdlc)
 244{
 245        struct tty_struct *tty = n_hdlc2tty (n_hdlc);
 246        struct n_hdlc_buf *buf;
 247        
 248        if (debuglevel >= DEBUG_LEVEL_INFO)     
 249                printk("%s(%d)n_hdlc_release() called\n",__FILE__,__LINE__);
 250                
 251        /* Ensure that the n_hdlcd process is not hanging on select()/poll() */
 252        wake_up_interruptible (&tty->read_wait);
 253        wake_up_interruptible (&tty->write_wait);
 254
 255        if (tty->disc_data == n_hdlc)
 256                tty->disc_data = NULL;  /* Break the tty->n_hdlc link */
 257
 258        /* Release transmit and receive buffers */
 259        for(;;) {
 260                buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
 261                if (buf) {
 262                        kfree(buf);
 263                } else
 264                        break;
 265        }
 266        for(;;) {
 267                buf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
 268                if (buf) {
 269                        kfree(buf);
 270                } else
 271                        break;
 272        }
 273        for(;;) {
 274                buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
 275                if (buf) {
 276                        kfree(buf);
 277                } else
 278                        break;
 279        }
 280        for(;;) {
 281                buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 282                if (buf) {
 283                        kfree(buf);
 284                } else
 285                        break;
 286        }
 287        kfree(n_hdlc->tbuf);
 288        kfree(n_hdlc);
 289        
 290}       /* end of n_hdlc_release() */
 291
 292/**
 293 * n_hdlc_tty_close - line discipline close
 294 * @tty - pointer to tty info structure
 295 *
 296 * Called when the line discipline is changed to something
 297 * else, the tty is closed, or the tty detects a hangup.
 298 */
 299static void n_hdlc_tty_close(struct tty_struct *tty)
 300{
 301        struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 302
 303        if (debuglevel >= DEBUG_LEVEL_INFO)     
 304                printk("%s(%d)n_hdlc_tty_close() called\n",__FILE__,__LINE__);
 305                
 306        if (n_hdlc != NULL) {
 307                if (n_hdlc->magic != HDLC_MAGIC) {
 308                        printk (KERN_WARNING"n_hdlc: trying to close unopened tty!\n");
 309                        return;
 310                }
 311#if defined(TTY_NO_WRITE_SPLIT)
 312                clear_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
 313#endif
 314                tty->disc_data = NULL;
 315                if (tty == n_hdlc->backup_tty)
 316                        n_hdlc->backup_tty = NULL;
 317                if (tty != n_hdlc->tty)
 318                        return;
 319                if (n_hdlc->backup_tty) {
 320                        n_hdlc->tty = n_hdlc->backup_tty;
 321                } else {
 322                        n_hdlc_release (n_hdlc);
 323                }
 324        }
 325        
 326        if (debuglevel >= DEBUG_LEVEL_INFO)     
 327                printk("%s(%d)n_hdlc_tty_close() success\n",__FILE__,__LINE__);
 328                
 329}       /* end of n_hdlc_tty_close() */
 330
 331/**
 332 * n_hdlc_tty_open - called when line discipline changed to n_hdlc
 333 * @tty - pointer to tty info structure
 334 *
 335 * Returns 0 if success, otherwise error code
 336 */
 337static int n_hdlc_tty_open (struct tty_struct *tty)
 338{
 339        struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 340
 341        if (debuglevel >= DEBUG_LEVEL_INFO)     
 342                printk("%s(%d)n_hdlc_tty_open() called (device=%s)\n",
 343                __FILE__,__LINE__,
 344                tty->name);
 345                
 346        /* There should not be an existing table for this slot. */
 347        if (n_hdlc) {
 348                printk (KERN_ERR"n_hdlc_tty_open:tty already associated!\n" );
 349                return -EEXIST;
 350        }
 351        
 352        n_hdlc = n_hdlc_alloc();
 353        if (!n_hdlc) {
 354                printk (KERN_ERR "n_hdlc_alloc failed\n");
 355                return -ENFILE;
 356        }
 357                
 358        tty->disc_data = n_hdlc;
 359        n_hdlc->tty    = tty;
 360        tty->receive_room = 65536;
 361        
 362#if defined(TTY_NO_WRITE_SPLIT)
 363        /* change tty_io write() to not split large writes into 8K chunks */
 364        set_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
 365#endif
 366        
 367        /* flush receive data from driver */
 368        tty_driver_flush_buffer(tty);
 369                
 370        if (debuglevel >= DEBUG_LEVEL_INFO)     
 371                printk("%s(%d)n_hdlc_tty_open() success\n",__FILE__,__LINE__);
 372                
 373        return 0;
 374        
 375}       /* end of n_tty_hdlc_open() */
 376
 377/**
 378 * n_hdlc_send_frames - send frames on pending send buffer list
 379 * @n_hdlc - pointer to ldisc instance data
 380 * @tty - pointer to tty instance data
 381 *
 382 * Send frames on pending send buffer list until the driver does not accept a
 383 * frame (busy) this function is called after adding a frame to the send buffer
 384 * list and by the tty wakeup callback.
 385 */
 386static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
 387{
 388        register int actual;
 389        unsigned long flags;
 390        struct n_hdlc_buf *tbuf;
 391
 392        if (debuglevel >= DEBUG_LEVEL_INFO)     
 393                printk("%s(%d)n_hdlc_send_frames() called\n",__FILE__,__LINE__);
 394 check_again:
 395                
 396        spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
 397        if (n_hdlc->tbusy) {
 398                n_hdlc->woke_up = 1;
 399                spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 400                return;
 401        }
 402        n_hdlc->tbusy = 1;
 403        n_hdlc->woke_up = 0;
 404        spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 405
 406        /* get current transmit buffer or get new transmit */
 407        /* buffer from list of pending transmit buffers */
 408                
 409        tbuf = n_hdlc->tbuf;
 410        if (!tbuf)
 411                tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 412                
 413        while (tbuf) {
 414                if (debuglevel >= DEBUG_LEVEL_INFO)     
 415                        printk("%s(%d)sending frame %p, count=%d\n",
 416                                __FILE__,__LINE__,tbuf,tbuf->count);
 417                        
 418                /* Send the next block of data to device */
 419                set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 420                actual = tty->ops->write(tty, tbuf->buf, tbuf->count);
 421
 422                /* rollback was possible and has been done */
 423                if (actual == -ERESTARTSYS) {
 424                        n_hdlc->tbuf = tbuf;
 425                        break;
 426                }
 427                /* if transmit error, throw frame away by */
 428                /* pretending it was accepted by driver */
 429                if (actual < 0)
 430                        actual = tbuf->count;
 431                
 432                if (actual == tbuf->count) {
 433                        if (debuglevel >= DEBUG_LEVEL_INFO)     
 434                                printk("%s(%d)frame %p completed\n",
 435                                        __FILE__,__LINE__,tbuf);
 436                                        
 437                        /* free current transmit buffer */
 438                        n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf);
 439                        
 440                        /* this tx buffer is done */
 441                        n_hdlc->tbuf = NULL;
 442                        
 443                        /* wait up sleeping writers */
 444                        wake_up_interruptible(&tty->write_wait);
 445        
 446                        /* get next pending transmit buffer */
 447                        tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 448                } else {
 449                        if (debuglevel >= DEBUG_LEVEL_INFO)     
 450                                printk("%s(%d)frame %p pending\n",
 451                                        __FILE__,__LINE__,tbuf);
 452                                        
 453                        /* buffer not accepted by driver */
 454                        /* set this buffer as pending buffer */
 455                        n_hdlc->tbuf = tbuf;
 456                        break;
 457                }
 458        }
 459        
 460        if (!tbuf)
 461                clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 462        
 463        /* Clear the re-entry flag */
 464        spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
 465        n_hdlc->tbusy = 0;
 466        spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags); 
 467        
 468        if (n_hdlc->woke_up)
 469          goto check_again;
 470
 471        if (debuglevel >= DEBUG_LEVEL_INFO)     
 472                printk("%s(%d)n_hdlc_send_frames() exit\n",__FILE__,__LINE__);
 473                
 474}       /* end of n_hdlc_send_frames() */
 475
 476/**
 477 * n_hdlc_tty_wakeup - Callback for transmit wakeup
 478 * @tty - pointer to associated tty instance data
 479 *
 480 * Called when low level device driver can accept more send data.
 481 */
 482static void n_hdlc_tty_wakeup(struct tty_struct *tty)
 483{
 484        struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 485
 486        if (debuglevel >= DEBUG_LEVEL_INFO)     
 487                printk("%s(%d)n_hdlc_tty_wakeup() called\n",__FILE__,__LINE__);
 488                
 489        if (!n_hdlc)
 490                return;
 491
 492        if (tty != n_hdlc->tty) {
 493                clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 494                return;
 495        }
 496
 497        n_hdlc_send_frames (n_hdlc, tty);
 498                
 499}       /* end of n_hdlc_tty_wakeup() */
 500
 501/**
 502 * n_hdlc_tty_receive - Called by tty driver when receive data is available
 503 * @tty - pointer to tty instance data
 504 * @data - pointer to received data
 505 * @flags - pointer to flags for data
 506 * @count - count of received data in bytes
 507 *
 508 * Called by tty low level driver when receive data is available. Data is
 509 * interpreted as one HDLC frame.
 510 */
 511static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
 512                               char *flags, int count)
 513{
 514        register struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 515        register struct n_hdlc_buf *buf;
 516
 517        if (debuglevel >= DEBUG_LEVEL_INFO)     
 518                printk("%s(%d)n_hdlc_tty_receive() called count=%d\n",
 519                        __FILE__,__LINE__, count);
 520                
 521        /* This can happen if stuff comes in on the backup tty */
 522        if (!n_hdlc || tty != n_hdlc->tty)
 523                return;
 524                
 525        /* verify line is using HDLC discipline */
 526        if (n_hdlc->magic != HDLC_MAGIC) {
 527                printk("%s(%d) line not using HDLC discipline\n",
 528                        __FILE__,__LINE__);
 529                return;
 530        }
 531        
 532        if ( count>maxframe ) {
 533                if (debuglevel >= DEBUG_LEVEL_INFO)     
 534                        printk("%s(%d) rx count>maxframesize, data discarded\n",
 535                               __FILE__,__LINE__);
 536                return;
 537        }
 538
 539        /* get a free HDLC buffer */    
 540        buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
 541        if (!buf) {
 542                /* no buffers in free list, attempt to allocate another rx buffer */
 543                /* unless the maximum count has been reached */
 544                if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT)
 545                        buf = kmalloc(N_HDLC_BUF_SIZE, GFP_ATOMIC);
 546        }
 547        
 548        if (!buf) {
 549                if (debuglevel >= DEBUG_LEVEL_INFO)     
 550                        printk("%s(%d) no more rx buffers, data discarded\n",
 551                               __FILE__,__LINE__);
 552                return;
 553        }
 554                
 555        /* copy received data to HDLC buffer */
 556        memcpy(buf->buf,data,count);
 557        buf->count=count;
 558
 559        /* add HDLC buffer to list of received frames */
 560        n_hdlc_buf_put(&n_hdlc->rx_buf_list, buf);
 561        
 562        /* wake up any blocked reads and perform async signalling */
 563        wake_up_interruptible (&tty->read_wait);
 564        if (n_hdlc->tty->fasync != NULL)
 565                kill_fasync (&n_hdlc->tty->fasync, SIGIO, POLL_IN);
 566
 567}       /* end of n_hdlc_tty_receive() */
 568
 569/**
 570 * n_hdlc_tty_read - Called to retrieve one frame of data (if available)
 571 * @tty - pointer to tty instance data
 572 * @file - pointer to open file object
 573 * @buf - pointer to returned data buffer
 574 * @nr - size of returned data buffer
 575 *      
 576 * Returns the number of bytes returned or error code.
 577 */
 578static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 579                           __u8 __user *buf, size_t nr)
 580{
 581        struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 582        int ret = 0;
 583        struct n_hdlc_buf *rbuf;
 584        DECLARE_WAITQUEUE(wait, current);
 585
 586        if (debuglevel >= DEBUG_LEVEL_INFO)     
 587                printk("%s(%d)n_hdlc_tty_read() called\n",__FILE__,__LINE__);
 588                
 589        /* Validate the pointers */
 590        if (!n_hdlc)
 591                return -EIO;
 592
 593        /* verify user access to buffer */
 594        if (!access_ok(VERIFY_WRITE, buf, nr)) {
 595                printk(KERN_WARNING "%s(%d) n_hdlc_tty_read() can't verify user "
 596                "buffer\n", __FILE__, __LINE__);
 597                return -EFAULT;
 598        }
 599
 600        add_wait_queue(&tty->read_wait, &wait);
 601
 602        for (;;) {
 603                if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
 604                        ret = -EIO;
 605                        break;
 606                }
 607                if (tty_hung_up_p(file))
 608                        break;
 609
 610                set_current_state(TASK_INTERRUPTIBLE);
 611
 612                rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
 613                if (rbuf) {
 614                        if (rbuf->count > nr) {
 615                                /* too large for caller's buffer */
 616                                ret = -EOVERFLOW;
 617                        } else {
 618                                if (copy_to_user(buf, rbuf->buf, rbuf->count))
 619                                        ret = -EFAULT;
 620                                else
 621                                        ret = rbuf->count;
 622                        }
 623
 624                        if (n_hdlc->rx_free_buf_list.count >
 625                            DEFAULT_RX_BUF_COUNT)
 626                                kfree(rbuf);
 627                        else
 628                                n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
 629                        break;
 630                }
 631                        
 632                /* no data */
 633                if (file->f_flags & O_NONBLOCK) {
 634                        ret = -EAGAIN;
 635                        break;
 636                }
 637
 638                schedule();
 639
 640                if (signal_pending(current)) {
 641                        ret = -EINTR;
 642                        break;
 643                }
 644        }
 645
 646        remove_wait_queue(&tty->read_wait, &wait);
 647        __set_current_state(TASK_RUNNING);
 648
 649        return ret;
 650        
 651}       /* end of n_hdlc_tty_read() */
 652
 653/**
 654 * n_hdlc_tty_write - write a single frame of data to device
 655 * @tty - pointer to associated tty device instance data
 656 * @file - pointer to file object data
 657 * @data - pointer to transmit data (one frame)
 658 * @count - size of transmit frame in bytes
 659 *              
 660 * Returns the number of bytes written (or error code).
 661 */
 662static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 663                            const unsigned char *data, size_t count)
 664{
 665        struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 666        int error = 0;
 667        DECLARE_WAITQUEUE(wait, current);
 668        struct n_hdlc_buf *tbuf;
 669
 670        if (debuglevel >= DEBUG_LEVEL_INFO)     
 671                printk("%s(%d)n_hdlc_tty_write() called count=%Zd\n",
 672                        __FILE__,__LINE__,count);
 673                
 674        /* Verify pointers */
 675        if (!n_hdlc)
 676                return -EIO;
 677
 678        if (n_hdlc->magic != HDLC_MAGIC)
 679                return -EIO;
 680
 681        /* verify frame size */
 682        if (count > maxframe ) {
 683                if (debuglevel & DEBUG_LEVEL_INFO)
 684                        printk (KERN_WARNING
 685                                "n_hdlc_tty_write: truncating user packet "
 686                                "from %lu to %d\n", (unsigned long) count,
 687                                maxframe );
 688                count = maxframe;
 689        }
 690        
 691        add_wait_queue(&tty->write_wait, &wait);
 692
 693        for (;;) {
 694                set_current_state(TASK_INTERRUPTIBLE);
 695        
 696                tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
 697                if (tbuf)
 698                        break;
 699
 700                if (file->f_flags & O_NONBLOCK) {
 701                        error = -EAGAIN;
 702                        break;
 703                }
 704                schedule();
 705                        
 706                n_hdlc = tty2n_hdlc (tty);
 707                if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC || 
 708                    tty != n_hdlc->tty) {
 709                        printk("n_hdlc_tty_write: %p invalid after wait!\n", n_hdlc);
 710                        error = -EIO;
 711                        break;
 712                }
 713                        
 714                if (signal_pending(current)) {
 715                        error = -EINTR;
 716                        break;
 717                }
 718        }
 719
 720        __set_current_state(TASK_RUNNING);
 721        remove_wait_queue(&tty->write_wait, &wait);
 722
 723        if (!error) {           
 724                /* Retrieve the user's buffer */
 725                memcpy(tbuf->buf, data, count);
 726
 727                /* Send the data */
 728                tbuf->count = error = count;
 729                n_hdlc_buf_put(&n_hdlc->tx_buf_list,tbuf);
 730                n_hdlc_send_frames(n_hdlc,tty);
 731        }
 732
 733        return error;
 734        
 735}       /* end of n_hdlc_tty_write() */
 736
 737/**
 738 * n_hdlc_tty_ioctl - process IOCTL system call for the tty device.
 739 * @tty - pointer to tty instance data
 740 * @file - pointer to open file object for device
 741 * @cmd - IOCTL command code
 742 * @arg - argument for IOCTL call (cmd dependent)
 743 *
 744 * Returns command dependent result.
 745 */
 746static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
 747                            unsigned int cmd, unsigned long arg)
 748{
 749        struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 750        int error = 0;
 751        int count;
 752        unsigned long flags;
 753        
 754        if (debuglevel >= DEBUG_LEVEL_INFO)     
 755                printk("%s(%d)n_hdlc_tty_ioctl() called %d\n",
 756                        __FILE__,__LINE__,cmd);
 757                
 758        /* Verify the status of the device */
 759        if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC)
 760                return -EBADF;
 761
 762        switch (cmd) {
 763        case FIONREAD:
 764                /* report count of read data available */
 765                /* in next available frame (if any) */
 766                spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock,flags);
 767                if (n_hdlc->rx_buf_list.head)
 768                        count = n_hdlc->rx_buf_list.head->count;
 769                else
 770                        count = 0;
 771                spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock,flags);
 772                error = put_user(count, (int __user *)arg);
 773                break;
 774
 775        case TIOCOUTQ:
 776                /* get the pending tx byte count in the driver */
 777                count = tty_chars_in_buffer(tty);
 778                /* add size of next output frame in queue */
 779                spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock,flags);
 780                if (n_hdlc->tx_buf_list.head)
 781                        count += n_hdlc->tx_buf_list.head->count;
 782                spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock,flags);
 783                error = put_user(count, (int __user *)arg);
 784                break;
 785
 786        case TCFLSH:
 787                switch (arg) {
 788                case TCIOFLUSH:
 789                case TCOFLUSH:
 790                        flush_tx_queue(tty);
 791                }
 792                /* fall through to default */
 793
 794        default:
 795                error = n_tty_ioctl_helper(tty, file, cmd, arg);
 796                break;
 797        }
 798        return error;
 799        
 800}       /* end of n_hdlc_tty_ioctl() */
 801
 802/**
 803 * n_hdlc_tty_poll - TTY callback for poll system call
 804 * @tty - pointer to tty instance data
 805 * @filp - pointer to open file object for device
 806 * @poll_table - wait queue for operations
 807 * 
 808 * Determine which operations (read/write) will not block and return info
 809 * to caller.
 810 * Returns a bit mask containing info on which ops will not block.
 811 */
 812static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
 813                                    poll_table *wait)
 814{
 815        struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 816        unsigned int mask = 0;
 817
 818        if (debuglevel >= DEBUG_LEVEL_INFO)     
 819                printk("%s(%d)n_hdlc_tty_poll() called\n",__FILE__,__LINE__);
 820                
 821        if (n_hdlc && n_hdlc->magic == HDLC_MAGIC && tty == n_hdlc->tty) {
 822                /* queue current process into any wait queue that */
 823                /* may awaken in the future (read and write) */
 824
 825                poll_wait(filp, &tty->read_wait, wait);
 826                poll_wait(filp, &tty->write_wait, wait);
 827
 828                /* set bits for operations that won't block */
 829                if (n_hdlc->rx_buf_list.head)
 830                        mask |= POLLIN | POLLRDNORM;    /* readable */
 831                if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 832                        mask |= POLLHUP;
 833                if (tty_hung_up_p(filp))
 834                        mask |= POLLHUP;
 835                if (!tty_is_writelocked(tty) &&
 836                                n_hdlc->tx_free_buf_list.head)
 837                        mask |= POLLOUT | POLLWRNORM;   /* writable */
 838        }
 839        return mask;
 840}       /* end of n_hdlc_tty_poll() */
 841
 842/**
 843 * n_hdlc_alloc - allocate an n_hdlc instance data structure
 844 *
 845 * Returns a pointer to newly created structure if success, otherwise %NULL
 846 */
 847static struct n_hdlc *n_hdlc_alloc(void)
 848{
 849        struct n_hdlc_buf *buf;
 850        int i;
 851        struct n_hdlc *n_hdlc = kmalloc(sizeof(*n_hdlc), GFP_KERNEL);
 852
 853        if (!n_hdlc)
 854                return NULL;
 855
 856        memset(n_hdlc, 0, sizeof(*n_hdlc));
 857
 858        n_hdlc_buf_list_init(&n_hdlc->rx_free_buf_list);
 859        n_hdlc_buf_list_init(&n_hdlc->tx_free_buf_list);
 860        n_hdlc_buf_list_init(&n_hdlc->rx_buf_list);
 861        n_hdlc_buf_list_init(&n_hdlc->tx_buf_list);
 862        
 863        /* allocate free rx buffer list */
 864        for(i=0;i<DEFAULT_RX_BUF_COUNT;i++) {
 865                buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
 866                if (buf)
 867                        n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,buf);
 868                else if (debuglevel >= DEBUG_LEVEL_INFO)        
 869                        printk("%s(%d)n_hdlc_alloc(), kalloc() failed for rx buffer %d\n",__FILE__,__LINE__, i);
 870        }
 871        
 872        /* allocate free tx buffer list */
 873        for(i=0;i<DEFAULT_TX_BUF_COUNT;i++) {
 874                buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
 875                if (buf)
 876                        n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,buf);
 877                else if (debuglevel >= DEBUG_LEVEL_INFO)        
 878                        printk("%s(%d)n_hdlc_alloc(), kalloc() failed for tx buffer %d\n",__FILE__,__LINE__, i);
 879        }
 880        
 881        /* Initialize the control block */
 882        n_hdlc->magic  = HDLC_MAGIC;
 883        n_hdlc->flags  = 0;
 884        
 885        return n_hdlc;
 886        
 887}       /* end of n_hdlc_alloc() */
 888
 889/**
 890 * n_hdlc_buf_list_init - initialize specified HDLC buffer list
 891 * @list - pointer to buffer list
 892 */
 893static void n_hdlc_buf_list_init(struct n_hdlc_buf_list *list)
 894{
 895        memset(list, 0, sizeof(*list));
 896        spin_lock_init(&list->spinlock);
 897}       /* end of n_hdlc_buf_list_init() */
 898
 899/**
 900 * n_hdlc_buf_put - add specified HDLC buffer to tail of specified list
 901 * @list - pointer to buffer list
 902 * @buf - pointer to buffer
 903 */
 904static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
 905                           struct n_hdlc_buf *buf)
 906{
 907        unsigned long flags;
 908        spin_lock_irqsave(&list->spinlock,flags);
 909        
 910        buf->link=NULL;
 911        if (list->tail)
 912                list->tail->link = buf;
 913        else
 914                list->head = buf;
 915        list->tail = buf;
 916        (list->count)++;
 917        
 918        spin_unlock_irqrestore(&list->spinlock,flags);
 919        
 920}       /* end of n_hdlc_buf_put() */
 921
 922/**
 923 * n_hdlc_buf_get - remove and return an HDLC buffer from list
 924 * @list - pointer to HDLC buffer list
 925 * 
 926 * Remove and return an HDLC buffer from the head of the specified HDLC buffer
 927 * list.
 928 * Returns a pointer to HDLC buffer if available, otherwise %NULL.
 929 */
 930static struct n_hdlc_buf* n_hdlc_buf_get(struct n_hdlc_buf_list *list)
 931{
 932        unsigned long flags;
 933        struct n_hdlc_buf *buf;
 934        spin_lock_irqsave(&list->spinlock,flags);
 935        
 936        buf = list->head;
 937        if (buf) {
 938                list->head = buf->link;
 939                (list->count)--;
 940        }
 941        if (!list->head)
 942                list->tail = NULL;
 943        
 944        spin_unlock_irqrestore(&list->spinlock,flags);
 945        return buf;
 946        
 947}       /* end of n_hdlc_buf_get() */
 948
 949static char hdlc_banner[] __initdata =
 950        KERN_INFO "HDLC line discipline maxframe=%u\n";
 951static char hdlc_register_ok[] __initdata =
 952        KERN_INFO "N_HDLC line discipline registered.\n";
 953static char hdlc_register_fail[] __initdata =
 954        KERN_ERR "error registering line discipline: %d\n";
 955static char hdlc_init_fail[] __initdata =
 956        KERN_INFO "N_HDLC: init failure %d\n";
 957
 958static int __init n_hdlc_init(void)
 959{
 960        int status;
 961
 962        /* range check maxframe arg */
 963        if (maxframe < 4096)
 964                maxframe = 4096;
 965        else if (maxframe > 65535)
 966                maxframe = 65535;
 967
 968        printk(hdlc_banner, maxframe);
 969
 970        status = tty_register_ldisc(N_HDLC, &n_hdlc_ldisc);
 971        if (!status)
 972                printk(hdlc_register_ok);
 973        else
 974                printk(hdlc_register_fail, status);
 975
 976        if (status)
 977                printk(hdlc_init_fail, status);
 978        return status;
 979        
 980}       /* end of init_module() */
 981
 982static char hdlc_unregister_ok[] __exitdata =
 983        KERN_INFO "N_HDLC: line discipline unregistered\n";
 984static char hdlc_unregister_fail[] __exitdata =
 985        KERN_ERR "N_HDLC: can't unregister line discipline (err = %d)\n";
 986
 987static void __exit n_hdlc_exit(void)
 988{
 989        /* Release tty registration of line discipline */
 990        int status = tty_unregister_ldisc(N_HDLC);
 991
 992        if (status)
 993                printk(hdlc_unregister_fail, status);
 994        else
 995                printk(hdlc_unregister_ok);
 996}
 997
 998module_init(n_hdlc_init);
 999module_exit(n_hdlc_exit);
1000
1001MODULE_LICENSE("GPL");
1002MODULE_AUTHOR("Paul Fulghum paulkf@microgate.com");
1003module_param(debuglevel, int, 0);
1004module_param(maxframe, int, 0);
1005MODULE_ALIAS_LDISC(N_HDLC);
1006
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