linux/drivers/tty/n_hdlc.c
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   1// SPDX-License-Identifier: GPL-1.0+
   2/* generic HDLC line discipline for Linux
   3 *
   4 * Written by Paul Fulghum paulkf@microgate.com
   5 * for Microgate Corporation
   6 *
   7 * Microgate and SyncLink are registered trademarks of Microgate Corporation
   8 *
   9 * Adapted from ppp.c, written by Michael Callahan <callahan@maths.ox.ac.uk>,
  10 *      Al Longyear <longyear@netcom.com>,
  11 *      Paul Mackerras <Paul.Mackerras@cs.anu.edu.au>
  12 *
  13 * Original release 01/11/99
  14 *
  15 * This module implements the tty line discipline N_HDLC for use with
  16 * tty device drivers that support bit-synchronous HDLC communications.
  17 *
  18 * All HDLC data is frame oriented which means:
  19 *
  20 * 1. tty write calls represent one complete transmit frame of data
  21 *    The device driver should accept the complete frame or none of 
  22 *    the frame (busy) in the write method. Each write call should have
  23 *    a byte count in the range of 2-65535 bytes (2 is min HDLC frame
  24 *    with 1 addr byte and 1 ctrl byte). The max byte count of 65535
  25 *    should include any crc bytes required. For example, when using
  26 *    CCITT CRC32, 4 crc bytes are required, so the maximum size frame
  27 *    the application may transmit is limited to 65531 bytes. For CCITT
  28 *    CRC16, the maximum application frame size would be 65533.
  29 *
  30 *
  31 * 2. receive callbacks from the device driver represents
  32 *    one received frame. The device driver should bypass
  33 *    the tty flip buffer and call the line discipline receive
  34 *    callback directly to avoid fragmenting or concatenating
  35 *    multiple frames into a single receive callback.
  36 *
  37 *    The HDLC line discipline queues the receive frames in separate
  38 *    buffers so complete receive frames can be returned by the
  39 *    tty read calls.
  40 *
  41 * 3. tty read calls returns an entire frame of data or nothing.
  42 *    
  43 * 4. all send and receive data is considered raw. No processing
  44 *    or translation is performed by the line discipline, regardless
  45 *    of the tty flags
  46 *
  47 * 5. When line discipline is queried for the amount of receive
  48 *    data available (FIOC), 0 is returned if no data available,
  49 *    otherwise the count of the next available frame is returned.
  50 *    (instead of the sum of all received frame counts).
  51 *
  52 * These conventions allow the standard tty programming interface
  53 * to be used for synchronous HDLC applications when used with
  54 * this line discipline (or another line discipline that is frame
  55 * oriented such as N_PPP).
  56 *
  57 * The SyncLink driver (synclink.c) implements both asynchronous
  58 * (using standard line discipline N_TTY) and synchronous HDLC
  59 * (using N_HDLC) communications, with the latter using the above
  60 * conventions.
  61 *
  62 * This implementation is very basic and does not maintain
  63 * any statistics. The main point is to enforce the raw data
  64 * and frame orientation of HDLC communications.
  65 *
  66 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
  67 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  68 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  69 * DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
  70 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  71 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  72 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  73 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  74 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  75 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
  76 * OF THE POSSIBILITY OF SUCH DAMAGE.
  77 */
  78
  79#define HDLC_MAGIC 0x239e
  80
  81#include <linux/module.h>
  82#include <linux/init.h>
  83#include <linux/kernel.h>
  84#include <linux/sched.h>
  85#include <linux/types.h>
  86#include <linux/fcntl.h>
  87#include <linux/interrupt.h>
  88#include <linux/ptrace.h>
  89
  90#undef VERSION
  91#define VERSION(major,minor,patch) (((((major)<<8)+(minor))<<8)+(patch))
  92
  93#include <linux/poll.h>
  94#include <linux/in.h>
  95#include <linux/ioctl.h>
  96#include <linux/slab.h>
  97#include <linux/tty.h>
  98#include <linux/errno.h>
  99#include <linux/string.h>       /* used in new tty drivers */
 100#include <linux/signal.h>       /* used in new tty drivers */
 101#include <linux/if.h>
 102#include <linux/bitops.h>
 103
 104#include <asm/termios.h>
 105#include <linux/uaccess.h>
 106
 107/*
 108 * Buffers for individual HDLC frames
 109 */
 110#define MAX_HDLC_FRAME_SIZE 65535 
 111#define DEFAULT_RX_BUF_COUNT 10
 112#define MAX_RX_BUF_COUNT 60
 113#define DEFAULT_TX_BUF_COUNT 3
 114
 115struct n_hdlc_buf {
 116        struct list_head  list_item;
 117        int               count;
 118        char              buf[1];
 119};
 120
 121#define N_HDLC_BUF_SIZE (sizeof(struct n_hdlc_buf) + maxframe)
 122
 123struct n_hdlc_buf_list {
 124        struct list_head  list;
 125        int               count;
 126        spinlock_t        spinlock;
 127};
 128
 129/**
 130 * struct n_hdlc - per device instance data structure
 131 * @magic - magic value for structure
 132 * @flags - miscellaneous control flags
 133 * @tty - ptr to TTY structure
 134 * @backup_tty - TTY to use if tty gets closed
 135 * @tbusy - reentrancy flag for tx wakeup code
 136 * @woke_up - FIXME: describe this field
 137 * @tx_buf_list - list of pending transmit frame buffers
 138 * @rx_buf_list - list of received frame buffers
 139 * @tx_free_buf_list - list unused transmit frame buffers
 140 * @rx_free_buf_list - list unused received frame buffers
 141 */
 142struct n_hdlc {
 143        int                     magic;
 144        __u32                   flags;
 145        struct tty_struct       *tty;
 146        struct tty_struct       *backup_tty;
 147        int                     tbusy;
 148        int                     woke_up;
 149        struct n_hdlc_buf_list  tx_buf_list;
 150        struct n_hdlc_buf_list  rx_buf_list;
 151        struct n_hdlc_buf_list  tx_free_buf_list;
 152        struct n_hdlc_buf_list  rx_free_buf_list;
 153};
 154
 155/*
 156 * HDLC buffer list manipulation functions
 157 */
 158static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
 159                                                struct n_hdlc_buf *buf);
 160static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
 161                           struct n_hdlc_buf *buf);
 162static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
 163
 164/* Local functions */
 165
 166static struct n_hdlc *n_hdlc_alloc (void);
 167
 168/* debug level can be set by insmod for debugging purposes */
 169#define DEBUG_LEVEL_INFO        1
 170static int debuglevel;
 171
 172/* max frame size for memory allocations */
 173static int maxframe = 4096;
 174
 175/* TTY callbacks */
 176
 177static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 178                           __u8 __user *buf, size_t nr);
 179static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 180                            const unsigned char *buf, size_t nr);
 181static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
 182                            unsigned int cmd, unsigned long arg);
 183static __poll_t n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
 184                                    poll_table *wait);
 185static int n_hdlc_tty_open(struct tty_struct *tty);
 186static void n_hdlc_tty_close(struct tty_struct *tty);
 187static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *cp,
 188                               char *fp, int count);
 189static void n_hdlc_tty_wakeup(struct tty_struct *tty);
 190
 191#define bset(p,b)       ((p)[(b) >> 5] |= (1 << ((b) & 0x1f)))
 192
 193#define tty2n_hdlc(tty) ((struct n_hdlc *) ((tty)->disc_data))
 194#define n_hdlc2tty(n_hdlc)      ((n_hdlc)->tty)
 195
 196static void flush_rx_queue(struct tty_struct *tty)
 197{
 198        struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 199        struct n_hdlc_buf *buf;
 200
 201        while ((buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list)))
 202                n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, buf);
 203}
 204
 205static void flush_tx_queue(struct tty_struct *tty)
 206{
 207        struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 208        struct n_hdlc_buf *buf;
 209
 210        while ((buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list)))
 211                n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, buf);
 212}
 213
 214static struct tty_ldisc_ops n_hdlc_ldisc = {
 215        .owner          = THIS_MODULE,
 216        .magic          = TTY_LDISC_MAGIC,
 217        .name           = "hdlc",
 218        .open           = n_hdlc_tty_open,
 219        .close          = n_hdlc_tty_close,
 220        .read           = n_hdlc_tty_read,
 221        .write          = n_hdlc_tty_write,
 222        .ioctl          = n_hdlc_tty_ioctl,
 223        .poll           = n_hdlc_tty_poll,
 224        .receive_buf    = n_hdlc_tty_receive,
 225        .write_wakeup   = n_hdlc_tty_wakeup,
 226        .flush_buffer   = flush_rx_queue,
 227};
 228
 229/**
 230 * n_hdlc_release - release an n_hdlc per device line discipline info structure
 231 * @n_hdlc - per device line discipline info structure
 232 */
 233static void n_hdlc_release(struct n_hdlc *n_hdlc)
 234{
 235        struct tty_struct *tty = n_hdlc2tty (n_hdlc);
 236        struct n_hdlc_buf *buf;
 237        
 238        if (debuglevel >= DEBUG_LEVEL_INFO)     
 239                printk("%s(%d)n_hdlc_release() called\n",__FILE__,__LINE__);
 240                
 241        /* Ensure that the n_hdlcd process is not hanging on select()/poll() */
 242        wake_up_interruptible (&tty->read_wait);
 243        wake_up_interruptible (&tty->write_wait);
 244
 245        if (tty->disc_data == n_hdlc)
 246                tty->disc_data = NULL;  /* Break the tty->n_hdlc link */
 247
 248        /* Release transmit and receive buffers */
 249        for(;;) {
 250                buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
 251                if (buf) {
 252                        kfree(buf);
 253                } else
 254                        break;
 255        }
 256        for(;;) {
 257                buf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
 258                if (buf) {
 259                        kfree(buf);
 260                } else
 261                        break;
 262        }
 263        for(;;) {
 264                buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
 265                if (buf) {
 266                        kfree(buf);
 267                } else
 268                        break;
 269        }
 270        for(;;) {
 271                buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 272                if (buf) {
 273                        kfree(buf);
 274                } else
 275                        break;
 276        }
 277        kfree(n_hdlc);
 278        
 279}       /* end of n_hdlc_release() */
 280
 281/**
 282 * n_hdlc_tty_close - line discipline close
 283 * @tty - pointer to tty info structure
 284 *
 285 * Called when the line discipline is changed to something
 286 * else, the tty is closed, or the tty detects a hangup.
 287 */
 288static void n_hdlc_tty_close(struct tty_struct *tty)
 289{
 290        struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 291
 292        if (debuglevel >= DEBUG_LEVEL_INFO)     
 293                printk("%s(%d)n_hdlc_tty_close() called\n",__FILE__,__LINE__);
 294                
 295        if (n_hdlc != NULL) {
 296                if (n_hdlc->magic != HDLC_MAGIC) {
 297                        printk (KERN_WARNING"n_hdlc: trying to close unopened tty!\n");
 298                        return;
 299                }
 300#if defined(TTY_NO_WRITE_SPLIT)
 301                clear_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
 302#endif
 303                tty->disc_data = NULL;
 304                if (tty == n_hdlc->backup_tty)
 305                        n_hdlc->backup_tty = NULL;
 306                if (tty != n_hdlc->tty)
 307                        return;
 308                if (n_hdlc->backup_tty) {
 309                        n_hdlc->tty = n_hdlc->backup_tty;
 310                } else {
 311                        n_hdlc_release (n_hdlc);
 312                }
 313        }
 314        
 315        if (debuglevel >= DEBUG_LEVEL_INFO)     
 316                printk("%s(%d)n_hdlc_tty_close() success\n",__FILE__,__LINE__);
 317                
 318}       /* end of n_hdlc_tty_close() */
 319
 320/**
 321 * n_hdlc_tty_open - called when line discipline changed to n_hdlc
 322 * @tty - pointer to tty info structure
 323 *
 324 * Returns 0 if success, otherwise error code
 325 */
 326static int n_hdlc_tty_open (struct tty_struct *tty)
 327{
 328        struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 329
 330        if (debuglevel >= DEBUG_LEVEL_INFO)     
 331                printk("%s(%d)n_hdlc_tty_open() called (device=%s)\n",
 332                __FILE__,__LINE__,
 333                tty->name);
 334                
 335        /* There should not be an existing table for this slot. */
 336        if (n_hdlc) {
 337                printk (KERN_ERR"n_hdlc_tty_open:tty already associated!\n" );
 338                return -EEXIST;
 339        }
 340        
 341        n_hdlc = n_hdlc_alloc();
 342        if (!n_hdlc) {
 343                printk (KERN_ERR "n_hdlc_alloc failed\n");
 344                return -ENFILE;
 345        }
 346                
 347        tty->disc_data = n_hdlc;
 348        n_hdlc->tty    = tty;
 349        tty->receive_room = 65536;
 350        
 351#if defined(TTY_NO_WRITE_SPLIT)
 352        /* change tty_io write() to not split large writes into 8K chunks */
 353        set_bit(TTY_NO_WRITE_SPLIT,&tty->flags);
 354#endif
 355        
 356        /* flush receive data from driver */
 357        tty_driver_flush_buffer(tty);
 358                
 359        if (debuglevel >= DEBUG_LEVEL_INFO)     
 360                printk("%s(%d)n_hdlc_tty_open() success\n",__FILE__,__LINE__);
 361                
 362        return 0;
 363        
 364}       /* end of n_tty_hdlc_open() */
 365
 366/**
 367 * n_hdlc_send_frames - send frames on pending send buffer list
 368 * @n_hdlc - pointer to ldisc instance data
 369 * @tty - pointer to tty instance data
 370 *
 371 * Send frames on pending send buffer list until the driver does not accept a
 372 * frame (busy) this function is called after adding a frame to the send buffer
 373 * list and by the tty wakeup callback.
 374 */
 375static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
 376{
 377        register int actual;
 378        unsigned long flags;
 379        struct n_hdlc_buf *tbuf;
 380
 381        if (debuglevel >= DEBUG_LEVEL_INFO)     
 382                printk("%s(%d)n_hdlc_send_frames() called\n",__FILE__,__LINE__);
 383 check_again:
 384                
 385        spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
 386        if (n_hdlc->tbusy) {
 387                n_hdlc->woke_up = 1;
 388                spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 389                return;
 390        }
 391        n_hdlc->tbusy = 1;
 392        n_hdlc->woke_up = 0;
 393        spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 394
 395        tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 396        while (tbuf) {
 397                if (debuglevel >= DEBUG_LEVEL_INFO)     
 398                        printk("%s(%d)sending frame %p, count=%d\n",
 399                                __FILE__,__LINE__,tbuf,tbuf->count);
 400                        
 401                /* Send the next block of data to device */
 402                set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 403                actual = tty->ops->write(tty, tbuf->buf, tbuf->count);
 404
 405                /* rollback was possible and has been done */
 406                if (actual == -ERESTARTSYS) {
 407                        n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
 408                        break;
 409                }
 410                /* if transmit error, throw frame away by */
 411                /* pretending it was accepted by driver */
 412                if (actual < 0)
 413                        actual = tbuf->count;
 414                
 415                if (actual == tbuf->count) {
 416                        if (debuglevel >= DEBUG_LEVEL_INFO)     
 417                                printk("%s(%d)frame %p completed\n",
 418                                        __FILE__,__LINE__,tbuf);
 419                                        
 420                        /* free current transmit buffer */
 421                        n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf);
 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                        /*
 434                         * the buffer was not accepted by driver,
 435                         * return it back into tx queue
 436                         */
 437                        n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
 438                        break;
 439                }
 440        }
 441        
 442        if (!tbuf)
 443                clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 444        
 445        /* Clear the re-entry flag */
 446        spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
 447        n_hdlc->tbusy = 0;
 448        spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags); 
 449        
 450        if (n_hdlc->woke_up)
 451          goto check_again;
 452
 453        if (debuglevel >= DEBUG_LEVEL_INFO)     
 454                printk("%s(%d)n_hdlc_send_frames() exit\n",__FILE__,__LINE__);
 455                
 456}       /* end of n_hdlc_send_frames() */
 457
 458/**
 459 * n_hdlc_tty_wakeup - Callback for transmit wakeup
 460 * @tty - pointer to associated tty instance data
 461 *
 462 * Called when low level device driver can accept more send data.
 463 */
 464static void n_hdlc_tty_wakeup(struct tty_struct *tty)
 465{
 466        struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 467
 468        if (debuglevel >= DEBUG_LEVEL_INFO)     
 469                printk("%s(%d)n_hdlc_tty_wakeup() called\n",__FILE__,__LINE__);
 470                
 471        if (!n_hdlc)
 472                return;
 473
 474        if (tty != n_hdlc->tty) {
 475                clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 476                return;
 477        }
 478
 479        n_hdlc_send_frames (n_hdlc, tty);
 480                
 481}       /* end of n_hdlc_tty_wakeup() */
 482
 483/**
 484 * n_hdlc_tty_receive - Called by tty driver when receive data is available
 485 * @tty - pointer to tty instance data
 486 * @data - pointer to received data
 487 * @flags - pointer to flags for data
 488 * @count - count of received data in bytes
 489 *
 490 * Called by tty low level driver when receive data is available. Data is
 491 * interpreted as one HDLC frame.
 492 */
 493static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
 494                               char *flags, int count)
 495{
 496        register struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 497        register struct n_hdlc_buf *buf;
 498
 499        if (debuglevel >= DEBUG_LEVEL_INFO)     
 500                printk("%s(%d)n_hdlc_tty_receive() called count=%d\n",
 501                        __FILE__,__LINE__, count);
 502                
 503        /* This can happen if stuff comes in on the backup tty */
 504        if (!n_hdlc || tty != n_hdlc->tty)
 505                return;
 506                
 507        /* verify line is using HDLC discipline */
 508        if (n_hdlc->magic != HDLC_MAGIC) {
 509                printk("%s(%d) line not using HDLC discipline\n",
 510                        __FILE__,__LINE__);
 511                return;
 512        }
 513        
 514        if ( count>maxframe ) {
 515                if (debuglevel >= DEBUG_LEVEL_INFO)     
 516                        printk("%s(%d) rx count>maxframesize, data discarded\n",
 517                               __FILE__,__LINE__);
 518                return;
 519        }
 520
 521        /* get a free HDLC buffer */    
 522        buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
 523        if (!buf) {
 524                /* no buffers in free list, attempt to allocate another rx buffer */
 525                /* unless the maximum count has been reached */
 526                if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT)
 527                        buf = kmalloc(N_HDLC_BUF_SIZE, GFP_ATOMIC);
 528        }
 529        
 530        if (!buf) {
 531                if (debuglevel >= DEBUG_LEVEL_INFO)     
 532                        printk("%s(%d) no more rx buffers, data discarded\n",
 533                               __FILE__,__LINE__);
 534                return;
 535        }
 536                
 537        /* copy received data to HDLC buffer */
 538        memcpy(buf->buf,data,count);
 539        buf->count=count;
 540
 541        /* add HDLC buffer to list of received frames */
 542        n_hdlc_buf_put(&n_hdlc->rx_buf_list, buf);
 543        
 544        /* wake up any blocked reads and perform async signalling */
 545        wake_up_interruptible (&tty->read_wait);
 546        if (n_hdlc->tty->fasync != NULL)
 547                kill_fasync (&n_hdlc->tty->fasync, SIGIO, POLL_IN);
 548
 549}       /* end of n_hdlc_tty_receive() */
 550
 551/**
 552 * n_hdlc_tty_read - Called to retrieve one frame of data (if available)
 553 * @tty - pointer to tty instance data
 554 * @file - pointer to open file object
 555 * @buf - pointer to returned data buffer
 556 * @nr - size of returned data buffer
 557 *      
 558 * Returns the number of bytes returned or error code.
 559 */
 560static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 561                           __u8 __user *buf, size_t nr)
 562{
 563        struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 564        int ret = 0;
 565        struct n_hdlc_buf *rbuf;
 566        DECLARE_WAITQUEUE(wait, current);
 567
 568        if (debuglevel >= DEBUG_LEVEL_INFO)     
 569                printk("%s(%d)n_hdlc_tty_read() called\n",__FILE__,__LINE__);
 570                
 571        /* Validate the pointers */
 572        if (!n_hdlc)
 573                return -EIO;
 574
 575        /* verify user access to buffer */
 576        if (!access_ok(buf, nr)) {
 577                printk(KERN_WARNING "%s(%d) n_hdlc_tty_read() can't verify user "
 578                "buffer\n", __FILE__, __LINE__);
 579                return -EFAULT;
 580        }
 581
 582        add_wait_queue(&tty->read_wait, &wait);
 583
 584        for (;;) {
 585                if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
 586                        ret = -EIO;
 587                        break;
 588                }
 589                if (tty_hung_up_p(file))
 590                        break;
 591
 592                set_current_state(TASK_INTERRUPTIBLE);
 593
 594                rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
 595                if (rbuf) {
 596                        if (rbuf->count > nr) {
 597                                /* too large for caller's buffer */
 598                                ret = -EOVERFLOW;
 599                        } else {
 600                                __set_current_state(TASK_RUNNING);
 601                                if (copy_to_user(buf, rbuf->buf, rbuf->count))
 602                                        ret = -EFAULT;
 603                                else
 604                                        ret = rbuf->count;
 605                        }
 606
 607                        if (n_hdlc->rx_free_buf_list.count >
 608                            DEFAULT_RX_BUF_COUNT)
 609                                kfree(rbuf);
 610                        else
 611                                n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
 612                        break;
 613                }
 614                        
 615                /* no data */
 616                if (tty_io_nonblock(tty, file)) {
 617                        ret = -EAGAIN;
 618                        break;
 619                }
 620
 621                schedule();
 622
 623                if (signal_pending(current)) {
 624                        ret = -EINTR;
 625                        break;
 626                }
 627        }
 628
 629        remove_wait_queue(&tty->read_wait, &wait);
 630        __set_current_state(TASK_RUNNING);
 631
 632        return ret;
 633        
 634}       /* end of n_hdlc_tty_read() */
 635
 636/**
 637 * n_hdlc_tty_write - write a single frame of data to device
 638 * @tty - pointer to associated tty device instance data
 639 * @file - pointer to file object data
 640 * @data - pointer to transmit data (one frame)
 641 * @count - size of transmit frame in bytes
 642 *              
 643 * Returns the number of bytes written (or error code).
 644 */
 645static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 646                            const unsigned char *data, size_t count)
 647{
 648        struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 649        int error = 0;
 650        DECLARE_WAITQUEUE(wait, current);
 651        struct n_hdlc_buf *tbuf;
 652
 653        if (debuglevel >= DEBUG_LEVEL_INFO)     
 654                printk("%s(%d)n_hdlc_tty_write() called count=%zd\n",
 655                        __FILE__,__LINE__,count);
 656                
 657        /* Verify pointers */
 658        if (!n_hdlc)
 659                return -EIO;
 660
 661        if (n_hdlc->magic != HDLC_MAGIC)
 662                return -EIO;
 663
 664        /* verify frame size */
 665        if (count > maxframe ) {
 666                if (debuglevel & DEBUG_LEVEL_INFO)
 667                        printk (KERN_WARNING
 668                                "n_hdlc_tty_write: truncating user packet "
 669                                "from %lu to %d\n", (unsigned long) count,
 670                                maxframe );
 671                count = maxframe;
 672        }
 673        
 674        add_wait_queue(&tty->write_wait, &wait);
 675
 676        for (;;) {
 677                set_current_state(TASK_INTERRUPTIBLE);
 678        
 679                tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
 680                if (tbuf)
 681                        break;
 682
 683                if (tty_io_nonblock(tty, file)) {
 684                        error = -EAGAIN;
 685                        break;
 686                }
 687                schedule();
 688                        
 689                n_hdlc = tty2n_hdlc (tty);
 690                if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC || 
 691                    tty != n_hdlc->tty) {
 692                        printk("n_hdlc_tty_write: %p invalid after wait!\n", n_hdlc);
 693                        error = -EIO;
 694                        break;
 695                }
 696                        
 697                if (signal_pending(current)) {
 698                        error = -EINTR;
 699                        break;
 700                }
 701        }
 702
 703        __set_current_state(TASK_RUNNING);
 704        remove_wait_queue(&tty->write_wait, &wait);
 705
 706        if (!error) {           
 707                /* Retrieve the user's buffer */
 708                memcpy(tbuf->buf, data, count);
 709
 710                /* Send the data */
 711                tbuf->count = error = count;
 712                n_hdlc_buf_put(&n_hdlc->tx_buf_list,tbuf);
 713                n_hdlc_send_frames(n_hdlc,tty);
 714        }
 715
 716        return error;
 717        
 718}       /* end of n_hdlc_tty_write() */
 719
 720/**
 721 * n_hdlc_tty_ioctl - process IOCTL system call for the tty device.
 722 * @tty - pointer to tty instance data
 723 * @file - pointer to open file object for device
 724 * @cmd - IOCTL command code
 725 * @arg - argument for IOCTL call (cmd dependent)
 726 *
 727 * Returns command dependent result.
 728 */
 729static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
 730                            unsigned int cmd, unsigned long arg)
 731{
 732        struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 733        int error = 0;
 734        int count;
 735        unsigned long flags;
 736        struct n_hdlc_buf *buf = NULL;
 737
 738        if (debuglevel >= DEBUG_LEVEL_INFO)     
 739                printk("%s(%d)n_hdlc_tty_ioctl() called %d\n",
 740                        __FILE__,__LINE__,cmd);
 741                
 742        /* Verify the status of the device */
 743        if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC)
 744                return -EBADF;
 745
 746        switch (cmd) {
 747        case FIONREAD:
 748                /* report count of read data available */
 749                /* in next available frame (if any) */
 750                spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock,flags);
 751                buf = list_first_entry_or_null(&n_hdlc->rx_buf_list.list,
 752                                                struct n_hdlc_buf, list_item);
 753                if (buf)
 754                        count = buf->count;
 755                else
 756                        count = 0;
 757                spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock,flags);
 758                error = put_user(count, (int __user *)arg);
 759                break;
 760
 761        case TIOCOUTQ:
 762                /* get the pending tx byte count in the driver */
 763                count = tty_chars_in_buffer(tty);
 764                /* add size of next output frame in queue */
 765                spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock,flags);
 766                buf = list_first_entry_or_null(&n_hdlc->tx_buf_list.list,
 767                                                struct n_hdlc_buf, list_item);
 768                if (buf)
 769                        count += buf->count;
 770                spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock,flags);
 771                error = put_user(count, (int __user *)arg);
 772                break;
 773
 774        case TCFLSH:
 775                switch (arg) {
 776                case TCIOFLUSH:
 777                case TCOFLUSH:
 778                        flush_tx_queue(tty);
 779                }
 780                /* fall through - to default */
 781
 782        default:
 783                error = n_tty_ioctl_helper(tty, file, cmd, arg);
 784                break;
 785        }
 786        return error;
 787        
 788}       /* end of n_hdlc_tty_ioctl() */
 789
 790/**
 791 * n_hdlc_tty_poll - TTY callback for poll system call
 792 * @tty - pointer to tty instance data
 793 * @filp - pointer to open file object for device
 794 * @poll_table - wait queue for operations
 795 * 
 796 * Determine which operations (read/write) will not block and return info
 797 * to caller.
 798 * Returns a bit mask containing info on which ops will not block.
 799 */
 800static __poll_t n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
 801                                    poll_table *wait)
 802{
 803        struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 804        __poll_t mask = 0;
 805
 806        if (debuglevel >= DEBUG_LEVEL_INFO)     
 807                printk("%s(%d)n_hdlc_tty_poll() called\n",__FILE__,__LINE__);
 808                
 809        if (n_hdlc && n_hdlc->magic == HDLC_MAGIC && tty == n_hdlc->tty) {
 810                /* queue current process into any wait queue that */
 811                /* may awaken in the future (read and write) */
 812
 813                poll_wait(filp, &tty->read_wait, wait);
 814                poll_wait(filp, &tty->write_wait, wait);
 815
 816                /* set bits for operations that won't block */
 817                if (!list_empty(&n_hdlc->rx_buf_list.list))
 818                        mask |= EPOLLIN | EPOLLRDNORM;  /* readable */
 819                if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 820                        mask |= EPOLLHUP;
 821                if (tty_hung_up_p(filp))
 822                        mask |= EPOLLHUP;
 823                if (!tty_is_writelocked(tty) &&
 824                                !list_empty(&n_hdlc->tx_free_buf_list.list))
 825                        mask |= EPOLLOUT | EPOLLWRNORM; /* writable */
 826        }
 827        return mask;
 828}       /* end of n_hdlc_tty_poll() */
 829
 830/**
 831 * n_hdlc_alloc - allocate an n_hdlc instance data structure
 832 *
 833 * Returns a pointer to newly created structure if success, otherwise %NULL
 834 */
 835static struct n_hdlc *n_hdlc_alloc(void)
 836{
 837        struct n_hdlc_buf *buf;
 838        int i;
 839        struct n_hdlc *n_hdlc = kzalloc(sizeof(*n_hdlc), GFP_KERNEL);
 840
 841        if (!n_hdlc)
 842                return NULL;
 843
 844        spin_lock_init(&n_hdlc->rx_free_buf_list.spinlock);
 845        spin_lock_init(&n_hdlc->tx_free_buf_list.spinlock);
 846        spin_lock_init(&n_hdlc->rx_buf_list.spinlock);
 847        spin_lock_init(&n_hdlc->tx_buf_list.spinlock);
 848
 849        INIT_LIST_HEAD(&n_hdlc->rx_free_buf_list.list);
 850        INIT_LIST_HEAD(&n_hdlc->tx_free_buf_list.list);
 851        INIT_LIST_HEAD(&n_hdlc->rx_buf_list.list);
 852        INIT_LIST_HEAD(&n_hdlc->tx_buf_list.list);
 853
 854        /* allocate free rx buffer list */
 855        for(i=0;i<DEFAULT_RX_BUF_COUNT;i++) {
 856                buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
 857                if (buf)
 858                        n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,buf);
 859                else if (debuglevel >= DEBUG_LEVEL_INFO)        
 860                        printk("%s(%d)n_hdlc_alloc(), kalloc() failed for rx buffer %d\n",__FILE__,__LINE__, i);
 861        }
 862        
 863        /* allocate free tx buffer list */
 864        for(i=0;i<DEFAULT_TX_BUF_COUNT;i++) {
 865                buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
 866                if (buf)
 867                        n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,buf);
 868                else if (debuglevel >= DEBUG_LEVEL_INFO)        
 869                        printk("%s(%d)n_hdlc_alloc(), kalloc() failed for tx buffer %d\n",__FILE__,__LINE__, i);
 870        }
 871        
 872        /* Initialize the control block */
 873        n_hdlc->magic  = HDLC_MAGIC;
 874        n_hdlc->flags  = 0;
 875        
 876        return n_hdlc;
 877        
 878}       /* end of n_hdlc_alloc() */
 879
 880/**
 881 * n_hdlc_buf_return - put the HDLC buffer after the head of the specified list
 882 * @buf_list - pointer to the buffer list
 883 * @buf - pointer to the buffer
 884 */
 885static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
 886                                                struct n_hdlc_buf *buf)
 887{
 888        unsigned long flags;
 889
 890        spin_lock_irqsave(&buf_list->spinlock, flags);
 891
 892        list_add(&buf->list_item, &buf_list->list);
 893        buf_list->count++;
 894
 895        spin_unlock_irqrestore(&buf_list->spinlock, flags);
 896}
 897
 898/**
 899 * n_hdlc_buf_put - add specified HDLC buffer to tail of specified list
 900 * @buf_list - pointer to buffer list
 901 * @buf - pointer to buffer
 902 */
 903static void n_hdlc_buf_put(struct n_hdlc_buf_list *buf_list,
 904                           struct n_hdlc_buf *buf)
 905{
 906        unsigned long flags;
 907
 908        spin_lock_irqsave(&buf_list->spinlock, flags);
 909
 910        list_add_tail(&buf->list_item, &buf_list->list);
 911        buf_list->count++;
 912
 913        spin_unlock_irqrestore(&buf_list->spinlock, flags);
 914}       /* end of n_hdlc_buf_put() */
 915
 916/**
 917 * n_hdlc_buf_get - remove and return an HDLC buffer from list
 918 * @buf_list - pointer to HDLC buffer list
 919 * 
 920 * Remove and return an HDLC buffer from the head of the specified HDLC buffer
 921 * list.
 922 * Returns a pointer to HDLC buffer if available, otherwise %NULL.
 923 */
 924static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *buf_list)
 925{
 926        unsigned long flags;
 927        struct n_hdlc_buf *buf;
 928
 929        spin_lock_irqsave(&buf_list->spinlock, flags);
 930
 931        buf = list_first_entry_or_null(&buf_list->list,
 932                                                struct n_hdlc_buf, list_item);
 933        if (buf) {
 934                list_del(&buf->list_item);
 935                buf_list->count--;
 936        }
 937
 938        spin_unlock_irqrestore(&buf_list->spinlock, flags);
 939        return buf;
 940}       /* end of n_hdlc_buf_get() */
 941
 942static const char hdlc_banner[] __initconst =
 943        KERN_INFO "HDLC line discipline maxframe=%u\n";
 944static const char hdlc_register_ok[] __initconst =
 945        KERN_INFO "N_HDLC line discipline registered.\n";
 946static const char hdlc_register_fail[] __initconst =
 947        KERN_ERR "error registering line discipline: %d\n";
 948
 949static int __init n_hdlc_init(void)
 950{
 951        int status;
 952
 953        /* range check maxframe arg */
 954        if (maxframe < 4096)
 955                maxframe = 4096;
 956        else if (maxframe > 65535)
 957                maxframe = 65535;
 958
 959        printk(hdlc_banner, maxframe);
 960
 961        status = tty_register_ldisc(N_HDLC, &n_hdlc_ldisc);
 962        if (!status)
 963                printk(hdlc_register_ok);
 964        else
 965                printk(hdlc_register_fail, status);
 966
 967        return status;
 968        
 969}       /* end of init_module() */
 970
 971#ifdef CONFIG_SPARC
 972#undef __exitdata
 973#define __exitdata
 974#endif
 975
 976static const char hdlc_unregister_ok[] __exitdata =
 977        KERN_INFO "N_HDLC: line discipline unregistered\n";
 978static const char hdlc_unregister_fail[] __exitdata =
 979        KERN_ERR "N_HDLC: can't unregister line discipline (err = %d)\n";
 980
 981static void __exit n_hdlc_exit(void)
 982{
 983        /* Release tty registration of line discipline */
 984        int status = tty_unregister_ldisc(N_HDLC);
 985
 986        if (status)
 987                printk(hdlc_unregister_fail, status);
 988        else
 989                printk(hdlc_unregister_ok);
 990}
 991
 992module_init(n_hdlc_init);
 993module_exit(n_hdlc_exit);
 994
 995MODULE_LICENSE("GPL");
 996MODULE_AUTHOR("Paul Fulghum paulkf@microgate.com");
 997module_param(debuglevel, int, 0);
 998module_param(maxframe, int, 0);
 999MODULE_ALIAS_LDISC(N_HDLC);
1000