drivers/tty/n_hdlc.c

   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
 115 struct 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
 123 struct 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  */
 142 struct 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  */
 158 static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
 159                                                 struct n_hdlc_buf *buf);
 160 static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
 161                            struct n_hdlc_buf *buf);
 162 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
 163
 164 /* Local functions */
 165
 166 static 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
 170 static int debuglevel;
 171
 172 /* max frame size for memory allocations */
 173 static int maxframe = 4096;
 174
 175 /* TTY callbacks */
 176
 177 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 178                            __u8 __user *buf, size_t nr);
 179 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 180                             const unsigned char *buf, size_t nr);
 181 static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
 182                             unsigned int cmd, unsigned long arg);
 183 static __poll_t n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
 184                                     poll_table *wait);
 185 static int n_hdlc_tty_open(struct tty_struct *tty);
 186 static void n_hdlc_tty_close(struct tty_struct *tty);
 187 static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *cp,
 188                                char *fp, int count);
 189 static 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
 196 static 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
 205 static 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
 214 static 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  */
 233 static 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  */
 288 static 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  */
 326 static 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  */
 375 static 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  */
 464 static 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  */
 493 static 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  */
 560 static 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(VERIFY_WRITE, 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                                 if (copy_to_user(buf, rbuf->buf, rbuf->count))
 601                                         ret = -EFAULT;
 602                                 else
 603                                         ret = rbuf->count;
 604                         }
 605
 606                         if (n_hdlc->rx_free_buf_list.count >
 607                             DEFAULT_RX_BUF_COUNT)
 608                                 kfree(rbuf);
 609                         else
 610                                 n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
 611                         break;
 612                 }
 613
 614                 /* no data */
 615                 if (file->f_flags & O_NONBLOCK) {
 616                         ret = -EAGAIN;
 617                         break;
 618                 }
 619
 620                 schedule();
 621
 622                 if (signal_pending(current)) {
 623                         ret = -EINTR;
 624                         break;
 625                 }
 626         }
 627
 628         remove_wait_queue(&tty->read_wait, &wait);
 629         __set_current_state(TASK_RUNNING);
 630
 631         return ret;
 632
 633 }       /* end of n_hdlc_tty_read() */
 634
 635 /**
 636  * n_hdlc_tty_write - write a single frame of data to device
 637  * @tty - pointer to associated tty device instance data
 638  * @file - pointer to file object data
 639  * @data - pointer to transmit data (one frame)
 640  * @count - size of transmit frame in bytes
 641  *
 642  * Returns the number of bytes written (or error code).
 643  */
 644 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 645                             const unsigned char *data, size_t count)
 646 {
 647         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 648         int error = 0;
 649         DECLARE_WAITQUEUE(wait, current);
 650         struct n_hdlc_buf *tbuf;
 651
 652         if (debuglevel >= DEBUG_LEVEL_INFO)
 653                 printk("%s(%d)n_hdlc_tty_write() called count=%zd\n",
 654                         __FILE__,__LINE__,count);
 655
 656         /* Verify pointers */
 657         if (!n_hdlc)
 658                 return -EIO;
 659
 660         if (n_hdlc->magic != HDLC_MAGIC)
 661                 return -EIO;
 662
 663         /* verify frame size */
 664         if (count > maxframe ) {
 665                 if (debuglevel & DEBUG_LEVEL_INFO)
 666                         printk (KERN_WARNING
 667                                 "n_hdlc_tty_write: truncating user packet "
 668                                 "from %lu to %d\n", (unsigned long) count,
 669                                 maxframe );
 670                 count = maxframe;
 671         }
 672
 673         add_wait_queue(&tty->write_wait, &wait);
 674
 675         for (;;) {
 676                 set_current_state(TASK_INTERRUPTIBLE);
 677
 678                 tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
 679                 if (tbuf)
 680                         break;
 681
 682                 if (file->f_flags & O_NONBLOCK) {
 683                         error = -EAGAIN;
 684                         break;
 685                 }
 686                 schedule();
 687
 688                 n_hdlc = tty2n_hdlc (tty);
 689                 if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC ||
 690                     tty != n_hdlc->tty) {
 691                         printk("n_hdlc_tty_write: %p invalid after wait!\n", n_hdlc);
 692                         error = -EIO;
 693                         break;
 694                 }
 695
 696                 if (signal_pending(current)) {
 697                         error = -EINTR;
 698                         break;
 699                 }
 700         }
 701
 702         __set_current_state(TASK_RUNNING);
 703         remove_wait_queue(&tty->write_wait, &wait);
 704
 705         if (!error) {
 706                 /* Retrieve the user's buffer */
 707                 memcpy(tbuf->buf, data, count);
 708
 709                 /* Send the data */
 710                 tbuf->count = error = count;
 711                 n_hdlc_buf_put(&n_hdlc->tx_buf_list,tbuf);
 712                 n_hdlc_send_frames(n_hdlc,tty);
 713         }
 714
 715         return error;
 716
 717 }       /* end of n_hdlc_tty_write() */
 718
 719 /**
 720  * n_hdlc_tty_ioctl - process IOCTL system call for the tty device.
 721  * @tty - pointer to tty instance data
 722  * @file - pointer to open file object for device
 723  * @cmd - IOCTL command code
 724  * @arg - argument for IOCTL call (cmd dependent)
 725  *
 726  * Returns command dependent result.
 727  */
 728 static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
 729                             unsigned int cmd, unsigned long arg)
 730 {
 731         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 732         int error = 0;
 733         int count;
 734         unsigned long flags;
 735         struct n_hdlc_buf *buf = NULL;
 736
 737         if (debuglevel >= DEBUG_LEVEL_INFO)
 738                 printk("%s(%d)n_hdlc_tty_ioctl() called %d\n",
 739                         __FILE__,__LINE__,cmd);
 740
 741         /* Verify the status of the device */
 742         if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC)
 743                 return -EBADF;
 744
 745         switch (cmd) {
 746         case FIONREAD:
 747                 /* report count of read data available */
 748                 /* in next available frame (if any) */
 749                 spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock,flags);
 750                 buf = list_first_entry_or_null(&n_hdlc->rx_buf_list.list,
 751                                                 struct n_hdlc_buf, list_item);
 752                 if (buf)
 753                         count = buf->count;
 754                 else
 755                         count = 0;
 756                 spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock,flags);
 757                 error = put_user(count, (int __user *)arg);
 758                 break;
 759
 760         case TIOCOUTQ:
 761                 /* get the pending tx byte count in the driver */
 762                 count = tty_chars_in_buffer(tty);
 763                 /* add size of next output frame in queue */
 764                 spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock,flags);
 765                 buf = list_first_entry_or_null(&n_hdlc->tx_buf_list.list,
 766                                                 struct n_hdlc_buf, list_item);
 767                 if (buf)
 768                         count += buf->count;
 769                 spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock,flags);
 770                 error = put_user(count, (int __user *)arg);
 771                 break;
 772
 773         case TCFLSH:
 774                 switch (arg) {
 775                 case TCIOFLUSH:
 776                 case TCOFLUSH:
 777                         flush_tx_queue(tty);
 778                 }
 779                 /* fall through to default */
 780
 781         default:
 782                 error = n_tty_ioctl_helper(tty, file, cmd, arg);
 783                 break;
 784         }
 785         return error;
 786
 787 }       /* end of n_hdlc_tty_ioctl() */
 788
 789 /**
 790  * n_hdlc_tty_poll - TTY callback for poll system call
 791  * @tty - pointer to tty instance data
 792  * @filp - pointer to open file object for device
 793  * @poll_table - wait queue for operations
 794  *
 795  * Determine which operations (read/write) will not block and return info
 796  * to caller.
 797  * Returns a bit mask containing info on which ops will not block.
 798  */
 799 static __poll_t n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
 800                                     poll_table *wait)
 801 {
 802         struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
 803         __poll_t mask = 0;
 804
 805         if (debuglevel >= DEBUG_LEVEL_INFO)
 806                 printk("%s(%d)n_hdlc_tty_poll() called\n",__FILE__,__LINE__);
 807
 808         if (n_hdlc && n_hdlc->magic == HDLC_MAGIC && tty == n_hdlc->tty) {
 809                 /* queue current process into any wait queue that */
 810                 /* may awaken in the future (read and write) */
 811
 812                 poll_wait(filp, &tty->read_wait, wait);
 813                 poll_wait(filp, &tty->write_wait, wait);
 814
 815                 /* set bits for operations that won't block */
 816                 if (!list_empty(&n_hdlc->rx_buf_list.list))
 817                         mask |= EPOLLIN | EPOLLRDNORM;  /* readable */
 818                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 819                         mask |= EPOLLHUP;
 820                 if (tty_hung_up_p(filp))
 821                         mask |= EPOLLHUP;
 822                 if (!tty_is_writelocked(tty) &&
 823                                 !list_empty(&n_hdlc->tx_free_buf_list.list))
 824                         mask |= EPOLLOUT | EPOLLWRNORM; /* writable */
 825         }
 826         return mask;
 827 }       /* end of n_hdlc_tty_poll() */
 828
 829 /**
 830  * n_hdlc_alloc - allocate an n_hdlc instance data structure
 831  *
 832  * Returns a pointer to newly created structure if success, otherwise %NULL
 833  */
 834 static struct n_hdlc *n_hdlc_alloc(void)
 835 {
 836         struct n_hdlc_buf *buf;
 837         int i;
 838         struct n_hdlc *n_hdlc = kzalloc(sizeof(*n_hdlc), GFP_KERNEL);
 839
 840         if (!n_hdlc)
 841                 return NULL;
 842
 843         spin_lock_init(&n_hdlc->rx_free_buf_list.spinlock);
 844         spin_lock_init(&n_hdlc->tx_free_buf_list.spinlock);
 845         spin_lock_init(&n_hdlc->rx_buf_list.spinlock);
 846         spin_lock_init(&n_hdlc->tx_buf_list.spinlock);
 847
 848         INIT_LIST_HEAD(&n_hdlc->rx_free_buf_list.list);
 849         INIT_LIST_HEAD(&n_hdlc->tx_free_buf_list.list);
 850         INIT_LIST_HEAD(&n_hdlc->rx_buf_list.list);
 851         INIT_LIST_HEAD(&n_hdlc->tx_buf_list.list);
 852
 853         /* allocate free rx buffer list */
 854         for(i=0;i<DEFAULT_RX_BUF_COUNT;i++) {
 855                 buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
 856                 if (buf)
 857                         n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,buf);
 858                 else if (debuglevel >= DEBUG_LEVEL_INFO)
 859                         printk("%s(%d)n_hdlc_alloc(), kalloc() failed for rx buffer %d\n",__FILE__,__LINE__, i);
 860         }
 861
 862         /* allocate free tx buffer list */
 863         for(i=0;i<DEFAULT_TX_BUF_COUNT;i++) {
 864                 buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
 865                 if (buf)
 866                         n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,buf);
 867                 else if (debuglevel >= DEBUG_LEVEL_INFO)
 868                         printk("%s(%d)n_hdlc_alloc(), kalloc() failed for tx buffer %d\n",__FILE__,__LINE__, i);
 869         }
 870
 871         /* Initialize the control block */
 872         n_hdlc->magic  = HDLC_MAGIC;
 873         n_hdlc->flags  = 0;
 874
 875         return n_hdlc;
 876
 877 }       /* end of n_hdlc_alloc() */
 878
 879 /**
 880  * n_hdlc_buf_return - put the HDLC buffer after the head of the specified list
 881  * @buf_list - pointer to the buffer list
 882  * @buf - pointer to the buffer
 883  */
 884 static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
 885                                                 struct n_hdlc_buf *buf)
 886 {
 887         unsigned long flags;
 888
 889         spin_lock_irqsave(&buf_list->spinlock, flags);
 890
 891         list_add(&buf->list_item, &buf_list->list);
 892         buf_list->count++;
 893
 894         spin_unlock_irqrestore(&buf_list->spinlock, flags);
 895 }
 896
 897 /**
 898  * n_hdlc_buf_put - add specified HDLC buffer to tail of specified list
 899  * @buf_list - pointer to buffer list
 900  * @buf - pointer to buffer
 901  */
 902 static void n_hdlc_buf_put(struct n_hdlc_buf_list *buf_list,
 903                            struct n_hdlc_buf *buf)
 904 {
 905         unsigned long flags;
 906
 907         spin_lock_irqsave(&buf_list->spinlock, flags);
 908
 909         list_add_tail(&buf->list_item, &buf_list->list);
 910         buf_list->count++;
 911
 912         spin_unlock_irqrestore(&buf_list->spinlock, flags);
 913 }       /* end of n_hdlc_buf_put() */
 914
 915 /**
 916  * n_hdlc_buf_get - remove and return an HDLC buffer from list
 917  * @buf_list - pointer to HDLC buffer list
 918  *
 919  * Remove and return an HDLC buffer from the head of the specified HDLC buffer
 920  * list.
 921  * Returns a pointer to HDLC buffer if available, otherwise %NULL.
 922  */
 923 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *buf_list)
 924 {
 925         unsigned long flags;
 926         struct n_hdlc_buf *buf;
 927
 928         spin_lock_irqsave(&buf_list->spinlock, flags);
 929
 930         buf = list_first_entry_or_null(&buf_list->list,
 931                                                 struct n_hdlc_buf, list_item);
 932         if (buf) {
 933                 list_del(&buf->list_item);
 934                 buf_list->count--;
 935         }
 936
 937         spin_unlock_irqrestore(&buf_list->spinlock, flags);
 938         return buf;
 939 }       /* end of n_hdlc_buf_get() */
 940
 941 static const char hdlc_banner[] __initconst =
 942         KERN_INFO "HDLC line discipline maxframe=%u\n";
 943 static const char hdlc_register_ok[] __initconst =
 944         KERN_INFO "N_HDLC line discipline registered.\n";
 945 static const char hdlc_register_fail[] __initconst =
 946         KERN_ERR "error registering line discipline: %d\n";
 947
 948 static int __init n_hdlc_init(void)
 949 {
 950         int status;
 951
 952         /* range check maxframe arg */
 953         if (maxframe < 4096)
 954                 maxframe = 4096;
 955         else if (maxframe > 65535)
 956                 maxframe = 65535;
 957
 958         printk(hdlc_banner, maxframe);
 959
 960         status = tty_register_ldisc(N_HDLC, &n_hdlc_ldisc);
 961         if (!status)
 962                 printk(hdlc_register_ok);
 963         else
 964                 printk(hdlc_register_fail, status);
 965
 966         return status;
 967
 968 }       /* end of init_module() */
 969
 970 static const char hdlc_unregister_ok[] __exitdata =
 971         KERN_INFO "N_HDLC: line discipline unregistered\n";
 972 static const char hdlc_unregister_fail[] __exitdata =
 973         KERN_ERR "N_HDLC: can't unregister line discipline (err = %d)\n";
 974
 975 static void __exit n_hdlc_exit(void)
 976 {
 977         /* Release tty registration of line discipline */
 978         int status = tty_unregister_ldisc(N_HDLC);
 979
 980         if (status)
 981                 printk(hdlc_unregister_fail, status);
 982         else
 983                 printk(hdlc_unregister_ok);
 984 }
 985
 986 module_init(n_hdlc_init);
 987 module_exit(n_hdlc_exit);
 988
 989 MODULE_LICENSE("GPL");
 990 MODULE_AUTHOR("Paul Fulghum paulkf@microgate.com");
 991 module_param(debuglevel, int, 0);
 992 module_param(maxframe, int, 0);
 993 MODULE_ALIAS_LDISC(N_HDLC);