release/src-rt-6.x/linux/linux-2.6/drivers/net/ppp_synctty.c

   1 /*
   2  * PPP synchronous tty channel driver for Linux.
   3  *
   4  * This is a ppp channel driver that can be used with tty device drivers
   5  * that are frame oriented, such as synchronous HDLC devices.
   6  *
   7  * Complete PPP frames without encoding/decoding are exchanged between
   8  * the channel driver and the device driver.
   9  *
  10  * The async map IOCTL codes are implemented to keep the user mode
  11  * applications happy if they call them. Synchronous PPP does not use
  12  * the async maps.
  13  *
  14  * Copyright 1999 Paul Mackerras.
  15  *
  16  * Also touched by the grubby hands of Paul Fulghum paulkf@microgate.com
  17  *
  18  *  This program is free software; you can redistribute it and/or
  19  *  modify it under the terms of the GNU General Public License
  20  *  as published by the Free Software Foundation; either version
  21  *  2 of the License, or (at your option) any later version.
  22  *
  23  * This driver provides the encapsulation and framing for sending
  24  * and receiving PPP frames over sync serial lines.  It relies on
  25  * the generic PPP layer to give it frames to send and to process
  26  * received frames.  It implements the PPP line discipline.
  27  *
  28  * Part of the code in this driver was inspired by the old async-only
  29  * PPP driver, written by Michael Callahan and Al Longyear, and
  30  * subsequently hacked by Paul Mackerras.
  31  *
  32  * ==FILEVERSION 20040616==
  33  */
  34
  35 #include <linux/module.h>
  36 #include <linux/kernel.h>
  37 #include <linux/skbuff.h>
  38 #include <linux/tty.h>
  39 #include <linux/netdevice.h>
  40 #include <linux/poll.h>
  41 #include <linux/ppp_defs.h>
  42 #include <linux/if_ppp.h>
  43 #include <linux/ppp_channel.h>
  44 #include <linux/spinlock.h>
  45 #include <linux/init.h>
  46 #include <asm/uaccess.h>
  47 #include <asm/semaphore.h>
  48
  49 #define PPP_VERSION     "2.4.2"
  50
  51 /* Structure for storing local state. */
  52 struct syncppp {
  53         struct tty_struct *tty;
  54         unsigned int    flags;
  55         unsigned int    rbits;
  56         int             mru;
  57         spinlock_t      xmit_lock;
  58         spinlock_t      recv_lock;
  59         unsigned long   xmit_flags;
  60         u32             xaccm[8];
  61         u32             raccm;
  62         unsigned int    bytes_sent;
  63         unsigned int    bytes_rcvd;
  64
  65         struct sk_buff  *tpkt;
  66         unsigned long   last_xmit;
  67
  68         struct sk_buff_head rqueue;
  69
  70         struct tasklet_struct tsk;
  71
  72         atomic_t        refcnt;
  73         struct semaphore dead_sem;
  74         struct ppp_channel chan;        /* interface to generic ppp layer */
  75 };
  76
  77 /* Bit numbers in xmit_flags */
  78 #define XMIT_WAKEUP     0
  79 #define XMIT_FULL       1
  80
  81 /* Bits in rbits */
  82 #define SC_RCV_BITS     (SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)
  83
  84 #define PPPSYNC_MAX_RQLEN       32      /* arbitrary */
  85
  86 /*
  87  * Prototypes.
  88  */
  89 static struct sk_buff* ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *);
  90 static int ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb);
  91 static int ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd,
  92                           unsigned long arg);
  93 static void ppp_sync_process(unsigned long arg);
  94 static int ppp_sync_push(struct syncppp *ap);
  95 static void ppp_sync_flush_output(struct syncppp *ap);
  96 static void ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
  97                            char *flags, int count);
  98
  99 static struct ppp_channel_ops sync_ops = {
 100         ppp_sync_send,
 101         ppp_sync_ioctl
 102 };
 103
 104 /*
 105  * Utility procedures to print a buffer in hex/ascii
 106  */
 107 static void
 108 ppp_print_hex (register __u8 * out, const __u8 * in, int count)
 109 {
 110         register __u8 next_ch;
 111         static const char hex[] = "0123456789ABCDEF";
 112
 113         while (count-- > 0) {
 114                 next_ch = *in++;
 115                 *out++ = hex[(next_ch >> 4) & 0x0F];
 116                 *out++ = hex[next_ch & 0x0F];
 117                 ++out;
 118         }
 119 }
 120
 121 static void
 122 ppp_print_char (register __u8 * out, const __u8 * in, int count)
 123 {
 124         register __u8 next_ch;
 125
 126         while (count-- > 0) {
 127                 next_ch = *in++;
 128
 129                 if (next_ch < 0x20 || next_ch > 0x7e)
 130                         *out++ = '.';
 131                 else {
 132                         *out++ = next_ch;
 133                         if (next_ch == '%')   /* printk/syslogd has a bug !! */
 134                                 *out++ = '%';
 135                 }
 136         }
 137         *out = '\0';
 138 }
 139
 140 static void
 141 ppp_print_buffer (const char *name, const __u8 *buf, int count)
 142 {
 143         __u8 line[44];
 144
 145         if (name != NULL)
 146                 printk(KERN_DEBUG "ppp_synctty: %s, count = %d\n", name, count);
 147
 148         while (count > 8) {
 149                 memset (line, 32, 44);
 150                 ppp_print_hex (line, buf, 8);
 151                 ppp_print_char (&line[8 * 3], buf, 8);
 152                 printk(KERN_DEBUG "%s\n", line);
 153                 count -= 8;
 154                 buf += 8;
 155         }
 156
 157         if (count > 0) {
 158                 memset (line, 32, 44);
 159                 ppp_print_hex (line, buf, count);
 160                 ppp_print_char (&line[8 * 3], buf, count);
 161                 printk(KERN_DEBUG "%s\n", line);
 162         }
 163 }
 164
 165
 166 /*
 167  * Routines implementing the synchronous PPP line discipline.
 168  */
 169
 170 /*
 171  * We have a potential race on dereferencing tty->disc_data,
 172  * because the tty layer provides no locking at all - thus one
 173  * cpu could be running ppp_synctty_receive while another
 174  * calls ppp_synctty_close, which zeroes tty->disc_data and
 175  * frees the memory that ppp_synctty_receive is using.  The best
 176  * way to fix this is to use a rwlock in the tty struct, but for now
 177  * we use a single global rwlock for all ttys in ppp line discipline.
 178  *
 179  * FIXME: Fixed in tty_io nowdays.
 180  */
 181 static DEFINE_RWLOCK(disc_data_lock);
 182
 183 static struct syncppp *sp_get(struct tty_struct *tty)
 184 {
 185         unsigned long flags;
 186         struct syncppp *ap;
 187
 188         read_lock_irqsave(&disc_data_lock, flags);
 189         ap = tty->disc_data;
 190         if (ap != NULL)
 191                 atomic_inc(&ap->refcnt);
 192         read_unlock_irqrestore(&disc_data_lock, flags);
 193
 194         return ap;
 195 }
 196
 197 static void sp_put(struct syncppp *ap)
 198 {
 199         if (atomic_dec_and_test(&ap->refcnt))
 200                 up(&ap->dead_sem);
 201 }
 202
 203 /*
 204  * Called when a tty is put into sync-PPP line discipline.
 205  */
 206 static int
 207 ppp_sync_open(struct tty_struct *tty)
 208 {
 209         struct syncppp *ap;
 210         int err;
 211
 212         ap = kzalloc(sizeof(*ap), GFP_KERNEL);
 213         err = -ENOMEM;
 214         if (ap == 0)
 215                 goto out;
 216
 217         /* initialize the syncppp structure */
 218         ap->tty = tty;
 219         ap->mru = PPP_MRU;
 220         spin_lock_init(&ap->xmit_lock);
 221         spin_lock_init(&ap->recv_lock);
 222         ap->xaccm[0] = ~0U;
 223         ap->xaccm[3] = 0x60000000U;
 224         ap->raccm = ~0U;
 225
 226         skb_queue_head_init(&ap->rqueue);
 227         tasklet_init(&ap->tsk, ppp_sync_process, (unsigned long) ap);
 228
 229         atomic_set(&ap->refcnt, 1);
 230         init_MUTEX_LOCKED(&ap->dead_sem);
 231
 232         ap->chan.private = ap;
 233         ap->chan.ops = &sync_ops;
 234         ap->chan.mtu = PPP_MRU;
 235         ap->chan.hdrlen = 2;    /* for A/C bytes */
 236         err = ppp_register_channel(&ap->chan);
 237         if (err)
 238                 goto out_free;
 239
 240         tty->disc_data = ap;
 241         tty->receive_room = 65536;
 242         return 0;
 243
 244  out_free:
 245         kfree(ap);
 246  out:
 247         return err;
 248 }
 249
 250 /*
 251  * Called when the tty is put into another line discipline
 252  * or it hangs up.  We have to wait for any cpu currently
 253  * executing in any of the other ppp_synctty_* routines to
 254  * finish before we can call ppp_unregister_channel and free
 255  * the syncppp struct.  This routine must be called from
 256  * process context, not interrupt or softirq context.
 257  */
 258 static void
 259 ppp_sync_close(struct tty_struct *tty)
 260 {
 261         unsigned long flags;
 262         struct syncppp *ap;
 263
 264         write_lock_irqsave(&disc_data_lock, flags);
 265         ap = tty->disc_data;
 266         tty->disc_data = NULL;
 267         write_unlock_irqrestore(&disc_data_lock, flags);
 268         if (!ap)
 269                 return;
 270
 271         /*
 272          * We have now ensured that nobody can start using ap from now
 273          * on, but we have to wait for all existing users to finish.
 274          * Note that ppp_unregister_channel ensures that no calls to
 275          * our channel ops (i.e. ppp_sync_send/ioctl) are in progress
 276          * by the time it returns.
 277          */
 278         if (!atomic_dec_and_test(&ap->refcnt))
 279                 down(&ap->dead_sem);
 280         tasklet_kill(&ap->tsk);
 281
 282         ppp_unregister_channel(&ap->chan);
 283         skb_queue_purge(&ap->rqueue);
 284         if (ap->tpkt != 0)
 285                 kfree_skb(ap->tpkt);
 286         kfree(ap);
 287 }
 288
 289 /*
 290  * Called on tty hangup in process context.
 291  *
 292  * Wait for I/O to driver to complete and unregister PPP channel.
 293  * This is already done by the close routine, so just call that.
 294  */
 295 static int ppp_sync_hangup(struct tty_struct *tty)
 296 {
 297         ppp_sync_close(tty);
 298         return 0;
 299 }
 300
 301 /*
 302  * Read does nothing - no data is ever available this way.
 303  * Pppd reads and writes packets via /dev/ppp instead.
 304  */
 305 static ssize_t
 306 ppp_sync_read(struct tty_struct *tty, struct file *file,
 307                unsigned char __user *buf, size_t count)
 308 {
 309         return -EAGAIN;
 310 }
 311
 312 /*
 313  * Write on the tty does nothing, the packets all come in
 314  * from the ppp generic stuff.
 315  */
 316 static ssize_t
 317 ppp_sync_write(struct tty_struct *tty, struct file *file,
 318                 const unsigned char *buf, size_t count)
 319 {
 320         return -EAGAIN;
 321 }
 322
 323 static int
 324 ppp_synctty_ioctl(struct tty_struct *tty, struct file *file,
 325                   unsigned int cmd, unsigned long arg)
 326 {
 327         struct syncppp *ap = sp_get(tty);
 328         int __user *p = (int __user *)arg;
 329         int err, val;
 330
 331         if (ap == 0)
 332                 return -ENXIO;
 333         err = -EFAULT;
 334         switch (cmd) {
 335         case PPPIOCGCHAN:
 336                 err = -ENXIO;
 337                 if (ap == 0)
 338                         break;
 339                 err = -EFAULT;
 340                 if (put_user(ppp_channel_index(&ap->chan), p))
 341                         break;
 342                 err = 0;
 343                 break;
 344
 345         case PPPIOCGUNIT:
 346                 err = -ENXIO;
 347                 if (ap == 0)
 348                         break;
 349                 err = -EFAULT;
 350                 if (put_user(ppp_unit_number(&ap->chan), p))
 351                         break;
 352                 err = 0;
 353                 break;
 354
 355         case TCGETS:
 356         case TCGETA:
 357                 err = n_tty_ioctl(tty, file, cmd, arg);
 358                 break;
 359
 360         case TCFLSH:
 361                 /* flush our buffers and the serial port's buffer */
 362                 if (arg == TCIOFLUSH || arg == TCOFLUSH)
 363                         ppp_sync_flush_output(ap);
 364                 err = n_tty_ioctl(tty, file, cmd, arg);
 365                 break;
 366
 367         case FIONREAD:
 368                 val = 0;
 369                 if (put_user(val, p))
 370                         break;
 371                 err = 0;
 372                 break;
 373
 374         default:
 375                 err = -ENOIOCTLCMD;
 376         }
 377
 378         sp_put(ap);
 379         return err;
 380 }
 381
 382 /* No kernel lock - fine */
 383 static unsigned int
 384 ppp_sync_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
 385 {
 386         return 0;
 387 }
 388
 389 /*
 390  * This can now be called from hard interrupt level as well
 391  * as soft interrupt level or mainline.
 392  */
 393 static void
 394 ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
 395                   char *cflags, int count)
 396 {
 397         struct syncppp *ap = sp_get(tty);
 398         unsigned long flags;
 399
 400         if (ap == 0)
 401                 return;
 402         spin_lock_irqsave(&ap->recv_lock, flags);
 403         ppp_sync_input(ap, buf, cflags, count);
 404         spin_unlock_irqrestore(&ap->recv_lock, flags);
 405         if (!skb_queue_empty(&ap->rqueue))
 406                 tasklet_schedule(&ap->tsk);
 407         sp_put(ap);
 408         if (test_and_clear_bit(TTY_THROTTLED, &tty->flags)
 409             && tty->driver->unthrottle)
 410                 tty->driver->unthrottle(tty);
 411 }
 412
 413 static void
 414 ppp_sync_wakeup(struct tty_struct *tty)
 415 {
 416         struct syncppp *ap = sp_get(tty);
 417
 418         clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 419         if (ap == 0)
 420                 return;
 421         set_bit(XMIT_WAKEUP, &ap->xmit_flags);
 422         tasklet_schedule(&ap->tsk);
 423         sp_put(ap);
 424 }
 425
 426
 427 static struct tty_ldisc ppp_sync_ldisc = {
 428         .owner  = THIS_MODULE,
 429         .magic  = TTY_LDISC_MAGIC,
 430         .name   = "pppsync",
 431         .open   = ppp_sync_open,
 432         .close  = ppp_sync_close,
 433         .hangup = ppp_sync_hangup,
 434         .read   = ppp_sync_read,
 435         .write  = ppp_sync_write,
 436         .ioctl  = ppp_synctty_ioctl,
 437         .poll   = ppp_sync_poll,
 438         .receive_buf = ppp_sync_receive,
 439         .write_wakeup = ppp_sync_wakeup,
 440 };
 441
 442 static int __init
 443 ppp_sync_init(void)
 444 {
 445         int err;
 446
 447         err = tty_register_ldisc(N_SYNC_PPP, &ppp_sync_ldisc);
 448         if (err != 0)
 449                 printk(KERN_ERR "PPP_sync: error %d registering line disc.\n",
 450                        err);
 451         return err;
 452 }
 453
 454 /*
 455  * The following routines provide the PPP channel interface.
 456  */
 457 static int
 458 ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
 459 {
 460         struct syncppp *ap = chan->private;
 461         int err, val;
 462         u32 accm[8];
 463         void __user *argp = (void __user *)arg;
 464         u32 __user *p = argp;
 465
 466         err = -EFAULT;
 467         switch (cmd) {
 468         case PPPIOCGFLAGS:
 469                 val = ap->flags | ap->rbits;
 470                 if (put_user(val, (int __user *) argp))
 471                         break;
 472                 err = 0;
 473                 break;
 474         case PPPIOCSFLAGS:
 475                 if (get_user(val, (int __user *) argp))
 476                         break;
 477                 ap->flags = val & ~SC_RCV_BITS;
 478                 spin_lock_irq(&ap->recv_lock);
 479                 ap->rbits = val & SC_RCV_BITS;
 480                 spin_unlock_irq(&ap->recv_lock);
 481                 err = 0;
 482                 break;
 483
 484         case PPPIOCGASYNCMAP:
 485                 if (put_user(ap->xaccm[0], p))
 486                         break;
 487                 err = 0;
 488                 break;
 489         case PPPIOCSASYNCMAP:
 490                 if (get_user(ap->xaccm[0], p))
 491                         break;
 492                 err = 0;
 493                 break;
 494
 495         case PPPIOCGRASYNCMAP:
 496                 if (put_user(ap->raccm, p))
 497                         break;
 498                 err = 0;
 499                 break;
 500         case PPPIOCSRASYNCMAP:
 501                 if (get_user(ap->raccm, p))
 502                         break;
 503                 err = 0;
 504                 break;
 505
 506         case PPPIOCGXASYNCMAP:
 507                 if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
 508                         break;
 509                 err = 0;
 510                 break;
 511         case PPPIOCSXASYNCMAP:
 512                 if (copy_from_user(accm, argp, sizeof(accm)))
 513                         break;
 514                 accm[2] &= ~0x40000000U;        /* can't escape 0x5e */
 515                 accm[3] |= 0x60000000U;         /* must escape 0x7d, 0x7e */
 516                 memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
 517                 err = 0;
 518                 break;
 519
 520         case PPPIOCGMRU:
 521                 if (put_user(ap->mru, (int __user *) argp))
 522                         break;
 523                 err = 0;
 524                 break;
 525         case PPPIOCSMRU:
 526                 if (get_user(val, (int __user *) argp))
 527                         break;
 528                 if (val < PPP_MRU)
 529                         val = PPP_MRU;
 530                 ap->mru = val;
 531                 err = 0;
 532                 break;
 533
 534         default:
 535                 err = -ENOTTY;
 536         }
 537         return err;
 538 }
 539
 540 /*
 541  * This is called at softirq level to deliver received packets
 542  * to the ppp_generic code, and to tell the ppp_generic code
 543  * if we can accept more output now.
 544  */
 545 static void ppp_sync_process(unsigned long arg)
 546 {
 547         struct syncppp *ap = (struct syncppp *) arg;
 548         struct sk_buff *skb;
 549
 550         /* process received packets */
 551         while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
 552                 if (skb->len == 0) {
 553                         /* zero length buffers indicate error */
 554                         ppp_input_error(&ap->chan, 0);
 555                         kfree_skb(skb);
 556                 }
 557                 else
 558                         ppp_input(&ap->chan, skb);
 559         }
 560
 561         /* try to push more stuff out */
 562         if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_sync_push(ap))
 563                 ppp_output_wakeup(&ap->chan);
 564 }
 565
 566 /*
 567  * Procedures for encapsulation and framing.
 568  */
 569
 570 struct sk_buff*
 571 ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb)
 572 {
 573         int proto;
 574         unsigned char *data;
 575         int islcp;
 576
 577         data  = skb->data;
 578         proto = (data[0] << 8) + data[1];
 579
 580         /* LCP packets with codes between 1 (configure-request)
 581          * and 7 (code-reject) must be sent as though no options
 582          * have been negotiated.
 583          */
 584         islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
 585
 586         /* compress protocol field if option enabled */
 587         if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp)
 588                 skb_pull(skb,1);
 589
 590         /* prepend address/control fields if necessary */
 591         if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
 592                 if (skb_headroom(skb) < 2) {
 593                         struct sk_buff *npkt = dev_alloc_skb(skb->len + 2);
 594                         if (npkt == NULL) {
 595                                 kfree_skb(skb);
 596                                 return NULL;
 597                         }
 598                         skb_reserve(npkt,2);
 599                         skb_copy_from_linear_data(skb,
 600                                       skb_put(npkt, skb->len), skb->len);
 601                         kfree_skb(skb);
 602                         skb = npkt;
 603                 }
 604                 skb_push(skb,2);
 605                 skb->data[0] = PPP_ALLSTATIONS;
 606                 skb->data[1] = PPP_UI;
 607         }
 608
 609         ap->last_xmit = jiffies;
 610
 611         if (skb && ap->flags & SC_LOG_OUTPKT)
 612                 ppp_print_buffer ("send buffer", skb->data, skb->len);
 613
 614         return skb;
 615 }
 616
 617 /*
 618  * Transmit-side routines.
 619  */
 620
 621 /*
 622  * Send a packet to the peer over an sync tty line.
 623  * Returns 1 iff the packet was accepted.
 624  * If the packet was not accepted, we will call ppp_output_wakeup
 625  * at some later time.
 626  */
 627 static int
 628 ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb)
 629 {
 630         struct syncppp *ap = chan->private;
 631
 632         ppp_sync_push(ap);
 633
 634         if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
 635                 return 0;       /* already full */
 636         skb = ppp_sync_txmunge(ap, skb);
 637         if (skb != NULL)
 638                 ap->tpkt = skb;
 639         else
 640                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 641
 642         ppp_sync_push(ap);
 643         return 1;
 644 }
 645
 646 /*
 647  * Push as much data as possible out to the tty.
 648  */
 649 static int
 650 ppp_sync_push(struct syncppp *ap)
 651 {
 652         int sent, done = 0;
 653         struct tty_struct *tty = ap->tty;
 654         int tty_stuffed = 0;
 655
 656         if (!spin_trylock_bh(&ap->xmit_lock))
 657                 return 0;
 658         for (;;) {
 659                 if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
 660                         tty_stuffed = 0;
 661                 if (!tty_stuffed && ap->tpkt != 0) {
 662                         set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 663                         sent = tty->driver->write(tty, ap->tpkt->data, ap->tpkt->len);
 664                         if (sent < 0)
 665                                 goto flush;     /* error, e.g. loss of CD */
 666                         if (sent < ap->tpkt->len) {
 667                                 tty_stuffed = 1;
 668                         } else {
 669                                 kfree_skb(ap->tpkt);
 670                                 ap->tpkt = NULL;
 671                                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 672                                 done = 1;
 673                         }
 674                         continue;
 675                 }
 676                 /* haven't made any progress */
 677                 spin_unlock_bh(&ap->xmit_lock);
 678                 if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags)
 679                       || (!tty_stuffed && ap->tpkt != 0)))
 680                         break;
 681                 if (!spin_trylock_bh(&ap->xmit_lock))
 682                         break;
 683         }
 684         return done;
 685
 686 flush:
 687         if (ap->tpkt != 0) {
 688                 kfree_skb(ap->tpkt);
 689                 ap->tpkt = NULL;
 690                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 691                 done = 1;
 692         }
 693         spin_unlock_bh(&ap->xmit_lock);
 694         return done;
 695 }
 696
 697 /*
 698  * Flush output from our internal buffers.
 699  * Called for the TCFLSH ioctl.
 700  */
 701 static void
 702 ppp_sync_flush_output(struct syncppp *ap)
 703 {
 704         int done = 0;
 705
 706         spin_lock_bh(&ap->xmit_lock);
 707         if (ap->tpkt != NULL) {
 708                 kfree_skb(ap->tpkt);
 709                 ap->tpkt = NULL;
 710                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 711                 done = 1;
 712         }
 713         spin_unlock_bh(&ap->xmit_lock);
 714         if (done)
 715                 ppp_output_wakeup(&ap->chan);
 716 }
 717
 718 /*
 719  * Receive-side routines.
 720  */
 721
 722 /* called when the tty driver has data for us.
 723  *
 724  * Data is frame oriented: each call to ppp_sync_input is considered
 725  * a whole frame. If the 1st flag byte is non-zero then the whole
 726  * frame is considered to be in error and is tossed.
 727  */
 728 static void
 729 ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
 730                 char *flags, int count)
 731 {
 732         struct sk_buff *skb;
 733         unsigned char *p;
 734
 735         if (count == 0)
 736                 return;
 737
 738         if (ap->flags & SC_LOG_INPKT)
 739                 ppp_print_buffer ("receive buffer", buf, count);
 740
 741         /* stuff the chars in the skb */
 742         if ((skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2)) == 0) {
 743                 printk(KERN_ERR "PPPsync: no memory (input pkt)\n");
 744                 goto err;
 745         }
 746         /* Try to get the payload 4-byte aligned */
 747         if (buf[0] != PPP_ALLSTATIONS)
 748                 skb_reserve(skb, 2 + (buf[0] & 1));
 749
 750         if (flags != 0 && *flags) {
 751                 /* error flag set, ignore frame */
 752                 goto err;
 753         } else if (count > skb_tailroom(skb)) {
 754                 /* packet overflowed MRU */
 755                 goto err;
 756         }
 757
 758         p = skb_put(skb, count);
 759         memcpy(p, buf, count);
 760
 761         /* strip address/control field if present */
 762         p = skb->data;
 763         if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
 764                 /* chop off address/control */
 765                 if (skb->len < 3)
 766                         goto err;
 767                 p = skb_pull(skb, 2);
 768         }
 769
 770         /* decompress protocol field if compressed */
 771         if (p[0] & 1) {
 772                 /* protocol is compressed */
 773                 skb_push(skb, 1)[0] = 0;
 774         } else if (skb->len < 2)
 775                 goto err;
 776
 777         /* queue the frame to be processed */
 778         skb_queue_tail(&ap->rqueue, skb);
 779         return;
 780
 781 err:
 782         /* queue zero length packet as error indication */
 783         if (skb || (skb = dev_alloc_skb(0))) {
 784                 skb_trim(skb, 0);
 785                 skb_queue_tail(&ap->rqueue, skb);
 786         }
 787 }
 788
 789 static void __exit
 790 ppp_sync_cleanup(void)
 791 {
 792         if (tty_unregister_ldisc(N_SYNC_PPP) != 0)
 793                 printk(KERN_ERR "failed to unregister Sync PPP line discipline\n");
 794 }
 795
 796 module_init(ppp_sync_init);
 797 module_exit(ppp_sync_cleanup);
 798 MODULE_LICENSE("GPL");
 799 MODULE_ALIAS_LDISC(N_SYNC_PPP);