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 20020125==
  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  *rpkt;
  69
  70         atomic_t        refcnt;
  71         struct semaphore dead_sem;
  72         struct ppp_channel chan;        /* interface to generic ppp layer */
  73 };
  74
  75 /* Bit numbers in xmit_flags */
  76 #define XMIT_WAKEUP     0
  77 #define XMIT_FULL       1
  78
  79 /* Bits in rbits */
  80 #define SC_RCV_BITS     (SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)
  81
  82 #define PPPSYNC_MAX_RQLEN       32      /* arbitrary */
  83
  84 /*
  85  * Prototypes.
  86  */
  87 static struct sk_buff* ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *);
  88 static int ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb);
  89 static int ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd,
  90                           unsigned long arg);
  91 static int ppp_sync_push(struct syncppp *ap);
  92 static void ppp_sync_flush_output(struct syncppp *ap);
  93 static void ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
  94                            char *flags, int count);
  95
  96 static struct ppp_channel_ops sync_ops = {
  97         ppp_sync_send,
  98         ppp_sync_ioctl
  99 };
 100
 101 /*
 102  * Utility procedures to print a buffer in hex/ascii
 103  */
 104 static void
 105 ppp_print_hex (register __u8 * out, const __u8 * in, int count)
 106 {
 107         register __u8 next_ch;
 108         static char hex[] = "0123456789ABCDEF";
 109
 110         while (count-- > 0) {
 111                 next_ch = *in++;
 112                 *out++ = hex[(next_ch >> 4) & 0x0F];
 113                 *out++ = hex[next_ch & 0x0F];
 114                 ++out;
 115         }
 116 }
 117
 118 static void
 119 ppp_print_char (register __u8 * out, const __u8 * in, int count)
 120 {
 121         register __u8 next_ch;
 122
 123         while (count-- > 0) {
 124                 next_ch = *in++;
 125
 126                 if (next_ch < 0x20 || next_ch > 0x7e)
 127                         *out++ = '.';
 128                 else {
 129                         *out++ = next_ch;
 130                         if (next_ch == '%')   /* printk/syslogd has a bug !! */
 131                                 *out++ = '%';
 132                 }
 133         }
 134         *out = '\0';
 135 }
 136
 137 static void
 138 ppp_print_buffer (const char *name, const __u8 *buf, int count)
 139 {
 140         __u8 line[44];
 141
 142         if (name != NULL)
 143                 printk(KERN_DEBUG "ppp_synctty: %s, count = %d\n", name, count);
 144
 145         while (count > 8) {
 146                 memset (line, 32, 44);
 147                 ppp_print_hex (line, buf, 8);
 148                 ppp_print_char (&line[8 * 3], buf, 8);
 149                 printk(KERN_DEBUG "%s\n", line);
 150                 count -= 8;
 151                 buf += 8;
 152         }
 153
 154         if (count > 0) {
 155                 memset (line, 32, 44);
 156                 ppp_print_hex (line, buf, count);
 157                 ppp_print_char (&line[8 * 3], buf, count);
 158                 printk(KERN_DEBUG "%s\n", line);
 159         }
 160 }
 161
 162
 163 /*
 164  * Routines implementing the synchronous PPP line discipline.
 165  */
 166
 167 /*
 168  * We have a potential race on dereferencing tty->disc_data,
 169  * because the tty layer provides no locking at all - thus one
 170  * cpu could be running ppp_synctty_receive while another
 171  * calls ppp_synctty_close, which zeroes tty->disc_data and
 172  * frees the memory that ppp_synctty_receive is using.  The best
 173  * way to fix this is to use a rwlock in the tty struct, but for now
 174  * we use a single global rwlock for all ttys in ppp line discipline.
 175  */
 176 static rwlock_t disc_data_lock = RW_LOCK_UNLOCKED;
 177
 178 static struct syncppp *sp_get(struct tty_struct *tty)
 179 {
 180         struct syncppp *ap;
 181
 182         read_lock(&disc_data_lock);
 183         ap = tty->disc_data;
 184         if (ap != NULL)
 185                 atomic_inc(&ap->refcnt);
 186         read_unlock(&disc_data_lock);
 187         return ap;
 188 }
 189
 190 static void sp_put(struct syncppp *ap)
 191 {
 192         if (atomic_dec_and_test(&ap->refcnt))
 193                 up(&ap->dead_sem);
 194 }
 195
 196 /*
 197  * Called when a tty is put into sync-PPP line discipline.
 198  */
 199 static int
 200 ppp_sync_open(struct tty_struct *tty)
 201 {
 202         struct syncppp *ap;
 203         int err;
 204
 205         ap = kmalloc(sizeof(*ap), GFP_KERNEL);
 206         err = -ENOMEM;
 207         if (ap == 0)
 208                 goto out;
 209
 210         /* initialize the syncppp structure */
 211         memset(ap, 0, sizeof(*ap));
 212         ap->tty = tty;
 213         ap->mru = PPP_MRU;
 214         spin_lock_init(&ap->xmit_lock);
 215         spin_lock_init(&ap->recv_lock);
 216         ap->xaccm[0] = ~0U;
 217         ap->xaccm[3] = 0x60000000U;
 218         ap->raccm = ~0U;
 219
 220         atomic_set(&ap->refcnt, 1);
 221         init_MUTEX_LOCKED(&ap->dead_sem);
 222
 223         ap->chan.private = ap;
 224         ap->chan.ops = &sync_ops;
 225         ap->chan.mtu = PPP_MRU;
 226         ap->chan.hdrlen = 2;    /* for A/C bytes */
 227         err = ppp_register_channel(&ap->chan);
 228         if (err)
 229                 goto out_free;
 230
 231         tty->disc_data = ap;
 232
 233         return 0;
 234
 235  out_free:
 236         kfree(ap);
 237  out:
 238         return err;
 239 }
 240
 241 /*
 242  * Called when the tty is put into another line discipline
 243  * or it hangs up.  We have to wait for any cpu currently
 244  * executing in any of the other ppp_synctty_* routines to
 245  * finish before we can call ppp_unregister_channel and free
 246  * the syncppp struct.  This routine must be called from
 247  * process context, not interrupt or softirq context.
 248  */
 249 static void
 250 ppp_sync_close(struct tty_struct *tty)
 251 {
 252         struct syncppp *ap;
 253
 254         write_lock(&disc_data_lock);
 255         ap = tty->disc_data;
 256         tty->disc_data = 0;
 257         write_unlock(&disc_data_lock);
 258         if (ap == 0)
 259                 return;
 260
 261         /*
 262          * We have now ensured that nobody can start using ap from now
 263          * on, but we have to wait for all existing users to finish.
 264          * Note that ppp_unregister_channel ensures that no calls to
 265          * our channel ops (i.e. ppp_sync_send/ioctl) are in progress
 266          * by the time it returns.
 267          */
 268         if (!atomic_dec_and_test(&ap->refcnt))
 269                 down(&ap->dead_sem);
 270
 271         ppp_unregister_channel(&ap->chan);
 272         if (ap->rpkt != 0)
 273                 kfree_skb(ap->rpkt);
 274         if (ap->tpkt != 0)
 275                 kfree_skb(ap->tpkt);
 276         kfree(ap);
 277 }
 278
 279 /*
 280  * Read does nothing - no data is ever available this way.
 281  * Pppd reads and writes packets via /dev/ppp instead.
 282  */
 283 static ssize_t
 284 ppp_sync_read(struct tty_struct *tty, struct file *file,
 285                unsigned char *buf, size_t count)
 286 {
 287         return -EAGAIN;
 288 }
 289
 290 /*
 291  * Write on the tty does nothing, the packets all come in
 292  * from the ppp generic stuff.
 293  */
 294 static ssize_t
 295 ppp_sync_write(struct tty_struct *tty, struct file *file,
 296                 const unsigned char *buf, size_t count)
 297 {
 298         return -EAGAIN;
 299 }
 300
 301 static int
 302 ppp_synctty_ioctl(struct tty_struct *tty, struct file *file,
 303                   unsigned int cmd, unsigned long arg)
 304 {
 305         struct syncppp *ap = sp_get(tty);
 306         int err, val;
 307
 308         if (ap == 0)
 309                 return -ENXIO;
 310         err = -EFAULT;
 311         switch (cmd) {
 312         case PPPIOCGCHAN:
 313                 err = -ENXIO;
 314                 if (ap == 0)
 315                         break;
 316                 err = -EFAULT;
 317                 if (put_user(ppp_channel_index(&ap->chan), (int *) arg))
 318                         break;
 319                 err = 0;
 320                 break;
 321
 322         case PPPIOCGUNIT:
 323                 err = -ENXIO;
 324                 if (ap == 0)
 325                         break;
 326                 err = -EFAULT;
 327                 if (put_user(ppp_unit_number(&ap->chan), (int *) arg))
 328                         break;
 329                 err = 0;
 330                 break;
 331
 332         case TCGETS:
 333         case TCGETA:
 334                 err = n_tty_ioctl(tty, file, cmd, arg);
 335                 break;
 336
 337         case TCFLSH:
 338                 /* flush our buffers and the serial port's buffer */
 339                 if (arg == TCIOFLUSH || arg == TCOFLUSH)
 340                         ppp_sync_flush_output(ap);
 341                 err = n_tty_ioctl(tty, file, cmd, arg);
 342                 break;
 343
 344         case FIONREAD:
 345                 val = 0;
 346                 if (put_user(val, (int *) arg))
 347                         break;
 348                 err = 0;
 349                 break;
 350
 351         default:
 352                 err = -ENOIOCTLCMD;
 353         }
 354
 355         sp_put(ap);
 356         return err;
 357 }
 358
 359 /* No kernel lock - fine */
 360 static unsigned int
 361 ppp_sync_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
 362 {
 363         return 0;
 364 }
 365
 366 static int
 367 ppp_sync_room(struct tty_struct *tty)
 368 {
 369         return 65535;
 370 }
 371
 372 static void
 373 ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
 374                   char *flags, int count)
 375 {
 376         struct syncppp *ap = sp_get(tty);
 377
 378         if (ap == 0)
 379                 return;
 380         spin_lock_bh(&ap->recv_lock);
 381         ppp_sync_input(ap, buf, flags, count);
 382         spin_unlock_bh(&ap->recv_lock);
 383         sp_put(ap);
 384         if (test_and_clear_bit(TTY_THROTTLED, &tty->flags)
 385             && tty->driver->unthrottle)
 386                 tty->driver->unthrottle(tty);
 387 }
 388
 389 static void
 390 ppp_sync_wakeup(struct tty_struct *tty)
 391 {
 392         struct syncppp *ap = sp_get(tty);
 393
 394         clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 395         if (ap == 0)
 396                 return;
 397         if (ppp_sync_push(ap))
 398                 ppp_output_wakeup(&ap->chan);
 399         sp_put(ap);
 400 }
 401
 402
 403 static struct tty_ldisc ppp_sync_ldisc = {
 404         .owner  = THIS_MODULE,
 405         .magic  = TTY_LDISC_MAGIC,
 406         .name   = "pppsync",
 407         .open   = ppp_sync_open,
 408         .close  = ppp_sync_close,
 409         .read   = ppp_sync_read,
 410         .write  = ppp_sync_write,
 411         .ioctl  = ppp_synctty_ioctl,
 412         .poll   = ppp_sync_poll,
 413         .receive_room = ppp_sync_room,
 414         .receive_buf = ppp_sync_receive,
 415         .write_wakeup = ppp_sync_wakeup,
 416 };
 417
 418 static int __init
 419 ppp_sync_init(void)
 420 {
 421         int err;
 422
 423         err = tty_register_ldisc(N_SYNC_PPP, &ppp_sync_ldisc);
 424         if (err != 0)
 425                 printk(KERN_ERR "PPP_sync: error %d registering line disc.\n",
 426                        err);
 427         return err;
 428 }
 429
 430 /*
 431  * The following routines provide the PPP channel interface.
 432  */
 433 static int
 434 ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
 435 {
 436         struct syncppp *ap = chan->private;
 437         int err, val;
 438         u32 accm[8];
 439
 440         err = -EFAULT;
 441         switch (cmd) {
 442         case PPPIOCGFLAGS:
 443                 val = ap->flags | ap->rbits;
 444                 if (put_user(val, (int *) arg))
 445                         break;
 446                 err = 0;
 447                 break;
 448         case PPPIOCSFLAGS:
 449                 if (get_user(val, (int *) arg))
 450                         break;
 451                 ap->flags = val & ~SC_RCV_BITS;
 452                 spin_lock_bh(&ap->recv_lock);
 453                 ap->rbits = val & SC_RCV_BITS;
 454                 spin_unlock_bh(&ap->recv_lock);
 455                 err = 0;
 456                 break;
 457
 458         case PPPIOCGASYNCMAP:
 459                 if (put_user(ap->xaccm[0], (u32 *) arg))
 460                         break;
 461                 err = 0;
 462                 break;
 463         case PPPIOCSASYNCMAP:
 464                 if (get_user(ap->xaccm[0], (u32 *) arg))
 465                         break;
 466                 err = 0;
 467                 break;
 468
 469         case PPPIOCGRASYNCMAP:
 470                 if (put_user(ap->raccm, (u32 *) arg))
 471                         break;
 472                 err = 0;
 473                 break;
 474         case PPPIOCSRASYNCMAP:
 475                 if (get_user(ap->raccm, (u32 *) arg))
 476                         break;
 477                 err = 0;
 478                 break;
 479
 480         case PPPIOCGXASYNCMAP:
 481                 if (copy_to_user((void *) arg, ap->xaccm, sizeof(ap->xaccm)))
 482                         break;
 483                 err = 0;
 484                 break;
 485         case PPPIOCSXASYNCMAP:
 486                 if (copy_from_user(accm, (void *) arg, sizeof(accm)))
 487                         break;
 488                 accm[2] &= ~0x40000000U;        /* can't escape 0x5e */
 489                 accm[3] |= 0x60000000U;         /* must escape 0x7d, 0x7e */
 490                 memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
 491                 err = 0;
 492                 break;
 493
 494         case PPPIOCGMRU:
 495                 if (put_user(ap->mru, (int *) arg))
 496                         break;
 497                 err = 0;
 498                 break;
 499         case PPPIOCSMRU:
 500                 if (get_user(val, (int *) arg))
 501                         break;
 502                 if (val < PPP_MRU)
 503                         val = PPP_MRU;
 504                 ap->mru = val;
 505                 err = 0;
 506                 break;
 507
 508         default:
 509                 err = -ENOTTY;
 510         }
 511         return err;
 512 }
 513
 514 /*
 515  * Procedures for encapsulation and framing.
 516  */
 517
 518 struct sk_buff*
 519 ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb)
 520 {
 521         int proto;
 522         unsigned char *data;
 523         int islcp;
 524
 525         data  = skb->data;
 526         proto = (data[0] << 8) + data[1];
 527
 528         /* LCP packets with codes between 1 (configure-request)
 529          * and 7 (code-reject) must be sent as though no options
 530          * have been negotiated.
 531          */
 532         islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
 533
 534         /* compress protocol field if option enabled */
 535         if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp)
 536                 skb_pull(skb,1);
 537
 538         /* prepend address/control fields if necessary */
 539         if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
 540                 if (skb_headroom(skb) < 2) {
 541                         struct sk_buff *npkt = dev_alloc_skb(skb->len + 2);
 542                         if (npkt == NULL) {
 543                                 kfree_skb(skb);
 544                                 return NULL;
 545                         }
 546                         skb_reserve(npkt,2);
 547                         memcpy(skb_put(npkt,skb->len), skb->data, skb->len);
 548                         kfree_skb(skb);
 549                         skb = npkt;
 550                 }
 551                 skb_push(skb,2);
 552                 skb->data[0] = PPP_ALLSTATIONS;
 553                 skb->data[1] = PPP_UI;
 554         }
 555
 556         ap->last_xmit = jiffies;
 557
 558         if (skb && ap->flags & SC_LOG_OUTPKT)
 559                 ppp_print_buffer ("send buffer", skb->data, skb->len);
 560
 561         return skb;
 562 }
 563
 564 /*
 565  * Transmit-side routines.
 566  */
 567
 568 /*
 569  * Send a packet to the peer over an sync tty line.
 570  * Returns 1 iff the packet was accepted.
 571  * If the packet was not accepted, we will call ppp_output_wakeup
 572  * at some later time.
 573  */
 574 static int
 575 ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb)
 576 {
 577         struct syncppp *ap = chan->private;
 578
 579         ppp_sync_push(ap);
 580
 581         if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
 582                 return 0;       /* already full */
 583         skb = ppp_sync_txmunge(ap, skb);
 584         if (skb != NULL)
 585                 ap->tpkt = skb;
 586         else
 587                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 588
 589         ppp_sync_push(ap);
 590         return 1;
 591 }
 592
 593 /*
 594  * Push as much data as possible out to the tty.
 595  */
 596 static int
 597 ppp_sync_push(struct syncppp *ap)
 598 {
 599         int sent, done = 0;
 600         struct tty_struct *tty = ap->tty;
 601         int tty_stuffed = 0;
 602
 603         set_bit(XMIT_WAKEUP, &ap->xmit_flags);
 604         if (!spin_trylock_bh(&ap->xmit_lock))
 605                 return 0;
 606         for (;;) {
 607                 if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
 608                         tty_stuffed = 0;
 609                 if (!tty_stuffed && ap->tpkt != 0) {
 610                         set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 611                         sent = tty->driver->write(tty, 0, ap->tpkt->data, ap->tpkt->len);
 612                         if (sent < 0)
 613                                 goto flush;     /* error, e.g. loss of CD */
 614                         if (sent < ap->tpkt->len) {
 615                                 tty_stuffed = 1;
 616                         } else {
 617                                 kfree_skb(ap->tpkt);
 618                                 ap->tpkt = 0;
 619                                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 620                                 done = 1;
 621                         }
 622                         continue;
 623                 }
 624                 /* haven't made any progress */
 625                 spin_unlock_bh(&ap->xmit_lock);
 626                 if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags)
 627                       || (!tty_stuffed && ap->tpkt != 0)))
 628                         break;
 629                 if (!spin_trylock_bh(&ap->xmit_lock))
 630                         break;
 631         }
 632         return done;
 633
 634 flush:
 635         if (ap->tpkt != 0) {
 636                 kfree_skb(ap->tpkt);
 637                 ap->tpkt = 0;
 638                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 639                 done = 1;
 640         }
 641         spin_unlock_bh(&ap->xmit_lock);
 642         return done;
 643 }
 644
 645 /*
 646  * Flush output from our internal buffers.
 647  * Called for the TCFLSH ioctl.
 648  */
 649 static void
 650 ppp_sync_flush_output(struct syncppp *ap)
 651 {
 652         int done = 0;
 653
 654         spin_lock_bh(&ap->xmit_lock);
 655         if (ap->tpkt != NULL) {
 656                 kfree_skb(ap->tpkt);
 657                 ap->tpkt = 0;
 658                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 659                 done = 1;
 660         }
 661         spin_unlock_bh(&ap->xmit_lock);
 662         if (done)
 663                 ppp_output_wakeup(&ap->chan);
 664 }
 665
 666 /*
 667  * Receive-side routines.
 668  */
 669
 670 static inline void
 671 process_input_packet(struct syncppp *ap)
 672 {
 673         struct sk_buff *skb;
 674         unsigned char *p;
 675         int code = 0;
 676
 677         skb = ap->rpkt;
 678         ap->rpkt = 0;
 679
 680         /* strip address/control field if present */
 681         p = skb->data;
 682         if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
 683                 /* chop off address/control */
 684                 if (skb->len < 3)
 685                         goto err;
 686                 p = skb_pull(skb, 2);
 687         }
 688
 689         /* decompress protocol field if compressed */
 690         if (p[0] & 1) {
 691                 /* protocol is compressed */
 692                 skb_push(skb, 1)[0] = 0;
 693         } else if (skb->len < 2)
 694                 goto err;
 695
 696         /* pass to generic layer */
 697         ppp_input(&ap->chan, skb);
 698         return;
 699
 700  err:
 701         kfree_skb(skb);
 702         ppp_input_error(&ap->chan, code);
 703 }
 704
 705 /* called when the tty driver has data for us.
 706  *
 707  * Data is frame oriented: each call to ppp_sync_input is considered
 708  * a whole frame. If the 1st flag byte is non-zero then the whole
 709  * frame is considered to be in error and is tossed.
 710  */
 711 static void
 712 ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
 713                 char *flags, int count)
 714 {
 715         struct sk_buff *skb;
 716         unsigned char *sp;
 717
 718         if (count == 0)
 719                 return;
 720
 721         /* if flag set, then error, ignore frame */
 722         if (flags != 0 && *flags) {
 723                 ppp_input_error(&ap->chan, *flags);
 724                 return;
 725         }
 726
 727         if (ap->flags & SC_LOG_INPKT)
 728                 ppp_print_buffer ("receive buffer", buf, count);
 729
 730         /* stuff the chars in the skb */
 731         if ((skb = ap->rpkt) == 0) {
 732                 if ((skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2)) == 0) {
 733                         printk(KERN_ERR "PPPsync: no memory (input pkt)\n");
 734                         ppp_input_error(&ap->chan, 0);
 735                         return;
 736                 }
 737                 /* Try to get the payload 4-byte aligned */
 738                 if (buf[0] != PPP_ALLSTATIONS)
 739                         skb_reserve(skb, 2 + (buf[0] & 1));
 740                 ap->rpkt = skb;
 741         }
 742         if (count > skb_tailroom(skb)) {
 743                 /* packet overflowed MRU */
 744                 ppp_input_error(&ap->chan, 1);
 745         } else {
 746                 sp = skb_put(skb, count);
 747                 memcpy(sp, buf, count);
 748                 process_input_packet(ap);
 749         }
 750 }
 751
 752 static void __exit
 753 ppp_sync_cleanup(void)
 754 {
 755         if (tty_register_ldisc(N_SYNC_PPP, NULL) != 0)
 756                 printk(KERN_ERR "failed to unregister Sync PPP line discipline\n");
 757 }
 758
 759 module_init(ppp_sync_init);
 760 module_exit(ppp_sync_cleanup);
 761 MODULE_LICENSE("GPL");