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 sync-only
  29  * PPP driver, written by Michael Callahan and Al Longyear, and
  30  * subsequently hacked by Paul Mackerras.
  31  *
  32  * ==FILEVERSION 20000322==
  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/init.h>
  45 #include <asm/uaccess.h>
  46
  47 #ifndef spin_trylock_bh
  48 #define spin_trylock_bh(lock)   ({ int __r; local_bh_disable(); \
  49                                    __r = spin_trylock(lock);    \
  50                                    if (!__r) local_bh_enable(); \
  51                                    __r; })
  52 #endif
  53
  54 #define PPP_VERSION     "2.4.1"
  55
  56 /* Structure for storing local state. */
  57 struct syncppp {
  58         struct tty_struct *tty;
  59         unsigned int    flags;
  60         unsigned int    rbits;
  61         int             mru;
  62         spinlock_t      xmit_lock;
  63         spinlock_t      recv_lock;
  64         unsigned long   xmit_flags;
  65         u32             xaccm[8];
  66         u32             raccm;
  67         unsigned int    bytes_sent;
  68         unsigned int    bytes_rcvd;
  69
  70         struct sk_buff  *tpkt;
  71         unsigned long   last_xmit;
  72
  73         struct sk_buff  *rpkt;
  74
  75         struct ppp_channel chan;        /* interface to generic ppp layer */
  76 };
  77
  78 /* Bit numbers in xmit_flags */
  79 #define XMIT_WAKEUP     0
  80 #define XMIT_FULL       1
  81
  82 /* Bits in rbits */
  83 #define SC_RCV_BITS     (SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)
  84
  85 #define PPPSYNC_MAX_RQLEN       32      /* arbitrary */
  86
  87 /*
  88  * Prototypes.
  89  */
  90 static struct sk_buff* ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *);
  91 static int ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb);
  92 static int ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd,
  93                           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 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 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  * Called when a tty is put into line discipline.
 172  */
 173 static int
 174 ppp_sync_open(struct tty_struct *tty)
 175 {
 176         struct syncppp *ap;
 177         int err;
 178
 179         MOD_INC_USE_COUNT;
 180         ap = kmalloc(sizeof(*ap), GFP_KERNEL);
 181         err = -ENOMEM;
 182         if (ap == 0)
 183                 goto out;
 184
 185         /* initialize the syncppp structure */
 186         memset(ap, 0, sizeof(*ap));
 187         ap->tty = tty;
 188         ap->mru = PPP_MRU;
 189         spin_lock_init(&ap->xmit_lock);
 190         spin_lock_init(&ap->recv_lock);
 191         ap->xaccm[0] = ~0U;
 192         ap->xaccm[3] = 0x60000000U;
 193         ap->raccm = ~0U;
 194
 195         ap->chan.private = ap;
 196         ap->chan.ops = &sync_ops;
 197         ap->chan.mtu = PPP_MRU;
 198         ap->chan.hdrlen = 2;    /* for A/C bytes */
 199         err = ppp_register_channel(&ap->chan);
 200         if (err)
 201                 goto out_free;
 202
 203         tty->disc_data = ap;
 204
 205         return 0;
 206
 207  out_free:
 208         kfree(ap);
 209  out:
 210         MOD_DEC_USE_COUNT;
 211         return err;
 212 }
 213
 214 /*
 215  * Called when the tty is put into another line discipline
 216  * (or it hangs up).
 217  */
 218 static void
 219 ppp_sync_close(struct tty_struct *tty)
 220 {
 221         struct syncppp *ap = tty->disc_data;
 222
 223         if (ap == 0)
 224                 return;
 225         tty->disc_data = 0;
 226         ppp_unregister_channel(&ap->chan);
 227         if (ap->rpkt != 0)
 228                 kfree_skb(ap->rpkt);
 229         if (ap->tpkt != 0)
 230                 kfree_skb(ap->tpkt);
 231         kfree(ap);
 232         MOD_DEC_USE_COUNT;
 233 }
 234
 235 /*
 236  * Read a PPP frame, for compatibility until pppd is updated.
 237  */
 238 static ssize_t
 239 ppp_sync_read(struct tty_struct *tty, struct file *file,
 240                unsigned char *buf, size_t count)
 241 {
 242         struct syncppp *ap = tty->disc_data;
 243
 244         if (ap == 0)
 245                 return -ENXIO;
 246         return ppp_channel_read(&ap->chan, file, buf, count);
 247 }
 248
 249 /*
 250  * Write a ppp frame, for compatibility until pppd is updated.
 251  */
 252 static ssize_t
 253 ppp_sync_write(struct tty_struct *tty, struct file *file,
 254                 const unsigned char *buf, size_t count)
 255 {
 256         struct syncppp *ap = tty->disc_data;
 257
 258         if (ap == 0)
 259                 return -ENXIO;
 260         return ppp_channel_write(&ap->chan, buf, count);
 261 }
 262
 263 static int
 264 ppp_synctty_ioctl(struct tty_struct *tty, struct file *file,
 265                   unsigned int cmd, unsigned long arg)
 266 {
 267         struct syncppp *ap = tty->disc_data;
 268         int err, val;
 269
 270         err = -EFAULT;
 271         switch (cmd) {
 272         case PPPIOCGCHAN:
 273                 err = -ENXIO;
 274                 if (ap == 0)
 275                         break;
 276                 err = -EFAULT;
 277                 if (put_user(ppp_channel_index(&ap->chan), (int *) arg))
 278                         break;
 279                 err = 0;
 280                 break;
 281
 282         case PPPIOCGUNIT:
 283                 err = -ENXIO;
 284                 if (ap == 0)
 285                         break;
 286                 err = -EFAULT;
 287                 if (put_user(ppp_unit_number(&ap->chan), (int *) arg))
 288                         break;
 289                 err = 0;
 290                 break;
 291
 292         case TCGETS:
 293         case TCGETA:
 294                 err = n_tty_ioctl(tty, file, cmd, arg);
 295                 break;
 296
 297         case TCFLSH:
 298                 /* flush our buffers and the serial port's buffer */
 299                 if (arg == TCIOFLUSH || arg == TCOFLUSH)
 300                         ppp_sync_flush_output(ap);
 301                 err = n_tty_ioctl(tty, file, cmd, arg);
 302                 break;
 303
 304         case FIONREAD:
 305                 val = 0;
 306                 if (put_user(val, (int *) arg))
 307                         break;
 308                 err = 0;
 309                 break;
 310
 311         /*
 312          * Compatibility calls until pppd is updated.
 313          */
 314         case PPPIOCGFLAGS:
 315         case PPPIOCSFLAGS:
 316         case PPPIOCGASYNCMAP:
 317         case PPPIOCSASYNCMAP:
 318         case PPPIOCGRASYNCMAP:
 319         case PPPIOCSRASYNCMAP:
 320         case PPPIOCGXASYNCMAP:
 321         case PPPIOCSXASYNCMAP:
 322         case PPPIOCGMRU:
 323         case PPPIOCSMRU:
 324                 err = -EPERM;
 325                 if (!capable(CAP_NET_ADMIN))
 326                         break;
 327                 err = ppp_sync_ioctl(&ap->chan, cmd, arg);
 328                 break;
 329
 330         case PPPIOCATTACH:
 331         case PPPIOCDETACH:
 332                 err = ppp_channel_ioctl(&ap->chan, cmd, arg);
 333                 break;
 334
 335         default:
 336                 err = -ENOIOCTLCMD;
 337         }
 338
 339         return err;
 340 }
 341
 342 /* No kernel lock - fine */
 343 static unsigned int
 344 ppp_sync_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
 345 {
 346         struct syncppp *ap = tty->disc_data;
 347         unsigned int mask;
 348
 349         mask = POLLOUT | POLLWRNORM;
 350         /* compatibility for old pppd */
 351         if (ap != 0)
 352                 mask |= ppp_channel_poll(&ap->chan, file, wait);
 353         if (test_bit(TTY_OTHER_CLOSED, &tty->flags) || tty_hung_up_p(file))
 354                 mask |= POLLHUP;
 355         return mask;
 356 }
 357
 358 static int
 359 ppp_sync_room(struct tty_struct *tty)
 360 {
 361         return 65535;
 362 }
 363
 364 static void
 365 ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
 366                   char *flags, int count)
 367 {
 368         struct syncppp *ap = tty->disc_data;
 369
 370         if (ap == 0)
 371                 return;
 372         spin_lock_bh(&ap->recv_lock);
 373         ppp_sync_input(ap, buf, flags, count);
 374         spin_unlock_bh(&ap->recv_lock);
 375         if (test_and_clear_bit(TTY_THROTTLED, &tty->flags)
 376             && tty->driver.unthrottle)
 377                 tty->driver.unthrottle(tty);
 378 }
 379
 380 static void
 381 ppp_sync_wakeup(struct tty_struct *tty)
 382 {
 383         struct syncppp *ap = tty->disc_data;
 384
 385         clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 386         if (ap == 0)
 387                 return;
 388         if (ppp_sync_push(ap))
 389                 ppp_output_wakeup(&ap->chan);
 390 }
 391
 392
 393 static struct tty_ldisc ppp_sync_ldisc = {
 394         magic:  TTY_LDISC_MAGIC,
 395         name:   "pppsync",
 396         open:   ppp_sync_open,
 397         close:  ppp_sync_close,
 398         read:   ppp_sync_read,
 399         write:  ppp_sync_write,
 400         ioctl:  ppp_synctty_ioctl,
 401         poll:   ppp_sync_poll,
 402         receive_room: ppp_sync_room,
 403         receive_buf: ppp_sync_receive,
 404         write_wakeup: ppp_sync_wakeup,
 405 };
 406
 407 int
 408 ppp_sync_init(void)
 409 {
 410         int err;
 411
 412         err = tty_register_ldisc(N_SYNC_PPP, &ppp_sync_ldisc);
 413         if (err != 0)
 414                 printk(KERN_ERR "PPP_sync: error %d registering line disc.\n",
 415                        err);
 416         return err;
 417 }
 418
 419 /*
 420  * The following routines provide the PPP channel interface.
 421  */
 422 static int
 423 ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
 424 {
 425         struct syncppp *ap = chan->private;
 426         int err, val;
 427         u32 accm[8];
 428
 429         err = -EFAULT;
 430         switch (cmd) {
 431         case PPPIOCGFLAGS:
 432                 val = ap->flags | ap->rbits;
 433                 if (put_user(val, (int *) arg))
 434                         break;
 435                 err = 0;
 436                 break;
 437         case PPPIOCSFLAGS:
 438                 if (get_user(val, (int *) arg))
 439                         break;
 440                 ap->flags = val & ~SC_RCV_BITS;
 441                 spin_lock_bh(&ap->recv_lock);
 442                 ap->rbits = val & SC_RCV_BITS;
 443                 spin_unlock_bh(&ap->recv_lock);
 444                 err = 0;
 445                 break;
 446
 447         case PPPIOCGASYNCMAP:
 448                 if (put_user(ap->xaccm[0], (u32 *) arg))
 449                         break;
 450                 err = 0;
 451                 break;
 452         case PPPIOCSASYNCMAP:
 453                 if (get_user(ap->xaccm[0], (u32 *) arg))
 454                         break;
 455                 err = 0;
 456                 break;
 457
 458         case PPPIOCGRASYNCMAP:
 459                 if (put_user(ap->raccm, (u32 *) arg))
 460                         break;
 461                 err = 0;
 462                 break;
 463         case PPPIOCSRASYNCMAP:
 464                 if (get_user(ap->raccm, (u32 *) arg))
 465                         break;
 466                 err = 0;
 467                 break;
 468
 469         case PPPIOCGXASYNCMAP:
 470                 if (copy_to_user((void *) arg, ap->xaccm, sizeof(ap->xaccm)))
 471                         break;
 472                 err = 0;
 473                 break;
 474         case PPPIOCSXASYNCMAP:
 475                 if (copy_from_user(accm, (void *) arg, sizeof(accm)))
 476                         break;
 477                 accm[2] &= ~0x40000000U;        /* can't escape 0x5e */
 478                 accm[3] |= 0x60000000U;         /* must escape 0x7d, 0x7e */
 479                 memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
 480                 err = 0;
 481                 break;
 482
 483         case PPPIOCGMRU:
 484                 if (put_user(ap->mru, (int *) arg))
 485                         break;
 486                 err = 0;
 487                 break;
 488         case PPPIOCSMRU:
 489                 if (get_user(val, (int *) arg))
 490                         break;
 491                 if (val < PPP_MRU)
 492                         val = PPP_MRU;
 493                 ap->mru = val;
 494                 err = 0;
 495                 break;
 496
 497         default:
 498                 err = -ENOTTY;
 499         }
 500         return err;
 501 }
 502
 503 /*
 504  * Procedures for encapsulation and framing.
 505  */
 506
 507 struct sk_buff*
 508 ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb)
 509 {
 510         int proto;
 511         unsigned char *data;
 512         int islcp;
 513
 514         data  = skb->data;
 515         proto = (data[0] << 8) + data[1];
 516
 517         /* LCP packets with codes between 1 (configure-request)
 518          * and 7 (code-reject) must be sent as though no options
 519          * have been negotiated.
 520          */
 521         islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
 522
 523         /* compress protocol field if option enabled */
 524         if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp)
 525                 skb_pull(skb,1);
 526
 527         /* prepend address/control fields if necessary */
 528         if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
 529                 if (skb_headroom(skb) < 2) {
 530                         struct sk_buff *npkt = dev_alloc_skb(skb->len + 2);
 531                         if (npkt == NULL) {
 532                                 kfree_skb(skb);
 533                                 return NULL;
 534                         }
 535                         skb_reserve(npkt,2);
 536                         memcpy(skb_put(npkt,skb->len), skb->data, skb->len);
 537                         kfree_skb(skb);
 538                         skb = npkt;
 539                 }
 540                 skb_push(skb,2);
 541                 skb->data[0] = PPP_ALLSTATIONS;
 542                 skb->data[1] = PPP_UI;
 543         }
 544
 545         ap->last_xmit = jiffies;
 546
 547         if (skb && ap->flags & SC_LOG_OUTPKT)
 548                 ppp_print_buffer ("send buffer", skb->data, skb->len);
 549
 550         return skb;
 551 }
 552
 553 /*
 554  * Transmit-side routines.
 555  */
 556
 557 /*
 558  * Send a packet to the peer over an sync tty line.
 559  * Returns 1 iff the packet was accepted.
 560  * If the packet was not accepted, we will call ppp_output_wakeup
 561  * at some later time.
 562  */
 563 static int
 564 ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb)
 565 {
 566         struct syncppp *ap = chan->private;
 567
 568         ppp_sync_push(ap);
 569
 570         if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
 571                 return 0;       /* already full */
 572         skb = ppp_sync_txmunge(ap, skb);
 573         if (skb != NULL)
 574                 ap->tpkt = skb;
 575         else
 576                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 577
 578         ppp_sync_push(ap);
 579         return 1;
 580 }
 581
 582 /*
 583  * Push as much data as possible out to the tty.
 584  */
 585 static int
 586 ppp_sync_push(struct syncppp *ap)
 587 {
 588         int sent, done = 0;
 589         struct tty_struct *tty = ap->tty;
 590         int tty_stuffed = 0;
 591
 592         set_bit(XMIT_WAKEUP, &ap->xmit_flags);
 593         if (!spin_trylock_bh(&ap->xmit_lock))
 594                 return 0;
 595         for (;;) {
 596                 if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
 597                         tty_stuffed = 0;
 598                 if (!tty_stuffed && ap->tpkt != 0) {
 599                         set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 600                         sent = tty->driver.write(tty, 0, ap->tpkt->data, ap->tpkt->len);
 601                         if (sent < 0)
 602                                 goto flush;     /* error, e.g. loss of CD */
 603                         if (sent < ap->tpkt->len) {
 604                                 tty_stuffed = 1;
 605                         } else {
 606                                 kfree_skb(ap->tpkt);
 607                                 ap->tpkt = 0;
 608                                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 609                                 done = 1;
 610                         }
 611                         continue;
 612                 }
 613                 /* haven't made any progress */
 614                 spin_unlock_bh(&ap->xmit_lock);
 615                 if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags)
 616                       || (!tty_stuffed && ap->tpkt != 0)))
 617                         break;
 618                 if (!spin_trylock_bh(&ap->xmit_lock))
 619                         break;
 620         }
 621         return done;
 622
 623 flush:
 624         if (ap->tpkt != 0) {
 625                 kfree_skb(ap->tpkt);
 626                 ap->tpkt = 0;
 627                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 628                 done = 1;
 629         }
 630         spin_unlock_bh(&ap->xmit_lock);
 631         return done;
 632 }
 633
 634 /*
 635  * Flush output from our internal buffers.
 636  * Called for the TCFLSH ioctl.
 637  */
 638 static void
 639 ppp_sync_flush_output(struct syncppp *ap)
 640 {
 641         int done = 0;
 642
 643         spin_lock_bh(&ap->xmit_lock);
 644         if (ap->tpkt != NULL) {
 645                 kfree_skb(ap->tpkt);
 646                 ap->tpkt = 0;
 647                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 648                 done = 1;
 649         }
 650         spin_unlock_bh(&ap->xmit_lock);
 651         if (done)
 652                 ppp_output_wakeup(&ap->chan);
 653 }
 654
 655 /*
 656  * Receive-side routines.
 657  */
 658
 659 static inline void
 660 process_input_packet(struct syncppp *ap)
 661 {
 662         struct sk_buff *skb;
 663         unsigned char *p;
 664         int code = 0;
 665
 666         skb = ap->rpkt;
 667         ap->rpkt = 0;
 668
 669         /* strip address/control field if present */
 670         p = skb->data;
 671         if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
 672                 /* chop off address/control */
 673                 if (skb->len < 3)
 674                         goto err;
 675                 p = skb_pull(skb, 2);
 676         }
 677
 678         /* decompress protocol field if compressed */
 679         if (p[0] & 1) {
 680                 /* protocol is compressed */
 681                 skb_push(skb, 1)[0] = 0;
 682         } else if (skb->len < 2)
 683                 goto err;
 684
 685         /* pass to generic layer */
 686         ppp_input(&ap->chan, skb);
 687         return;
 688
 689  err:
 690         kfree_skb(skb);
 691         ppp_input_error(&ap->chan, code);
 692 }
 693
 694 /* called when the tty driver has data for us.
 695  *
 696  * Data is frame oriented: each call to ppp_sync_input is considered
 697  * a whole frame. If the 1st flag byte is non-zero then the whole
 698  * frame is considered to be in error and is tossed.
 699  */
 700 static void
 701 ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
 702                 char *flags, int count)
 703 {
 704         struct sk_buff *skb;
 705         unsigned char *sp;
 706
 707         if (count == 0)
 708                 return;
 709
 710         /* if flag set, then error, ignore frame */
 711         if (flags != 0 && *flags) {
 712                 ppp_input_error(&ap->chan, *flags);
 713                 return;
 714         }
 715
 716         if (ap->flags & SC_LOG_INPKT)
 717                 ppp_print_buffer ("receive buffer", buf, count);
 718
 719         /* stuff the chars in the skb */
 720         if ((skb = ap->rpkt) == 0) {
 721                 if ((skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2)) == 0) {
 722                         printk(KERN_ERR "PPPsync: no memory (input pkt)\n");
 723                         ppp_input_error(&ap->chan, 0);
 724                         return;
 725                 }
 726                 /* Try to get the payload 4-byte aligned */
 727                 if (buf[0] != PPP_ALLSTATIONS)
 728                         skb_reserve(skb, 2 + (buf[0] & 1));
 729                 ap->rpkt = skb;
 730         }
 731         if (count > skb_tailroom(skb)) {
 732                 /* packet overflowed MRU */
 733                 ppp_input_error(&ap->chan, 1);
 734         } else {
 735                 sp = skb_put(skb, count);
 736                 memcpy(sp, buf, count);
 737                 process_input_packet(ap);
 738         }
 739 }
 740
 741 void __exit
 742 ppp_sync_cleanup(void)
 743 {
 744         if (tty_register_ldisc(N_SYNC_PPP, NULL) != 0)
 745                 printk(KERN_ERR "failed to unregister Sync PPP line discipline\n");
 746 }
 747
 748 module_init(ppp_sync_init);
 749 module_exit(ppp_sync_cleanup);