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 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         struct syncppp *ap;
 186
 187         read_lock(&disc_data_lock);
 188         ap = tty->disc_data;
 189         if (ap != NULL)
 190                 atomic_inc(&ap->refcnt);
 191         read_unlock(&disc_data_lock);
 192         return ap;
 193 }
 194
 195 static void sp_put(struct syncppp *ap)
 196 {
 197         if (atomic_dec_and_test(&ap->refcnt))
 198                 up(&ap->dead_sem);
 199 }
 200
 201 /*
 202  * Called when a tty is put into sync-PPP line discipline.
 203  */
 204 static int
 205 ppp_sync_open(struct tty_struct *tty)
 206 {
 207         struct syncppp *ap;
 208         int err;
 209
 210         ap = kmalloc(sizeof(*ap), GFP_KERNEL);
 211         err = -ENOMEM;
 212         if (ap == 0)
 213                 goto out;
 214
 215         /* initialize the syncppp structure */
 216         memset(ap, 0, sizeof(*ap));
 217         ap->tty = tty;
 218         ap->mru = PPP_MRU;
 219         spin_lock_init(&ap->xmit_lock);
 220         spin_lock_init(&ap->recv_lock);
 221         ap->xaccm[0] = ~0U;
 222         ap->xaccm[3] = 0x60000000U;
 223         ap->raccm = ~0U;
 224
 225         skb_queue_head_init(&ap->rqueue);
 226         tasklet_init(&ap->tsk, ppp_sync_process, (unsigned long) ap);
 227
 228         atomic_set(&ap->refcnt, 1);
 229         init_MUTEX_LOCKED(&ap->dead_sem);
 230
 231         ap->chan.private = ap;
 232         ap->chan.ops = &sync_ops;
 233         ap->chan.mtu = PPP_MRU;
 234         ap->chan.hdrlen = 2;    /* for A/C bytes */
 235         err = ppp_register_channel(&ap->chan);
 236         if (err)
 237                 goto out_free;
 238
 239         tty->disc_data = ap;
 240
 241         return 0;
 242
 243  out_free:
 244         kfree(ap);
 245  out:
 246         return err;
 247 }
 248
 249 /*
 250  * Called when the tty is put into another line discipline
 251  * or it hangs up.  We have to wait for any cpu currently
 252  * executing in any of the other ppp_synctty_* routines to
 253  * finish before we can call ppp_unregister_channel and free
 254  * the syncppp struct.  This routine must be called from
 255  * process context, not interrupt or softirq context.
 256  */
 257 static void
 258 ppp_sync_close(struct tty_struct *tty)
 259 {
 260         struct syncppp *ap;
 261
 262         write_lock_irq(&disc_data_lock);
 263         ap = tty->disc_data;
 264         tty->disc_data = NULL;
 265         write_unlock_irq(&disc_data_lock);
 266         if (ap == 0)
 267                 return;
 268
 269         /*
 270          * We have now ensured that nobody can start using ap from now
 271          * on, but we have to wait for all existing users to finish.
 272          * Note that ppp_unregister_channel ensures that no calls to
 273          * our channel ops (i.e. ppp_sync_send/ioctl) are in progress
 274          * by the time it returns.
 275          */
 276         if (!atomic_dec_and_test(&ap->refcnt))
 277                 down(&ap->dead_sem);
 278         tasklet_kill(&ap->tsk);
 279
 280         ppp_unregister_channel(&ap->chan);
 281         skb_queue_purge(&ap->rqueue);
 282         if (ap->tpkt != 0)
 283                 kfree_skb(ap->tpkt);
 284         kfree(ap);
 285 }
 286
 287 /*
 288  * Called on tty hangup in process context.
 289  *
 290  * Wait for I/O to driver to complete and unregister PPP channel.
 291  * This is already done by the close routine, so just call that.
 292  */
 293 static int ppp_sync_hangup(struct tty_struct *tty)
 294 {
 295         ppp_sync_close(tty);
 296         return 0;
 297 }
 298
 299 /*
 300  * Read does nothing - no data is ever available this way.
 301  * Pppd reads and writes packets via /dev/ppp instead.
 302  */
 303 static ssize_t
 304 ppp_sync_read(struct tty_struct *tty, struct file *file,
 305                unsigned char __user *buf, size_t count)
 306 {
 307         return -EAGAIN;
 308 }
 309
 310 /*
 311  * Write on the tty does nothing, the packets all come in
 312  * from the ppp generic stuff.
 313  */
 314 static ssize_t
 315 ppp_sync_write(struct tty_struct *tty, struct file *file,
 316                 const unsigned char *buf, size_t count)
 317 {
 318         return -EAGAIN;
 319 }
 320
 321 static int
 322 ppp_synctty_ioctl(struct tty_struct *tty, struct file *file,
 323                   unsigned int cmd, unsigned long arg)
 324 {
 325         struct syncppp *ap = sp_get(tty);
 326         int __user *p = (int __user *)arg;
 327         int err, val;
 328
 329         if (ap == 0)
 330                 return -ENXIO;
 331         err = -EFAULT;
 332         switch (cmd) {
 333         case PPPIOCGCHAN:
 334                 err = -ENXIO;
 335                 if (ap == 0)
 336                         break;
 337                 err = -EFAULT;
 338                 if (put_user(ppp_channel_index(&ap->chan), p))
 339                         break;
 340                 err = 0;
 341                 break;
 342
 343         case PPPIOCGUNIT:
 344                 err = -ENXIO;
 345                 if (ap == 0)
 346                         break;
 347                 err = -EFAULT;
 348                 if (put_user(ppp_unit_number(&ap->chan), p))
 349                         break;
 350                 err = 0;
 351                 break;
 352
 353         case TCGETS:
 354         case TCGETA:
 355                 err = n_tty_ioctl(tty, file, cmd, arg);
 356                 break;
 357
 358         case TCFLSH:
 359                 /* flush our buffers and the serial port's buffer */
 360                 if (arg == TCIOFLUSH || arg == TCOFLUSH)
 361                         ppp_sync_flush_output(ap);
 362                 err = n_tty_ioctl(tty, file, cmd, arg);
 363                 break;
 364
 365         case FIONREAD:
 366                 val = 0;
 367                 if (put_user(val, p))
 368                         break;
 369                 err = 0;
 370                 break;
 371
 372         default:
 373                 err = -ENOIOCTLCMD;
 374         }
 375
 376         sp_put(ap);
 377         return err;
 378 }
 379
 380 /* No kernel lock - fine */
 381 static unsigned int
 382 ppp_sync_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
 383 {
 384         return 0;
 385 }
 386
 387 static int
 388 ppp_sync_room(struct tty_struct *tty)
 389 {
 390         return 65535;
 391 }
 392
 393 /*
 394  * This can now be called from hard interrupt level as well
 395  * as soft interrupt level or mainline.
 396  */
 397 static void
 398 ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
 399                   char *cflags, int count)
 400 {
 401         struct syncppp *ap = sp_get(tty);
 402         unsigned long flags;
 403
 404         if (ap == 0)
 405                 return;
 406         spin_lock_irqsave(&ap->recv_lock, flags);
 407         ppp_sync_input(ap, buf, cflags, count);
 408         spin_unlock_irqrestore(&ap->recv_lock, flags);
 409         if (skb_queue_len(&ap->rqueue))
 410                 tasklet_schedule(&ap->tsk);
 411         sp_put(ap);
 412         if (test_and_clear_bit(TTY_THROTTLED, &tty->flags)
 413             && tty->driver->unthrottle)
 414                 tty->driver->unthrottle(tty);
 415 }
 416
 417 static void
 418 ppp_sync_wakeup(struct tty_struct *tty)
 419 {
 420         struct syncppp *ap = sp_get(tty);
 421
 422         clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 423         if (ap == 0)
 424                 return;
 425         set_bit(XMIT_WAKEUP, &ap->xmit_flags);
 426         tasklet_schedule(&ap->tsk);
 427         sp_put(ap);
 428 }
 429
 430
 431 static struct tty_ldisc ppp_sync_ldisc = {
 432         .owner  = THIS_MODULE,
 433         .magic  = TTY_LDISC_MAGIC,
 434         .name   = "pppsync",
 435         .open   = ppp_sync_open,
 436         .close  = ppp_sync_close,
 437         .hangup = ppp_sync_hangup,
 438         .read   = ppp_sync_read,
 439         .write  = ppp_sync_write,
 440         .ioctl  = ppp_synctty_ioctl,
 441         .poll   = ppp_sync_poll,
 442         .receive_room = ppp_sync_room,
 443         .receive_buf = ppp_sync_receive,
 444         .write_wakeup = ppp_sync_wakeup,
 445 };
 446
 447 static int __init
 448 ppp_sync_init(void)
 449 {
 450         int err;
 451
 452         err = tty_register_ldisc(N_SYNC_PPP, &ppp_sync_ldisc);
 453         if (err != 0)
 454                 printk(KERN_ERR "PPP_sync: error %d registering line disc.\n",
 455                        err);
 456         return err;
 457 }
 458
 459 /*
 460  * The following routines provide the PPP channel interface.
 461  */
 462 static int
 463 ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
 464 {
 465         struct syncppp *ap = chan->private;
 466         int err, val;
 467         u32 accm[8];
 468         void __user *argp = (void __user *)arg;
 469         u32 __user *p = argp;
 470
 471         err = -EFAULT;
 472         switch (cmd) {
 473         case PPPIOCGFLAGS:
 474                 val = ap->flags | ap->rbits;
 475                 if (put_user(val, (int __user *) argp))
 476                         break;
 477                 err = 0;
 478                 break;
 479         case PPPIOCSFLAGS:
 480                 if (get_user(val, (int __user *) argp))
 481                         break;
 482                 ap->flags = val & ~SC_RCV_BITS;
 483                 spin_lock_irq(&ap->recv_lock);
 484                 ap->rbits = val & SC_RCV_BITS;
 485                 spin_unlock_irq(&ap->recv_lock);
 486                 err = 0;
 487                 break;
 488
 489         case PPPIOCGASYNCMAP:
 490                 if (put_user(ap->xaccm[0], p))
 491                         break;
 492                 err = 0;
 493                 break;
 494         case PPPIOCSASYNCMAP:
 495                 if (get_user(ap->xaccm[0], p))
 496                         break;
 497                 err = 0;
 498                 break;
 499
 500         case PPPIOCGRASYNCMAP:
 501                 if (put_user(ap->raccm, p))
 502                         break;
 503                 err = 0;
 504                 break;
 505         case PPPIOCSRASYNCMAP:
 506                 if (get_user(ap->raccm, p))
 507                         break;
 508                 err = 0;
 509                 break;
 510
 511         case PPPIOCGXASYNCMAP:
 512                 if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
 513                         break;
 514                 err = 0;
 515                 break;
 516         case PPPIOCSXASYNCMAP:
 517                 if (copy_from_user(accm, argp, sizeof(accm)))
 518                         break;
 519                 accm[2] &= ~0x40000000U;        /* can't escape 0x5e */
 520                 accm[3] |= 0x60000000U;         /* must escape 0x7d, 0x7e */
 521                 memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
 522                 err = 0;
 523                 break;
 524
 525         case PPPIOCGMRU:
 526                 if (put_user(ap->mru, (int __user *) argp))
 527                         break;
 528                 err = 0;
 529                 break;
 530         case PPPIOCSMRU:
 531                 if (get_user(val, (int __user *) argp))
 532                         break;
 533                 if (val < PPP_MRU)
 534                         val = PPP_MRU;
 535                 ap->mru = val;
 536                 err = 0;
 537                 break;
 538
 539         default:
 540                 err = -ENOTTY;
 541         }
 542         return err;
 543 }
 544
 545 /*
 546  * This is called at softirq level to deliver received packets
 547  * to the ppp_generic code, and to tell the ppp_generic code
 548  * if we can accept more output now.
 549  */
 550 static void ppp_sync_process(unsigned long arg)
 551 {
 552         struct syncppp *ap = (struct syncppp *) arg;
 553         struct sk_buff *skb;
 554
 555         /* process received packets */
 556         while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
 557                 if (skb->len == 0) {
 558                         /* zero length buffers indicate error */
 559                         ppp_input_error(&ap->chan, 0);
 560                         kfree_skb(skb);
 561                 }
 562                 else
 563                         ppp_input(&ap->chan, skb);
 564         }
 565
 566         /* try to push more stuff out */
 567         if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_sync_push(ap))
 568                 ppp_output_wakeup(&ap->chan);
 569 }
 570
 571 /*
 572  * Procedures for encapsulation and framing.
 573  */
 574
 575 struct sk_buff*
 576 ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb)
 577 {
 578         int proto;
 579         unsigned char *data;
 580         int islcp;
 581
 582         data  = skb->data;
 583         proto = (data[0] << 8) + data[1];
 584
 585         /* LCP packets with codes between 1 (configure-request)
 586          * and 7 (code-reject) must be sent as though no options
 587          * have been negotiated.
 588          */
 589         islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
 590
 591         /* compress protocol field if option enabled */
 592         if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp)
 593                 skb_pull(skb,1);
 594
 595         /* prepend address/control fields if necessary */
 596         if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
 597                 if (skb_headroom(skb) < 2) {
 598                         struct sk_buff *npkt = dev_alloc_skb(skb->len + 2);
 599                         if (npkt == NULL) {
 600                                 kfree_skb(skb);
 601                                 return NULL;
 602                         }
 603                         skb_reserve(npkt,2);
 604                         memcpy(skb_put(npkt,skb->len), skb->data, skb->len);
 605                         kfree_skb(skb);
 606                         skb = npkt;
 607                 }
 608                 skb_push(skb,2);
 609                 skb->data[0] = PPP_ALLSTATIONS;
 610                 skb->data[1] = PPP_UI;
 611         }
 612
 613         ap->last_xmit = jiffies;
 614
 615         if (skb && ap->flags & SC_LOG_OUTPKT)
 616                 ppp_print_buffer ("send buffer", skb->data, skb->len);
 617
 618         return skb;
 619 }
 620
 621 /*
 622  * Transmit-side routines.
 623  */
 624
 625 /*
 626  * Send a packet to the peer over an sync tty line.
 627  * Returns 1 iff the packet was accepted.
 628  * If the packet was not accepted, we will call ppp_output_wakeup
 629  * at some later time.
 630  */
 631 static int
 632 ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb)
 633 {
 634         struct syncppp *ap = chan->private;
 635
 636         ppp_sync_push(ap);
 637
 638         if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
 639                 return 0;       /* already full */
 640         skb = ppp_sync_txmunge(ap, skb);
 641         if (skb != NULL)
 642                 ap->tpkt = skb;
 643         else
 644                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 645
 646         ppp_sync_push(ap);
 647         return 1;
 648 }
 649
 650 /*
 651  * Push as much data as possible out to the tty.
 652  */
 653 static int
 654 ppp_sync_push(struct syncppp *ap)
 655 {
 656         int sent, done = 0;
 657         struct tty_struct *tty = ap->tty;
 658         int tty_stuffed = 0;
 659
 660         if (!spin_trylock_bh(&ap->xmit_lock))
 661                 return 0;
 662         for (;;) {
 663                 if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
 664                         tty_stuffed = 0;
 665                 if (!tty_stuffed && ap->tpkt != 0) {
 666                         set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 667                         sent = tty->driver->write(tty, ap->tpkt->data, ap->tpkt->len);
 668                         if (sent < 0)
 669                                 goto flush;     /* error, e.g. loss of CD */
 670                         if (sent < ap->tpkt->len) {
 671                                 tty_stuffed = 1;
 672                         } else {
 673                                 kfree_skb(ap->tpkt);
 674                                 ap->tpkt = NULL;
 675                                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 676                                 done = 1;
 677                         }
 678                         continue;
 679                 }
 680                 /* haven't made any progress */
 681                 spin_unlock_bh(&ap->xmit_lock);
 682                 if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags)
 683                       || (!tty_stuffed && ap->tpkt != 0)))
 684                         break;
 685                 if (!spin_trylock_bh(&ap->xmit_lock))
 686                         break;
 687         }
 688         return done;
 689
 690 flush:
 691         if (ap->tpkt != 0) {
 692                 kfree_skb(ap->tpkt);
 693                 ap->tpkt = NULL;
 694                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 695                 done = 1;
 696         }
 697         spin_unlock_bh(&ap->xmit_lock);
 698         return done;
 699 }
 700
 701 /*
 702  * Flush output from our internal buffers.
 703  * Called for the TCFLSH ioctl.
 704  */
 705 static void
 706 ppp_sync_flush_output(struct syncppp *ap)
 707 {
 708         int done = 0;
 709
 710         spin_lock_bh(&ap->xmit_lock);
 711         if (ap->tpkt != NULL) {
 712                 kfree_skb(ap->tpkt);
 713                 ap->tpkt = NULL;
 714                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 715                 done = 1;
 716         }
 717         spin_unlock_bh(&ap->xmit_lock);
 718         if (done)
 719                 ppp_output_wakeup(&ap->chan);
 720 }
 721
 722 /*
 723  * Receive-side routines.
 724  */
 725
 726 /* called when the tty driver has data for us.
 727  *
 728  * Data is frame oriented: each call to ppp_sync_input is considered
 729  * a whole frame. If the 1st flag byte is non-zero then the whole
 730  * frame is considered to be in error and is tossed.
 731  */
 732 static void
 733 ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
 734                 char *flags, int count)
 735 {
 736         struct sk_buff *skb;
 737         unsigned char *p;
 738
 739         if (count == 0)
 740                 return;
 741
 742         if (ap->flags & SC_LOG_INPKT)
 743                 ppp_print_buffer ("receive buffer", buf, count);
 744
 745         /* stuff the chars in the skb */
 746         if ((skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2)) == 0) {
 747                 printk(KERN_ERR "PPPsync: no memory (input pkt)\n");
 748                 goto err;
 749         }
 750         /* Try to get the payload 4-byte aligned */
 751         if (buf[0] != PPP_ALLSTATIONS)
 752                 skb_reserve(skb, 2 + (buf[0] & 1));
 753
 754         if (flags != 0 && *flags) {
 755                 /* error flag set, ignore frame */
 756                 goto err;
 757         } else if (count > skb_tailroom(skb)) {
 758                 /* packet overflowed MRU */
 759                 goto err;
 760         }
 761
 762         p = skb_put(skb, count);
 763         memcpy(p, buf, count);
 764
 765         /* strip address/control field if present */
 766         p = skb->data;
 767         if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
 768                 /* chop off address/control */
 769                 if (skb->len < 3)
 770                         goto err;
 771                 p = skb_pull(skb, 2);
 772         }
 773
 774         /* decompress protocol field if compressed */
 775         if (p[0] & 1) {
 776                 /* protocol is compressed */
 777                 skb_push(skb, 1)[0] = 0;
 778         } else if (skb->len < 2)
 779                 goto err;
 780
 781         /* queue the frame to be processed */
 782         skb_queue_tail(&ap->rqueue, skb);
 783         return;
 784
 785 err:
 786         /* queue zero length packet as error indication */
 787         if (skb || (skb = dev_alloc_skb(0))) {
 788                 skb_trim(skb, 0);
 789                 skb_queue_tail(&ap->rqueue, skb);
 790         }
 791 }
 792
 793 static void __exit
 794 ppp_sync_cleanup(void)
 795 {
 796         if (tty_register_ldisc(N_SYNC_PPP, NULL) != 0)
 797                 printk(KERN_ERR "failed to unregister Sync PPP line discipline\n");
 798 }
 799
 800 module_init(ppp_sync_init);
 801 module_exit(ppp_sync_cleanup);
 802 MODULE_LICENSE("GPL");
 803 MODULE_ALIAS_LDISC(N_SYNC_PPP);