release/src-rt-6.x.4708/linux/linux-2.6.36/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/completion.h>
  46 #include <linux/init.h>
  47 #include <linux/slab.h>
  48 #include <asm/uaccess.h>
  49
  50 #define PPP_VERSION     "2.4.2"
  51
  52 /* Structure for storing local state. */
  53 struct syncppp {
  54         struct tty_struct *tty;
  55         unsigned int    flags;
  56         unsigned int    rbits;
  57         int             mru;
  58         spinlock_t      xmit_lock;
  59         spinlock_t      recv_lock;
  60         unsigned long   xmit_flags;
  61         u32             xaccm[8];
  62         u32             raccm;
  63         unsigned int    bytes_sent;
  64         unsigned int    bytes_rcvd;
  65
  66         struct sk_buff  *tpkt;
  67         unsigned long   last_xmit;
  68
  69         struct sk_buff_head rqueue;
  70
  71         struct tasklet_struct tsk;
  72
  73         atomic_t        refcnt;
  74         struct completion dead_cmp;
  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 void ppp_sync_process(unsigned long arg);
  95 static int ppp_sync_push(struct syncppp *ap);
  96 static void ppp_sync_flush_output(struct syncppp *ap);
  97 static void ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
  98                            char *flags, int count);
  99
 100 static const struct ppp_channel_ops sync_ops = {
 101         .start_xmit = ppp_sync_send,
 102         .ioctl      = ppp_sync_ioctl,
 103 };
 104
 105 /*
 106  * Utility procedures to print a buffer in hex/ascii
 107  */
 108 static void
 109 ppp_print_hex (register __u8 * out, const __u8 * in, int count)
 110 {
 111         register __u8 next_ch;
 112         static const char hex[] = "0123456789ABCDEF";
 113
 114         while (count-- > 0) {
 115                 next_ch = *in++;
 116                 *out++ = hex[(next_ch >> 4) & 0x0F];
 117                 *out++ = hex[next_ch & 0x0F];
 118                 ++out;
 119         }
 120 }
 121
 122 static void
 123 ppp_print_char (register __u8 * out, const __u8 * in, int count)
 124 {
 125         register __u8 next_ch;
 126
 127         while (count-- > 0) {
 128                 next_ch = *in++;
 129
 130                 if (next_ch < 0x20 || next_ch > 0x7e)
 131                         *out++ = '.';
 132                 else {
 133                         *out++ = next_ch;
 134                         if (next_ch == '%')   /* printk/syslogd has a bug !! */
 135                                 *out++ = '%';
 136                 }
 137         }
 138         *out = '\0';
 139 }
 140
 141 static void
 142 ppp_print_buffer (const char *name, const __u8 *buf, int count)
 143 {
 144         __u8 line[44];
 145
 146         if (name != NULL)
 147                 printk(KERN_DEBUG "ppp_synctty: %s, count = %d\n", name, count);
 148
 149         while (count > 8) {
 150                 memset (line, 32, 44);
 151                 ppp_print_hex (line, buf, 8);
 152                 ppp_print_char (&line[8 * 3], buf, 8);
 153                 printk(KERN_DEBUG "%s\n", line);
 154                 count -= 8;
 155                 buf += 8;
 156         }
 157
 158         if (count > 0) {
 159                 memset (line, 32, 44);
 160                 ppp_print_hex (line, buf, count);
 161                 ppp_print_char (&line[8 * 3], buf, count);
 162                 printk(KERN_DEBUG "%s\n", line);
 163         }
 164 }
 165
 166
 167 /*
 168  * Routines implementing the synchronous PPP line discipline.
 169  */
 170
 171 static DEFINE_RWLOCK(disc_data_lock);
 172
 173 static struct syncppp *sp_get(struct tty_struct *tty)
 174 {
 175         struct syncppp *ap;
 176
 177         read_lock(&disc_data_lock);
 178         ap = tty->disc_data;
 179         if (ap != NULL)
 180                 atomic_inc(&ap->refcnt);
 181         read_unlock(&disc_data_lock);
 182         return ap;
 183 }
 184
 185 static void sp_put(struct syncppp *ap)
 186 {
 187         if (atomic_dec_and_test(&ap->refcnt))
 188                 complete(&ap->dead_cmp);
 189 }
 190
 191 /*
 192  * Called when a tty is put into sync-PPP line discipline.
 193  */
 194 static int
 195 ppp_sync_open(struct tty_struct *tty)
 196 {
 197         struct syncppp *ap;
 198         int err;
 199         int speed;
 200
 201         if (tty->ops->write == NULL)
 202                 return -EOPNOTSUPP;
 203
 204         ap = kzalloc(sizeof(*ap), GFP_KERNEL);
 205         err = -ENOMEM;
 206         if (!ap)
 207                 goto out;
 208
 209         /* initialize the syncppp structure */
 210         ap->tty = tty;
 211         ap->mru = PPP_MRU;
 212         spin_lock_init(&ap->xmit_lock);
 213         spin_lock_init(&ap->recv_lock);
 214         ap->xaccm[0] = ~0U;
 215         ap->xaccm[3] = 0x60000000U;
 216         ap->raccm = ~0U;
 217
 218         skb_queue_head_init(&ap->rqueue);
 219         tasklet_init(&ap->tsk, ppp_sync_process, (unsigned long) ap);
 220
 221         atomic_set(&ap->refcnt, 1);
 222         init_completion(&ap->dead_cmp);
 223
 224         ap->chan.private = ap;
 225         ap->chan.ops = &sync_ops;
 226         ap->chan.mtu = PPP_MRU;
 227         ap->chan.hdrlen = 2;    /* for A/C bytes */
 228         speed = tty_get_baud_rate(tty);
 229         ap->chan.speed = speed;
 230         err = ppp_register_channel(&ap->chan);
 231         if (err)
 232                 goto out_free;
 233
 234         tty->disc_data = ap;
 235         tty->receive_room = 65536;
 236         return 0;
 237
 238  out_free:
 239         kfree(ap);
 240  out:
 241         return err;
 242 }
 243
 244 /*
 245  * Called when the tty is put into another line discipline
 246  * or it hangs up.  We have to wait for any cpu currently
 247  * executing in any of the other ppp_synctty_* routines to
 248  * finish before we can call ppp_unregister_channel and free
 249  * the syncppp struct.  This routine must be called from
 250  * process context, not interrupt or softirq context.
 251  */
 252 static void
 253 ppp_sync_close(struct tty_struct *tty)
 254 {
 255         struct syncppp *ap;
 256
 257         write_lock_irq(&disc_data_lock);
 258         ap = tty->disc_data;
 259         tty->disc_data = NULL;
 260         write_unlock_irq(&disc_data_lock);
 261         if (!ap)
 262                 return;
 263
 264         /*
 265          * We have now ensured that nobody can start using ap from now
 266          * on, but we have to wait for all existing users to finish.
 267          * Note that ppp_unregister_channel ensures that no calls to
 268          * our channel ops (i.e. ppp_sync_send/ioctl) are in progress
 269          * by the time it returns.
 270          */
 271         if (!atomic_dec_and_test(&ap->refcnt))
 272                 wait_for_completion(&ap->dead_cmp);
 273         tasklet_kill(&ap->tsk);
 274
 275         ppp_unregister_channel(&ap->chan);
 276         skb_queue_purge(&ap->rqueue);
 277         kfree_skb(ap->tpkt);
 278         kfree(ap);
 279 }
 280
 281 /*
 282  * Called on tty hangup in process context.
 283  *
 284  * Wait for I/O to driver to complete and unregister PPP channel.
 285  * This is already done by the close routine, so just call that.
 286  */
 287 static int ppp_sync_hangup(struct tty_struct *tty)
 288 {
 289         ppp_sync_close(tty);
 290         return 0;
 291 }
 292
 293 /*
 294  * Read does nothing - no data is ever available this way.
 295  * Pppd reads and writes packets via /dev/ppp instead.
 296  */
 297 static ssize_t
 298 ppp_sync_read(struct tty_struct *tty, struct file *file,
 299                unsigned char __user *buf, size_t count)
 300 {
 301         return -EAGAIN;
 302 }
 303
 304 /*
 305  * Write on the tty does nothing, the packets all come in
 306  * from the ppp generic stuff.
 307  */
 308 static ssize_t
 309 ppp_sync_write(struct tty_struct *tty, struct file *file,
 310                 const unsigned char *buf, size_t count)
 311 {
 312         return -EAGAIN;
 313 }
 314
 315 static int
 316 ppp_synctty_ioctl(struct tty_struct *tty, struct file *file,
 317                   unsigned int cmd, unsigned long arg)
 318 {
 319         struct syncppp *ap = sp_get(tty);
 320         int __user *p = (int __user *)arg;
 321         int err, val;
 322
 323         if (!ap)
 324                 return -ENXIO;
 325         err = -EFAULT;
 326         switch (cmd) {
 327         case PPPIOCGCHAN:
 328                 err = -EFAULT;
 329                 if (put_user(ppp_channel_index(&ap->chan), p))
 330                         break;
 331                 err = 0;
 332                 break;
 333
 334         case PPPIOCGUNIT:
 335                 err = -EFAULT;
 336                 if (put_user(ppp_unit_number(&ap->chan), p))
 337                         break;
 338                 err = 0;
 339                 break;
 340
 341         case TCFLSH:
 342                 /* flush our buffers and the serial port's buffer */
 343                 if (arg == TCIOFLUSH || arg == TCOFLUSH)
 344                         ppp_sync_flush_output(ap);
 345                 err = tty_perform_flush(tty, arg);
 346                 break;
 347
 348         case FIONREAD:
 349                 val = 0;
 350                 if (put_user(val, p))
 351                         break;
 352                 err = 0;
 353                 break;
 354
 355         default:
 356                 err = tty_mode_ioctl(tty, file, cmd, arg);
 357                 break;
 358         }
 359
 360         sp_put(ap);
 361         return err;
 362 }
 363
 364 /* No kernel lock - fine */
 365 static unsigned int
 366 ppp_sync_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
 367 {
 368         return 0;
 369 }
 370
 371 /* May sleep, don't call from interrupt level or with interrupts disabled */
 372 static void
 373 ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
 374                   char *cflags, int count)
 375 {
 376         struct syncppp *ap = sp_get(tty);
 377         unsigned long flags;
 378
 379         if (!ap)
 380                 return;
 381         spin_lock_irqsave(&ap->recv_lock, flags);
 382         ppp_sync_input(ap, buf, cflags, count);
 383         spin_unlock_irqrestore(&ap->recv_lock, flags);
 384         if (!skb_queue_empty(&ap->rqueue))
 385                 tasklet_schedule(&ap->tsk);
 386         sp_put(ap);
 387         tty_unthrottle(tty);
 388 }
 389
 390 static void
 391 ppp_sync_wakeup(struct tty_struct *tty)
 392 {
 393         struct syncppp *ap = sp_get(tty);
 394
 395         clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 396         if (!ap)
 397                 return;
 398         set_bit(XMIT_WAKEUP, &ap->xmit_flags);
 399         tasklet_schedule(&ap->tsk);
 400         sp_put(ap);
 401 }
 402
 403
 404 static struct tty_ldisc_ops ppp_sync_ldisc = {
 405         .owner  = THIS_MODULE,
 406         .magic  = TTY_LDISC_MAGIC,
 407         .name   = "pppsync",
 408         .open   = ppp_sync_open,
 409         .close  = ppp_sync_close,
 410         .hangup = ppp_sync_hangup,
 411         .read   = ppp_sync_read,
 412         .write  = ppp_sync_write,
 413         .ioctl  = ppp_synctty_ioctl,
 414         .poll   = ppp_sync_poll,
 415         .receive_buf = ppp_sync_receive,
 416         .write_wakeup = ppp_sync_wakeup,
 417 };
 418
 419 static int __init
 420 ppp_sync_init(void)
 421 {
 422         int err;
 423
 424         err = tty_register_ldisc(N_SYNC_PPP, &ppp_sync_ldisc);
 425         if (err != 0)
 426                 printk(KERN_ERR "PPP_sync: error %d registering line disc.\n",
 427                        err);
 428         return err;
 429 }
 430
 431 /*
 432  * The following routines provide the PPP channel interface.
 433  */
 434 static int
 435 ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
 436 {
 437         struct syncppp *ap = chan->private;
 438         int err, val;
 439         u32 accm[8];
 440         void __user *argp = (void __user *)arg;
 441         u32 __user *p = argp;
 442
 443         err = -EFAULT;
 444         switch (cmd) {
 445         case PPPIOCGFLAGS:
 446                 val = ap->flags | ap->rbits;
 447                 if (put_user(val, (int __user *) argp))
 448                         break;
 449                 err = 0;
 450                 break;
 451         case PPPIOCSFLAGS:
 452                 if (get_user(val, (int __user *) argp))
 453                         break;
 454                 ap->flags = val & ~SC_RCV_BITS;
 455                 spin_lock_irq(&ap->recv_lock);
 456                 ap->rbits = val & SC_RCV_BITS;
 457                 spin_unlock_irq(&ap->recv_lock);
 458                 err = 0;
 459                 break;
 460
 461         case PPPIOCGASYNCMAP:
 462                 if (put_user(ap->xaccm[0], p))
 463                         break;
 464                 err = 0;
 465                 break;
 466         case PPPIOCSASYNCMAP:
 467                 if (get_user(ap->xaccm[0], p))
 468                         break;
 469                 err = 0;
 470                 break;
 471
 472         case PPPIOCGRASYNCMAP:
 473                 if (put_user(ap->raccm, p))
 474                         break;
 475                 err = 0;
 476                 break;
 477         case PPPIOCSRASYNCMAP:
 478                 if (get_user(ap->raccm, p))
 479                         break;
 480                 err = 0;
 481                 break;
 482
 483         case PPPIOCGXASYNCMAP:
 484                 if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
 485                         break;
 486                 err = 0;
 487                 break;
 488         case PPPIOCSXASYNCMAP:
 489                 if (copy_from_user(accm, argp, sizeof(accm)))
 490                         break;
 491                 accm[2] &= ~0x40000000U;        /* can't escape 0x5e */
 492                 accm[3] |= 0x60000000U;         /* must escape 0x7d, 0x7e */
 493                 memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
 494                 err = 0;
 495                 break;
 496
 497         case PPPIOCGMRU:
 498                 if (put_user(ap->mru, (int __user *) argp))
 499                         break;
 500                 err = 0;
 501                 break;
 502         case PPPIOCSMRU:
 503                 if (get_user(val, (int __user *) argp))
 504                         break;
 505                 if (val < PPP_MRU)
 506                         val = PPP_MRU;
 507                 ap->mru = val;
 508                 err = 0;
 509                 break;
 510
 511         default:
 512                 err = -ENOTTY;
 513         }
 514         return err;
 515 }
 516
 517 /*
 518  * This is called at softirq level to deliver received packets
 519  * to the ppp_generic code, and to tell the ppp_generic code
 520  * if we can accept more output now.
 521  */
 522 static void ppp_sync_process(unsigned long arg)
 523 {
 524         struct syncppp *ap = (struct syncppp *) arg;
 525         struct sk_buff *skb;
 526
 527         /* process received packets */
 528         while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
 529                 if (skb->len == 0) {
 530                         /* zero length buffers indicate error */
 531                         ppp_input_error(&ap->chan, 0);
 532                         kfree_skb(skb);
 533                 }
 534                 else
 535                         ppp_input(&ap->chan, skb);
 536         }
 537
 538         /* try to push more stuff out */
 539         if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_sync_push(ap))
 540                 ppp_output_wakeup(&ap->chan);
 541 }
 542
 543 /*
 544  * Procedures for encapsulation and framing.
 545  */
 546
 547 static struct sk_buff*
 548 ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb)
 549 {
 550         int proto;
 551         unsigned char *data;
 552         int islcp;
 553
 554         data  = skb->data;
 555         proto = (data[0] << 8) + data[1];
 556
 557         /* LCP packets with codes between 1 (configure-request)
 558          * and 7 (code-reject) must be sent as though no options
 559          * have been negotiated.
 560          */
 561         islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
 562
 563         /* compress protocol field if option enabled */
 564         if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp)
 565                 skb_pull(skb,1);
 566
 567         /* prepend address/control fields if necessary */
 568         if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
 569                 if (skb_headroom(skb) < 2) {
 570                         struct sk_buff *npkt = dev_alloc_skb(skb->len + 2);
 571                         if (npkt == NULL) {
 572                                 kfree_skb(skb);
 573                                 return NULL;
 574                         }
 575                         skb_reserve(npkt,2);
 576                         skb_copy_from_linear_data(skb,
 577                                       skb_put(npkt, skb->len), skb->len);
 578                         kfree_skb(skb);
 579                         skb = npkt;
 580                 }
 581                 skb_push(skb,2);
 582                 skb->data[0] = PPP_ALLSTATIONS;
 583                 skb->data[1] = PPP_UI;
 584         }
 585
 586         ap->last_xmit = jiffies;
 587
 588         if (skb && ap->flags & SC_LOG_OUTPKT)
 589                 ppp_print_buffer ("send buffer", skb->data, skb->len);
 590
 591         return skb;
 592 }
 593
 594 /*
 595  * Transmit-side routines.
 596  */
 597
 598 /*
 599  * Send a packet to the peer over an sync tty line.
 600  * Returns 1 iff the packet was accepted.
 601  * If the packet was not accepted, we will call ppp_output_wakeup
 602  * at some later time.
 603  */
 604 static int
 605 ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb)
 606 {
 607         struct syncppp *ap = chan->private;
 608
 609         ppp_sync_push(ap);
 610
 611         if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
 612                 return 0;       /* already full */
 613         skb = ppp_sync_txmunge(ap, skb);
 614         if (skb != NULL)
 615                 ap->tpkt = skb;
 616         else
 617                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 618
 619         ppp_sync_push(ap);
 620         return 1;
 621 }
 622
 623 /*
 624  * Push as much data as possible out to the tty.
 625  */
 626 static int
 627 ppp_sync_push(struct syncppp *ap)
 628 {
 629         int sent, done = 0;
 630         struct tty_struct *tty = ap->tty;
 631         int tty_stuffed = 0;
 632
 633         if (!spin_trylock_bh(&ap->xmit_lock))
 634                 return 0;
 635         for (;;) {
 636                 if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
 637                         tty_stuffed = 0;
 638                 if (!tty_stuffed && ap->tpkt) {
 639                         set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 640                         sent = tty->ops->write(tty, ap->tpkt->data, ap->tpkt->len);
 641                         if (sent < 0)
 642                                 goto flush;     /* error, e.g. loss of CD */
 643                         if (sent < ap->tpkt->len) {
 644                                 tty_stuffed = 1;
 645                         } else {
 646                                 kfree_skb(ap->tpkt);
 647                                 ap->tpkt = NULL;
 648                                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 649                                 done = 1;
 650                         }
 651                         continue;
 652                 }
 653                 /* haven't made any progress */
 654                 spin_unlock_bh(&ap->xmit_lock);
 655                 if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags) ||
 656                       (!tty_stuffed && ap->tpkt)))
 657                         break;
 658                 if (!spin_trylock_bh(&ap->xmit_lock))
 659                         break;
 660         }
 661         return done;
 662
 663 flush:
 664         if (ap->tpkt) {
 665                 kfree_skb(ap->tpkt);
 666                 ap->tpkt = NULL;
 667                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 668                 done = 1;
 669         }
 670         spin_unlock_bh(&ap->xmit_lock);
 671         return done;
 672 }
 673
 674 /*
 675  * Flush output from our internal buffers.
 676  * Called for the TCFLSH ioctl.
 677  */
 678 static void
 679 ppp_sync_flush_output(struct syncppp *ap)
 680 {
 681         int done = 0;
 682
 683         spin_lock_bh(&ap->xmit_lock);
 684         if (ap->tpkt != NULL) {
 685                 kfree_skb(ap->tpkt);
 686                 ap->tpkt = NULL;
 687                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 688                 done = 1;
 689         }
 690         spin_unlock_bh(&ap->xmit_lock);
 691         if (done)
 692                 ppp_output_wakeup(&ap->chan);
 693 }
 694
 695 /*
 696  * Receive-side routines.
 697  */
 698
 699 /* called when the tty driver has data for us.
 700  *
 701  * Data is frame oriented: each call to ppp_sync_input is considered
 702  * a whole frame. If the 1st flag byte is non-zero then the whole
 703  * frame is considered to be in error and is tossed.
 704  */
 705 static void
 706 ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
 707                 char *flags, int count)
 708 {
 709         struct sk_buff *skb;
 710         unsigned char *p;
 711
 712         if (count == 0)
 713                 return;
 714
 715         if (ap->flags & SC_LOG_INPKT)
 716                 ppp_print_buffer ("receive buffer", buf, count);
 717
 718         /* stuff the chars in the skb */
 719         skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2);
 720         if (!skb) {
 721                 printk(KERN_ERR "PPPsync: no memory (input pkt)\n");
 722                 goto err;
 723         }
 724         /* Try to get the payload 4-byte aligned */
 725         if (buf[0] != PPP_ALLSTATIONS)
 726                 skb_reserve(skb, 2 + (buf[0] & 1));
 727
 728         if (flags && *flags) {
 729                 /* error flag set, ignore frame */
 730                 goto err;
 731         } else if (count > skb_tailroom(skb)) {
 732                 /* packet overflowed MRU */
 733                 goto err;
 734         }
 735
 736         p = skb_put(skb, count);
 737         memcpy(p, buf, count);
 738
 739         /* strip address/control field if present */
 740         p = skb->data;
 741         if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
 742                 /* chop off address/control */
 743                 if (skb->len < 3)
 744                         goto err;
 745                 p = skb_pull(skb, 2);
 746         }
 747
 748         /* decompress protocol field if compressed */
 749         if (p[0] & 1) {
 750                 /* protocol is compressed */
 751                 skb_push(skb, 1)[0] = 0;
 752         } else if (skb->len < 2)
 753                 goto err;
 754
 755         /* queue the frame to be processed */
 756         skb_queue_tail(&ap->rqueue, skb);
 757         return;
 758
 759 err:
 760         /* queue zero length packet as error indication */
 761         if (skb || (skb = dev_alloc_skb(0))) {
 762                 skb_trim(skb, 0);
 763                 skb_queue_tail(&ap->rqueue, skb);
 764         }
 765 }
 766
 767 static void __exit
 768 ppp_sync_cleanup(void)
 769 {
 770         if (tty_unregister_ldisc(N_SYNC_PPP) != 0)
 771                 printk(KERN_ERR "failed to unregister Sync PPP line discipline\n");
 772 }
 773
 774 module_init(ppp_sync_init);
 775 module_exit(ppp_sync_cleanup);
 776 MODULE_LICENSE("GPL");
 777 MODULE_ALIAS_LDISC(N_SYNC_PPP);