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