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 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                 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         tty->receive_room = 65536;
 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 /*
 388  * This can now be called from hard interrupt level as well
 389  * as soft interrupt level or mainline.
 390  */
 391 static void
 392 ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
 393                   char *cflags, int count)
 394 {
 395         struct syncppp *ap = sp_get(tty);
 396         unsigned long flags;
 397
 398         if (ap == 0)
 399                 return;
 400         spin_lock_irqsave(&ap->recv_lock, flags);
 401         ppp_sync_input(ap, buf, cflags, count);
 402         spin_unlock_irqrestore(&ap->recv_lock, flags);
 403         if (!skb_queue_empty(&ap->rqueue))
 404                 tasklet_schedule(&ap->tsk);
 405         sp_put(ap);
 406         if (test_and_clear_bit(TTY_THROTTLED, &tty->flags)
 407             && tty->driver->unthrottle)
 408                 tty->driver->unthrottle(tty);
 409 }
 410
 411 static void
 412 ppp_sync_wakeup(struct tty_struct *tty)
 413 {
 414         struct syncppp *ap = sp_get(tty);
 415
 416         clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 417         if (ap == 0)
 418                 return;
 419         set_bit(XMIT_WAKEUP, &ap->xmit_flags);
 420         tasklet_schedule(&ap->tsk);
 421         sp_put(ap);
 422 }
 423
 424
 425 static struct tty_ldisc ppp_sync_ldisc = {
 426         .owner  = THIS_MODULE,
 427         .magic  = TTY_LDISC_MAGIC,
 428         .name   = "pppsync",
 429         .open   = ppp_sync_open,
 430         .close  = ppp_sync_close,
 431         .hangup = ppp_sync_hangup,
 432         .read   = ppp_sync_read,
 433         .write  = ppp_sync_write,
 434         .ioctl  = ppp_synctty_ioctl,
 435         .poll   = ppp_sync_poll,
 436         .receive_buf = ppp_sync_receive,
 437         .write_wakeup = ppp_sync_wakeup,
 438 };
 439
 440 static int __init
 441 ppp_sync_init(void)
 442 {
 443         int err;
 444
 445         err = tty_register_ldisc(N_SYNC_PPP, &ppp_sync_ldisc);
 446         if (err != 0)
 447                 printk(KERN_ERR "PPP_sync: error %d registering line disc.\n",
 448                        err);
 449         return err;
 450 }
 451
 452 /*
 453  * The following routines provide the PPP channel interface.
 454  */
 455 static int
 456 ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
 457 {
 458         struct syncppp *ap = chan->private;
 459         int err, val;
 460         u32 accm[8];
 461         void __user *argp = (void __user *)arg;
 462         u32 __user *p = argp;
 463
 464         err = -EFAULT;
 465         switch (cmd) {
 466         case PPPIOCGFLAGS:
 467                 val = ap->flags | ap->rbits;
 468                 if (put_user(val, (int __user *) argp))
 469                         break;
 470                 err = 0;
 471                 break;
 472         case PPPIOCSFLAGS:
 473                 if (get_user(val, (int __user *) argp))
 474                         break;
 475                 ap->flags = val & ~SC_RCV_BITS;
 476                 spin_lock_irq(&ap->recv_lock);
 477                 ap->rbits = val & SC_RCV_BITS;
 478                 spin_unlock_irq(&ap->recv_lock);
 479                 err = 0;
 480                 break;
 481
 482         case PPPIOCGASYNCMAP:
 483                 if (put_user(ap->xaccm[0], p))
 484                         break;
 485                 err = 0;
 486                 break;
 487         case PPPIOCSASYNCMAP:
 488                 if (get_user(ap->xaccm[0], p))
 489                         break;
 490                 err = 0;
 491                 break;
 492
 493         case PPPIOCGRASYNCMAP:
 494                 if (put_user(ap->raccm, p))
 495                         break;
 496                 err = 0;
 497                 break;
 498         case PPPIOCSRASYNCMAP:
 499                 if (get_user(ap->raccm, p))
 500                         break;
 501                 err = 0;
 502                 break;
 503
 504         case PPPIOCGXASYNCMAP:
 505                 if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
 506                         break;
 507                 err = 0;
 508                 break;
 509         case PPPIOCSXASYNCMAP:
 510                 if (copy_from_user(accm, argp, sizeof(accm)))
 511                         break;
 512                 accm[2] &= ~0x40000000U;        /* can't escape 0x5e */
 513                 accm[3] |= 0x60000000U;         /* must escape 0x7d, 0x7e */
 514                 memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
 515                 err = 0;
 516                 break;
 517
 518         case PPPIOCGMRU:
 519                 if (put_user(ap->mru, (int __user *) argp))
 520                         break;
 521                 err = 0;
 522                 break;
 523         case PPPIOCSMRU:
 524                 if (get_user(val, (int __user *) argp))
 525                         break;
 526                 if (val < PPP_MRU)
 527                         val = PPP_MRU;
 528                 ap->mru = val;
 529                 err = 0;
 530                 break;
 531
 532         default:
 533                 err = -ENOTTY;
 534         }
 535         return err;
 536 }
 537
 538 /*
 539  * This is called at softirq level to deliver received packets
 540  * to the ppp_generic code, and to tell the ppp_generic code
 541  * if we can accept more output now.
 542  */
 543 static void ppp_sync_process(unsigned long arg)
 544 {
 545         struct syncppp *ap = (struct syncppp *) arg;
 546         struct sk_buff *skb;
 547
 548         /* process received packets */
 549         while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
 550                 if (skb->len == 0) {
 551                         /* zero length buffers indicate error */
 552                         ppp_input_error(&ap->chan, 0);
 553                         kfree_skb(skb);
 554                 }
 555                 else
 556                         ppp_input(&ap->chan, skb);
 557         }
 558
 559         /* try to push more stuff out */
 560         if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_sync_push(ap))
 561                 ppp_output_wakeup(&ap->chan);
 562 }
 563
 564 /*
 565  * Procedures for encapsulation and framing.
 566  */
 567
 568 struct sk_buff*
 569 ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb)
 570 {
 571         int proto;
 572         unsigned char *data;
 573         int islcp;
 574
 575         data  = skb->data;
 576         proto = (data[0] << 8) + data[1];
 577
 578         /* LCP packets with codes between 1 (configure-request)
 579          * and 7 (code-reject) must be sent as though no options
 580          * have been negotiated.
 581          */
 582         islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
 583
 584         /* compress protocol field if option enabled */
 585         if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp)
 586                 skb_pull(skb,1);
 587
 588         /* prepend address/control fields if necessary */
 589         if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
 590                 if (skb_headroom(skb) < 2) {
 591                         struct sk_buff *npkt = dev_alloc_skb(skb->len + 2);
 592                         if (npkt == NULL) {
 593                                 kfree_skb(skb);
 594                                 return NULL;
 595                         }
 596                         skb_reserve(npkt,2);
 597                         memcpy(skb_put(npkt,skb->len), skb->data, skb->len);
 598                         kfree_skb(skb);
 599                         skb = npkt;
 600                 }
 601                 skb_push(skb,2);
 602                 skb->data[0] = PPP_ALLSTATIONS;
 603                 skb->data[1] = PPP_UI;
 604         }
 605
 606         ap->last_xmit = jiffies;
 607
 608         if (skb && ap->flags & SC_LOG_OUTPKT)
 609                 ppp_print_buffer ("send buffer", skb->data, skb->len);
 610
 611         return skb;
 612 }
 613
 614 /*
 615  * Transmit-side routines.
 616  */
 617
 618 /*
 619  * Send a packet to the peer over an sync tty line.
 620  * Returns 1 iff the packet was accepted.
 621  * If the packet was not accepted, we will call ppp_output_wakeup
 622  * at some later time.
 623  */
 624 static int
 625 ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb)
 626 {
 627         struct syncppp *ap = chan->private;
 628
 629         ppp_sync_push(ap);
 630
 631         if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
 632                 return 0;       /* already full */
 633         skb = ppp_sync_txmunge(ap, skb);
 634         if (skb != NULL)
 635                 ap->tpkt = skb;
 636         else
 637                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 638
 639         ppp_sync_push(ap);
 640         return 1;
 641 }
 642
 643 /*
 644  * Push as much data as possible out to the tty.
 645  */
 646 static int
 647 ppp_sync_push(struct syncppp *ap)
 648 {
 649         int sent, done = 0;
 650         struct tty_struct *tty = ap->tty;
 651         int tty_stuffed = 0;
 652
 653         if (!spin_trylock_bh(&ap->xmit_lock))
 654                 return 0;
 655         for (;;) {
 656                 if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
 657                         tty_stuffed = 0;
 658                 if (!tty_stuffed && ap->tpkt != 0) {
 659                         set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 660                         sent = tty->driver->write(tty, ap->tpkt->data, ap->tpkt->len);
 661                         if (sent < 0)
 662                                 goto flush;     /* error, e.g. loss of CD */
 663                         if (sent < ap->tpkt->len) {
 664                                 tty_stuffed = 1;
 665                         } else {
 666                                 kfree_skb(ap->tpkt);
 667                                 ap->tpkt = NULL;
 668                                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 669                                 done = 1;
 670                         }
 671                         continue;
 672                 }
 673                 /* haven't made any progress */
 674                 spin_unlock_bh(&ap->xmit_lock);
 675                 if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags)
 676                       || (!tty_stuffed && ap->tpkt != 0)))
 677                         break;
 678                 if (!spin_trylock_bh(&ap->xmit_lock))
 679                         break;
 680         }
 681         return done;
 682
 683 flush:
 684         if (ap->tpkt != 0) {
 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         return done;
 692 }
 693
 694 /*
 695  * Flush output from our internal buffers.
 696  * Called for the TCFLSH ioctl.
 697  */
 698 static void
 699 ppp_sync_flush_output(struct syncppp *ap)
 700 {
 701         int done = 0;
 702
 703         spin_lock_bh(&ap->xmit_lock);
 704         if (ap->tpkt != NULL) {
 705                 kfree_skb(ap->tpkt);
 706                 ap->tpkt = NULL;
 707                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 708                 done = 1;
 709         }
 710         spin_unlock_bh(&ap->xmit_lock);
 711         if (done)
 712                 ppp_output_wakeup(&ap->chan);
 713 }
 714
 715 /*
 716  * Receive-side routines.
 717  */
 718
 719 /* called when the tty driver has data for us.
 720  *
 721  * Data is frame oriented: each call to ppp_sync_input is considered
 722  * a whole frame. If the 1st flag byte is non-zero then the whole
 723  * frame is considered to be in error and is tossed.
 724  */
 725 static void
 726 ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
 727                 char *flags, int count)
 728 {
 729         struct sk_buff *skb;
 730         unsigned char *p;
 731
 732         if (count == 0)
 733                 return;
 734
 735         if (ap->flags & SC_LOG_INPKT)
 736                 ppp_print_buffer ("receive buffer", buf, count);
 737
 738         /* stuff the chars in the skb */
 739         if ((skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2)) == 0) {
 740                 printk(KERN_ERR "PPPsync: no memory (input pkt)\n");
 741                 goto err;
 742         }
 743         /* Try to get the payload 4-byte aligned */
 744         if (buf[0] != PPP_ALLSTATIONS)
 745                 skb_reserve(skb, 2 + (buf[0] & 1));
 746
 747         if (flags != 0 && *flags) {
 748                 /* error flag set, ignore frame */
 749                 goto err;
 750         } else if (count > skb_tailroom(skb)) {
 751                 /* packet overflowed MRU */
 752                 goto err;
 753         }
 754
 755         p = skb_put(skb, count);
 756         memcpy(p, buf, count);
 757
 758         /* strip address/control field if present */
 759         p = skb->data;
 760         if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
 761                 /* chop off address/control */
 762                 if (skb->len < 3)
 763                         goto err;
 764                 p = skb_pull(skb, 2);
 765         }
 766
 767         /* decompress protocol field if compressed */
 768         if (p[0] & 1) {
 769                 /* protocol is compressed */
 770                 skb_push(skb, 1)[0] = 0;
 771         } else if (skb->len < 2)
 772                 goto err;
 773
 774         /* queue the frame to be processed */
 775         skb_queue_tail(&ap->rqueue, skb);
 776         return;
 777
 778 err:
 779         /* queue zero length packet as error indication */
 780         if (skb || (skb = dev_alloc_skb(0))) {
 781                 skb_trim(skb, 0);
 782                 skb_queue_tail(&ap->rqueue, skb);
 783         }
 784 }
 785
 786 static void __exit
 787 ppp_sync_cleanup(void)
 788 {
 789         if (tty_unregister_ldisc(N_SYNC_PPP) != 0)
 790                 printk(KERN_ERR "failed to unregister Sync PPP line discipline\n");
 791 }
 792
 793 module_init(ppp_sync_init);
 794 module_exit(ppp_sync_cleanup);
 795 MODULE_LICENSE("GPL");
 796 MODULE_ALIAS_LDISC(N_SYNC_PPP);