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/unaligned.h>
  49 #include <asm/uaccess.h>
  50
  51 #define PPP_VERSION     "2.4.2"
  52
  53 /* Structure for storing local state. */
  54 struct syncppp {
  55         struct tty_struct *tty;
  56         unsigned int    flags;
  57         unsigned int    rbits;
  58         int             mru;
  59         spinlock_t      xmit_lock;
  60         spinlock_t      recv_lock;
  61         unsigned long   xmit_flags;
  62         u32             xaccm[8];
  63         u32             raccm;
  64         unsigned int    bytes_sent;
  65         unsigned int    bytes_rcvd;
  66
  67         struct sk_buff  *tpkt;
  68         unsigned long   last_xmit;
  69
  70         struct sk_buff_head rqueue;
  71
  72         struct tasklet_struct tsk;
  73
  74         atomic_t        refcnt;
  75         struct completion dead_cmp;
  76         struct ppp_channel chan;        /* interface to generic ppp layer */
  77 };
  78
  79 /* Bit numbers in xmit_flags */
  80 #define XMIT_WAKEUP     0
  81 #define XMIT_FULL       1
  82
  83 /* Bits in rbits */
  84 #define SC_RCV_BITS     (SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)
  85
  86 #define PPPSYNC_MAX_RQLEN       32      /* arbitrary */
  87
  88 /*
  89  * Prototypes.
  90  */
  91 static struct sk_buff* ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *);
  92 static int ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb);
  93 static int ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd,
  94                           unsigned long arg);
  95 static void ppp_sync_process(unsigned long arg);
  96 static int ppp_sync_push(struct syncppp *ap);
  97 static void ppp_sync_flush_output(struct syncppp *ap);
  98 static void ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
  99                            char *flags, int count);
 100
 101 static const struct ppp_channel_ops sync_ops = {
 102         .start_xmit = ppp_sync_send,
 103         .ioctl      = ppp_sync_ioctl,
 104 };
 105
 106 /*
 107  * Utility procedures to print a buffer in hex/ascii
 108  */
 109 static void
 110 ppp_print_hex (register __u8 * out, const __u8 * in, int count)
 111 {
 112         register __u8 next_ch;
 113         static const char hex[] = "0123456789ABCDEF";
 114
 115         while (count-- > 0) {
 116                 next_ch = *in++;
 117                 *out++ = hex[(next_ch >> 4) & 0x0F];
 118                 *out++ = hex[next_ch & 0x0F];
 119                 ++out;
 120         }
 121 }
 122
 123 static void
 124 ppp_print_char (register __u8 * out, const __u8 * in, int count)
 125 {
 126         register __u8 next_ch;
 127
 128         while (count-- > 0) {
 129                 next_ch = *in++;
 130
 131                 if (next_ch < 0x20 || next_ch > 0x7e)
 132                         *out++ = '.';
 133                 else {
 134                         *out++ = next_ch;
 135                         if (next_ch == '%')   /* printk/syslogd has a bug !! */
 136                                 *out++ = '%';
 137                 }
 138         }
 139         *out = '\0';
 140 }
 141
 142 static void
 143 ppp_print_buffer (const char *name, const __u8 *buf, int count)
 144 {
 145         __u8 line[44];
 146
 147         if (name != NULL)
 148                 printk(KERN_DEBUG "ppp_synctty: %s, count = %d\n", name, count);
 149
 150         while (count > 8) {
 151                 memset (line, 32, 44);
 152                 ppp_print_hex (line, buf, 8);
 153                 ppp_print_char (&line[8 * 3], buf, 8);
 154                 printk(KERN_DEBUG "%s\n", line);
 155                 count -= 8;
 156                 buf += 8;
 157         }
 158
 159         if (count > 0) {
 160                 memset (line, 32, 44);
 161                 ppp_print_hex (line, buf, count);
 162                 ppp_print_char (&line[8 * 3], buf, count);
 163                 printk(KERN_DEBUG "%s\n", line);
 164         }
 165 }
 166
 167
 168 /*
 169  * Routines implementing the synchronous PPP line discipline.
 170  */
 171
 172 /*
 173  * We have a potential race on dereferencing tty->disc_data,
 174  * because the tty layer provides no locking at all - thus one
 175  * cpu could be running ppp_synctty_receive while another
 176  * calls ppp_synctty_close, which zeroes tty->disc_data and
 177  * frees the memory that ppp_synctty_receive is using.  The best
 178  * way to fix this is to use a rwlock in the tty struct, but for now
 179  * we use a single global rwlock for all ttys in ppp line discipline.
 180  *
 181  * FIXME: Fixed in tty_io nowadays.
 182  */
 183 static DEFINE_RWLOCK(disc_data_lock);
 184
 185 static struct syncppp *sp_get(struct tty_struct *tty)
 186 {
 187         struct syncppp *ap;
 188
 189         read_lock(&disc_data_lock);
 190         ap = tty->disc_data;
 191         if (ap != NULL)
 192                 atomic_inc(&ap->refcnt);
 193         read_unlock(&disc_data_lock);
 194         return ap;
 195 }
 196
 197 static void sp_put(struct syncppp *ap)
 198 {
 199         if (atomic_dec_and_test(&ap->refcnt))
 200                 complete(&ap->dead_cmp);
 201 }
 202
 203 /*
 204  * Called when a tty is put into sync-PPP line discipline.
 205  */
 206 static int
 207 ppp_sync_open(struct tty_struct *tty)
 208 {
 209         struct syncppp *ap;
 210         int err;
 211         int speed;
 212
 213         if (tty->ops->write == NULL)
 214                 return -EOPNOTSUPP;
 215
 216         ap = kzalloc(sizeof(*ap), GFP_KERNEL);
 217         err = -ENOMEM;
 218         if (!ap)
 219                 goto out;
 220
 221         /* initialize the syncppp structure */
 222         ap->tty = tty;
 223         ap->mru = PPP_MRU;
 224         spin_lock_init(&ap->xmit_lock);
 225         spin_lock_init(&ap->recv_lock);
 226         ap->xaccm[0] = ~0U;
 227         ap->xaccm[3] = 0x60000000U;
 228         ap->raccm = ~0U;
 229
 230         skb_queue_head_init(&ap->rqueue);
 231         tasklet_init(&ap->tsk, ppp_sync_process, (unsigned long) ap);
 232
 233         atomic_set(&ap->refcnt, 1);
 234         init_completion(&ap->dead_cmp);
 235
 236         ap->chan.private = ap;
 237         ap->chan.ops = &sync_ops;
 238         ap->chan.mtu = PPP_MRU;
 239         ap->chan.hdrlen = 2;    /* for A/C bytes */
 240         speed = tty_get_baud_rate(tty);
 241         ap->chan.speed = speed;
 242         err = ppp_register_channel(&ap->chan);
 243         if (err)
 244                 goto out_free;
 245
 246         tty->disc_data = ap;
 247         tty->receive_room = 65536;
 248         return 0;
 249
 250  out_free:
 251         kfree(ap);
 252  out:
 253         return err;
 254 }
 255
 256 /*
 257  * Called when the tty is put into another line discipline
 258  * or it hangs up.  We have to wait for any cpu currently
 259  * executing in any of the other ppp_synctty_* routines to
 260  * finish before we can call ppp_unregister_channel and free
 261  * the syncppp struct.  This routine must be called from
 262  * process context, not interrupt or softirq context.
 263  */
 264 static void
 265 ppp_sync_close(struct tty_struct *tty)
 266 {
 267         struct syncppp *ap;
 268
 269         write_lock_irq(&disc_data_lock);
 270         ap = tty->disc_data;
 271         tty->disc_data = NULL;
 272         write_unlock_irq(&disc_data_lock);
 273         if (!ap)
 274                 return;
 275
 276         /*
 277          * We have now ensured that nobody can start using ap from now
 278          * on, but we have to wait for all existing users to finish.
 279          * Note that ppp_unregister_channel ensures that no calls to
 280          * our channel ops (i.e. ppp_sync_send/ioctl) are in progress
 281          * by the time it returns.
 282          */
 283         if (!atomic_dec_and_test(&ap->refcnt))
 284                 wait_for_completion(&ap->dead_cmp);
 285         tasklet_kill(&ap->tsk);
 286
 287         ppp_unregister_channel(&ap->chan);
 288         skb_queue_purge(&ap->rqueue);
 289         kfree_skb(ap->tpkt);
 290         kfree(ap);
 291 }
 292
 293 /*
 294  * Called on tty hangup in process context.
 295  *
 296  * Wait for I/O to driver to complete and unregister PPP channel.
 297  * This is already done by the close routine, so just call that.
 298  */
 299 static int ppp_sync_hangup(struct tty_struct *tty)
 300 {
 301         ppp_sync_close(tty);
 302         return 0;
 303 }
 304
 305 /*
 306  * Read does nothing - no data is ever available this way.
 307  * Pppd reads and writes packets via /dev/ppp instead.
 308  */
 309 static ssize_t
 310 ppp_sync_read(struct tty_struct *tty, struct file *file,
 311                unsigned char __user *buf, size_t count)
 312 {
 313         return -EAGAIN;
 314 }
 315
 316 /*
 317  * Write on the tty does nothing, the packets all come in
 318  * from the ppp generic stuff.
 319  */
 320 static ssize_t
 321 ppp_sync_write(struct tty_struct *tty, struct file *file,
 322                 const unsigned char *buf, size_t count)
 323 {
 324         return -EAGAIN;
 325 }
 326
 327 static int
 328 ppp_synctty_ioctl(struct tty_struct *tty, struct file *file,
 329                   unsigned int cmd, unsigned long arg)
 330 {
 331         struct syncppp *ap = sp_get(tty);
 332         int __user *p = (int __user *)arg;
 333         int err, val;
 334
 335         if (!ap)
 336                 return -ENXIO;
 337         err = -EFAULT;
 338         switch (cmd) {
 339         case PPPIOCGCHAN:
 340                 err = -EFAULT;
 341                 if (put_user(ppp_channel_index(&ap->chan), p))
 342                         break;
 343                 err = 0;
 344                 break;
 345
 346         case PPPIOCGUNIT:
 347                 err = -EFAULT;
 348                 if (put_user(ppp_unit_number(&ap->chan), p))
 349                         break;
 350                 err = 0;
 351                 break;
 352
 353         case TCFLSH:
 354                 /* flush our buffers and the serial port's buffer */
 355                 if (arg == TCIOFLUSH || arg == TCOFLUSH)
 356                         ppp_sync_flush_output(ap);
 357                 err = tty_perform_flush(tty, arg);
 358                 break;
 359
 360         case FIONREAD:
 361                 val = 0;
 362                 if (put_user(val, p))
 363                         break;
 364                 err = 0;
 365                 break;
 366
 367         default:
 368                 err = tty_mode_ioctl(tty, file, cmd, arg);
 369                 break;
 370         }
 371
 372         sp_put(ap);
 373         return err;
 374 }
 375
 376 /* No kernel lock - fine */
 377 static unsigned int
 378 ppp_sync_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
 379 {
 380         return 0;
 381 }
 382
 383 /* May sleep, don't call from interrupt level or with interrupts disabled */
 384 static unsigned int
 385 ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
 386                   char *cflags, int count)
 387 {
 388         struct syncppp *ap = sp_get(tty);
 389         unsigned long flags;
 390
 391         if (!ap)
 392                 return -ENODEV;
 393         spin_lock_irqsave(&ap->recv_lock, flags);
 394         ppp_sync_input(ap, buf, cflags, count);
 395         spin_unlock_irqrestore(&ap->recv_lock, flags);
 396         if (!skb_queue_empty(&ap->rqueue))
 397                 tasklet_schedule(&ap->tsk);
 398         sp_put(ap);
 399         tty_unthrottle(tty);
 400
 401         return count;
 402 }
 403
 404 static void
 405 ppp_sync_wakeup(struct tty_struct *tty)
 406 {
 407         struct syncppp *ap = sp_get(tty);
 408
 409         clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 410         if (!ap)
 411                 return;
 412         set_bit(XMIT_WAKEUP, &ap->xmit_flags);
 413         tasklet_schedule(&ap->tsk);
 414         sp_put(ap);
 415 }
 416
 417
 418 static struct tty_ldisc_ops ppp_sync_ldisc = {
 419         .owner  = THIS_MODULE,
 420         .magic  = TTY_LDISC_MAGIC,
 421         .name   = "pppsync",
 422         .open   = ppp_sync_open,
 423         .close  = ppp_sync_close,
 424         .hangup = ppp_sync_hangup,
 425         .read   = ppp_sync_read,
 426         .write  = ppp_sync_write,
 427         .ioctl  = ppp_synctty_ioctl,
 428         .poll   = ppp_sync_poll,
 429         .receive_buf = ppp_sync_receive,
 430         .write_wakeup = ppp_sync_wakeup,
 431 };
 432
 433 static int __init
 434 ppp_sync_init(void)
 435 {
 436         int err;
 437
 438         err = tty_register_ldisc(N_SYNC_PPP, &ppp_sync_ldisc);
 439         if (err != 0)
 440                 printk(KERN_ERR "PPP_sync: error %d registering line disc.\n",
 441                        err);
 442         return err;
 443 }
 444
 445 /*
 446  * The following routines provide the PPP channel interface.
 447  */
 448 static int
 449 ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
 450 {
 451         struct syncppp *ap = chan->private;
 452         int err, val;
 453         u32 accm[8];
 454         void __user *argp = (void __user *)arg;
 455         u32 __user *p = argp;
 456
 457         err = -EFAULT;
 458         switch (cmd) {
 459         case PPPIOCGFLAGS:
 460                 val = ap->flags | ap->rbits;
 461                 if (put_user(val, (int __user *) argp))
 462                         break;
 463                 err = 0;
 464                 break;
 465         case PPPIOCSFLAGS:
 466                 if (get_user(val, (int __user *) argp))
 467                         break;
 468                 ap->flags = val & ~SC_RCV_BITS;
 469                 spin_lock_irq(&ap->recv_lock);
 470                 ap->rbits = val & SC_RCV_BITS;
 471                 spin_unlock_irq(&ap->recv_lock);
 472                 err = 0;
 473                 break;
 474
 475         case PPPIOCGASYNCMAP:
 476                 if (put_user(ap->xaccm[0], p))
 477                         break;
 478                 err = 0;
 479                 break;
 480         case PPPIOCSASYNCMAP:
 481                 if (get_user(ap->xaccm[0], p))
 482                         break;
 483                 err = 0;
 484                 break;
 485
 486         case PPPIOCGRASYNCMAP:
 487                 if (put_user(ap->raccm, p))
 488                         break;
 489                 err = 0;
 490                 break;
 491         case PPPIOCSRASYNCMAP:
 492                 if (get_user(ap->raccm, p))
 493                         break;
 494                 err = 0;
 495                 break;
 496
 497         case PPPIOCGXASYNCMAP:
 498                 if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
 499                         break;
 500                 err = 0;
 501                 break;
 502         case PPPIOCSXASYNCMAP:
 503                 if (copy_from_user(accm, argp, sizeof(accm)))
 504                         break;
 505                 accm[2] &= ~0x40000000U;        /* can't escape 0x5e */
 506                 accm[3] |= 0x60000000U;         /* must escape 0x7d, 0x7e */
 507                 memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
 508                 err = 0;
 509                 break;
 510
 511         case PPPIOCGMRU:
 512                 if (put_user(ap->mru, (int __user *) argp))
 513                         break;
 514                 err = 0;
 515                 break;
 516         case PPPIOCSMRU:
 517                 if (get_user(val, (int __user *) argp))
 518                         break;
 519                 if (val < PPP_MRU)
 520                         val = PPP_MRU;
 521                 ap->mru = val;
 522                 err = 0;
 523                 break;
 524
 525         default:
 526                 err = -ENOTTY;
 527         }
 528         return err;
 529 }
 530
 531 /*
 532  * This is called at softirq level to deliver received packets
 533  * to the ppp_generic code, and to tell the ppp_generic code
 534  * if we can accept more output now.
 535  */
 536 static void ppp_sync_process(unsigned long arg)
 537 {
 538         struct syncppp *ap = (struct syncppp *) arg;
 539         struct sk_buff *skb;
 540
 541         /* process received packets */
 542         while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
 543                 if (skb->len == 0) {
 544                         /* zero length buffers indicate error */
 545                         ppp_input_error(&ap->chan, 0);
 546                         kfree_skb(skb);
 547                 }
 548                 else
 549                         ppp_input(&ap->chan, skb);
 550         }
 551
 552         /* try to push more stuff out */
 553         if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_sync_push(ap))
 554                 ppp_output_wakeup(&ap->chan);
 555 }
 556
 557 /*
 558  * Procedures for encapsulation and framing.
 559  */
 560
 561 static struct sk_buff*
 562 ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb)
 563 {
 564         int proto;
 565         unsigned char *data;
 566         int islcp;
 567
 568         data  = skb->data;
 569         proto = get_unaligned_be16(data);
 570
 571         /* LCP packets with codes between 1 (configure-request)
 572          * and 7 (code-reject) must be sent as though no options
 573          * have been negotiated.
 574          */
 575         islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
 576
 577         /* compress protocol field if option enabled */
 578         if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp)
 579                 skb_pull(skb,1);
 580
 581         /* prepend address/control fields if necessary */
 582         if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
 583                 if (skb_headroom(skb) < 2) {
 584                         struct sk_buff *npkt = dev_alloc_skb(skb->len + 2);
 585                         if (npkt == NULL) {
 586                                 kfree_skb(skb);
 587                                 return NULL;
 588                         }
 589                         skb_reserve(npkt,2);
 590                         skb_copy_from_linear_data(skb,
 591                                       skb_put(npkt, skb->len), skb->len);
 592                         kfree_skb(skb);
 593                         skb = npkt;
 594                 }
 595                 skb_push(skb,2);
 596                 skb->data[0] = PPP_ALLSTATIONS;
 597                 skb->data[1] = PPP_UI;
 598         }
 599
 600         ap->last_xmit = jiffies;
 601
 602         if (skb && ap->flags & SC_LOG_OUTPKT)
 603                 ppp_print_buffer ("send buffer", skb->data, skb->len);
 604
 605         return skb;
 606 }
 607
 608 /*
 609  * Transmit-side routines.
 610  */
 611
 612 /*
 613  * Send a packet to the peer over an sync tty line.
 614  * Returns 1 iff the packet was accepted.
 615  * If the packet was not accepted, we will call ppp_output_wakeup
 616  * at some later time.
 617  */
 618 static int
 619 ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb)
 620 {
 621         struct syncppp *ap = chan->private;
 622
 623         ppp_sync_push(ap);
 624
 625         if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
 626                 return 0;       /* already full */
 627         skb = ppp_sync_txmunge(ap, skb);
 628         if (skb != NULL)
 629                 ap->tpkt = skb;
 630         else
 631                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 632
 633         ppp_sync_push(ap);
 634         return 1;
 635 }
 636
 637 /*
 638  * Push as much data as possible out to the tty.
 639  */
 640 static int
 641 ppp_sync_push(struct syncppp *ap)
 642 {
 643         int sent, done = 0;
 644         struct tty_struct *tty = ap->tty;
 645         int tty_stuffed = 0;
 646
 647         if (!spin_trylock_bh(&ap->xmit_lock))
 648                 return 0;
 649         for (;;) {
 650                 if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
 651                         tty_stuffed = 0;
 652                 if (!tty_stuffed && ap->tpkt) {
 653                         set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 654                         sent = tty->ops->write(tty, ap->tpkt->data, ap->tpkt->len);
 655                         if (sent < 0)
 656                                 goto flush;     /* error, e.g. loss of CD */
 657                         if (sent < ap->tpkt->len) {
 658                                 tty_stuffed = 1;
 659                         } else {
 660                                 kfree_skb(ap->tpkt);
 661                                 ap->tpkt = NULL;
 662                                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 663                                 done = 1;
 664                         }
 665                         continue;
 666                 }
 667                 /* haven't made any progress */
 668                 spin_unlock_bh(&ap->xmit_lock);
 669                 if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags) ||
 670                       (!tty_stuffed && ap->tpkt)))
 671                         break;
 672                 if (!spin_trylock_bh(&ap->xmit_lock))
 673                         break;
 674         }
 675         return done;
 676
 677 flush:
 678         if (ap->tpkt) {
 679                 kfree_skb(ap->tpkt);
 680                 ap->tpkt = NULL;
 681                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 682                 done = 1;
 683         }
 684         spin_unlock_bh(&ap->xmit_lock);
 685         return done;
 686 }
 687
 688 /*
 689  * Flush output from our internal buffers.
 690  * Called for the TCFLSH ioctl.
 691  */
 692 static void
 693 ppp_sync_flush_output(struct syncppp *ap)
 694 {
 695         int done = 0;
 696
 697         spin_lock_bh(&ap->xmit_lock);
 698         if (ap->tpkt != NULL) {
 699                 kfree_skb(ap->tpkt);
 700                 ap->tpkt = NULL;
 701                 clear_bit(XMIT_FULL, &ap->xmit_flags);
 702                 done = 1;
 703         }
 704         spin_unlock_bh(&ap->xmit_lock);
 705         if (done)
 706                 ppp_output_wakeup(&ap->chan);
 707 }
 708
 709 /*
 710  * Receive-side routines.
 711  */
 712
 713 /* called when the tty driver has data for us.
 714  *
 715  * Data is frame oriented: each call to ppp_sync_input is considered
 716  * a whole frame. If the 1st flag byte is non-zero then the whole
 717  * frame is considered to be in error and is tossed.
 718  */
 719 static void
 720 ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
 721                 char *flags, int count)
 722 {
 723         struct sk_buff *skb;
 724         unsigned char *p;
 725
 726         if (count == 0)
 727                 return;
 728
 729         if (ap->flags & SC_LOG_INPKT)
 730                 ppp_print_buffer ("receive buffer", buf, count);
 731
 732         /* stuff the chars in the skb */
 733         skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2);
 734         if (!skb) {
 735                 printk(KERN_ERR "PPPsync: no memory (input pkt)\n");
 736                 goto err;
 737         }
 738         /* Try to get the payload 4-byte aligned */
 739         if (buf[0] != PPP_ALLSTATIONS)
 740                 skb_reserve(skb, 2 + (buf[0] & 1));
 741
 742         if (flags && *flags) {
 743                 /* error flag set, ignore frame */
 744                 goto err;
 745         } else if (count > skb_tailroom(skb)) {
 746                 /* packet overflowed MRU */
 747                 goto err;
 748         }
 749
 750         p = skb_put(skb, count);
 751         memcpy(p, buf, count);
 752
 753         /* strip address/control field if present */
 754         p = skb->data;
 755         if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
 756                 /* chop off address/control */
 757                 if (skb->len < 3)
 758                         goto err;
 759                 p = skb_pull(skb, 2);
 760         }
 761
 762         /* decompress protocol field if compressed */
 763         if (p[0] & 1) {
 764                 /* protocol is compressed */
 765                 skb_push(skb, 1)[0] = 0;
 766         } else if (skb->len < 2)
 767                 goto err;
 768
 769         /* queue the frame to be processed */
 770         skb_queue_tail(&ap->rqueue, skb);
 771         return;
 772
 773 err:
 774         /* queue zero length packet as error indication */
 775         if (skb || (skb = dev_alloc_skb(0))) {
 776                 skb_trim(skb, 0);
 777                 skb_queue_tail(&ap->rqueue, skb);
 778         }
 779 }
 780
 781 static void __exit
 782 ppp_sync_cleanup(void)
 783 {
 784         if (tty_unregister_ldisc(N_SYNC_PPP) != 0)
 785                 printk(KERN_ERR "failed to unregister Sync PPP line discipline\n");
 786 }
 787
 788 module_init(ppp_sync_init);
 789 module_exit(ppp_sync_cleanup);
 790 MODULE_LICENSE("GPL");
 791 MODULE_ALIAS_LDISC(N_SYNC_PPP);