drivers/net/ppp_synctty.c

   1 /*
   2  * PPP synchronous tty channel driver for Linux.
   3  *
   4  * This is a ppp channel driver that can be used with tty device drivers
   5  * that are frame oriented, such as synchronous HDLC devices.
   6  *
   7  * Complete PPP frames without encoding/decoding are exchanged between
   8  * the channel driver and the device driver.
   9  *
  10  * The async map IOCTL codes are implemented to keep the user mode
  11  * applications happy if they call them. Synchronous PPP does not use
  12  * the async maps.
  13  *
  14  * Copyright 1999 Paul Mackerras.
  15  *
  16  * Also touched by the grubby hands of Paul Fulghum paulkf@microgate.com
  17  *
  18  *  This program is free software; you can redistribute it and/or
  19  *  modify it under the terms of the GNU General Public License
  20  *  as published by the Free Software Foundation; either version
  21  *  2 of the License, or (at your option) any later version.
  22  *
  23  * This driver provides the encapsulation and framing for sending
  24  * and receiving PPP frames over sync serial lines.  It relies on
  25  * the generic PPP layer to give it frames to send and to process
  26  * received frames.  It implements the PPP line discipline.
  27  *
  28  * Part of the code in this driver was inspired by the old async-only
  29  * PPP driver, written by Michael Callahan and Al Longyear, and
  30  * subsequently hacked by Paul Mackerras.
  31  *
  32  * ==FILEVERSION 20040616==
  33  */
  34
  35 #include <linux/module.h>
  36 #include <linux/kernel.h>
  37 #include <linux/skbuff.h>
  38 #include <linux/tty.h>
  39 #include <linux/netdevice.h>
  40 #include <linux/poll.h>
  41 #include <linux/ppp_defs.h>
  42 #include <linux/if_ppp.h>
  43 #include <linux/ppp_channel.h>
  44 #include <linux/spinlock.h>
  45 #include <linux/init.h>
  46 #include <asm/uaccess.h>
  47 #include <asm/semaphore.h>
  48
  49 #define PPP_VERSION     "2.4.2"
  50
  51 /* Structure for storing local state. */
  52 struct syncppp {
  53         struct tty_struct *tty;
  54         unsigned int    flags;
  55         unsigned int    rbits;
  56         int             mru;
  57         spinlock_t      xmit_lock;
  58         spinlock_t      recv_lock;
  59         unsigned long   xmit_flags;
  60         u32             xaccm[8];
  61         u32             raccm;
  62         unsigned int    bytes_sent;
  63         unsigned int    bytes_rcvd;
  64
  65         struct sk_buff  *tpkt;
  66         unsigned long   last_xmit;
  67
  68         struct sk_buff_head rqueue;
  69
  70         struct tasklet_struct tsk;
  71
  72         atomic_t        refcnt;
  73         struct semaphore dead_sem;
  74         struct ppp_channel chan;        /* interface to generic ppp layer */
  75 };
  76
  77 /* Bit numbers in xmit_flags */
  78 #define XMIT_WAKEUP     0
  79 #define XMIT_FULL       1
  80
  81 /* Bits in rbits */
  82 #define SC_RCV_BITS     (SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)
  83
  84 #define PPPSYNC_MAX_RQLEN       32      /* arbitrary */
  85
  86 /*
  87  * Prototypes.
  88  */
  89 static struct sk_buff* ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *);
  90 static int ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb);
  91 static int ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd,
  92                           unsigned long arg);
  93 static void ppp_sync_process(unsigned long arg);
  94 static int ppp_sync_push(struct syncppp *ap);
  95 static void ppp_sync_flush_output(struct syncppp *ap);
  96 static void ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
  97                            char *flags, int count);
  98
  99 static struct ppp_channel_ops sync_ops = {
 100         ppp_sync_send,
 101         ppp_sync_ioctl
 102 };
 103
 104 /*
 105  * Utility procedures to print a buffer in hex/ascii
 106  */
 107 static void
 108 ppp_print_hex (register __u8 * out, const __u8 * in, int count)
 109 {
 110         register __u8 next_ch;
 111         static char hex[] = "0123456789ABCDEF";
 112
 113         while (count-- > 0) {
 114                 next_ch = *in++;
 115                 *out++ = hex[(next_ch >> 4) & 0x0F];
 116                 *out++ = hex[next_ch & 0x0F];
 117                 ++out;
 118         }
 119 }
 120
 121 static void
 122 ppp_print_char (register __u8 * out, const __u8 * in, int count)
 123 {
 124         register __u8 next_ch;
 125
 126         while (count-- > 0) {
 127                 next_ch = *in++;
 128
 129                 if (next_ch < 0x20 || next_ch > 0x7e)
 130                         *out++ = '.';
 131                 else {
 132                         *out++ = next_ch;
 133                         if (next_ch == '%')   /* printk/syslogd has a bug !! */
 134                                 *out++ = '%';
 135                 }
 136         }
 137         *out = '\0';
 138 }
 139
 140 static void
 141 ppp_print_buffer (const char *name, const __u8 *buf, int count)
 142 {
 143         __u8 line[44];
 144
 145         if (name != NULL)
 146                 printk(KERN_DEBUG "ppp_synctty: %s, count = %d\n", name, count);
 147
 148         while (count > 8) {
 149                 memset (line, 32, 44);
 150                 ppp_print_hex (line, buf, 8);
 151                 ppp_print_char (&line[8 * 3], buf, 8);
 152                 printk(KERN_DEBUG "%s\n", line);
 153                 count -= 8;
 154                 buf += 8;
 155         }
 156
 157         if (count > 0) {
 158                 memset (line, 32, 44);
 159                 ppp_print_hex (line, buf, count);
 160                 ppp_print_char (&line[8 * 3], buf, count);
 161                 printk(KERN_DEBUG "%s\n", line);
 162         }
 163 }
 164
 165
 166 /*
 167  * Routines implementing the synchronous PPP line discipline.
 168  */
 169
 170 /*
 171  * We have a potential race on dereferencing tty->disc_data,
 172  * because the tty layer provides no locking at all - thus one
 173  * cpu could be running ppp_synctty_receive while another
 174  * calls ppp_synctty_close, which zeroes tty->disc_data and
 175  * frees the memory that ppp_synctty_receive is using.  The best
 176  * way to fix this is to use a rwlock in the tty struct, but for now
 177  * we use a single global rwlock for all ttys in ppp line discipline.
 178  *
 179  * FIXME: Fixed in tty_io nowdays.
 180  */
 181 static rwlock_t disc_data_lock = RW_LOCK_UNLOCKED;
 182
 183 static struct syncppp *sp_get(struct tty_struct *tty)
 184 {
 185         struct syncppp *ap;
 186
 187         read_lock(&disc_data_lock);
 188         ap = tty->disc_data;
 189         if (ap != NULL)
 190                 atomic_inc(&ap->refcnt);
 191         read_unlock(&disc_data_lock);
 192         return ap;
 193 }
 194
 195 static void sp_put(struct syncppp *ap)
 196 {
 197         if (atomic_dec_and_test(&ap->refcnt))
 198                 up(&ap->dead_sem);
 199 }
 200
 201 /*
 202  * Called when a tty is put into sync-PPP line discipline.
 203  */
 204 static int
 205 ppp_sync_open(struct tty_struct *tty)
 206 {
 207         struct syncppp *ap;
 208         int err;
 209
 210         ap = kmalloc(sizeof(*ap), GFP_KERNEL);
 211         err = -ENOMEM;
 212         if (ap == 0)
 213                 goto out;
 214
 215         /* initialize the syncppp structure */
 216         memset(ap, 0, sizeof(*ap));
 217         ap->tty = tty;
 218         ap->mru = PPP_MRU;
 219         spin_lock_init(&ap->xmit_lock);
 220         spin_lock_init(&ap->recv_lock);
 221         ap->xaccm[0] = ~0U;
 222         ap->xaccm[3] = 0x60000000U;
 223         ap->raccm = ~0U;
 224
 225         skb_queue_head_init(&ap->rqueue);
 226         tasklet_init(&ap->tsk, ppp_sync_process, (unsigned long) ap);
 227
 228         atomic_set(&ap->refcnt, 1);
 229         init_MUTEX_LOCKED(&ap->dead_sem);
 230
 231         ap->chan.private = ap;
 232         ap->chan.ops = &sync_ops;
 233         ap->chan.mtu = PPP_MRU;
 234         ap->chan.hdrlen = 2;    /* for A/C bytes */
 235         err = ppp_register_channel(&ap->chan);
 236         if (err)
 237                 goto out_free;
 238
 239         tty->disc_data = ap;
 240
 241         return 0;
 242
 243  out_free:
 244         kfree(ap);
 245  out:
 246         return err;
 247 }
 248
 249 /*
 250  * Called when the tty is put into another line discipline
 251  * or it hangs up.  We have to wait for any cpu currently
 252  * executing in any of the other ppp_synctty_* routines to
 253  * finish before we can call ppp_unregister_channel and free
 254  * the syncppp struct.  This routine must be called from
 255  * process context, not interrupt or softirq context.
 256  */
 257 static void
 258 ppp_sync_close(struct tty_struct *tty)
 259 {
 260         struct syncppp *ap;
 261
 262         write_lock_irq(&disc_data_lock);
 263         ap = tty->disc_data;
 264         tty->disc_data = NULL;
 265         write_unlock_irq(&disc_data_lock);
 266         if (ap == 0)
 267                 return;
 268
 269         /*
 270          * We have now ensured that nobody can start using ap from now
 271          * on, but we have to wait for all existing users to finish.
 272          * Note that ppp_unregister_channel ensures that no calls to
 273          * our channel ops (i.e. ppp_sync_send/ioctl) are in progress
 274          * by the time it returns.
 275          */
 276         if (!atomic_dec_and_test(&ap->refcnt))
 277                 down(&ap->dead_sem);
 278         tasklet_kill(&ap->tsk);
 279
 280         ppp_unregister_channel(&ap->chan);
 281         skb_queue_purge(&ap->rqueue);
 282         if (ap->tpkt != 0)
 283                 kfree_skb(ap->tpkt);
 284         kfree(ap);
 285 }
 286
 287 /*
 288  * Read does nothing - no data is ever available this way.
 289  * Pppd reads and writes packets via /dev/ppp instead.
 290  */
 291 static ssize_t
 292 ppp_sync_read(struct tty_struct *tty, struct file *file,
 293                unsigned char __user *buf, size_t count)
 294 {
 295         return -EAGAIN;
 296 }
 297
 298 /*
 299  * Write on the tty does nothing, the packets all come in
 300  * from the ppp generic stuff.
 301  */
 302 static ssize_t
 303 ppp_sync_write(struct tty_struct *tty, struct file *file,
 304                 const unsigned char __user *buf, size_t count)
 305 {
 306         return -EAGAIN;
 307 }
 308
 309 static int
 310 ppp_synctty_ioctl(struct tty_struct *tty, struct file *file,
 311                   unsigned int cmd, unsigned long arg)
 312 {
 313         struct syncppp *ap = sp_get(tty);
 314         int __user *p = (int __user *)arg;
 315         int err, val;
 316
 317         if (ap == 0)
 318                 return -ENXIO;
 319         err = -EFAULT;
 320         switch (cmd) {
 321         case PPPIOCGCHAN:
 322                 err = -ENXIO;
 323                 if (ap == 0)
 324                         break;
 325                 err = -EFAULT;
 326                 if (put_user(ppp_channel_index(&ap->chan), p))
 327                         break;
 328                 err = 0;
 329                 break;
 330
 331         case PPPIOCGUNIT:
 332                 err = -ENXIO;
 333                 if (ap == 0)
 334                         break;
 335                 err = -EFAULT;
 336                 if (put_user(ppp_unit_number(&ap->chan), p))
 337                         break;
 338                 err = 0;
 339                 break;
 340
 341         case TCGETS:
 342         case TCGETA:
 343                 err = n_tty_ioctl(tty, file, cmd, arg);
 344                 break;
 345
 346         case TCFLSH:
 347                 /* flush our buffers and the serial port's buffer */
 348                 if (arg == TCIOFLUSH || arg == TCOFLUSH)
 349                         ppp_sync_flush_output(ap);
 350                 err = n_tty_ioctl(tty, file, cmd, arg);
 351                 break;
 352
 353         case FIONREAD:
 354                 val = 0;
 355                 if (put_user(val, p))
 356                         break;
 357                 err = 0;
 358                 break;
 359
 360         default:
 361                 err = -ENOIOCTLCMD;
 362         }
 363
 364         sp_put(ap);
 365         return err;
 366 }
 367
 368 /* No kernel lock - fine */
 369 static unsigned int
 370 ppp_sync_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
 371 {
 372         return 0;
 373 }
 374
 375 static int
 376 ppp_sync_room(struct tty_struct *tty)
 377 {
 378         return 65535;
 379 }
 380
 381 /*
 382  * This can now be called from hard interrupt level as well
 383  * as soft interrupt level or mainline.
 384  */
 385 static void
 386 ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
 387                   char *cflags, int count)
 388 {
 389         struct syncppp *ap = sp_get(tty);
 390         unsigned long flags;
 391
 392         if (ap == 0)
 393                 return;
 394         spin_lock_irqsave(&ap->recv_lock, flags);
 395         ppp_sync_input(ap, buf, cflags, count);
 396         spin_unlock_irqrestore(&ap->recv_lock, flags);
 397         if (skb_queue_len(&ap->rqueue))
 398                 tasklet_schedule(&ap->tsk);
 399         sp_put(ap);
 400         if (test_and_clear_bit(TTY_THROTTLED, &tty->flags)
 401             && tty->driver->unthrottle)
 402                 tty->driver->unthrottle(tty);
 403 }
 404
 405 static void
 406 ppp_sync_wakeup(struct tty_struct *tty)
 407 {
 408         struct syncppp *ap = sp_get(tty);
 409
 410         clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 411         if (ap == 0)
 412                 return;
 413         set_bit(XMIT_WAKEUP, &ap->xmit_flags);
 414         tasklet_schedule(&ap->tsk);
 415         sp_put(ap);
 416 }
 417
 418
 419 static struct tty_ldisc ppp_sync_ldisc = {
 420         .owner  = THIS_MODULE,
 421         .magic  = TTY_LDISC_MAGIC,
 422         .name   = "pppsync",
 423         .open   = ppp_sync_open,
 424         .close  = ppp_sync_close,
 425         .read   = ppp_sync_read,
 426         .write  = ppp_sync_write,
 427         .ioctl  = ppp_synctty_ioctl,
 428         .poll   = ppp_sync_poll,
 429         .receive_room = ppp_sync_room,
 430         .receive_buf = ppp_sync_receive,
 431         .write_wakeup = ppp_sync_wakeup,
 432 };
 433
 434 static int __init
 435 ppp_sync_init(void)
 436 {
 437         int err;
 438
 439         err = tty_register_ldisc(N_SYNC_PPP, &ppp_sync_ldisc);
 440         if (err != 0)
 441                 printk(KERN_ERR "PPP_sync: error %d registering line disc.\n",
 442                        err);
 443         return err;
 444 }
 445
 446 /*
 447  * The following routines provide the PPP channel interface.
 448  */
 449 static int
 450 ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
 451 {
 452         struct syncppp *ap = chan->private;
 453         int err, val;
 454         u32 accm[8];
 455         void __user *argp = (void __user *)arg;
 456         u32 __user *p = argp;
 457
 458         err = -EFAULT;
 459         switch (cmd) {
 460         case PPPIOCGFLAGS:
 461                 val = ap->flags | ap->rbits;
 462                 if (put_user(val, (int __user *) argp))
 463                         break;
 464                 err = 0;
 465                 break;
 466         case PPPIOCSFLAGS:
 467                 if (get_user(val, (int __user *) argp))
 468                         break;
 469                 ap->flags = val & ~SC_RCV_BITS;
 470                 spin_lock_irq(&ap->recv_lock);
 471                 ap->rbits = val & SC_RCV_BITS;
 472                 spin_unlock_irq(&ap->recv_lock);
 473                 err = 0;
 474                 break;
 475
 476         case PPPIOCGASYNCMAP:
 477                 if (put_user(ap->xaccm[0], p))
 478                         break;
 479                 err = 0;
 480                 break;
 481         case PPPIOCSASYNCMAP:
 482                 if (get_user(ap->xaccm[0], p))
 483                         break;
 484                 err = 0;
 485                 break;
 486
 487         case PPPIOCGRASYNCMAP:
 488                 if (put_user(ap->raccm, p))
 489                         break;
 490                 err = 0;
 491                 break;
 492         case PPPIOCSRASYNCMAP:
 493                 if (get_user(ap->raccm, p))
 494                         break;
 495                 err = 0;
 496                 break;
 497
 498         case PPPIOCGXASYNCMAP:
 499                 if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
 500                         break;
 501                 err = 0;
 502                 break;
 503         case PPPIOCSXASYNCMAP:
 504                 if (copy_from_user(accm, argp, sizeof(accm)))
 505                         break;
 506                 accm[2] &= ~0x40000000U;        /* can't escape 0x5e */
 507                 accm[3] |= 0x60000000U;         /* must escape 0x7d, 0x7e */
 508                 memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
 509                 err = 0;
 510                 break;
 511
 512         case PPPIOCGMRU:
 513                 if (put_user(ap->mru, (int __user *) argp))
 514                         break;
 515                 err = 0;
 516                 break;
 517         case PPPIOCSMRU:
 518                 if (get_user(val, (int __user *) argp))
 519                         break;
 520                 if (val < PPP_MRU)
 521                         val = PPP_MRU;
 522                 ap->mru = val;
 523                 err = 0;
 524                 break;
 525
 526         default:
 527                 err = -ENOTTY;
 528         }
 529         return err;
 530 }
 531
 532 /*
 533  * This is called at softirq level to deliver received packets
 534  * to the ppp_generic code, and to tell the ppp_generic code
 535  * if we can accept more output now.
 536  */
 537 static void ppp_sync_process(unsigned long arg)
 538 {
 539         struct syncppp *ap = (struct syncppp *) arg;
 540         struct sk_buff *skb;
 541
 542         /* process received packets */
 543         while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
 544                 if (skb->len == 0) {
 545                         /* zero length buffers indicate error */
 546                         ppp_input_error(&ap->chan, 0);
 547                         kfree_skb(skb);
 548                 }
 549                 else
 550                         ppp_input(&ap->chan, skb);
 551         }
 552
 553         /* try to push more stuff out */
 554         if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_sync_push(ap))
 555                 ppp_output_wakeup(&ap->chan);
 556 }
 557
 558 /*
 559  * Procedures for encapsulation and framing.
 560  */
 561
 562 struct sk_buff*
 563 ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb)
 564 {
 565         int proto;
 566         unsigned char *data;
 567         int islcp;
 568
 569         data  = skb->data;
 570         proto = (data[0] << 8) + data[1];
 571
 572         /* LCP packets with codes between 1 (configure-request)
 573          * and 7 (code-reject) must be sent as though no options
 574          * have been negotiated.
 575          */
 576         islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
 577
 578         /* compress protocol field if option enabled */
 579         if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp)
 580                 skb_pull(skb,1);
 581
 582         /* prepend address/control fields if necessary */
 583         if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
 584                 if (skb_headroom(skb) < 2) {
 585                         struct sk_buff *npkt = dev_alloc_skb(skb->len + 2);
 586                         if (npkt == NULL) {
 587                                 kfree_skb(skb);
 588                                 return NULL;
 589                         }
 590                         skb_reserve(npkt,2);
 591                         memcpy(skb_put(npkt,skb->len), skb->data, 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 != 0) {
 653                         set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 654                         sent = tty->driver->write(tty, 0, 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 != 0)))
 671                         break;
 672                 if (!spin_trylock_bh(&ap->xmit_lock))
 673                         break;
 674         }
 675         return done;
 676
 677 flush:
 678         if (ap->tpkt != 0) {
 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         if ((skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2)) == 0) {
 734                 printk(KERN_ERR "PPPsync: no memory (input pkt)\n");
 735                 goto err;
 736         }
 737         /* Try to get the payload 4-byte aligned */
 738         if (buf[0] != PPP_ALLSTATIONS)
 739                 skb_reserve(skb, 2 + (buf[0] & 1));
 740
 741         if (flags != 0 && *flags) {
 742                 /* error flag set, ignore frame */
 743                 goto err;
 744         } else if (count > skb_tailroom(skb)) {
 745                 /* packet overflowed MRU */
 746                 goto err;
 747         }
 748
 749         p = skb_put(skb, count);
 750         memcpy(p, buf, count);
 751
 752         /* strip address/control field if present */
 753         p = skb->data;
 754         if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
 755                 /* chop off address/control */
 756                 if (skb->len < 3)
 757                         goto err;
 758                 p = skb_pull(skb, 2);
 759         }
 760
 761         /* decompress protocol field if compressed */
 762         if (p[0] & 1) {
 763                 /* protocol is compressed */
 764                 skb_push(skb, 1)[0] = 0;
 765         } else if (skb->len < 2)
 766                 goto err;
 767
 768         /* queue the frame to be processed */
 769         skb_queue_tail(&ap->rqueue, skb);
 770         return;
 771
 772 err:
 773         /* queue zero length packet as error indication */
 774         if (skb || (skb = dev_alloc_skb(0))) {
 775                 skb_trim(skb, 0);
 776                 skb_queue_tail(&ap->rqueue, skb);
 777         }
 778 }
 779
 780 static void __exit
 781 ppp_sync_cleanup(void)
 782 {
 783         if (tty_register_ldisc(N_SYNC_PPP, NULL) != 0)
 784                 printk(KERN_ERR "failed to unregister Sync PPP line discipline\n");
 785 }
 786
 787 module_init(ppp_sync_init);
 788 module_exit(ppp_sync_cleanup);
 789 MODULE_LICENSE("GPL");
 790 MODULE_ALIAS_LDISC(N_SYNC_PPP);