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/ppp-ioctl.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/interrupt.h> 48 #include <linux/slab.h> 49 #include <asm/unaligned.h> 50 #include <asm/uaccess.h> 51 52 #define PPP_VERSION "2.4.2" 53 54 /* Structure for storing local state. */ 55 struct syncppp { 56 struct tty_struct *tty; 57 unsigned int flags; 58 unsigned int rbits; 59 int mru; 60 spinlock_t xmit_lock; 61 spinlock_t recv_lock; 62 unsigned long xmit_flags; 63 u32 xaccm[8]; 64 u32 raccm; 65 unsigned int bytes_sent; 66 unsigned int bytes_rcvd; 67 68 struct sk_buff *tpkt; 69 unsigned long last_xmit; 70 71 struct sk_buff_head rqueue; 72 73 struct tasklet_struct tsk; 74 75 atomic_t refcnt; 76 struct completion dead_cmp; 77 struct ppp_channel chan; /* interface to generic ppp layer */ 78 }; 79 80 /* Bit numbers in xmit_flags */ 81 #define XMIT_WAKEUP 0 82 #define XMIT_FULL 1 83 84 /* Bits in rbits */ 85 #define SC_RCV_BITS (SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP) 86 87 #define PPPSYNC_MAX_RQLEN 32 /* arbitrary */ 88 89 /* 90 * Prototypes. 91 */ 92 static struct sk_buff* ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *); 93 static int ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb); 94 static int ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, 95 unsigned long arg); 96 static void ppp_sync_process(unsigned long arg); 97 static int ppp_sync_push(struct syncppp *ap); 98 static void ppp_sync_flush_output(struct syncppp *ap); 99 static void ppp_sync_input(struct syncppp *ap, const unsigned char *buf, 100 char *flags, int count); 101 102 static const struct ppp_channel_ops sync_ops = { 103 .start_xmit = ppp_sync_send, 104 .ioctl = ppp_sync_ioctl, 105 }; 106 107 /* 108 * Utility procedures to print a buffer in hex/ascii 109 */ 110 static void 111 ppp_print_hex (register __u8 * out, const __u8 * in, int count) 112 { 113 register __u8 next_ch; 114 static const char hex[] = "0123456789ABCDEF"; 115 116 while (count-- > 0) { 117 next_ch = *in++; 118 *out++ = hex[(next_ch >> 4) & 0x0F]; 119 *out++ = hex[next_ch & 0x0F]; 120 ++out; 121 } 122 } 123 124 static void 125 ppp_print_char (register __u8 * out, const __u8 * in, int count) 126 { 127 register __u8 next_ch; 128 129 while (count-- > 0) { 130 next_ch = *in++; 131 132 if (next_ch < 0x20 || next_ch > 0x7e) 133 *out++ = '.'; 134 else { 135 *out++ = next_ch; 136 if (next_ch == '%') /* printk/syslogd has a bug !! */ 137 *out++ = '%'; 138 } 139 } 140 *out = '\0'; 141 } 142 143 static void 144 ppp_print_buffer (const char *name, const __u8 *buf, int count) 145 { 146 __u8 line[44]; 147 148 if (name != NULL) 149 printk(KERN_DEBUG "ppp_synctty: %s, count = %d\n", name, count); 150 151 while (count > 8) { 152 memset (line, 32, 44); 153 ppp_print_hex (line, buf, 8); 154 ppp_print_char (&line[8 * 3], buf, 8); 155 printk(KERN_DEBUG "%s\n", line); 156 count -= 8; 157 buf += 8; 158 } 159 160 if (count > 0) { 161 memset (line, 32, 44); 162 ppp_print_hex (line, buf, count); 163 ppp_print_char (&line[8 * 3], buf, count); 164 printk(KERN_DEBUG "%s\n", line); 165 } 166 } 167 168 169 /* 170 * Routines implementing the synchronous PPP line discipline. 171 */ 172 173 /* 174 * We have a potential race on dereferencing tty->disc_data, 175 * because the tty layer provides no locking at all - thus one 176 * cpu could be running ppp_synctty_receive while another 177 * calls ppp_synctty_close, which zeroes tty->disc_data and 178 * frees the memory that ppp_synctty_receive is using. The best 179 * way to fix this is to use a rwlock in the tty struct, but for now 180 * we use a single global rwlock for all ttys in ppp line discipline. 181 * 182 * FIXME: Fixed in tty_io nowadays. 183 */ 184 static DEFINE_RWLOCK(disc_data_lock); 185 186 static struct syncppp *sp_get(struct tty_struct *tty) 187 { 188 struct syncppp *ap; 189 190 read_lock(&disc_data_lock); 191 ap = tty->disc_data; 192 if (ap != NULL) 193 atomic_inc(&ap->refcnt); 194 read_unlock(&disc_data_lock); 195 return ap; 196 } 197 198 static void sp_put(struct syncppp *ap) 199 { 200 if (atomic_dec_and_test(&ap->refcnt)) 201 complete(&ap->dead_cmp); 202 } 203 204 /* 205 * Called when a tty is put into sync-PPP line discipline. 206 */ 207 static int 208 ppp_sync_open(struct tty_struct *tty) 209 { 210 struct syncppp *ap; 211 int err; 212 int speed; 213 214 if (tty->ops->write == NULL) 215 return -EOPNOTSUPP; 216 217 ap = kzalloc(sizeof(*ap), GFP_KERNEL); 218 err = -ENOMEM; 219 if (!ap) 220 goto out; 221 222 /* initialize the syncppp structure */ 223 ap->tty = tty; 224 ap->mru = PPP_MRU; 225 spin_lock_init(&ap->xmit_lock); 226 spin_lock_init(&ap->recv_lock); 227 ap->xaccm[0] = ~0U; 228 ap->xaccm[3] = 0x60000000U; 229 ap->raccm = ~0U; 230 231 skb_queue_head_init(&ap->rqueue); 232 tasklet_init(&ap->tsk, ppp_sync_process, (unsigned long) ap); 233 234 atomic_set(&ap->refcnt, 1); 235 init_completion(&ap->dead_cmp); 236 237 ap->chan.private = ap; 238 ap->chan.ops = &sync_ops; 239 ap->chan.mtu = PPP_MRU; 240 ap->chan.hdrlen = 2; /* for A/C bytes */ 241 speed = tty_get_baud_rate(tty); 242 ap->chan.speed = speed; 243 err = ppp_register_channel(&ap->chan); 244 if (err) 245 goto out_free; 246 247 tty->disc_data = ap; 248 tty->receive_room = 65536; 249 return 0; 250 251 out_free: 252 kfree(ap); 253 out: 254 return err; 255 } 256 257 /* 258 * Called when the tty is put into another line discipline 259 * or it hangs up. We have to wait for any cpu currently 260 * executing in any of the other ppp_synctty_* routines to 261 * finish before we can call ppp_unregister_channel and free 262 * the syncppp struct. This routine must be called from 263 * process context, not interrupt or softirq context. 264 */ 265 static void 266 ppp_sync_close(struct tty_struct *tty) 267 { 268 struct syncppp *ap; 269 270 write_lock_irq(&disc_data_lock); 271 ap = tty->disc_data; 272 tty->disc_data = NULL; 273 write_unlock_irq(&disc_data_lock); 274 if (!ap) 275 return; 276 277 /* 278 * We have now ensured that nobody can start using ap from now 279 * on, but we have to wait for all existing users to finish. 280 * Note that ppp_unregister_channel ensures that no calls to 281 * our channel ops (i.e. ppp_sync_send/ioctl) are in progress 282 * by the time it returns. 283 */ 284 if (!atomic_dec_and_test(&ap->refcnt)) 285 wait_for_completion(&ap->dead_cmp); 286 tasklet_kill(&ap->tsk); 287 288 ppp_unregister_channel(&ap->chan); 289 skb_queue_purge(&ap->rqueue); 290 kfree_skb(ap->tpkt); 291 kfree(ap); 292 } 293 294 /* 295 * Called on tty hangup in process context. 296 * 297 * Wait for I/O to driver to complete and unregister PPP channel. 298 * This is already done by the close routine, so just call that. 299 */ 300 static int ppp_sync_hangup(struct tty_struct *tty) 301 { 302 ppp_sync_close(tty); 303 return 0; 304 } 305 306 /* 307 * Read does nothing - no data is ever available this way. 308 * Pppd reads and writes packets via /dev/ppp instead. 309 */ 310 static ssize_t 311 ppp_sync_read(struct tty_struct *tty, struct file *file, 312 unsigned char __user *buf, size_t count) 313 { 314 return -EAGAIN; 315 } 316 317 /* 318 * Write on the tty does nothing, the packets all come in 319 * from the ppp generic stuff. 320 */ 321 static ssize_t 322 ppp_sync_write(struct tty_struct *tty, struct file *file, 323 const unsigned char *buf, size_t count) 324 { 325 return -EAGAIN; 326 } 327 328 static int 329 ppp_synctty_ioctl(struct tty_struct *tty, struct file *file, 330 unsigned int cmd, unsigned long arg) 331 { 332 struct syncppp *ap = sp_get(tty); 333 int __user *p = (int __user *)arg; 334 int err, val; 335 336 if (!ap) 337 return -ENXIO; 338 err = -EFAULT; 339 switch (cmd) { 340 case PPPIOCGCHAN: 341 err = -EFAULT; 342 if (put_user(ppp_channel_index(&ap->chan), p)) 343 break; 344 err = 0; 345 break; 346 347 case PPPIOCGUNIT: 348 err = -EFAULT; 349 if (put_user(ppp_unit_number(&ap->chan), p)) 350 break; 351 err = 0; 352 break; 353 354 case TCFLSH: 355 /* flush our buffers and the serial port's buffer */ 356 if (arg == TCIOFLUSH || arg == TCOFLUSH) 357 ppp_sync_flush_output(ap); 358 err = tty_perform_flush(tty, arg); 359 break; 360 361 case FIONREAD: 362 val = 0; 363 if (put_user(val, p)) 364 break; 365 err = 0; 366 break; 367 368 default: 369 err = tty_mode_ioctl(tty, file, cmd, arg); 370 break; 371 } 372 373 sp_put(ap); 374 return err; 375 } 376 377 /* No kernel lock - fine */ 378 static unsigned int 379 ppp_sync_poll(struct tty_struct *tty, struct file *file, poll_table *wait) 380 { 381 return 0; 382 } 383 384 /* May sleep, don't call from interrupt level or with interrupts disabled */ 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) 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_empty(&ap->rqueue)) 398 tasklet_schedule(&ap->tsk); 399 sp_put(ap); 400 tty_unthrottle(tty); 401 } 402 403 static void 404 ppp_sync_wakeup(struct tty_struct *tty) 405 { 406 struct syncppp *ap = sp_get(tty); 407 408 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags); 409 if (!ap) 410 return; 411 set_bit(XMIT_WAKEUP, &ap->xmit_flags); 412 tasklet_schedule(&ap->tsk); 413 sp_put(ap); 414 } 415 416 417 static struct tty_ldisc_ops ppp_sync_ldisc = { 418 .owner = THIS_MODULE, 419 .magic = TTY_LDISC_MAGIC, 420 .name = "pppsync", 421 .open = ppp_sync_open, 422 .close = ppp_sync_close, 423 .hangup = ppp_sync_hangup, 424 .read = ppp_sync_read, 425 .write = ppp_sync_write, 426 .ioctl = ppp_synctty_ioctl, 427 .poll = ppp_sync_poll, 428 .receive_buf = ppp_sync_receive, 429 .write_wakeup = ppp_sync_wakeup, 430 }; 431 432 static int __init 433 ppp_sync_init(void) 434 { 435 int err; 436 437 err = tty_register_ldisc(N_SYNC_PPP, &ppp_sync_ldisc); 438 if (err != 0) 439 printk(KERN_ERR "PPP_sync: error %d registering line disc.\n", 440 err); 441 return err; 442 } 443 444 /* 445 * The following routines provide the PPP channel interface. 446 */ 447 static int 448 ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg) 449 { 450 struct syncppp *ap = chan->private; 451 int err, val; 452 u32 accm[8]; 453 void __user *argp = (void __user *)arg; 454 u32 __user *p = argp; 455 456 err = -EFAULT; 457 switch (cmd) { 458 case PPPIOCGFLAGS: 459 val = ap->flags | ap->rbits; 460 if (put_user(val, (int __user *) argp)) 461 break; 462 err = 0; 463 break; 464 case PPPIOCSFLAGS: 465 if (get_user(val, (int __user *) argp)) 466 break; 467 ap->flags = val & ~SC_RCV_BITS; 468 spin_lock_irq(&ap->recv_lock); 469 ap->rbits = val & SC_RCV_BITS; 470 spin_unlock_irq(&ap->recv_lock); 471 err = 0; 472 break; 473 474 case PPPIOCGASYNCMAP: 475 if (put_user(ap->xaccm[0], p)) 476 break; 477 err = 0; 478 break; 479 case PPPIOCSASYNCMAP: 480 if (get_user(ap->xaccm[0], p)) 481 break; 482 err = 0; 483 break; 484 485 case PPPIOCGRASYNCMAP: 486 if (put_user(ap->raccm, p)) 487 break; 488 err = 0; 489 break; 490 case PPPIOCSRASYNCMAP: 491 if (get_user(ap->raccm, p)) 492 break; 493 err = 0; 494 break; 495 496 case PPPIOCGXASYNCMAP: 497 if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm))) 498 break; 499 err = 0; 500 break; 501 case PPPIOCSXASYNCMAP: 502 if (copy_from_user(accm, argp, sizeof(accm))) 503 break; 504 accm[2] &= ~0x40000000U; /* can't escape 0x5e */ 505 accm[3] |= 0x60000000U; /* must escape 0x7d, 0x7e */ 506 memcpy(ap->xaccm, accm, sizeof(ap->xaccm)); 507 err = 0; 508 break; 509 510 case PPPIOCGMRU: 511 if (put_user(ap->mru, (int __user *) argp)) 512 break; 513 err = 0; 514 break; 515 case PPPIOCSMRU: 516 if (get_user(val, (int __user *) argp)) 517 break; 518 if (val < PPP_MRU) 519 val = PPP_MRU; 520 ap->mru = val; 521 err = 0; 522 break; 523 524 default: 525 err = -ENOTTY; 526 } 527 return err; 528 } 529 530 /* 531 * This is called at softirq level to deliver received packets 532 * to the ppp_generic code, and to tell the ppp_generic code 533 * if we can accept more output now. 534 */ 535 static void ppp_sync_process(unsigned long arg) 536 { 537 struct syncppp *ap = (struct syncppp *) arg; 538 struct sk_buff *skb; 539 540 /* process received packets */ 541 while ((skb = skb_dequeue(&ap->rqueue)) != NULL) { 542 if (skb->len == 0) { 543 /* zero length buffers indicate error */ 544 ppp_input_error(&ap->chan, 0); 545 kfree_skb(skb); 546 } 547 else 548 ppp_input(&ap->chan, skb); 549 } 550 551 /* try to push more stuff out */ 552 if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_sync_push(ap)) 553 ppp_output_wakeup(&ap->chan); 554 } 555 556 /* 557 * Procedures for encapsulation and framing. 558 */ 559 560 static struct sk_buff* 561 ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb) 562 { 563 int proto; 564 unsigned char *data; 565 int islcp; 566 567 data = skb->data; 568 proto = get_unaligned_be16(data); 569 570 /* LCP packets with codes between 1 (configure-request) 571 * and 7 (code-reject) must be sent as though no options 572 * have been negotiated. 573 */ 574 islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7; 575 576 /* compress protocol field if option enabled */ 577 if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp) 578 skb_pull(skb,1); 579 580 /* prepend address/control fields if necessary */ 581 if ((ap->flags & SC_COMP_AC) == 0 || islcp) { 582 if (skb_headroom(skb) < 2) { 583 struct sk_buff *npkt = dev_alloc_skb(skb->len + 2); 584 if (npkt == NULL) { 585 kfree_skb(skb); 586 return NULL; 587 } 588 skb_reserve(npkt,2); 589 skb_copy_from_linear_data(skb, 590 skb_put(npkt, skb->len), skb->len); 591 kfree_skb(skb); 592 skb = npkt; 593 } 594 skb_push(skb,2); 595 skb->data[0] = PPP_ALLSTATIONS; 596 skb->data[1] = PPP_UI; 597 } 598 599 ap->last_xmit = jiffies; 600 601 if (skb && ap->flags & SC_LOG_OUTPKT) 602 ppp_print_buffer ("send buffer", skb->data, skb->len); 603 604 return skb; 605 } 606 607 /* 608 * Transmit-side routines. 609 */ 610 611 /* 612 * Send a packet to the peer over an sync tty line. 613 * Returns 1 iff the packet was accepted. 614 * If the packet was not accepted, we will call ppp_output_wakeup 615 * at some later time. 616 */ 617 static int 618 ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb) 619 { 620 struct syncppp *ap = chan->private; 621 622 ppp_sync_push(ap); 623 624 if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags)) 625 return 0; /* already full */ 626 skb = ppp_sync_txmunge(ap, skb); 627 if (skb != NULL) 628 ap->tpkt = skb; 629 else 630 clear_bit(XMIT_FULL, &ap->xmit_flags); 631 632 ppp_sync_push(ap); 633 return 1; 634 } 635 636 /* 637 * Push as much data as possible out to the tty. 638 */ 639 static int 640 ppp_sync_push(struct syncppp *ap) 641 { 642 int sent, done = 0; 643 struct tty_struct *tty = ap->tty; 644 int tty_stuffed = 0; 645 646 if (!spin_trylock_bh(&ap->xmit_lock)) 647 return 0; 648 for (;;) { 649 if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags)) 650 tty_stuffed = 0; 651 if (!tty_stuffed && ap->tpkt) { 652 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags); 653 sent = tty->ops->write(tty, ap->tpkt->data, ap->tpkt->len); 654 if (sent < 0) 655 goto flush; /* error, e.g. loss of CD */ 656 if (sent < ap->tpkt->len) { 657 tty_stuffed = 1; 658 } else { 659 kfree_skb(ap->tpkt); 660 ap->tpkt = NULL; 661 clear_bit(XMIT_FULL, &ap->xmit_flags); 662 done = 1; 663 } 664 continue; 665 } 666 /* haven't made any progress */ 667 spin_unlock_bh(&ap->xmit_lock); 668 if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags) || 669 (!tty_stuffed && ap->tpkt))) 670 break; 671 if (!spin_trylock_bh(&ap->xmit_lock)) 672 break; 673 } 674 return done; 675 676 flush: 677 if (ap->tpkt) { 678 kfree_skb(ap->tpkt); 679 ap->tpkt = NULL; 680 clear_bit(XMIT_FULL, &ap->xmit_flags); 681 done = 1; 682 } 683 spin_unlock_bh(&ap->xmit_lock); 684 return done; 685 } 686 687 /* 688 * Flush output from our internal buffers. 689 * Called for the TCFLSH ioctl. 690 */ 691 static void 692 ppp_sync_flush_output(struct syncppp *ap) 693 { 694 int done = 0; 695 696 spin_lock_bh(&ap->xmit_lock); 697 if (ap->tpkt != NULL) { 698 kfree_skb(ap->tpkt); 699 ap->tpkt = NULL; 700 clear_bit(XMIT_FULL, &ap->xmit_flags); 701 done = 1; 702 } 703 spin_unlock_bh(&ap->xmit_lock); 704 if (done) 705 ppp_output_wakeup(&ap->chan); 706 } 707 708 /* 709 * Receive-side routines. 710 */ 711 712 /* called when the tty driver has data for us. 713 * 714 * Data is frame oriented: each call to ppp_sync_input is considered 715 * a whole frame. If the 1st flag byte is non-zero then the whole 716 * frame is considered to be in error and is tossed. 717 */ 718 static void 719 ppp_sync_input(struct syncppp *ap, const unsigned char *buf, 720 char *flags, int count) 721 { 722 struct sk_buff *skb; 723 unsigned char *p; 724 725 if (count == 0) 726 return; 727 728 if (ap->flags & SC_LOG_INPKT) 729 ppp_print_buffer ("receive buffer", buf, count); 730 731 /* stuff the chars in the skb */ 732 skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2); 733 if (!skb) { 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 && *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_unregister_ldisc(N_SYNC_PPP) != 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); 791