summaryrefslogtreecommitdiffstats
path: root/drivers/net/ppp_async.c
blob: aa6540b39466d464f0c70f497469b90820458ac8 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
/*
 * PPP async serial channel driver for Linux.
 *
 * Copyright 1999 Paul Mackerras.
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 *
 * This driver provides the encapsulation and framing for sending
 * and receiving PPP frames over async serial lines.  It relies on
 * the generic PPP layer to give it frames to send and to process
 * received frames.  It implements the PPP line discipline.
 *
 * Part of the code in this driver was inspired by the old async-only
 * PPP driver, written by Michael Callahan and Al Longyear, and
 * subsequently hacked by Paul Mackerras.
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/tty.h>
#include <linux/netdevice.h>
#include <linux/poll.h>
#include <linux/crc-ccitt.h>
#include <linux/ppp_defs.h>
#include <linux/if_ppp.h>
#include <linux/ppp_channel.h>
#include <linux/spinlock.h>
#include <linux/init.h>
#include <asm/uaccess.h>
#include <asm/string.h>

#define PPP_VERSION	"2.4.2"

#define OBUFSIZE	256

/* Structure for storing local state. */
struct asyncppp {
	struct tty_struct *tty;
	unsigned int	flags;
	unsigned int	state;
	unsigned int	rbits;
	int		mru;
	spinlock_t	xmit_lock;
	spinlock_t	recv_lock;
	unsigned long	xmit_flags;
	u32		xaccm[8];
	u32		raccm;
	unsigned int	bytes_sent;
	unsigned int	bytes_rcvd;

	struct sk_buff	*tpkt;
	int		tpkt_pos;
	u16		tfcs;
	unsigned char	*optr;
	unsigned char	*olim;
	unsigned long	last_xmit;

	struct sk_buff	*rpkt;
	int		lcp_fcs;
	struct sk_buff_head rqueue;

	struct tasklet_struct tsk;

	atomic_t	refcnt;
	struct semaphore dead_sem;
	struct ppp_channel chan;	/* interface to generic ppp layer */
	unsigned char	obuf[OBUFSIZE];
};

/* Bit numbers in xmit_flags */
#define XMIT_WAKEUP	0
#define XMIT_FULL	1
#define XMIT_BUSY	2

/* State bits */
#define SC_TOSS		1
#define SC_ESCAPE	2
#define SC_PREV_ERROR	4

/* Bits in rbits */
#define SC_RCV_BITS	(SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)

static int flag_time = HZ;
module_param(flag_time, int, 0);
MODULE_PARM_DESC(flag_time, "ppp_async: interval between flagged packets (in clock ticks)");
MODULE_LICENSE("GPL");
MODULE_ALIAS_LDISC(N_PPP);

/*
 * Prototypes.
 */
static int ppp_async_encode(struct asyncppp *ap);
static int ppp_async_send(struct ppp_channel *chan, struct sk_buff *skb);
static int ppp_async_push(struct asyncppp *ap);
static void ppp_async_flush_output(struct asyncppp *ap);
static void ppp_async_input(struct asyncppp *ap, const unsigned char *buf,
			    char *flags, int count);
static int ppp_async_ioctl(struct ppp_channel *chan, unsigned int cmd,
			   unsigned long arg);
static void ppp_async_process(unsigned long arg);

static void async_lcp_peek(struct asyncppp *ap, unsigned char *data,
			   int len, int inbound);

static struct ppp_channel_ops async_ops = {
	ppp_async_send,
	ppp_async_ioctl
};

/*
 * Routines implementing the PPP line discipline.
 */

/*
 * We have a potential race on dereferencing tty->disc_data,
 * because the tty layer provides no locking at all - thus one
 * cpu could be running ppp_asynctty_receive while another
 * calls ppp_asynctty_close, which zeroes tty->disc_data and
 * frees the memory that ppp_asynctty_receive is using.  The best
 * way to fix this is to use a rwlock in the tty struct, but for now
 * we use a single global rwlock for all ttys in ppp line discipline.
 *
 * FIXME: this is no longer true. The _close path for the ldisc is 
 * now guaranteed to be sane. 
 */
static DEFINE_RWLOCK(disc_data_lock);

static struct asyncppp *ap_get(struct tty_struct *tty)
{
	struct asyncppp *ap;

	read_lock(&disc_data_lock);
	ap = tty->disc_data;
	if (ap != NULL)
		atomic_inc(&ap->refcnt);
	read_unlock(&disc_data_lock);
	return ap;
}

static void ap_put(struct asyncppp *ap)
{
	if (atomic_dec_and_test(&ap->refcnt))
		up(&ap->dead_sem);
}

/*
 * Called when a tty is put into PPP line discipline. Called in process
 * context.
 */
static int
ppp_asynctty_open(struct tty_struct *tty)
{
	struct asyncppp *ap;
	int err;

	err = -ENOMEM;
	ap = kmalloc(sizeof(*ap), GFP_KERNEL);
	if (ap == 0)
		goto out;

	/* initialize the asyncppp structure */
	memset(ap, 0, sizeof(*ap));
	ap->tty = tty;
	ap->mru = PPP_MRU;
	spin_lock_init(&ap->xmit_lock);
	spin_lock_init(&ap->recv_lock);
	ap->xaccm[0] = ~0U;
	ap->xaccm[3] = 0x60000000U;
	ap->raccm = ~0U;
	ap->optr = ap->obuf;
	ap->olim = ap->obuf;
	ap->lcp_fcs = -1;

	skb_queue_head_init(&ap->rqueue);
	tasklet_init(&ap->tsk, ppp_async_process, (unsigned long) ap);

	atomic_set(&ap->refcnt, 1);
	init_MUTEX_LOCKED(&ap->dead_sem);

	ap->chan.private = ap;
	ap->chan.ops = &async_ops;
	ap->chan.mtu = PPP_MRU;
	err = ppp_register_channel(&ap->chan);
	if (err)
		goto out_free;

	tty->disc_data = ap;
	tty->receive_room = 65536;
	return 0;

 out_free:
	kfree(ap);
 out:
	return err;
}

/*
 * Called when the tty is put into another line discipline
 * or it hangs up.  We have to wait for any cpu currently
 * executing in any of the other ppp_asynctty_* routines to
 * finish before we can call ppp_unregister_channel and free
 * the asyncppp struct.  This routine must be called from
 * process context, not interrupt or softirq context.
 */
static void
ppp_asynctty_close(struct tty_struct *tty)
{
	struct asyncppp *ap;

	write_lock_irq(&disc_data_lock);
	ap = tty->disc_data;
	tty->disc_data = NULL;
	write_unlock_irq(&disc_data_lock);
	if (ap == 0)
		return;

	/*
	 * We have now ensured that nobody can start using ap from now
	 * on, but we have to wait for all existing users to finish.
	 * Note that ppp_unregister_channel ensures that no calls to
	 * our channel ops (i.e. ppp_async_send/ioctl) are in progress
	 * by the time it returns.
	 */
	if (!atomic_dec_and_test(&ap->refcnt))
		down(&ap->dead_sem);
	tasklet_kill(&ap->tsk);

	ppp_unregister_channel(&ap->chan);
	if (ap->rpkt != 0)
		kfree_skb(ap->rpkt);
	skb_queue_purge(&ap->rqueue);
	if (ap->tpkt != 0)
		kfree_skb(ap->tpkt);
	kfree(ap);
}

/*
 * Called on tty hangup in process context.
 *
 * Wait for I/O to driver to complete and unregister PPP channel.
 * This is already done by the close routine, so just call that.
 */
static int ppp_asynctty_hangup(struct tty_struct *tty)
{
	ppp_asynctty_close(tty);
	return 0;
}

/*
 * Read does nothing - no data is ever available this way.
 * Pppd reads and writes packets via /dev/ppp instead.
 */
static ssize_t
ppp_asynctty_read(struct tty_struct *tty, struct file *file,
		  unsigned char __user *buf, size_t count)
{
	return -EAGAIN;
}

/*
 * Write on the tty does nothing, the packets all come in
 * from the ppp generic stuff.
 */
static ssize_t
ppp_asynctty_write(struct tty_struct *tty, struct file *file,
		   const unsigned char *buf, size_t count)
{
	return -EAGAIN;
}

/*
 * Called in process context only. May be re-entered by multiple
 * ioctl calling threads.
 */
 
static int
ppp_asynctty_ioctl(struct tty_struct *tty, struct file *file,
		   unsigned int cmd, unsigned long arg)
{
	struct asyncppp *ap = ap_get(tty);
	int err, val;
	int __user *p = (int __user *)arg;

	if (ap == 0)
		return -ENXIO;
	err = -EFAULT;
	switch (cmd) {
	case PPPIOCGCHAN:
		err = -ENXIO;
		if (ap == 0)
			break;
		err = -EFAULT;
		if (put_user(ppp_channel_index(&ap->chan), p))
			break;
		err = 0;
		break;

	case PPPIOCGUNIT:
		err = -ENXIO;
		if (ap == 0)
			break;
		err = -EFAULT;
		if (put_user(ppp_unit_number(&ap->chan), p))
			break;
		err = 0;
		break;

	case TCGETS:
	case TCGETA:
		err = n_tty_ioctl(tty, file, cmd, arg);
		break;

	case TCFLSH:
		/* flush our buffers and the serial port's buffer */
		if (arg == TCIOFLUSH || arg == TCOFLUSH)
			ppp_async_flush_output(ap);
		err = n_tty_ioctl(tty, file, cmd, arg);
		break;

	case FIONREAD:
		val = 0;
		if (put_user(val, p))
			break;
		err = 0;
		break;

	default:
		err = -ENOIOCTLCMD;
	}

	ap_put(ap);
	return err;
}

/* No kernel lock - fine */
static unsigned int
ppp_asynctty_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
{
	return 0;
}

/*
 * This can now be called from hard interrupt level as well
 * as soft interrupt level or mainline.
 */
static void
ppp_asynctty_receive(struct tty_struct *tty, const unsigned char *buf,
		  char *cflags, int count)
{
	struct asyncppp *ap = ap_get(tty);
	unsigned long flags;

	if (ap == 0)
		return;
	spin_lock_irqsave(&ap->recv_lock, flags);
	ppp_async_input(ap, buf, cflags, count);
	spin_unlock_irqrestore(&ap->recv_lock, flags);
	if (!skb_queue_empty(&ap->rqueue))
		tasklet_schedule(&ap->tsk);
	ap_put(ap);
	if (test_and_clear_bit(TTY_THROTTLED, &tty->flags)
	    && tty->driver->unthrottle)
		tty->driver->unthrottle(tty);
}

static void
ppp_asynctty_wakeup(struct tty_struct *tty)
{
	struct asyncppp *ap = ap_get(tty);

	clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
	if (ap == 0)
		return;
	set_bit(XMIT_WAKEUP, &ap->xmit_flags);
	tasklet_schedule(&ap->tsk);
	ap_put(ap);
}


static struct tty_ldisc ppp_ldisc = {
	.owner  = THIS_MODULE,
	.magic	= TTY_LDISC_MAGIC,
	.name	= "ppp",
	.open	= ppp_asynctty_open,
	.close	= ppp_asynctty_close,
	.hangup	= ppp_asynctty_hangup,
	.read	= ppp_asynctty_read,
	.write	= ppp_asynctty_write,
	.ioctl	= ppp_asynctty_ioctl,
	.poll	= ppp_asynctty_poll,
	.receive_buf = ppp_asynctty_receive,
	.write_wakeup = ppp_asynctty_wakeup,
};

static int __init
ppp_async_init(void)
{
	int err;

	err = tty_register_ldisc(N_PPP, &ppp_ldisc);
	if (err != 0)
		printk(KERN_ERR "PPP_async: error %d registering line disc.\n",
		       err);
	return err;
}

/*
 * The following routines provide the PPP channel interface.
 */
static int
ppp_async_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
{
	struct asyncppp *ap = chan->private;
	void __user *argp = (void __user *)arg;
	int __user *p = argp;
	int err, val;
	u32 accm[8];

	err = -EFAULT;
	switch (cmd) {
	case PPPIOCGFLAGS:
		val = ap->flags | ap->rbits;
		if (put_user(val, p))
			break;
		err = 0;
		break;
	case PPPIOCSFLAGS:
		if (get_user(val, p))
			break;
		ap->flags = val & ~SC_RCV_BITS;
		spin_lock_irq(&ap->recv_lock);
		ap->rbits = val & SC_RCV_BITS;
		spin_unlock_irq(&ap->recv_lock);
		err = 0;
		break;

	case PPPIOCGASYNCMAP:
		if (put_user(ap->xaccm[0], (u32 __user *)argp))
			break;
		err = 0;
		break;
	case PPPIOCSASYNCMAP:
		if (get_user(ap->xaccm[0], (u32 __user *)argp))
			break;
		err = 0;
		break;

	case PPPIOCGRASYNCMAP:
		if (put_user(ap->raccm, (u32 __user *)argp))
			break;
		err = 0;
		break;
	case PPPIOCSRASYNCMAP:
		if (get_user(ap->raccm, (u32 __user *)argp))
			break;
		err = 0;
		break;

	case PPPIOCGXASYNCMAP:
		if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
			break;
		err = 0;
		break;
	case PPPIOCSXASYNCMAP:
		if (copy_from_user(accm, argp, sizeof(accm)))
			break;
		accm[2] &= ~0x40000000U;	/* can't escape 0x5e */
		accm[3] |= 0x60000000U;		/* must escape 0x7d, 0x7e */
		memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
		err = 0;
		break;

	case PPPIOCGMRU:
		if (put_user(ap->mru, p))
			break;
		err = 0;
		break;
	case PPPIOCSMRU:
		if (get_user(val, p))
			break;
		if (val < PPP_MRU)
			val = PPP_MRU;
		ap->mru = val;
		err = 0;
		break;

	default:
		err = -ENOTTY;
	}

	return err;
}

/*
 * This is called at softirq level to deliver received packets
 * to the ppp_generic code, and to tell the ppp_generic code
 * if we can accept more output now.
 */
static void ppp_async_process(unsigned long arg)
{
	struct asyncppp *ap = (struct asyncppp *) arg;
	struct sk_buff *skb;

	/* process received packets */
	while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
		if (skb->cb[0])
			ppp_input_error(&ap->chan, 0);
		ppp_input(&ap->chan, skb);
	}

	/* try to push more stuff out */
	if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_async_push(ap))
		ppp_output_wakeup(&ap->chan);
}

/*
 * Procedures for encapsulation and framing.
 */

/*
 * Procedure to encode the data for async serial transmission.
 * Does octet stuffing (escaping), puts the address/control bytes
 * on if A/C compression is disabled, and does protocol compression.
 * Assumes ap->tpkt != 0 on entry.
 * Returns 1 if we finished the current frame, 0 otherwise.
 */

#define PUT_BYTE(ap, buf, c, islcp)	do {		\
	if ((islcp && c < 0x20) || (ap->xaccm[c >> 5] & (1 << (c & 0x1f)))) {\
		*buf++ = PPP_ESCAPE;			\
		*buf++ = c ^ 0x20;			\
	} else						\
		*buf++ = c;				\
} while (0)

static int
ppp_async_encode(struct asyncppp *ap)
{
	int fcs, i, count, c, proto;
	unsigned char *buf, *buflim;
	unsigned char *data;
	int islcp;

	buf = ap->obuf;
	ap->olim = buf;
	ap->optr = buf;
	i = ap->tpkt_pos;
	data = ap->tpkt->data;
	count = ap->tpkt->len;
	fcs = ap->tfcs;
	proto = (data[0] << 8) + data[1];

	/*
	 * LCP packets with code values between 1 (configure-reqest)
	 * and 7 (code-reject) must be sent as though no options
	 * had been negotiated.
	 */
	islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;

	if (i == 0) {
		if (islcp)
			async_lcp_peek(ap, data, count, 0);

		/*
		 * Start of a new packet - insert the leading FLAG
		 * character if necessary.
		 */
		if (islcp || flag_time == 0
		    || jiffies - ap->last_xmit >= flag_time)
			*buf++ = PPP_FLAG;
		ap->last_xmit = jiffies;
		fcs = PPP_INITFCS;

		/*
		 * Put in the address/control bytes if necessary
		 */
		if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
			PUT_BYTE(ap, buf, 0xff, islcp);
			fcs = PPP_FCS(fcs, 0xff);
			PUT_BYTE(ap, buf, 0x03, islcp);
			fcs = PPP_FCS(fcs, 0x03);
		}
	}

	/*
	 * Once we put in the last byte, we need to put in the FCS
	 * and closing flag, so make sure there is at least 7 bytes
	 * of free space in the output buffer.
	 */
	buflim = ap->obuf + OBUFSIZE - 6;
	while (i < count && buf < buflim) {
		c = data[i++];
		if (i == 1 && c == 0 && (ap->flags & SC_COMP_PROT))
			continue;	/* compress protocol field */
		fcs = PPP_FCS(fcs, c);
		PUT_BYTE(ap, buf, c, islcp);
	}

	if (i < count) {
		/*
		 * Remember where we are up to in this packet.
		 */
		ap->olim = buf;
		ap->tpkt_pos = i;
		ap->tfcs = fcs;
		return 0;
	}

	/*
	 * We have finished the packet.  Add the FCS and flag.
	 */
	fcs = ~fcs;
	c = fcs & 0xff;
	PUT_BYTE(ap, buf, c, islcp);
	c = (fcs >> 8) & 0xff;
	PUT_BYTE(ap, buf, c, islcp);
	*buf++ = PPP_FLAG;
	ap->olim = buf;

	kfree_skb(ap->tpkt);
	ap->tpkt = NULL;
	return 1;
}

/*
 * Transmit-side routines.
 */

/*
 * Send a packet to the peer over an async tty line.
 * Returns 1 iff the packet was accepted.
 * If the packet was not accepted, we will call ppp_output_wakeup
 * at some later time.
 */
static int
ppp_async_send(struct ppp_channel *chan, struct sk_buff *skb)
{
	struct asyncppp *ap = chan->private;

	ppp_async_push(ap);

	if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
		return 0;	/* already full */
	ap->tpkt = skb;
	ap->tpkt_pos = 0;

	ppp_async_push(ap);
	return 1;
}

/*
 * Push as much data as possible out to the tty.
 */
static int
ppp_async_push(struct asyncppp *ap)
{
	int avail, sent, done = 0;
	struct tty_struct *tty = ap->tty;
	int tty_stuffed = 0;

	/*
	 * We can get called recursively here if the tty write
	 * function calls our wakeup function.  This can happen
	 * for example on a pty with both the master and slave
	 * set to PPP line discipline.
	 * We use the XMIT_BUSY bit to detect this and get out,
	 * leaving the XMIT_WAKEUP bit set to tell the other
	 * instance that it may now be able to write more now.
	 */
	if (test_and_set_bit(XMIT_BUSY, &ap->xmit_flags))
		return 0;
	spin_lock_bh(&ap->xmit_lock);
	for (;;) {
		if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
			tty_stuffed = 0;
		if (!tty_stuffed && ap->optr < ap->olim) {
			avail = ap->olim - ap->optr;
			set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
			sent = tty->driver->write(tty, ap->optr, avail);
			if (sent < 0)
				goto flush;	/* error, e.g. loss of CD */
			ap->optr += sent;
			if (sent < avail)
				tty_stuffed = 1;
			continue;
		}
		if (ap->optr >= ap->olim && ap->tpkt != 0) {
			if (ppp_async_encode(ap)) {
				/* finished processing ap->tpkt */
				clear_bit(XMIT_FULL, &ap->xmit_flags);
				done = 1;
			}
			continue;
		}
		/*
		 * We haven't made any progress this time around.
		 * Clear XMIT_BUSY to let other callers in, but
		 * after doing so we have to check if anyone set
		 * XMIT_WAKEUP since we last checked it.  If they
		 * did, we should try again to set XMIT_BUSY and go
		 * around again in case XMIT_BUSY was still set when
		 * the other caller tried.
		 */
		clear_bit(XMIT_BUSY, &ap->xmit_flags);
		/* any more work to do? if not, exit the loop */
		if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags)
		      || (!tty_stuffed && ap->tpkt != 0)))
			break;
		/* more work to do, see if we can do it now */
		if (test_and_set_bit(XMIT_BUSY, &ap->xmit_flags))
			break;
	}
	spin_unlock_bh(&ap->xmit_lock);
	return done;

flush:
	clear_bit(XMIT_BUSY, &ap->xmit_flags);
	if (ap->tpkt != 0) {
		kfree_skb(ap->tpkt);
		ap->tpkt = NULL;
		clear_bit(XMIT_FULL, &ap->xmit_flags);
		done = 1;
	}
	ap->optr = ap->olim;
	spin_unlock_bh(&ap->xmit_lock);
	return done;
}

/*
 * Flush output from our internal buffers.
 * Called for the TCFLSH ioctl. Can be entered in parallel
 * but this is covered by the xmit_lock.
 */
static void
ppp_async_flush_output(struct asyncppp *ap)
{
	int done = 0;

	spin_lock_bh(&ap->xmit_lock);
	ap->optr = ap->olim;
	if (ap->tpkt != NULL) {
		kfree_skb(ap->tpkt);
		ap->tpkt = NULL;
		clear_bit(XMIT_FULL, &ap->xmit_flags);
		done = 1;
	}
	spin_unlock_bh(&ap->xmit_lock);
	if (done)
		ppp_output_wakeup(&ap->chan);
}

/*
 * Receive-side routines.
 */

/* see how many ordinary chars there are at the start of buf */
static inline int
scan_ordinary(struct asyncppp *ap, const unsigned char *buf, int count)
{
	int i, c;

	for (i = 0; i < count; ++i) {
		c = buf[i];
		if (c == PPP_ESCAPE || c == PPP_FLAG
		    || (c < 0x20 && (ap->raccm & (1 << c)) != 0))
			break;
	}
	return i;
}

/* called when a flag is seen - do end-of-packet processing */
static void
process_input_packet(struct asyncppp *ap)
{
	struct sk_buff *skb;
	unsigned char *p;
	unsigned int len, fcs, proto;

	skb = ap->rpkt;
	if (ap->state & (SC_TOSS | SC_ESCAPE))
		goto err;

	if (skb == NULL)
		return;		/* 0-length packet */

	/* check the FCS */
	p = skb->data;
	len = skb->len;
	if (len < 3)
		goto err;	/* too short */
	fcs = PPP_INITFCS;
	for (; len > 0; --len)
		fcs = PPP_FCS(fcs, *p++);
	if (fcs != PPP_GOODFCS)
		goto err;	/* bad FCS */
	skb_trim(skb, skb->len - 2);

	/* check for address/control and protocol compression */
	p = skb->data;
	if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
		/* chop off address/control */
		if (skb->len < 3)
			goto err;
		p = skb_pull(skb, 2);
	}
	proto = p[0];
	if (proto & 1) {
		/* protocol is compressed */
		skb_push(skb, 1)[0] = 0;
	} else {
		if (skb->len < 2)
			goto err;
		proto = (proto << 8) + p[1];
		if (proto == PPP_LCP)
			async_lcp_peek(ap, p, skb->len, 1);
	}

	/* queue the frame to be processed */
	skb->cb[0] = ap->state;
	skb_queue_tail(&ap->rqueue, skb);
	ap->rpkt = NULL;
	ap->state = 0;
	return;

 err:
	/* frame had an error, remember that, reset SC_TOSS & SC_ESCAPE */
	ap->state = SC_PREV_ERROR;
	if (skb) {
		/* make skb appear as freshly allocated */
		skb_trim(skb, 0);
		skb_reserve(skb, - skb_headroom(skb));
	}
}

/* Called when the tty driver has data for us. Runs parallel with the
   other ldisc functions but will not be re-entered */

static void
ppp_async_input(struct asyncppp *ap, const unsigned char *buf,
		char *flags, int count)
{
	struct sk_buff *skb;
	int c, i, j, n, s, f;
	unsigned char *sp;

	/* update bits used for 8-bit cleanness detection */
	if (~ap->rbits & SC_RCV_BITS) {
		s = 0;
		for (i = 0; i < count; ++i) {
			c = buf[i];
			if (flags != 0 && flags[i] != 0)
				continue;
			s |= (c & 0x80)? SC_RCV_B7_1: SC_RCV_B7_0;
			c = ((c >> 4) ^ c) & 0xf;
			s |= (0x6996 & (1 << c))? SC_RCV_ODDP: SC_RCV_EVNP;
		}
		ap->rbits |= s;
	}

	while (count > 0) {
		/* scan through and see how many chars we can do in bulk */
		if ((ap->state & SC_ESCAPE) && buf[0] == PPP_ESCAPE)
			n = 1;
		else
			n = scan_ordinary(ap, buf, count);

		f = 0;
		if (flags != 0 && (ap->state & SC_TOSS) == 0) {
			/* check the flags to see if any char had an error */
			for (j = 0; j < n; ++j)
				if ((f = flags[j]) != 0)
					break;
		}
		if (f != 0) {
			/* start tossing */
			ap->state |= SC_TOSS;

		} else if (n > 0 && (ap->state & SC_TOSS) == 0) {
			/* stuff the chars in the skb */
			skb = ap->rpkt;
			if (skb == 0) {
				skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2);
				if (skb == 0)
					goto nomem;
 				ap->rpkt = skb;
 			}
 			if (skb->len == 0) {
 				/* Try to get the payload 4-byte aligned.
 				 * This should match the
 				 * PPP_ALLSTATIONS/PPP_UI/compressed tests in
 				 * process_input_packet, but we do not have
 				 * enough chars here to test buf[1] and buf[2].
 				 */
				if (buf[0] != PPP_ALLSTATIONS)
					skb_reserve(skb, 2 + (buf[0] & 1));
			}
			if (n > skb_tailroom(skb)) {
				/* packet overflowed MRU */
				ap->state |= SC_TOSS;
			} else {
				sp = skb_put(skb, n);
				memcpy(sp, buf, n);
				if (ap->state & SC_ESCAPE) {
					sp[0] ^= 0x20;
					ap->state &= ~SC_ESCAPE;
				}
			}
		}

		if (n >= count)
			break;

		c = buf[n];
		if (flags != NULL && flags[n] != 0) {
			ap->state |= SC_TOSS;
		} else if (c == PPP_FLAG) {
			process_input_packet(ap);
		} else if (c == PPP_ESCAPE) {
			ap->state |= SC_ESCAPE;
		} else if (I_IXON(ap->tty)) {
			if (c == START_CHAR(ap->tty))
				start_tty(ap->tty);
			else if (c == STOP_CHAR(ap->tty))
				stop_tty(ap->tty);
		}
		/* otherwise it's a char in the recv ACCM */
		++n;

		buf += n;
		if (flags != 0)
			flags += n;
		count -= n;
	}
	return;

 nomem:
	printk(KERN_ERR "PPPasync: no memory (input pkt)\n");
	ap->state |= SC_TOSS;
}

/*
 * We look at LCP frames going past so that we can notice
 * and react to the LCP configure-ack from the peer.
 * In the situation where the peer has been sent a configure-ack
 * already, LCP is up once it has sent its configure-ack
 * so the immediately following packet can be sent with the
 * configured LCP options.  This allows us to process the following
 * packet correctly without pppd needing to respond quickly.
 *
 * We only respond to the received configure-ack if we have just
 * sent a configure-request, and the configure-ack contains the
 * same data (this is checked using a 16-bit crc of the data).
 */
#define CONFREQ		1	/* LCP code field values */
#define CONFACK		2
#define LCP_MRU		1	/* LCP option numbers */
#define LCP_ASYNCMAP	2

static void async_lcp_peek(struct asyncppp *ap, unsigned char *data,
			   int len, int inbound)
{
	int dlen, fcs, i, code;
	u32 val;

	data += 2;		/* skip protocol bytes */
	len -= 2;
	if (len < 4)		/* 4 = code, ID, length */
		return;
	code = data[0];
	if (code != CONFACK && code != CONFREQ)
		return;
	dlen = (data[2] << 8) + data[3];
	if (len < dlen)
		return;		/* packet got truncated or length is bogus */

	if (code == (inbound? CONFACK: CONFREQ)) {
		/*
		 * sent confreq or received confack:
		 * calculate the crc of the data from the ID field on.
		 */
		fcs = PPP_INITFCS;
		for (i = 1; i < dlen; ++i)
			fcs = PPP_FCS(fcs, data[i]);

		if (!inbound) {
			/* outbound confreq - remember the crc for later */
			ap->lcp_fcs = fcs;
			return;
		}

		/* received confack, check the crc */
		fcs ^= ap->lcp_fcs;
		ap->lcp_fcs = -1;
		if (fcs != 0)
			return;
	} else if (inbound)
		return;	/* not interested in received confreq */

	/* process the options in the confack */
	data += 4;
	dlen -= 4;
	/* data[0] is code, data[1] is length */
	while (dlen >= 2 && dlen >= data[1] && data[1] >= 2) {
		switch (data[0]) {
		case LCP_MRU:
			val = (data[2] << 8) + data[3];
			if (inbound)
				ap->mru = val;
			else
				ap->chan.mtu = val;
			break;
		case LCP_ASYNCMAP:
			val = (data[2] << 24) + (data[3] << 16)
				+ (data[4] << 8) + data[5];
			if (inbound)
				ap->raccm = val;
			else
				ap->xaccm[0] = val;
			break;
		}
		dlen -= data[1];
		data += data[1];
	}
}

static void __exit ppp_async_cleanup(void)
{
	if (tty_unregister_ldisc(N_PPP) != 0)
		printk(KERN_ERR "failed to unregister PPP line discipline\n");
}

module_init(ppp_async_init);
module_exit(ppp_async_cleanup);