aboutsummaryrefslogblamecommitdiffstats
path: root/drivers/net/ppp_generic.c
blob: d3c9958b00d06db4895a7d6e2b54a58726c2e088 (plain) (tree)
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
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
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271


















































































































































































































































































                                                                                
                               







































































































































































































































































































































































































































































































































































































                                                                              
                                                             



                                                 
                                                                                       











                                                                             

                                                            


















































































































































































































































































































































                                                                                      
                          
                                 


                          





                                 

                                                                            
                                                                        
              
                                                         

                                                           

                                                             

                                               
                         

                                                              
                 
                    
         






                                                                  









                                                                              






                                                                       
                       




                                                                        


                                                         
                              









                                                
                                      









                                                              











                                                                             

                                                                               

                                                                             

                                                    
                                          




                                      



                                                                    


                                       























                                                                          
                 
















                                                                         

                                                       





                                                            
                                            



                                                   
























                                                               
                                                         












                                                                             
                                             





































                                                                      
 






























































































































































































                                                                                     








































































                                                                               
                           

                                                                             
                                                            

















































                                                                               
                                                        




































































































































































































































































































































































































































































































                                                                                      
 
                                                         









































































































































































































































                                                                             



                                  


























                                                          
 
                                                       





                                                            
                                                       


































































































                                                                            

                                                             






























































































































                                                                              
/*
 * Generic PPP layer for Linux.
 *
 * Copyright 1999-2002 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.
 *
 * The generic PPP layer handles the PPP network interfaces, the
 * /dev/ppp device, packet and VJ compression, and multilink.
 * It talks to PPP `channels' via the interface defined in
 * include/linux/ppp_channel.h.  Channels provide the basic means for
 * sending and receiving PPP frames on some kind of communications
 * channel.
 *
 * 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.
 *
 * ==FILEVERSION 20041108==
 */

#include <linux/config.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/kmod.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/devfs_fs_kernel.h>
#include <linux/netdevice.h>
#include <linux/poll.h>
#include <linux/ppp_defs.h>
#include <linux/filter.h>
#include <linux/if_ppp.h>
#include <linux/ppp_channel.h>
#include <linux/ppp-comp.h>
#include <linux/skbuff.h>
#include <linux/rtnetlink.h>
#include <linux/if_arp.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/spinlock.h>
#include <linux/smp_lock.h>
#include <linux/rwsem.h>
#include <linux/stddef.h>
#include <linux/device.h>
#include <net/slhc_vj.h>
#include <asm/atomic.h>

#define PPP_VERSION	"2.4.2"

/*
 * Network protocols we support.
 */
#define NP_IP	0		/* Internet Protocol V4 */
#define NP_IPV6	1		/* Internet Protocol V6 */
#define NP_IPX	2		/* IPX protocol */
#define NP_AT	3		/* Appletalk protocol */
#define NP_MPLS_UC 4		/* MPLS unicast */
#define NP_MPLS_MC 5		/* MPLS multicast */
#define NUM_NP	6		/* Number of NPs. */

#define MPHDRLEN	6	/* multilink protocol header length */
#define MPHDRLEN_SSN	4	/* ditto with short sequence numbers */
#define MIN_FRAG_SIZE	64

/*
 * An instance of /dev/ppp can be associated with either a ppp
 * interface unit or a ppp channel.  In both cases, file->private_data
 * points to one of these.
 */
struct ppp_file {
	enum {
		INTERFACE=1, CHANNEL
	}		kind;
	struct sk_buff_head xq;		/* pppd transmit queue */
	struct sk_buff_head rq;		/* receive queue for pppd */
	wait_queue_head_t rwait;	/* for poll on reading /dev/ppp */
	atomic_t	refcnt;		/* # refs (incl /dev/ppp attached) */
	int		hdrlen;		/* space to leave for headers */
	int		index;		/* interface unit / channel number */
	int		dead;		/* unit/channel has been shut down */
};

#define PF_TO_X(pf, X)		((X *)((char *)(pf) - offsetof(X, file)))

#define PF_TO_PPP(pf)		PF_TO_X(pf, struct ppp)
#define PF_TO_CHANNEL(pf)	PF_TO_X(pf, struct channel)

#define ROUNDUP(n, x)		(((n) + (x) - 1) / (x))

/*
 * Data structure describing one ppp unit.
 * A ppp unit corresponds to a ppp network interface device
 * and represents a multilink bundle.
 * It can have 0 or more ppp channels connected to it.
 */
struct ppp {
	struct ppp_file	file;		/* stuff for read/write/poll 0 */
	struct file	*owner;		/* file that owns this unit 48 */
	struct list_head channels;	/* list of attached channels 4c */
	int		n_channels;	/* how many channels are attached 54 */
	spinlock_t	rlock;		/* lock for receive side 58 */
	spinlock_t	wlock;		/* lock for transmit side 5c */
	int		mru;		/* max receive unit 60 */
	unsigned int	flags;		/* control bits 64 */
	unsigned int	xstate;		/* transmit state bits 68 */
	unsigned int	rstate;		/* receive state bits 6c */
	int		debug;		/* debug flags 70 */
	struct slcompress *vj;		/* state for VJ header compression */
	enum NPmode	npmode[NUM_NP];	/* what to do with each net proto 78 */
	struct sk_buff	*xmit_pending;	/* a packet ready to go out 88 */
	struct compressor *xcomp;	/* transmit packet compressor 8c */
	void		*xc_state;	/* its internal state 90 */
	struct compressor *rcomp;	/* receive decompressor 94 */
	void		*rc_state;	/* its internal state 98 */
	unsigned long	last_xmit;	/* jiffies when last pkt sent 9c */
	unsigned long	last_recv;	/* jiffies when last pkt rcvd a0 */
	struct net_device *dev;		/* network interface device a4 */
#ifdef CONFIG_PPP_MULTILINK
	int		nxchan;		/* next channel to send something on */
	u32		nxseq;		/* next sequence number to send */
	int		mrru;		/* MP: max reconst. receive unit */
	u32		nextseq;	/* MP: seq no of next packet */
	u32		minseq;		/* MP: min of most recent seqnos */
	struct sk_buff_head mrq;	/* MP: receive reconstruction queue */
#endif /* CONFIG_PPP_MULTILINK */
	struct net_device_stats stats;	/* statistics */
#ifdef CONFIG_PPP_FILTER
	struct sock_filter *pass_filter;	/* filter for packets to pass */
	struct sock_filter *active_filter;/* filter for pkts to reset idle */
	unsigned pass_len, active_len;
#endif /* CONFIG_PPP_FILTER */
};

/*
 * Bits in flags: SC_NO_TCP_CCID, SC_CCP_OPEN, SC_CCP_UP, SC_LOOP_TRAFFIC,
 * SC_MULTILINK, SC_MP_SHORTSEQ, SC_MP_XSHORTSEQ, SC_COMP_TCP, SC_REJ_COMP_TCP.
 * Bits in rstate: SC_DECOMP_RUN, SC_DC_ERROR, SC_DC_FERROR.
 * Bits in xstate: SC_COMP_RUN
 */
#define SC_FLAG_BITS	(SC_NO_TCP_CCID|SC_CCP_OPEN|SC_CCP_UP|SC_LOOP_TRAFFIC \
			 |SC_MULTILINK|SC_MP_SHORTSEQ|SC_MP_XSHORTSEQ \
			 |SC_COMP_TCP|SC_REJ_COMP_TCP)

/*
 * Private data structure for each channel.
 * This includes the data structure used for multilink.
 */
struct channel {
	struct ppp_file	file;		/* stuff for read/write/poll */
	struct list_head list;		/* link in all/new_channels list */
	struct ppp_channel *chan;	/* public channel data structure */
	struct rw_semaphore chan_sem;	/* protects `chan' during chan ioctl */
	spinlock_t	downl;		/* protects `chan', file.xq dequeue */
	struct ppp	*ppp;		/* ppp unit we're connected to */
	struct list_head clist;		/* link in list of channels per unit */
	rwlock_t	upl;		/* protects `ppp' */
#ifdef CONFIG_PPP_MULTILINK
	u8		avail;		/* flag used in multilink stuff */
	u8		had_frag;	/* >= 1 fragments have been sent */
	u32		lastseq;	/* MP: last sequence # received */
#endif /* CONFIG_PPP_MULTILINK */
};

/*
 * SMP locking issues:
 * Both the ppp.rlock and ppp.wlock locks protect the ppp.channels
 * list and the ppp.n_channels field, you need to take both locks
 * before you modify them.
 * The lock ordering is: channel.upl -> ppp.wlock -> ppp.rlock ->
 * channel.downl.
 */

/*
 * A cardmap represents a mapping from unsigned integers to pointers,
 * and provides a fast "find lowest unused number" operation.
 * It uses a broad (32-way) tree with a bitmap at each level.
 * It is designed to be space-efficient for small numbers of entries
 * and time-efficient for large numbers of entries.
 */
#define CARDMAP_ORDER	5
#define CARDMAP_WIDTH	(1U << CARDMAP_ORDER)
#define CARDMAP_MASK	(CARDMAP_WIDTH - 1)

struct cardmap {
	int shift;
	unsigned long inuse;
	struct cardmap *parent;
	void *ptr[CARDMAP_WIDTH];
};
static void *cardmap_get(struct cardmap *map, unsigned int nr);
static void cardmap_set(struct cardmap **map, unsigned int nr, void *ptr);
static unsigned int cardmap_find_first_free(struct cardmap *map);
static void cardmap_destroy(struct cardmap **map);

/*
 * all_ppp_sem protects the all_ppp_units mapping.
 * It also ensures that finding a ppp unit in the all_ppp_units map
 * and updating its file.refcnt field is atomic.
 */
static DECLARE_MUTEX(all_ppp_sem);
static struct cardmap *all_ppp_units;
static atomic_t ppp_unit_count = ATOMIC_INIT(0);

/*
 * all_channels_lock protects all_channels and last_channel_index,
 * and the atomicity of find a channel and updating its file.refcnt
 * field.
 */
static DEFINE_SPINLOCK(all_channels_lock);
static LIST_HEAD(all_channels);
static LIST_HEAD(new_channels);
static int last_channel_index;
static atomic_t channel_count = ATOMIC_INIT(0);

/* Get the PPP protocol number from a skb */
#define PPP_PROTO(skb)	(((skb)->data[0] << 8) + (skb)->data[1])

/* We limit the length of ppp->file.rq to this (arbitrary) value */
#define PPP_MAX_RQLEN	32

/*
 * Maximum number of multilink fragments queued up.
 * This has to be large enough to cope with the maximum latency of
 * the slowest channel relative to the others.  Strictly it should
 * depend on the number of channels and their characteristics.
 */
#define PPP_MP_MAX_QLEN	128

/* Multilink header bits. */
#define B	0x80		/* this fragment begins a packet */
#define E	0x40		/* this fragment ends a packet */

/* Compare multilink sequence numbers (assumed to be 32 bits wide) */
#define seq_before(a, b)	((s32)((a) - (b)) < 0)
#define seq_after(a, b)		((s32)((a) - (b)) > 0)

/* Prototypes. */
static int ppp_unattached_ioctl(struct ppp_file *pf, struct file *file,
				unsigned int cmd, unsigned long arg);
static void ppp_xmit_process(struct ppp *ppp);
static void ppp_send_frame(struct ppp *ppp, struct sk_buff *skb);
static void ppp_push(struct ppp *ppp);
static void ppp_channel_push(struct channel *pch);
static void ppp_receive_frame(struct ppp *ppp, struct sk_buff *skb,
			      struct channel *pch);
static void ppp_receive_error(struct ppp *ppp);
static void ppp_receive_nonmp_frame(struct ppp *ppp, struct sk_buff *skb);
static struct sk_buff *ppp_decompress_frame(struct ppp *ppp,
					    struct sk_buff *skb);
#ifdef CONFIG_PPP_MULTILINK
static void ppp_receive_mp_frame(struct ppp *ppp, struct sk_buff *skb,
				struct channel *pch);
static void ppp_mp_insert(struct ppp *ppp, struct sk_buff *skb);
static struct sk_buff *ppp_mp_reconstruct(struct ppp *ppp);
static int ppp_mp_explode(struct ppp *ppp, struct sk_buff *skb);
#endif /* CONFIG_PPP_MULTILINK */
static int ppp_set_compress(struct ppp *ppp, unsigned long arg);
static void ppp_ccp_peek(struct ppp *ppp, struct sk_buff *skb, int inbound);
static void ppp_ccp_closed(struct ppp *ppp);
static struct compressor *find_compressor(int type);
static void ppp_get_stats(struct ppp *ppp, struct ppp_stats *st);
static struct ppp *ppp_create_interface(int unit, int *retp);
static void init_ppp_file(struct ppp_file *pf, int kind);
static void ppp_shutdown_interface(struct ppp *ppp);
static void ppp_destroy_interface(struct ppp *ppp);
static struct ppp *ppp_find_unit(int unit);
static struct channel *ppp_find_channel(int unit);
static int ppp_connect_channel(struct channel *pch, int unit);
static int ppp_disconnect_channel(struct channel *pch);
static void ppp_destroy_channel(struct channel *pch);

static struct class *ppp_class;

/* Translates a PPP protocol number to a NP index (NP == network protocol) */
static inline int proto_to_npindex(int proto)
{
	switch (proto) {
	case PPP_IP:
		return NP_IP;
	case PPP_IPV6:
		return NP_IPV6;
	case PPP_IPX:
		return NP_IPX;
	case PPP_AT:
		return NP_AT;
	case PPP_MPLS_UC:
		return NP_MPLS_UC;
	case PPP_MPLS_MC:
		return NP_MPLS_MC;
	}
	return -EINVAL;
}

/* Translates an NP index into a PPP protocol number */
static const int npindex_to_proto[NUM_NP] = {
	PPP_IP,
	PPP_IPV6,
	PPP_IPX,
	PPP_AT,
	PPP_MPLS_UC,
	PPP_MPLS_MC,
};
	
/* Translates an ethertype into an NP index */
static inline int ethertype_to_npindex(int ethertype)
{
	switch (ethertype) {
	case ETH_P_IP:
		return NP_IP;
	case ETH_P_IPV6:
		return NP_IPV6;
	case ETH_P_IPX:
		return NP_IPX;
	case ETH_P_PPPTALK:
	case ETH_P_ATALK:
		return NP_AT;
	case ETH_P_MPLS_UC:
		return NP_MPLS_UC;
	case ETH_P_MPLS_MC:
		return NP_MPLS_MC;
	}
	return -1;
}

/* Translates an NP index into an ethertype */
static const int npindex_to_ethertype[NUM_NP] = {
	ETH_P_IP,
	ETH_P_IPV6,
	ETH_P_IPX,
	ETH_P_PPPTALK,
	ETH_P_MPLS_UC,
	ETH_P_MPLS_MC,
};

/*
 * Locking shorthand.
 */
#define ppp_xmit_lock(ppp)	spin_lock_bh(&(ppp)->wlock)
#define ppp_xmit_unlock(ppp)	spin_unlock_bh(&(ppp)->wlock)
#define ppp_recv_lock(ppp)	spin_lock_bh(&(ppp)->rlock)
#define ppp_recv_unlock(ppp)	spin_unlock_bh(&(ppp)->rlock)
#define ppp_lock(ppp)		do { ppp_xmit_lock(ppp); \
				     ppp_recv_lock(ppp); } while (0)
#define ppp_unlock(ppp)		do { ppp_recv_unlock(ppp); \
				     ppp_xmit_unlock(ppp); } while (0)

/*
 * /dev/ppp device routines.
 * The /dev/ppp device is used by pppd to control the ppp unit.
 * It supports the read, write, ioctl and poll functions.
 * Open instances of /dev/ppp can be in one of three states:
 * unattached, attached to a ppp unit, or attached to a ppp channel.
 */
static int ppp_open(struct inode *inode, struct file *file)
{
	/*
	 * This could (should?) be enforced by the permissions on /dev/ppp.
	 */
	if (!capable(CAP_NET_ADMIN))
		return -EPERM;
	return 0;
}

static int ppp_release(struct inode *inode, struct file *file)
{
	struct ppp_file *pf = file->private_data;
	struct ppp *ppp;

	if (pf != 0) {
		file->private_data = NULL;
		if (pf->kind == INTERFACE) {
			ppp = PF_TO_PPP(pf);
			if (file == ppp->owner)
				ppp_shutdown_interface(ppp);
		}
		if (atomic_dec_and_test(&pf->refcnt)) {
			switch (pf->kind) {
			case INTERFACE:
				ppp_destroy_interface(PF_TO_PPP(pf));
				break;
			case CHANNEL:
				ppp_destroy_channel(PF_TO_CHANNEL(pf));
				break;
			}
		}
	}
	return 0;
}

static ssize_t ppp_read(struct file *file, char __user *buf,
			size_t count, loff_t *ppos)
{
	struct ppp_file *pf = file->private_data;
	DECLARE_WAITQUEUE(wait, current);
	ssize_t ret;
	struct sk_buff *skb = NULL;

	ret = count;

	if (pf == 0)
		return -ENXIO;
	add_wait_queue(&pf->rwait, &wait);
	for (;;) {
		set_current_state(TASK_INTERRUPTIBLE);
		skb = skb_dequeue(&pf->rq);
		if (skb)
			break;
		ret = 0;
		if (pf->dead)
			break;
		if (pf->kind == INTERFACE) {
			/*
			 * Return 0 (EOF) on an interface that has no
			 * channels connected, unless it is looping
			 * network traffic (demand mode).
			 */
			struct ppp *ppp = PF_TO_PPP(pf);
			if (ppp->n_channels == 0
			    && (ppp->flags & SC_LOOP_TRAFFIC) == 0)
				break;
		}
		ret = -EAGAIN;
		if (file->f_flags & O_NONBLOCK)
			break;
		ret = -ERESTARTSYS;
		if (signal_pending(current))
			break;
		schedule();
	}
	set_current_state(TASK_RUNNING);
	remove_wait_queue(&pf->rwait, &wait);

	if (skb == 0)
		goto out;

	ret = -EOVERFLOW;
	if (skb->len > count)
		goto outf;
	ret = -EFAULT;
	if (copy_to_user(buf, skb->data, skb->len))
		goto outf;
	ret = skb->len;

 outf:
	kfree_skb(skb);
 out:
	return ret;
}

static ssize_t ppp_write(struct file *file, const char __user *buf,
			 size_t count, loff_t *ppos)
{
	struct ppp_file *pf = file->private_data;
	struct sk_buff *skb;
	ssize_t ret;

	if (pf == 0)
		return -ENXIO;
	ret = -ENOMEM;
	skb = alloc_skb(count + pf->hdrlen, GFP_KERNEL);
	if (skb == 0)
		goto out;
	skb_reserve(skb, pf->hdrlen);
	ret = -EFAULT;
	if (copy_from_user(skb_put(skb, count), buf, count)) {
		kfree_skb(skb);
		goto out;
	}

	skb_queue_tail(&pf->xq, skb);

	switch (pf->kind) {
	case INTERFACE:
		ppp_xmit_process(PF_TO_PPP(pf));
		break;
	case CHANNEL:
		ppp_channel_push(PF_TO_CHANNEL(pf));
		break;
	}

	ret = count;

 out:
	return ret;
}

/* No kernel lock - fine */
static unsigned int ppp_poll(struct file *file, poll_table *wait)
{
	struct ppp_file *pf = file->private_data;
	unsigned int mask;

	if (pf == 0)
		return 0;
	poll_wait(file, &pf->rwait, wait);
	mask = POLLOUT | POLLWRNORM;
	if (skb_peek(&pf->rq) != 0)
		mask |= POLLIN | POLLRDNORM;
	if (pf->dead)
		mask |= POLLHUP;
	else if (pf->kind == INTERFACE) {
		/* see comment in ppp_read */
		struct ppp *ppp = PF_TO_PPP(pf);
		if (ppp->n_channels == 0
		    && (ppp->flags & SC_LOOP_TRAFFIC) == 0)
			mask |= POLLIN | POLLRDNORM;
	}

	return mask;
}

#ifdef CONFIG_PPP_FILTER
static int get_filter(void __user *arg, struct sock_filter **p)
{
	struct sock_fprog uprog;
	struct sock_filter *code = NULL;
	int len, err;

	if (copy_from_user(&uprog, arg, sizeof(uprog)))
		return -EFAULT;

	if (uprog.len > BPF_MAXINSNS)
		return -EINVAL;

	if (!uprog.len) {
		*p = NULL;
		return 0;
	}

	len = uprog.len * sizeof(struct sock_filter);
	code = kmalloc(len, GFP_KERNEL);
	if (code == NULL)
		return -ENOMEM;

	if (copy_from_user(code, uprog.filter, len)) {
		kfree(code);
		return -EFAULT;
	}

	err = sk_chk_filter(code, uprog.len);
	if (err) {
		kfree(code);
		return err;
	}

	*p = code;
	return uprog.len;
}
#endif /* CONFIG_PPP_FILTER */

static int ppp_ioctl(struct inode *inode, struct file *file,
		     unsigned int cmd, unsigned long arg)
{
	struct ppp_file *pf = file->private_data;
	struct ppp *ppp;
	int err = -EFAULT, val, val2, i;
	struct ppp_idle idle;
	struct npioctl npi;
	int unit, cflags;
	struct slcompress *vj;
	void __user *argp = (void __user *)arg;
	int __user *p = argp;

	if (pf == 0)
		return ppp_unattached_ioctl(pf, file, cmd, arg);

	if (cmd == PPPIOCDETACH) {
		/*
		 * We have to be careful here... if the file descriptor
		 * has been dup'd, we could have another process in the
		 * middle of a poll using the same file *, so we had
		 * better not free the interface data structures -
		 * instead we fail the ioctl.  Even in this case, we
		 * shut down the interface if we are the owner of it.
		 * Actually, we should get rid of PPPIOCDETACH, userland
		 * (i.e. pppd) could achieve the same effect by closing
		 * this fd and reopening /dev/ppp.
		 */
		err = -EINVAL;
		if (pf->kind == INTERFACE) {
			ppp = PF_TO_PPP(pf);
			if (file == ppp->owner)
				ppp_shutdown_interface(ppp);
		}
		if (atomic_read(&file->f_count) <= 2) {
			ppp_release(inode, file);
			err = 0;
		} else
			printk(KERN_DEBUG "PPPIOCDETACH file->f_count=%d\n",
			       atomic_read(&file->f_count));
		return err;
	}

	if (pf->kind == CHANNEL) {
		struct channel *pch = PF_TO_CHANNEL(pf);
		struct ppp_channel *chan;

		switch (cmd) {
		case PPPIOCCONNECT:
			if (get_user(unit, p))
				break;
			err = ppp_connect_channel(pch, unit);
			break;

		case PPPIOCDISCONN:
			err = ppp_disconnect_channel(pch);
			break;

		default:
			down_read(&pch->chan_sem);
			chan = pch->chan;
			err = -ENOTTY;
			if (chan && chan->ops->ioctl)
				err = chan->ops->ioctl(chan, cmd, arg);
			up_read(&pch->chan_sem);
		}
		return err;
	}

	if (pf->kind != INTERFACE) {
		/* can't happen */
		printk(KERN_ERR "PPP: not interface or channel??\n");
		return -EINVAL;
	}

	ppp = PF_TO_PPP(pf);
	switch (cmd) {
	case PPPIOCSMRU:
		if (get_user(val, p))
			break;
		ppp->mru = val;
		err = 0;
		break;

	case PPPIOCSFLAGS:
		if (get_user(val, p))
			break;
		ppp_lock(ppp);
		cflags = ppp->flags & ~val;
		ppp->flags = val & SC_FLAG_BITS;
		ppp_unlock(ppp);
		if (cflags & SC_CCP_OPEN)
			ppp_ccp_closed(ppp);
		err = 0;
		break;

	case PPPIOCGFLAGS:
		val = ppp->flags | ppp->xstate | ppp->rstate;
		if (put_user(val, p))
			break;
		err = 0;
		break;

	case PPPIOCSCOMPRESS:
		err = ppp_set_compress(ppp, arg);
		break;

	case PPPIOCGUNIT:
		if (put_user(ppp->file.index, p))
			break;
		err = 0;
		break;

	case PPPIOCSDEBUG:
		if (get_user(val, p))
			break;
		ppp->debug = val;
		err = 0;
		break;

	case PPPIOCGDEBUG:
		if (put_user(ppp->debug, p))
			break;
		err = 0;
		break;

	case PPPIOCGIDLE:
		idle.xmit_idle = (jiffies - ppp->last_xmit) / HZ;
		idle.recv_idle = (jiffies - ppp->last_recv) / HZ;
		if (copy_to_user(argp, &idle, sizeof(idle)))
			break;
		err = 0;
		break;

	case PPPIOCSMAXCID:
		if (get_user(val, p))
			break;
		val2 = 15;
		if ((val >> 16) != 0) {
			val2 = val >> 16;
			val &= 0xffff;
		}
		vj = slhc_init(val2+1, val+1);
		if (vj == 0) {
			printk(KERN_ERR "PPP: no memory (VJ compressor)\n");
			err = -ENOMEM;
			break;
		}
		ppp_lock(ppp);
		if (ppp->vj != 0)
			slhc_free(ppp->vj);
		ppp->vj = vj;
		ppp_unlock(ppp);
		err = 0;
		break;

	case PPPIOCGNPMODE:
	case PPPIOCSNPMODE:
		if (copy_from_user(&npi, argp, sizeof(npi)))
			break;
		err = proto_to_npindex(npi.protocol);
		if (err < 0)
			break;
		i = err;
		if (cmd == PPPIOCGNPMODE) {
			err = -EFAULT;
			npi.mode = ppp->npmode[i];
			if (copy_to_user(argp, &npi, sizeof(npi)))
				break;
		} else {
			ppp->npmode[i] = npi.mode;
			/* we may be able to transmit more packets now (??) */
			netif_wake_queue(ppp->dev);
		}
		err = 0;
		break;

#ifdef CONFIG_PPP_FILTER
	case PPPIOCSPASS:
	{
		struct sock_filter *code;
		err = get_filter(argp, &code);
		if (err >= 0) {
			ppp_lock(ppp);
			kfree(ppp->pass_filter);
			ppp->pass_filter = code;
			ppp->pass_len = err;
			ppp_unlock(ppp);
			err = 0;
		}
		break;
	}
	case PPPIOCSACTIVE:
	{
		struct sock_filter *code;
		err = get_filter(argp, &code);
		if (err >= 0) {
			ppp_lock(ppp);
			kfree(ppp->active_filter);
			ppp->active_filter = code;
			ppp->active_len = err;
			ppp_unlock(ppp);
			err = 0;
		}
		break;
	}
#endif /* CONFIG_PPP_FILTER */

#ifdef CONFIG_PPP_MULTILINK
	case PPPIOCSMRRU:
		if (get_user(val, p))
			break;
		ppp_recv_lock(ppp);
		ppp->mrru = val;
		ppp_recv_unlock(ppp);
		err = 0;
		break;
#endif /* CONFIG_PPP_MULTILINK */

	default:
		err = -ENOTTY;
	}

	return err;
}

static int ppp_unattached_ioctl(struct ppp_file *pf, struct file *file,
				unsigned int cmd, unsigned long arg)
{
	int unit, err = -EFAULT;
	struct ppp *ppp;
	struct channel *chan;
	int __user *p = (int __user *)arg;

	switch (cmd) {
	case PPPIOCNEWUNIT:
		/* Create a new ppp unit */
		if (get_user(unit, p))
			break;
		ppp = ppp_create_interface(unit, &err);
		if (ppp == 0)
			break;
		file->private_data = &ppp->file;
		ppp->owner = file;
		err = -EFAULT;
		if (put_user(ppp->file.index, p))
			break;
		err = 0;
		break;

	case PPPIOCATTACH:
		/* Attach to an existing ppp unit */
		if (get_user(unit, p))
			break;
		down(&all_ppp_sem);
		err = -ENXIO;
		ppp = ppp_find_unit(unit);
		if (ppp != 0) {
			atomic_inc(&ppp->file.refcnt);
			file->private_data = &ppp->file;
			err = 0;
		}
		up(&all_ppp_sem);
		break;

	case PPPIOCATTCHAN:
		if (get_user(unit, p))
			break;
		spin_lock_bh(&all_channels_lock);
		err = -ENXIO;
		chan = ppp_find_channel(unit);
		if (chan != 0) {
			atomic_inc(&chan->file.refcnt);
			file->private_data = &chan->file;
			err = 0;
		}
		spin_unlock_bh(&all_channels_lock);
		break;

	default:
		err = -ENOTTY;
	}
	return err;
}

static struct file_operations ppp_device_fops = {
	.owner		= THIS_MODULE,
	.read		= ppp_read,
	.write		= ppp_write,
	.poll		= ppp_poll,
	.ioctl		= ppp_ioctl,
	.open		= ppp_open,
	.release	= ppp_release
};

#define PPP_MAJOR	108

/* Called at boot time if ppp is compiled into the kernel,
   or at module load time (from init_module) if compiled as a module. */
static int __init ppp_init(void)
{
	int err;

	printk(KERN_INFO "PPP generic driver version " PPP_VERSION "\n");
	err = register_chrdev(PPP_MAJOR, "ppp", &ppp_device_fops);
	if (!err) {
		ppp_class = class_create(THIS_MODULE, "ppp");
		if (IS_ERR(ppp_class)) {
			err = PTR_ERR(ppp_class);
			goto out_chrdev;
		}
		class_device_create(ppp_class, NULL, MKDEV(PPP_MAJOR, 0), NULL, "ppp");
		err = devfs_mk_cdev(MKDEV(PPP_MAJOR, 0),
				S_IFCHR|S_IRUSR|S_IWUSR, "ppp");
		if (err)
			goto out_class;
	}

out:
	if (err)
		printk(KERN_ERR "failed to register PPP device (%d)\n", err);
	return err;

out_class:
	class_device_destroy(ppp_class, MKDEV(PPP_MAJOR,0));
	class_destroy(ppp_class);
out_chrdev:
	unregister_chrdev(PPP_MAJOR, "ppp");
	goto out;
}

/*
 * Network interface unit routines.
 */
static int
ppp_start_xmit(struct sk_buff *skb, struct net_device *dev)
{
	struct ppp *ppp = (struct ppp *) dev->priv;
	int npi, proto;
	unsigned char *pp;

	npi = ethertype_to_npindex(ntohs(skb->protocol));
	if (npi < 0)
		goto outf;

	/* Drop, accept or reject the packet */
	switch (ppp->npmode[npi]) {
	case NPMODE_PASS:
		break;
	case NPMODE_QUEUE:
		/* it would be nice to have a way to tell the network
		   system to queue this one up for later. */
		goto outf;
	case NPMODE_DROP:
	case NPMODE_ERROR:
		goto outf;
	}

	/* Put the 2-byte PPP protocol number on the front,
	   making sure there is room for the address and control fields. */
	if (skb_headroom(skb) < PPP_HDRLEN) {
		struct sk_buff *ns;

		ns = alloc_skb(skb->len + dev->hard_header_len, GFP_ATOMIC);
		if (ns == 0)
			goto outf;
		skb_reserve(ns, dev->hard_header_len);
		skb_copy_bits(skb, 0, skb_put(ns, skb->len), skb->len);
		kfree_skb(skb);
		skb = ns;
	}
	pp = skb_push(skb, 2);
	proto = npindex_to_proto[npi];
	pp[0] = proto >> 8;
	pp[1] = proto;

	netif_stop_queue(dev);
	skb_queue_tail(&ppp->file.xq, skb);
	ppp_xmit_process(ppp);
	return 0;

 outf:
	kfree_skb(skb);
	++ppp->stats.tx_dropped;
	return 0;
}

static struct net_device_stats *
ppp_net_stats(struct net_device *dev)
{
	struct ppp *ppp = (struct ppp *) dev->priv;

	return &ppp->stats;
}

static int
ppp_net_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
{
	struct ppp *ppp = dev->priv;
	int err = -EFAULT;
	void __user *addr = (void __user *) ifr->ifr_ifru.ifru_data;
	struct ppp_stats stats;
	struct ppp_comp_stats cstats;
	char *vers;

	switch (cmd) {
	case SIOCGPPPSTATS:
		ppp_get_stats(ppp, &stats);
		if (copy_to_user(addr, &stats, sizeof(stats)))
			break;
		err = 0;
		break;

	case SIOCGPPPCSTATS:
		memset(&cstats, 0, sizeof(cstats));
		if (ppp->xc_state != 0)
			ppp->xcomp->comp_stat(ppp->xc_state, &cstats.c);
		if (ppp->rc_state != 0)
			ppp->rcomp->decomp_stat(ppp->rc_state, &cstats.d);
		if (copy_to_user(addr, &cstats, sizeof(cstats)))
			break;
		err = 0;
		break;

	case SIOCGPPPVER:
		vers = PPP_VERSION;
		if (copy_to_user(addr, vers, strlen(vers) + 1))
			break;
		err = 0;
		break;

	default:
		err = -EINVAL;
	}

	return err;
}

static void ppp_setup(struct net_device *dev)
{
	dev->hard_header_len = PPP_HDRLEN;
	dev->mtu = PPP_MTU;
	dev->addr_len = 0;
	dev->tx_queue_len = 3;
	dev->type = ARPHRD_PPP;
	dev->flags = IFF_POINTOPOINT | IFF_NOARP | IFF_MULTICAST;
}

/*
 * Transmit-side routines.
 */

/*
 * Called to do any work queued up on the transmit side
 * that can now be done.
 */
static void
ppp_xmit_process(struct ppp *ppp)
{
	struct sk_buff *skb;

	ppp_xmit_lock(ppp);
	if (ppp->dev != 0) {
		ppp_push(ppp);
		while (ppp->xmit_pending == 0
		       && (skb = skb_dequeue(&ppp->file.xq)) != 0)
			ppp_send_frame(ppp, skb);
		/* If there's no work left to do, tell the core net
		   code that we can accept some more. */
		if (ppp->xmit_pending == 0 && skb_peek(&ppp->file.xq) == 0)
			netif_wake_queue(ppp->dev);
	}
	ppp_xmit_unlock(ppp);
}

/*
 * Compress and send a frame.
 * The caller should have locked the xmit path,
 * and xmit_pending should be 0.
 */
static void
ppp_send_frame(struct ppp *ppp, struct sk_buff *skb)
{
	int proto = PPP_PROTO(skb);
	struct sk_buff *new_skb;
	int len;
	unsigned char *cp;

	if (proto < 0x8000) {
#ifdef CONFIG_PPP_FILTER
		/* check if we should pass this packet */
		/* the filter instructions are constructed assuming
		   a four-byte PPP header on each packet */
		*skb_push(skb, 2) = 1;
		if (ppp->pass_filter
		    && sk_run_filter(skb, ppp->pass_filter,
				     ppp->pass_len) == 0) {
			if (ppp->debug & 1)
				printk(KERN_DEBUG "PPP: outbound frame not passed\n");
			kfree_skb(skb);
			return;
		}
		/* if this packet passes the active filter, record the time */
		if (!(ppp->active_filter
		      && sk_run_filter(skb, ppp->active_filter,
				       ppp->active_len) == 0))
			ppp->last_xmit = jiffies;
		skb_pull(skb, 2);
#else
		/* for data packets, record the time */
		ppp->last_xmit = jiffies;
#endif /* CONFIG_PPP_FILTER */
	}

	++ppp->stats.tx_packets;
	ppp->stats.tx_bytes += skb->len - 2;

	switch (proto) {
	case PPP_IP:
		if (ppp->vj == 0 || (ppp->flags & SC_COMP_TCP) == 0)
			break;
		/* try to do VJ TCP header compression */
		new_skb = alloc_skb(skb->len + ppp->dev->hard_header_len - 2,
				    GFP_ATOMIC);
		if (new_skb == 0) {
			printk(KERN_ERR "PPP: no memory (VJ comp pkt)\n");
			goto drop;
		}
		skb_reserve(new_skb, ppp->dev->hard_header_len - 2);
		cp = skb->data + 2;
		len = slhc_compress(ppp->vj, cp, skb->len - 2,
				    new_skb->data + 2, &cp,
				    !(ppp->flags & SC_NO_TCP_CCID));
		if (cp == skb->data + 2) {
			/* didn't compress */
			kfree_skb(new_skb);
		} else {
			if (cp[0] & SL_TYPE_COMPRESSED_TCP) {
				proto = PPP_VJC_COMP;
				cp[0] &= ~SL_TYPE_COMPRESSED_TCP;
			} else {
				proto = PPP_VJC_UNCOMP;
				cp[0] = skb->data[2];
			}
			kfree_skb(skb);
			skb = new_skb;
			cp = skb_put(skb, len + 2);
			cp[0] = 0;
			cp[1] = proto;
		}
		break;

	case PPP_CCP:
		/* peek at outbound CCP frames */
		ppp_ccp_peek(ppp, skb, 0);
		break;
	}

	/* try to do packet compression */
	if ((ppp->xstate & SC_COMP_RUN) && ppp->xc_state != 0
	    && proto != PPP_LCP && proto != PPP_CCP) {
		new_skb = alloc_skb(ppp->dev->mtu + ppp->dev->hard_header_len,
				    GFP_ATOMIC);
		if (new_skb == 0) {
			printk(KERN_ERR "PPP: no memory (comp pkt)\n");
			goto drop;
		}
		if (ppp->dev->hard_header_len > PPP_HDRLEN)
			skb_reserve(new_skb,
				    ppp->dev->hard_header_len - PPP_HDRLEN);

		/* compressor still expects A/C bytes in hdr */
		len = ppp->xcomp->compress(ppp->xc_state, skb->data - 2,
					   new_skb->data, skb->len + 2,
					   ppp->dev->mtu + PPP_HDRLEN);
		if (len > 0 && (ppp->flags & SC_CCP_UP)) {
			kfree_skb(skb);
			skb = new_skb;
			skb_put(skb, len);
			skb_pull(skb, 2);	/* pull off A/C bytes */
		} else {
			/* didn't compress, or CCP not up yet */
			kfree_skb(new_skb);
		}
	}

	/*
	 * If we are waiting for traffic (demand dialling),
	 * queue it up for pppd to receive.
	 */
	if (ppp->flags & SC_LOOP_TRAFFIC) {
		if (ppp->file.rq.qlen > PPP_MAX_RQLEN)
			goto drop;
		skb_queue_tail(&ppp->file.rq, skb);
		wake_up_interruptible(&ppp->file.rwait);
		return;
	}

	ppp->xmit_pending = skb;
	ppp_push(ppp);
	return;

 drop:
	kfree_skb(skb);
	++ppp->stats.tx_errors;
}

/*
 * Try to send the frame in xmit_pending.
 * The caller should have the xmit path locked.
 */
static void
ppp_push(struct ppp *ppp)
{
	struct list_head *list;
	struct channel *pch;
	struct sk_buff *skb = ppp->xmit_pending;

	if (skb == 0)
		return;

	list = &ppp->channels;
	if (list_empty(list)) {
		/* nowhere to send the packet, just drop it */
		ppp->xmit_pending = NULL;
		kfree_skb(skb);
		return;
	}

	if ((ppp->flags & SC_MULTILINK) == 0) {
		/* not doing multilink: send it down the first channel */
		list = list->next;
		pch = list_entry(list, struct channel, clist);

		spin_lock_bh(&pch->downl);
		if (pch->chan) {
			if (pch->chan->ops->start_xmit(pch->chan, skb))
				ppp->xmit_pending = NULL;
		} else {
			/* channel got unregistered */
			kfree_skb(skb);
			ppp->xmit_pending = NULL;
		}
		spin_unlock_bh(&pch->downl);
		return;
	}

#ifdef CONFIG_PPP_MULTILINK
	/* Multilink: fragment the packet over as many links
	   as can take the packet at the moment. */
	if (!ppp_mp_explode(ppp, skb))
		return;
#endif /* CONFIG_PPP_MULTILINK */

	ppp->xmit_pending = NULL;
	kfree_skb(skb);
}

#ifdef CONFIG_PPP_MULTILINK
/*
 * Divide a packet to be transmitted into fragments and
 * send them out the individual links.
 */
static int ppp_mp_explode(struct ppp *ppp, struct sk_buff *skb)
{
	int len, fragsize;
	int i, bits, hdrlen, mtu;
	int flen;
	int navail, nfree;
	int nbigger;
	unsigned char *p, *q;
	struct list_head *list;
	struct channel *pch;
	struct sk_buff *frag;
	struct ppp_channel *chan;

	nfree = 0;	/* # channels which have no packet already queued */
	navail = 0;	/* total # of usable channels (not deregistered) */
	hdrlen = (ppp->flags & SC_MP_XSHORTSEQ)? MPHDRLEN_SSN: MPHDRLEN;
	i = 0;
	list_for_each_entry(pch, &ppp->channels, clist) {
		navail += pch->avail = (pch->chan != NULL);
		if (pch->avail) {
			if (skb_queue_empty(&pch->file.xq) ||
			    !pch->had_frag) {
				pch->avail = 2;
				++nfree;
			}
			if (!pch->had_frag && i < ppp->nxchan)
				ppp->nxchan = i;
		}
		++i;
	}

	/*
	 * Don't start sending this packet unless at least half of
	 * the channels are free.  This gives much better TCP
	 * performance if we have a lot of channels.
	 */
	if (nfree == 0 || nfree < navail / 2)
		return 0;	/* can't take now, leave it in xmit_pending */

	/* Do protocol field compression (XXX this should be optional) */
	p = skb->data;
	len = skb->len;
	if (*p == 0) {
		++p;
		--len;
	}

	/*
	 * Decide on fragment size.
	 * We create a fragment for each free channel regardless of
	 * how small they are (i.e. even 0 length) in order to minimize
	 * the time that it will take to detect when a channel drops
	 * a fragment.
	 */
	fragsize = len;
	if (nfree > 1)
		fragsize = ROUNDUP(fragsize, nfree);
	/* nbigger channels get fragsize bytes, the rest get fragsize-1,
	   except if nbigger==0, then they all get fragsize. */
	nbigger = len % nfree;

	/* skip to the channel after the one we last used
	   and start at that one */
	list = &ppp->channels;
	for (i = 0; i < ppp->nxchan; ++i) {
		list = list->next;
		if (list == &ppp->channels) {
			i = 0;
			break;
		}
	}

	/* create a fragment for each channel */
	bits = B;
	while (nfree > 0 || len > 0) {
		list = list->next;
		if (list == &ppp->channels) {
			i = 0;
			continue;
		}
		pch = list_entry(list, struct channel, clist);
		++i;
		if (!pch->avail)
			continue;

		/*
		 * Skip this channel if it has a fragment pending already and
		 * we haven't given a fragment to all of the free channels.
		 */
		if (pch->avail == 1) {
			if (nfree > 0)
				continue;
		} else {
			--nfree;
			pch->avail = 1;
		}

		/* check the channel's mtu and whether it is still attached. */
		spin_lock_bh(&pch->downl);
		if (pch->chan == NULL) {
			/* can't use this channel, it's being deregistered */
			spin_unlock_bh(&pch->downl);
			pch->avail = 0;
			if (--navail == 0)
				break;
			continue;
		}

		/*
		 * Create a fragment for this channel of
		 * min(max(mtu+2-hdrlen, 4), fragsize, len) bytes.
		 * If mtu+2-hdrlen < 4, that is a ridiculously small
		 * MTU, so we use mtu = 2 + hdrlen.
		 */
		if (fragsize > len)
			fragsize = len;
		flen = fragsize;
		mtu = pch->chan->mtu + 2 - hdrlen;
		if (mtu < 4)
			mtu = 4;
		if (flen > mtu)
			flen = mtu;
		if (flen == len && nfree == 0)
			bits |= E;
		frag = alloc_skb(flen + hdrlen + (flen == 0), GFP_ATOMIC);
		if (frag == 0)
			goto noskb;
		q = skb_put(frag, flen + hdrlen);

		/* make the MP header */
		q[0] = PPP_MP >> 8;
		q[1] = PPP_MP;
		if (ppp->flags & SC_MP_XSHORTSEQ) {
			q[2] = bits + ((ppp->nxseq >> 8) & 0xf);
			q[3] = ppp->nxseq;
		} else {
			q[2] = bits;
			q[3] = ppp->nxseq >> 16;
			q[4] = ppp->nxseq >> 8;
			q[5] = ppp->nxseq;
		}

		/*
		 * Copy the data in.
		 * Unfortunately there is a bug in older versions of
		 * the Linux PPP multilink reconstruction code where it
		 * drops 0-length fragments.  Therefore we make sure the
		 * fragment has at least one byte of data.  Any bytes
		 * we add in this situation will end up as padding on the
		 * end of the reconstructed packet.
		 */
		if (flen == 0)
			*skb_put(frag, 1) = 0;
		else
			memcpy(q + hdrlen, p, flen);

		/* try to send it down the channel */
		chan = pch->chan;
		if (!skb_queue_empty(&pch->file.xq) ||
		    !chan->ops->start_xmit(chan, frag))
			skb_queue_tail(&pch->file.xq, frag);
		pch->had_frag = 1;
		p += flen;
		len -= flen;
		++ppp->nxseq;
		bits = 0;
		spin_unlock_bh(&pch->downl);

		if (--nbigger == 0 && fragsize > 0)
			--fragsize;
	}
	ppp->nxchan = i;

	return 1;

 noskb:
	spin_unlock_bh(&pch->downl);
	if (ppp->debug & 1)
		printk(KERN_ERR "PPP: no memory (fragment)\n");
	++ppp->stats.tx_errors;
	++ppp->nxseq;
	return 1;	/* abandon the frame */
}
#endif /* CONFIG_PPP_MULTILINK */

/*
 * Try to send data out on a channel.
 */
static void
ppp_channel_push(struct channel *pch)
{
	struct sk_buff *skb;
	struct ppp *ppp;

	spin_lock_bh(&pch->downl);
	if (pch->chan != 0) {
		while (!skb_queue_empty(&pch->file.xq)) {
			skb = skb_dequeue(&pch->file.xq);
			if (!pch->chan->ops->start_xmit(pch->chan, skb)) {
				/* put the packet back and try again later */
				skb_queue_head(&pch->file.xq, skb);
				break;
			}
		}
	} else {
		/* channel got deregistered */
		skb_queue_purge(&pch->file.xq);
	}
	spin_unlock_bh(&pch->downl);
	/* see if there is anything from the attached unit to be sent */
	if (skb_queue_empty(&pch->file.xq)) {
		read_lock_bh(&pch->upl);
		ppp = pch->ppp;
		if (ppp != 0)
			ppp_xmit_process(ppp);
		read_unlock_bh(&pch->upl);
	}
}

/*
 * Receive-side routines.
 */

/* misuse a few fields of the skb for MP reconstruction */
#define sequence	priority
#define BEbits		cb[0]

static inline void
ppp_do_recv(struct ppp *ppp, struct sk_buff *skb, struct channel *pch)
{
	ppp_recv_lock(ppp);
	/* ppp->dev == 0 means interface is closing down */
	if (ppp->dev != 0)
		ppp_receive_frame(ppp, skb, pch);
	else
		kfree_skb(skb);
	ppp_recv_unlock(ppp);
}

void
ppp_input(struct ppp_channel *chan, struct sk_buff *skb)
{
	struct channel *pch = chan->ppp;
	int proto;

	if (pch == 0 || skb->len == 0) {
		kfree_skb(skb);
		return;
	}

	proto = PPP_PROTO(skb);
	read_lock_bh(&pch->upl);
	if (pch->ppp == 0 || proto >= 0xc000 || proto == PPP_CCPFRAG) {
		/* put it on the channel queue */
		skb_queue_tail(&pch->file.rq, skb);
		/* drop old frames if queue too long */
		while (pch->file.rq.qlen > PPP_MAX_RQLEN
		       && (skb = skb_dequeue(&pch->file.rq)) != 0)
			kfree_skb(skb);
		wake_up_interruptible(&pch->file.rwait);
	} else {
		ppp_do_recv(pch->ppp, skb, pch);
	}
	read_unlock_bh(&pch->upl);
}

/* Put a 0-length skb in the receive queue as an error indication */
void
ppp_input_error(struct ppp_channel *chan, int code)
{
	struct channel *pch = chan->ppp;
	struct sk_buff *skb;

	if (pch == 0)
		return;

	read_lock_bh(&pch->upl);
	if (pch->ppp != 0) {
		skb = alloc_skb(0, GFP_ATOMIC);
		if (skb != 0) {
			skb->len = 0;		/* probably unnecessary */
			skb->cb[0] = code;
			ppp_do_recv(pch->ppp, skb, pch);
		}
	}
	read_unlock_bh(&pch->upl);
}

/*
 * We come in here to process a received frame.
 * The receive side of the ppp unit is locked.
 */
static void
ppp_receive_frame(struct ppp *ppp, struct sk_buff *skb, struct channel *pch)
{
	if (skb->len >= 2) {
#ifdef CONFIG_PPP_MULTILINK
		/* XXX do channel-level decompression here */
		if (PPP_PROTO(skb) == PPP_MP)
			ppp_receive_mp_frame(ppp, skb, pch);
		else
#endif /* CONFIG_PPP_MULTILINK */
			ppp_receive_nonmp_frame(ppp, skb);
		return;
	}

	if (skb->len > 0)
		/* note: a 0-length skb is used as an error indication */
		++ppp->stats.rx_length_errors;

	kfree_skb(skb);
	ppp_receive_error(ppp);
}

static void
ppp_receive_error(struct ppp *ppp)
{
	++ppp->stats.rx_errors;
	if (ppp->vj != 0)
		slhc_toss(ppp->vj);
}

static void
ppp_receive_nonmp_frame(struct ppp *ppp, struct sk_buff *skb)
{
	struct sk_buff *ns;
	int proto, len, npi;

	/*
	 * Decompress the frame, if compressed.
	 * Note that some decompressors need to see uncompressed frames
	 * that come in as well as compressed frames.
	 */
	if (ppp->rc_state != 0 && (ppp->rstate & SC_DECOMP_RUN)
	    && (ppp->rstate & (SC_DC_FERROR | SC_DC_ERROR)) == 0)
		skb = ppp_decompress_frame(ppp, skb);

	proto = PPP_PROTO(skb);
	switch (proto) {
	case PPP_VJC_COMP:
		/* decompress VJ compressed packets */
		if (ppp->vj == 0 || (ppp->flags & SC_REJ_COMP_TCP))
			goto err;

		if (skb_tailroom(skb) < 124) {
			/* copy to a new sk_buff with more tailroom */
			ns = dev_alloc_skb(skb->len + 128);
			if (ns == 0) {
				printk(KERN_ERR"PPP: no memory (VJ decomp)\n");
				goto err;
			}
			skb_reserve(ns, 2);
			skb_copy_bits(skb, 0, skb_put(ns, skb->len), skb->len);
			kfree_skb(skb);
			skb = ns;
		}
		else if (!pskb_may_pull(skb, skb->len))
			goto err;

		len = slhc_uncompress(ppp->vj, skb->data + 2, skb->len - 2);
		if (len <= 0) {
			printk(KERN_DEBUG "PPP: VJ decompression error\n");
			goto err;
		}
		len += 2;
		if (len > skb->len)
			skb_put(skb, len - skb->len);
		else if (len < skb->len)
			skb_trim(skb, len);
		proto = PPP_IP;
		break;

	case PPP_VJC_UNCOMP:
		if (ppp->vj == 0 || (ppp->flags & SC_REJ_COMP_TCP))
			goto err;
		
		/* Until we fix the decompressor need to make sure
		 * data portion is linear.
		 */
		if (!pskb_may_pull(skb, skb->len)) 
			goto err;

		if (slhc_remember(ppp->vj, skb->data + 2, skb->len - 2) <= 0) {
			printk(KERN_ERR "PPP: VJ uncompressed error\n");
			goto err;
		}
		proto = PPP_IP;
		break;

	case PPP_CCP:
		ppp_ccp_peek(ppp, skb, 1);
		break;
	}

	++ppp->stats.rx_packets;
	ppp->stats.rx_bytes += skb->len - 2;

	npi = proto_to_npindex(proto);
	if (npi < 0) {
		/* control or unknown frame - pass it to pppd */
		skb_queue_tail(&ppp->file.rq, skb);
		/* limit queue length by dropping old frames */
		while (ppp->file.rq.qlen > PPP_MAX_RQLEN
		       && (skb = skb_dequeue(&ppp->file.rq)) != 0)
			kfree_skb(skb);
		/* wake up any process polling or blocking on read */
		wake_up_interruptible(&ppp->file.rwait);

	} else {
		/* network protocol frame - give it to the kernel */

#ifdef CONFIG_PPP_FILTER
		/* check if the packet passes the pass and active filters */
		/* the filter instructions are constructed assuming
		   a four-byte PPP header on each packet */
		*skb_push(skb, 2) = 0;
		if (ppp->pass_filter
		    && sk_run_filter(skb, ppp->pass_filter,
				     ppp->pass_len) == 0) {
			if (ppp->debug & 1)
				printk(KERN_DEBUG "PPP: inbound frame not passed\n");
			kfree_skb(skb);
			return;
		}
		if (!(ppp->active_filter
		      && sk_run_filter(skb, ppp->active_filter,
				       ppp->active_len) == 0))
			ppp->last_recv = jiffies;
		skb_pull(skb, 2);
#else
		ppp->last_recv = jiffies;
#endif /* CONFIG_PPP_FILTER */

		if ((ppp->dev->flags & IFF_UP) == 0
		    || ppp->npmode[npi] != NPMODE_PASS) {
			kfree_skb(skb);
		} else {
			skb_pull(skb, 2);	/* chop off protocol */
			skb->dev = ppp->dev;
			skb->protocol = htons(npindex_to_ethertype[npi]);
			skb->mac.raw = skb->data;
			netif_rx(skb);
			ppp->dev->last_rx = jiffies;
		}
	}
	return;

 err:
	kfree_skb(skb);
	ppp_receive_error(ppp);
}

static struct sk_buff *
ppp_decompress_frame(struct ppp *ppp, struct sk_buff *skb)
{
	int proto = PPP_PROTO(skb);
	struct sk_buff *ns;
	int len;

	/* Until we fix all the decompressor's need to make sure
	 * data portion is linear.
	 */
	if (!pskb_may_pull(skb, skb->len))
		goto err;

	if (proto == PPP_COMP) {
		ns = dev_alloc_skb(ppp->mru + PPP_HDRLEN);
		if (ns == 0) {
			printk(KERN_ERR "ppp_decompress_frame: no memory\n");
			goto err;
		}
		/* the decompressor still expects the A/C bytes in the hdr */
		len = ppp->rcomp->decompress(ppp->rc_state, skb->data - 2,
				skb->len + 2, ns->data, ppp->mru + PPP_HDRLEN);
		if (len < 0) {
			/* Pass the compressed frame to pppd as an
			   error indication. */
			if (len == DECOMP_FATALERROR)
				ppp->rstate |= SC_DC_FERROR;
			kfree_skb(ns);
			goto err;
		}

		kfree_skb(skb);
		skb = ns;
		skb_put(skb, len);
		skb_pull(skb, 2);	/* pull off the A/C bytes */

	} else {
		/* Uncompressed frame - pass to decompressor so it
		   can update its dictionary if necessary. */
		if (ppp->rcomp->incomp)
			ppp->rcomp->incomp(ppp->rc_state, skb->data - 2,
					   skb->len + 2);
	}

	return skb;

 err:
	ppp->rstate |= SC_DC_ERROR;
	ppp_receive_error(ppp);
	return skb;
}

#ifdef CONFIG_PPP_MULTILINK
/*
 * Receive a multilink frame.
 * We put it on the reconstruction queue and then pull off
 * as many completed frames as we can.
 */
static void
ppp_receive_mp_frame(struct ppp *ppp, struct sk_buff *skb, struct channel *pch)
{
	u32 mask, seq;
	struct channel *ch;
	int mphdrlen = (ppp->flags & SC_MP_SHORTSEQ)? MPHDRLEN_SSN: MPHDRLEN;

	if (!pskb_may_pull(skb, mphdrlen) || ppp->mrru == 0)
		goto err;		/* no good, throw it away */

	/* Decode sequence number and begin/end bits */
	if (ppp->flags & SC_MP_SHORTSEQ) {
		seq = ((skb->data[2] & 0x0f) << 8) | skb->data[3];
		mask = 0xfff;
	} else {
		seq = (skb->data[3] << 16) | (skb->data[4] << 8)| skb->data[5];
		mask = 0xffffff;
	}
	skb->BEbits = skb->data[2];
	skb_pull(skb, mphdrlen);	/* pull off PPP and MP headers */

	/*
	 * Do protocol ID decompression on the first fragment of each packet.
	 */
	if ((skb->BEbits & B) && (skb->data[0] & 1))
		*skb_push(skb, 1) = 0;

	/*
	 * Expand sequence number to 32 bits, making it as close
	 * as possible to ppp->minseq.
	 */
	seq |= ppp->minseq & ~mask;
	if ((int)(ppp->minseq - seq) > (int)(mask >> 1))
		seq += mask + 1;
	else if ((int)(seq - ppp->minseq) > (int)(mask >> 1))
		seq -= mask + 1;	/* should never happen */
	skb->sequence = seq;
	pch->lastseq = seq;

	/*
	 * If this packet comes before the next one we were expecting,
	 * drop it.
	 */
	if (seq_before(seq, ppp->nextseq)) {
		kfree_skb(skb);
		++ppp->stats.rx_dropped;
		ppp_receive_error(ppp);
		return;
	}

	/*
	 * Reevaluate minseq, the minimum over all channels of the
	 * last sequence number received on each channel.  Because of
	 * the increasing sequence number rule, we know that any fragment
	 * before `minseq' which hasn't arrived is never going to arrive.
	 * The list of channels can't change because we have the receive
	 * side of the ppp unit locked.
	 */
	list_for_each_entry(ch, &ppp->channels, clist) {
		if (seq_before(ch->lastseq, seq))
			seq = ch->lastseq;
	}
	if (seq_before(ppp->minseq, seq))
		ppp->minseq = seq;

	/* Put the fragment on the reconstruction queue */
	ppp_mp_insert(ppp, skb);

	/* If the queue is getting long, don't wait any longer for packets
	   before the start of the queue. */
	if (skb_queue_len(&ppp->mrq) >= PPP_MP_MAX_QLEN
	    && seq_before(ppp->minseq, ppp->mrq.next->sequence))
		ppp->minseq = ppp->mrq.next->sequence;

	/* Pull completed packets off the queue and receive them. */
	while ((skb = ppp_mp_reconstruct(ppp)) != 0)
		ppp_receive_nonmp_frame(ppp, skb);

	return;

 err:
	kfree_skb(skb);
	ppp_receive_error(ppp);
}

/*
 * Insert a fragment on the MP reconstruction queue.
 * The queue is ordered by increasing sequence number.
 */
static void
ppp_mp_insert(struct ppp *ppp, struct sk_buff *skb)
{
	struct sk_buff *p;
	struct sk_buff_head *list = &ppp->mrq;
	u32 seq = skb->sequence;

	/* N.B. we don't need to lock the list lock because we have the
	   ppp unit receive-side lock. */
	for (p = list->next; p != (struct sk_buff *)list; p = p->next)
		if (seq_before(seq, p->sequence))
			break;
	__skb_insert(skb, p->prev, p, list);
}

/*
 * Reconstruct a packet from the MP fragment queue.
 * We go through increasing sequence numbers until we find a
 * complete packet, or we get to the sequence number for a fragment
 * which hasn't arrived but might still do so.
 */
struct sk_buff *
ppp_mp_reconstruct(struct ppp *ppp)
{
	u32 seq = ppp->nextseq;
	u32 minseq = ppp->minseq;
	struct sk_buff_head *list = &ppp->mrq;
	struct sk_buff *p, *next;
	struct sk_buff *head, *tail;
	struct sk_buff *skb = NULL;
	int lost = 0, len = 0;

	if (ppp->mrru == 0)	/* do nothing until mrru is set */
		return NULL;
	head = list->next;
	tail = NULL;
	for (p = head; p != (struct sk_buff *) list; p = next) {
		next = p->next;
		if (seq_before(p->sequence, seq)) {
			/* this can't happen, anyway ignore the skb */
			printk(KERN_ERR "ppp_mp_reconstruct bad seq %u < %u\n",
			       p->sequence, seq);
			head = next;
			continue;
		}
		if (p->sequence != seq) {
			/* Fragment `seq' is missing.  If it is after
			   minseq, it might arrive later, so stop here. */
			if (seq_after(seq, minseq))
				break;
			/* Fragment `seq' is lost, keep going. */
			lost = 1;
			seq = seq_before(minseq, p->sequence)?
				minseq + 1: p->sequence;
			next = p;
			continue;
		}

		/*
		 * At this point we know that all the fragments from
		 * ppp->nextseq to seq are either present or lost.
		 * Also, there are no complete packets in the queue
		 * that have no missing fragments and end before this
		 * fragment.
		 */

		/* B bit set indicates this fragment starts a packet */
		if (p->BEbits & B) {
			head = p;
			lost = 0;
			len = 0;
		}

		len += p->len;

		/* Got a complete packet yet? */
		if (lost == 0 && (p->BEbits & E) && (head->BEbits & B)) {
			if (len > ppp->mrru + 2) {
				++ppp->stats.rx_length_errors;
				printk(KERN_DEBUG "PPP: reconstructed packet"
				       " is too long (%d)\n", len);
			} else if (p == head) {
				/* fragment is complete packet - reuse skb */
				tail = p;
				skb = skb_get(p);
				break;
			} else if ((skb = dev_alloc_skb(len)) == NULL) {
				++ppp->stats.rx_missed_errors;
				printk(KERN_DEBUG "PPP: no memory for "
				       "reconstructed packet");
			} else {
				tail = p;
				break;
			}
			ppp->nextseq = seq + 1;
		}

		/*
		 * If this is the ending fragment of a packet,
		 * and we haven't found a complete valid packet yet,
		 * we can discard up to and including this fragment.
		 */
		if (p->BEbits & E)
			head = next;

		++seq;
	}

	/* If we have a complete packet, copy it all into one skb. */
	if (tail != NULL) {
		/* If we have discarded any fragments,
		   signal a receive error. */
		if (head->sequence != ppp->nextseq) {
			if (ppp->debug & 1)
				printk(KERN_DEBUG "  missed pkts %u..%u\n",
				       ppp->nextseq, head->sequence-1);
			++ppp->stats.rx_dropped;
			ppp_receive_error(ppp);
		}

		if (head != tail)
			/* copy to a single skb */
			for (p = head; p != tail->next; p = p->next)
				skb_copy_bits(p, 0, skb_put(skb, p->len), p->len);
		ppp->nextseq = tail->sequence + 1;
		head = tail->next;
	}

	/* Discard all the skbuffs that we have copied the data out of
	   or that we can't use. */
	while ((p = list->next) != head) {
		__skb_unlink(p, list);
		kfree_skb(p);
	}

	return skb;
}
#endif /* CONFIG_PPP_MULTILINK */

/*
 * Channel interface.
 */

/*
 * Create a new, unattached ppp channel.
 */
int
ppp_register_channel(struct ppp_channel *chan)
{
	struct channel *pch;

	pch = kmalloc(sizeof(struct channel), GFP_KERNEL);
	if (pch == 0)
		return -ENOMEM;
	memset(pch, 0, sizeof(struct channel));
	pch->ppp = NULL;
	pch->chan = chan;
	chan->ppp = pch;
	init_ppp_file(&pch->file, CHANNEL);
	pch->file.hdrlen = chan->hdrlen;
#ifdef CONFIG_PPP_MULTILINK
	pch->lastseq = -1;
#endif /* CONFIG_PPP_MULTILINK */
	init_rwsem(&pch->chan_sem);
	spin_lock_init(&pch->downl);
	rwlock_init(&pch->upl);
	spin_lock_bh(&all_channels_lock);
	pch->file.index = ++last_channel_index;
	list_add(&pch->list, &new_channels);
	atomic_inc(&channel_count);
	spin_unlock_bh(&all_channels_lock);
	return 0;
}

/*
 * Return the index of a channel.
 */
int ppp_channel_index(struct ppp_channel *chan)
{
	struct channel *pch = chan->ppp;

	if (pch != 0)
		return pch->file.index;
	return -1;
}

/*
 * Return the PPP unit number to which a channel is connected.
 */
int ppp_unit_number(struct ppp_channel *chan)
{
	struct channel *pch = chan->ppp;
	int unit = -1;

	if (pch != 0) {
		read_lock_bh(&pch->upl);
		if (pch->ppp != 0)
			unit = pch->ppp->file.index;
		read_unlock_bh(&pch->upl);
	}
	return unit;
}

/*
 * Disconnect a channel from the generic layer.
 * This must be called in process context.
 */
void
ppp_unregister_channel(struct ppp_channel *chan)
{
	struct channel *pch = chan->ppp;

	if (pch == 0)
		return;		/* should never happen */
	chan->ppp = NULL;

	/*
	 * This ensures that we have returned from any calls into the
	 * the channel's start_xmit or ioctl routine before we proceed.
	 */
	down_write(&pch->chan_sem);
	spin_lock_bh(&pch->downl);
	pch->chan = NULL;
	spin_unlock_bh(&pch->downl);
	up_write(&pch->chan_sem);
	ppp_disconnect_channel(pch);
	spin_lock_bh(&all_channels_lock);
	list_del(&pch->list);
	spin_unlock_bh(&all_channels_lock);
	pch->file.dead = 1;
	wake_up_interruptible(&pch->file.rwait);
	if (atomic_dec_and_test(&pch->file.refcnt))
		ppp_destroy_channel(pch);
}

/*
 * Callback from a channel when it can accept more to transmit.
 * This should be called at BH/softirq level, not interrupt level.
 */
void
ppp_output_wakeup(struct ppp_channel *chan)
{
	struct channel *pch = chan->ppp;

	if (pch == 0)
		return;
	ppp_channel_push(pch);
}

/*
 * Compression control.
 */

/* Process the PPPIOCSCOMPRESS ioctl. */
static int
ppp_set_compress(struct ppp *ppp, unsigned long arg)
{
	int err;
	struct compressor *cp, *ocomp;
	struct ppp_option_data data;
	void *state, *ostate;
	unsigned char ccp_option[CCP_MAX_OPTION_LENGTH];

	err = -EFAULT;
	if (copy_from_user(&data, (void __user *) arg, sizeof(data))
	    || (data.length <= CCP_MAX_OPTION_LENGTH
		&& copy_from_user(ccp_option, (void __user *) data.ptr, data.length)))
		goto out;
	err = -EINVAL;
	if (data.length > CCP_MAX_OPTION_LENGTH
	    || ccp_option[1] < 2 || ccp_option[1] > data.length)
		goto out;

	cp = find_compressor(ccp_option[0]);
#ifdef CONFIG_KMOD
	if (cp == 0) {
		request_module("ppp-compress-%d", ccp_option[0]);
		cp = find_compressor(ccp_option[0]);
	}
#endif /* CONFIG_KMOD */
	if (cp == 0)
		goto out;

	err = -ENOBUFS;
	if (data.transmit) {
		state = cp->comp_alloc(ccp_option, data.length);
		if (state != 0) {
			ppp_xmit_lock(ppp);
			ppp->xstate &= ~SC_COMP_RUN;
			ocomp = ppp->xcomp;
			ostate = ppp->xc_state;
			ppp->xcomp = cp;
			ppp->xc_state = state;
			ppp_xmit_unlock(ppp);
			if (ostate != 0) {
				ocomp->comp_free(ostate);
				module_put(ocomp->owner);
			}
			err = 0;
		} else
			module_put(cp->owner);

	} else {
		state = cp->decomp_alloc(ccp_option, data.length);
		if (state != 0) {
			ppp_recv_lock(ppp);
			ppp->rstate &= ~SC_DECOMP_RUN;
			ocomp = ppp->rcomp;
			ostate = ppp->rc_state;
			ppp->rcomp = cp;
			ppp->rc_state = state;
			ppp_recv_unlock(ppp);
			if (ostate != 0) {
				ocomp->decomp_free(ostate);
				module_put(ocomp->owner);
			}
			err = 0;
		} else
			module_put(cp->owner);
	}

 out:
	return err;
}

/*
 * Look at a CCP packet and update our state accordingly.
 * We assume the caller has the xmit or recv path locked.
 */
static void
ppp_ccp_peek(struct ppp *ppp, struct sk_buff *skb, int inbound)
{
	unsigned char *dp;
	int len;

	if (!pskb_may_pull(skb, CCP_HDRLEN + 2))
		return;	/* no header */
	dp = skb->data + 2;

	switch (CCP_CODE(dp)) {
	case CCP_CONFREQ:

		/* A ConfReq starts negotiation of compression 
		 * in one direction of transmission,
		 * and hence brings it down...but which way?
		 *
		 * Remember:
		 * A ConfReq indicates what the sender would like to receive
		 */
		if(inbound)
			/* He is proposing what I should send */
			ppp->xstate &= ~SC_COMP_RUN;
		else	
			/* I am proposing to what he should send */
			ppp->rstate &= ~SC_DECOMP_RUN;
		
		break;
		
	case CCP_TERMREQ:
	case CCP_TERMACK:
		/*
		 * CCP is going down, both directions of transmission 
		 */
		ppp->rstate &= ~SC_DECOMP_RUN;
		ppp->xstate &= ~SC_COMP_RUN;
		break;

	case CCP_CONFACK:
		if ((ppp->flags & (SC_CCP_OPEN | SC_CCP_UP)) != SC_CCP_OPEN)
			break;
		len = CCP_LENGTH(dp);
		if (!pskb_may_pull(skb, len + 2))
			return;		/* too short */
		dp += CCP_HDRLEN;
		len -= CCP_HDRLEN;
		if (len < CCP_OPT_MINLEN || len < CCP_OPT_LENGTH(dp))
			break;
		if (inbound) {
			/* we will start receiving compressed packets */
			if (ppp->rc_state == 0)
				break;
			if (ppp->rcomp->decomp_init(ppp->rc_state, dp, len,
					ppp->file.index, 0, ppp->mru, ppp->debug)) {
				ppp->rstate |= SC_DECOMP_RUN;
				ppp->rstate &= ~(SC_DC_ERROR | SC_DC_FERROR);
			}
		} else {
			/* we will soon start sending compressed packets */
			if (ppp->xc_state == 0)
				break;
			if (ppp->xcomp->comp_init(ppp->xc_state, dp, len,
					ppp->file.index, 0, ppp->debug))
				ppp->xstate |= SC_COMP_RUN;
		}
		break;

	case CCP_RESETACK:
		/* reset the [de]compressor */
		if ((ppp->flags & SC_CCP_UP) == 0)
			break;
		if (inbound) {
			if (ppp->rc_state && (ppp->rstate & SC_DECOMP_RUN)) {
				ppp->rcomp->decomp_reset(ppp->rc_state);
				ppp->rstate &= ~SC_DC_ERROR;
			}
		} else {
			if (ppp->xc_state && (ppp->xstate & SC_COMP_RUN))
				ppp->xcomp->comp_reset(ppp->xc_state);
		}
		break;
	}
}

/* Free up compression resources. */
static void
ppp_ccp_closed(struct ppp *ppp)
{
	void *xstate, *rstate;
	struct compressor *xcomp, *rcomp;

	ppp_lock(ppp);
	ppp->flags &= ~(SC_CCP_OPEN | SC_CCP_UP);
	ppp->xstate = 0;
	xcomp = ppp->xcomp;
	xstate = ppp->xc_state;
	ppp->xc_state = NULL;
	ppp->rstate = 0;
	rcomp = ppp->rcomp;
	rstate = ppp->rc_state;
	ppp->rc_state = NULL;
	ppp_unlock(ppp);

	if (xstate) {
		xcomp->comp_free(xstate);
		module_put(xcomp->owner);
	}
	if (rstate) {
		rcomp->decomp_free(rstate);
		module_put(rcomp->owner);
	}
}

/* List of compressors. */
static LIST_HEAD(compressor_list);
static DEFINE_SPINLOCK(compressor_list_lock);

struct compressor_entry {
	struct list_head list;
	struct compressor *comp;
};

static struct compressor_entry *
find_comp_entry(int proto)
{
	struct compressor_entry *ce;

	list_for_each_entry(ce, &compressor_list, list) {
		if (ce->comp->compress_proto == proto)
			return ce;
	}
	return NULL;
}

/* Register a compressor */
int
ppp_register_compressor(struct compressor *cp)
{
	struct compressor_entry *ce;
	int ret;
	spin_lock(&compressor_list_lock);
	ret = -EEXIST;
	if (find_comp_entry(cp->compress_proto) != 0)
		goto out;
	ret = -ENOMEM;
	ce = kmalloc(sizeof(struct compressor_entry), GFP_ATOMIC);
	if (ce == 0)
		goto out;
	ret = 0;
	ce->comp = cp;
	list_add(&ce->list, &compressor_list);
 out:
	spin_unlock(&compressor_list_lock);
	return ret;
}

/* Unregister a compressor */
void
ppp_unregister_compressor(struct compressor *cp)
{
	struct compressor_entry *ce;

	spin_lock(&compressor_list_lock);
	ce = find_comp_entry(cp->compress_proto);
	if (ce != 0 && ce->comp == cp) {
		list_del(&ce->list);
		kfree(ce);
	}
	spin_unlock(&compressor_list_lock);
}

/* Find a compressor. */
static struct compressor *
find_compressor(int type)
{
	struct compressor_entry *ce;
	struct compressor *cp = NULL;

	spin_lock(&compressor_list_lock);
	ce = find_comp_entry(type);
	if (ce != 0) {
		cp = ce->comp;
		if (!try_module_get(cp->owner))
			cp = NULL;
	}
	spin_unlock(&compressor_list_lock);
	return cp;
}

/*
 * Miscelleneous stuff.
 */

static void
ppp_get_stats(struct ppp *ppp, struct ppp_stats *st)
{
	struct slcompress *vj = ppp->vj;

	memset(st, 0, sizeof(*st));
	st->p.ppp_ipackets = ppp->stats.rx_packets;
	st->p.ppp_ierrors = ppp->stats.rx_errors;
	st->p.ppp_ibytes = ppp->stats.rx_bytes;
	st->p.ppp_opackets = ppp->stats.tx_packets;
	st->p.ppp_oerrors = ppp->stats.tx_errors;
	st->p.ppp_obytes = ppp->stats.tx_bytes;
	if (vj == 0)
		return;
	st->vj.vjs_packets = vj->sls_o_compressed + vj->sls_o_uncompressed;
	st->vj.vjs_compressed = vj->sls_o_compressed;
	st->vj.vjs_searches = vj->sls_o_searches;
	st->vj.vjs_misses = vj->sls_o_misses;
	st->vj.vjs_errorin = vj->sls_i_error;
	st->vj.vjs_tossed = vj->sls_i_tossed;
	st->vj.vjs_uncompressedin = vj->sls_i_uncompressed;
	st->vj.vjs_compressedin = vj->sls_i_compressed;
}

/*
 * Stuff for handling the lists of ppp units and channels
 * and for initialization.
 */

/*
 * Create a new ppp interface unit.  Fails if it can't allocate memory
 * or if there is already a unit with the requested number.
 * unit == -1 means allocate a new number.
 */
static struct ppp *
ppp_create_interface(int unit, int *retp)
{
	struct ppp *ppp;
	struct net_device *dev = NULL;
	int ret = -ENOMEM;
	int i;

	ppp = kmalloc(sizeof(struct ppp), GFP_KERNEL);
	if (!ppp)
		goto out;
	dev = alloc_netdev(0, "", ppp_setup);
	if (!dev)
		goto out1;
	memset(ppp, 0, sizeof(struct ppp));

	ppp->mru = PPP_MRU;
	init_ppp_file(&ppp->file, INTERFACE);
	ppp->file.hdrlen = PPP_HDRLEN - 2;	/* don't count proto bytes */
	for (i = 0; i < NUM_NP; ++i)
		ppp->npmode[i] = NPMODE_PASS;
	INIT_LIST_HEAD(&ppp->channels);
	spin_lock_init(&ppp->rlock);
	spin_lock_init(&ppp->wlock);
#ifdef CONFIG_PPP_MULTILINK
	ppp->minseq = -1;
	skb_queue_head_init(&ppp->mrq);
#endif /* CONFIG_PPP_MULTILINK */
	ppp->dev = dev;
	dev->priv = ppp;

	dev->hard_start_xmit = ppp_start_xmit;
	dev->get_stats = ppp_net_stats;
	dev->do_ioctl = ppp_net_ioctl;

	ret = -EEXIST;
	down(&all_ppp_sem);
	if (unit < 0)
		unit = cardmap_find_first_free(all_ppp_units);
	else if (cardmap_get(all_ppp_units, unit) != NULL)
		goto out2;	/* unit already exists */

	/* Initialize the new ppp unit */
	ppp->file.index = unit;
	sprintf(dev->name, "ppp%d", unit);

	ret = register_netdev(dev);
	if (ret != 0) {
		printk(KERN_ERR "PPP: couldn't register device %s (%d)\n",
		       dev->name, ret);
		goto out2;
	}

	atomic_inc(&ppp_unit_count);
	cardmap_set(&all_ppp_units, unit, ppp);
	up(&all_ppp_sem);
	*retp = 0;
	return ppp;

out2:
	up(&all_ppp_sem);
	free_netdev(dev);
out1:
	kfree(ppp);
out:
	*retp = ret;
	return NULL;
}

/*
 * Initialize a ppp_file structure.
 */
static void
init_ppp_file(struct ppp_file *pf, int kind)
{
	pf->kind = kind;
	skb_queue_head_init(&pf->xq);
	skb_queue_head_init(&pf->rq);
	atomic_set(&pf->refcnt, 1);
	init_waitqueue_head(&pf->rwait);
}

/*
 * Take down a ppp interface unit - called when the owning file
 * (the one that created the unit) is closed or detached.
 */
static void ppp_shutdown_interface(struct ppp *ppp)
{
	struct net_device *dev;

	down(&all_ppp_sem);
	ppp_lock(ppp);
	dev = ppp->dev;
	ppp->dev = NULL;
	ppp_unlock(ppp);
	/* This will call dev_close() for us. */
	if (dev) {
		unregister_netdev(dev);
		free_netdev(dev);
	}
	cardmap_set(&all_ppp_units, ppp->file.index, NULL);
	ppp->file.dead = 1;
	ppp->owner = NULL;
	wake_up_interruptible(&ppp->file.rwait);
	up(&all_ppp_sem);
}

/*
 * Free the memory used by a ppp unit.  This is only called once
 * there are no channels connected to the unit and no file structs
 * that reference the unit.
 */
static void ppp_destroy_interface(struct ppp *ppp)
{
	atomic_dec(&ppp_unit_count);

	if (!ppp->file.dead || ppp->n_channels) {
		/* "can't happen" */
		printk(KERN_ERR "ppp: destroying ppp struct %p but dead=%d "
		       "n_channels=%d !\n", ppp, ppp->file.dead,
		       ppp->n_channels);
		return;
	}

	ppp_ccp_closed(ppp);
	if (ppp->vj) {
		slhc_free(ppp->vj);
		ppp->vj = NULL;
	}
	skb_queue_purge(&ppp->file.xq);
	skb_queue_purge(&ppp->file.rq);
#ifdef CONFIG_PPP_MULTILINK
	skb_queue_purge(&ppp->mrq);
#endif /* CONFIG_PPP_MULTILINK */
#ifdef CONFIG_PPP_FILTER
	kfree(ppp->pass_filter);
	ppp->pass_filter = NULL;
	kfree(ppp->active_filter);
	ppp->active_filter = NULL;
#endif /* CONFIG_PPP_FILTER */

	kfree(ppp);
}

/*
 * Locate an existing ppp unit.
 * The caller should have locked the all_ppp_sem.
 */
static struct ppp *
ppp_find_unit(int unit)
{
	return cardmap_get(all_ppp_units, unit);
}

/*
 * Locate an existing ppp channel.
 * The caller should have locked the all_channels_lock.
 * First we look in the new_channels list, then in the
 * all_channels list.  If found in the new_channels list,
 * we move it to the all_channels list.  This is for speed
 * when we have a lot of channels in use.
 */
static struct channel *
ppp_find_channel(int unit)
{
	struct channel *pch;

	list_for_each_entry(pch, &new_channels, list) {
		if (pch->file.index == unit) {
			list_del(&pch->list);
			list_add(&pch->list, &all_channels);
			return pch;
		}
	}
	list_for_each_entry(pch, &all_channels, list) {
		if (pch->file.index == unit)
			return pch;
	}
	return NULL;
}

/*
 * Connect a PPP channel to a PPP interface unit.
 */
static int
ppp_connect_channel(struct channel *pch, int unit)
{
	struct ppp *ppp;
	int ret = -ENXIO;
	int hdrlen;

	down(&all_ppp_sem);
	ppp = ppp_find_unit(unit);
	if (ppp == 0)
		goto out;
	write_lock_bh(&pch->upl);
	ret = -EINVAL;
	if (pch->ppp != 0)
		goto outl;

	ppp_lock(ppp);
	if (pch->file.hdrlen > ppp->file.hdrlen)
		ppp->file.hdrlen = pch->file.hdrlen;
	hdrlen = pch->file.hdrlen + 2;	/* for protocol bytes */
	if (ppp->dev && hdrlen > ppp->dev->hard_header_len)
		ppp->dev->hard_header_len = hdrlen;
	list_add_tail(&pch->clist, &ppp->channels);
	++ppp->n_channels;
	pch->ppp = ppp;
	atomic_inc(&ppp->file.refcnt);
	ppp_unlock(ppp);
	ret = 0;

 outl:
	write_unlock_bh(&pch->upl);
 out:
	up(&all_ppp_sem);
	return ret;
}

/*
 * Disconnect a channel from its ppp unit.
 */
static int
ppp_disconnect_channel(struct channel *pch)
{
	struct ppp *ppp;
	int err = -EINVAL;

	write_lock_bh(&pch->upl);
	ppp = pch->ppp;
	pch->ppp = NULL;
	write_unlock_bh(&pch->upl);
	if (ppp != 0) {
		/* remove it from the ppp unit's list */
		ppp_lock(ppp);
		list_del(&pch->clist);
		if (--ppp->n_channels == 0)
			wake_up_interruptible(&ppp->file.rwait);
		ppp_unlock(ppp);
		if (atomic_dec_and_test(&ppp->file.refcnt))
			ppp_destroy_interface(ppp);
		err = 0;
	}
	return err;
}

/*
 * Free up the resources used by a ppp channel.
 */
static void ppp_destroy_channel(struct channel *pch)
{
	atomic_dec(&channel_count);

	if (!pch->file.dead) {
		/* "can't happen" */
		printk(KERN_ERR "ppp: destroying undead channel %p !\n",
		       pch);
		return;
	}
	skb_queue_purge(&pch->file.xq);
	skb_queue_purge(&pch->file.rq);
	kfree(pch);
}

static void __exit ppp_cleanup(void)
{
	/* should never happen */
	if (atomic_read(&ppp_unit_count) || atomic_read(&channel_count))
		printk(KERN_ERR "PPP: removing module but units remain!\n");
	cardmap_destroy(&all_ppp_units);
	if (unregister_chrdev(PPP_MAJOR, "ppp") != 0)
		printk(KERN_ERR "PPP: failed to unregister PPP device\n");
	devfs_remove("ppp");
	class_device_destroy(ppp_class, MKDEV(PPP_MAJOR, 0));
	class_destroy(ppp_class);
}

/*
 * Cardmap implementation.
 */
static void *cardmap_get(struct cardmap *map, unsigned int nr)
{
	struct cardmap *p;
	int i;

	for (p = map; p != NULL; ) {
		if ((i = nr >> p->shift) >= CARDMAP_WIDTH)
			return NULL;
		if (p->shift == 0)
			return p->ptr[i];
		nr &= ~(CARDMAP_MASK << p->shift);
		p = p->ptr[i];
	}
	return NULL;
}

static void cardmap_set(struct cardmap **pmap, unsigned int nr, void *ptr)
{
	struct cardmap *p;
	int i;

	p = *pmap;
	if (p == NULL || (nr >> p->shift) >= CARDMAP_WIDTH) {
		do {
			/* need a new top level */
			struct cardmap *np = kmalloc(sizeof(*np), GFP_KERNEL);
			memset(np, 0, sizeof(*np));
			np->ptr[0] = p;
			if (p != NULL) {
				np->shift = p->shift + CARDMAP_ORDER;
				p->parent = np;
			} else
				np->shift = 0;
			p = np;
		} while ((nr >> p->shift) >= CARDMAP_WIDTH);
		*pmap = p;
	}
	while (p->shift > 0) {
		i = (nr >> p->shift) & CARDMAP_MASK;
		if (p->ptr[i] == NULL) {
			struct cardmap *np = kmalloc(sizeof(*np), GFP_KERNEL);
			memset(np, 0, sizeof(*np));
			np->shift = p->shift - CARDMAP_ORDER;
			np->parent = p;
			p->ptr[i] = np;
		}
		if (ptr == NULL)
			clear_bit(i, &p->inuse);
		p = p->ptr[i];
	}
	i = nr & CARDMAP_MASK;
	p->ptr[i] = ptr;
	if (ptr != NULL)
		set_bit(i, &p->inuse);
	else
		clear_bit(i, &p->inuse);
}

static unsigned int cardmap_find_first_free(struct cardmap *map)
{
	struct cardmap *p;
	unsigned int nr = 0;
	int i;

	if ((p = map) == NULL)
		return 0;
	for (;;) {
		i = find_first_zero_bit(&p->inuse, CARDMAP_WIDTH);
		if (i >= CARDMAP_WIDTH) {
			if (p->parent == NULL)
				return CARDMAP_WIDTH << p->shift;
			p = p->parent;
			i = (nr >> p->shift) & CARDMAP_MASK;
			set_bit(i, &p->inuse);
			continue;
		}
		nr = (nr & (~CARDMAP_MASK << p->shift)) | (i << p->shift);
		if (p->shift == 0 || p->ptr[i] == NULL)
			return nr;
		p = p->ptr[i];
	}
}

static void cardmap_destroy(struct cardmap **pmap)
{
	struct cardmap *p, *np;
	int i;

	for (p = *pmap; p != NULL; p = np) {
		if (p->shift != 0) {
			for (i = 0; i < CARDMAP_WIDTH; ++i)
				if (p->ptr[i] != NULL)
					break;
			if (i < CARDMAP_WIDTH) {
				np = p->ptr[i];
				p->ptr[i] = NULL;
				continue;
			}
		}
		np = p->parent;
		kfree(p);
	}
	*pmap = NULL;
}

/* Module/initialization stuff */

module_init(ppp_init);
module_exit(ppp_cleanup);

EXPORT_SYMBOL(ppp_register_channel);
EXPORT_SYMBOL(ppp_unregister_channel);
EXPORT_SYMBOL(ppp_channel_index);
EXPORT_SYMBOL(ppp_unit_number);
EXPORT_SYMBOL(ppp_input);
EXPORT_SYMBOL(ppp_input_error);
EXPORT_SYMBOL(ppp_output_wakeup);
EXPORT_SYMBOL(ppp_register_compressor);
EXPORT_SYMBOL(ppp_unregister_compressor);
MODULE_LICENSE("GPL");
MODULE_ALIAS_CHARDEV_MAJOR(PPP_MAJOR);
MODULE_ALIAS("/dev/ppp");