summaryrefslogtreecommitdiff
path: root/util-linux/mdev.c
blob: 88c82b6fb898c0d3de4d97239fef5e177b896553 (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
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
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
/* vi: set sw=4 ts=4: */
/*
 * mdev - Mini udev for busybox
 *
 * Copyright 2005 Rob Landley <rob@landley.net>
 * Copyright 2005 Frank Sorenson <frank@tuxrocks.com>
 *
 * Licensed under GPLv2, see file LICENSE in this source tree.
 */
//config:config MDEV
//config:	bool "mdev (17 kb)"
//config:	default y
//config:	select PLATFORM_LINUX
//config:	help
//config:	mdev is a mini-udev implementation for dynamically creating device
//config:	nodes in the /dev directory.
//config:
//config:	For more information, please see docs/mdev.txt
//config:
//config:config FEATURE_MDEV_CONF
//config:	bool "Support /etc/mdev.conf"
//config:	default y
//config:	depends on MDEV
//config:	help
//config:	Add support for the mdev config file to control ownership and
//config:	permissions of the device nodes.
//config:
//config:	For more information, please see docs/mdev.txt
//config:
//config:config FEATURE_MDEV_RENAME
//config:	bool "Support subdirs/symlinks"
//config:	default y
//config:	depends on FEATURE_MDEV_CONF
//config:	help
//config:	Add support for renaming devices and creating symlinks.
//config:
//config:	For more information, please see docs/mdev.txt
//config:
//config:config FEATURE_MDEV_RENAME_REGEXP
//config:	bool "Support regular expressions substitutions when renaming device"
//config:	default y
//config:	depends on FEATURE_MDEV_RENAME
//config:	help
//config:	Add support for regular expressions substitutions when renaming
//config:	device.
//config:
//config:config FEATURE_MDEV_EXEC
//config:	bool "Support command execution at device addition/removal"
//config:	default y
//config:	depends on FEATURE_MDEV_CONF
//config:	help
//config:	This adds support for an optional field to /etc/mdev.conf for
//config:	executing commands when devices are created/removed.
//config:
//config:	For more information, please see docs/mdev.txt
//config:
//config:config FEATURE_MDEV_LOAD_FIRMWARE
//config:	bool "Support loading of firmware"
//config:	default y
//config:	depends on MDEV
//config:	help
//config:	Some devices need to load firmware before they can be usable.
//config:
//config:	These devices will request userspace look up the files in
//config:	/lib/firmware/ and if it exists, send it to the kernel for
//config:	loading into the hardware.
//config:
//config:config FEATURE_MDEV_DAEMON
//config:	bool "Support daemon mode"
//config:	default y
//config:	depends on MDEV
//config:	help
//config:	Adds the -d option to run mdev in daemon mode handling hotplug
//config:	events from the kernel like udev. If the system generates many
//config:	hotplug events this mode of operation will consume less
//config:	resources than registering mdev as hotplug helper or using the
//config:	uevent applet.

//applet:IF_MDEV(APPLET(mdev, BB_DIR_SBIN, BB_SUID_DROP))

//kbuild:lib-$(CONFIG_MDEV) += mdev.o

//usage:#define mdev_trivial_usage
//usage:       "[-s]" IF_FEATURE_MDEV_DAEMON(" | [-df]")
//usage:#define mdev_full_usage "\n\n"
//usage:       "mdev -s is to be run during boot to scan /sys and populate /dev.\n"
//usage:	IF_FEATURE_MDEV_DAEMON(
//usage:       "mdev -d[f]: daemon, listen on netlink.\n"
//usage:       "	-f: stay in foreground.\n"
//usage:	)
//usage:       "\n"
//usage:       "Bare mdev is a kernel hotplug helper. To activate it:\n"
//usage:       "	echo /sbin/mdev >/proc/sys/kernel/hotplug\n"
//usage:	IF_FEATURE_MDEV_CONF(
//usage:       "\n"
//usage:       "It uses /etc/mdev.conf with lines\n"
//usage:       "	[-][ENV=regex;]...DEVNAME UID:GID PERM"
//usage:			IF_FEATURE_MDEV_RENAME(" [>|=PATH]|[!]")
//usage:			IF_FEATURE_MDEV_EXEC(" [@|$|*PROG]")
//usage:       "\n"
//usage:       "where DEVNAME is device name regex, @major,minor[-minor2], or\n"
//usage:       "environment variable regex. A common use of the latter is\n"
//usage:       "to load modules for hotplugged devices:\n"
//usage:       "	$MODALIAS=.* 0:0 660 @modprobe \"$MODALIAS\"\n"
//usage:	)
//usage:       "\n"
//usage:       "If /dev/mdev.seq file exists, mdev will wait for its value\n"
//usage:       "to match $SEQNUM variable. This prevents plug/unplug races.\n"
//usage:       "To activate this feature, create empty /dev/mdev.seq at boot.\n"
//usage:       "\n"
//usage:       "If /dev/mdev.log file exists, debug log will be appended to it."

#include "libbb.h"
#include "common_bufsiz.h"
#include "xregex.h"
#include <linux/netlink.h>

/* "mdev -s" scans /sys/class/xxx, looking for directories which have dev
 * file (it is of the form "M:m\n"). Example: /sys/class/tty/tty0/dev
 * contains "4:0\n". Directory name is taken as device name, path component
 * directly after /sys/class/ as subsystem. In this example, "tty0" and "tty".
 * Then mdev creates the /dev/device_name node.
 * If /sys/class/.../dev file does not exist, mdev still may act
 * on this device: see "@|$|*command args..." parameter in config file.
 *
 * mdev w/o parameters is called as hotplug helper. It takes device
 * and subsystem names from $DEVPATH and $SUBSYSTEM, extracts
 * maj,min from "/sys/$DEVPATH/dev" and also examines
 * $ACTION ("add"/"delete") and $FIRMWARE.
 *
 * If action is "add", mdev creates /dev/device_name similarly to mdev -s.
 * (todo: explain "delete" and $FIRMWARE)
 *
 * If /etc/mdev.conf exists, it may modify /dev/device_name's properties.
 *
 * Leading minus in 1st field means "don't stop on this line", otherwise
 * search is stopped after the matching line is encountered.
 *
 * $envvar=regex format is useful for loading modules for hot-plugged devices
 * which do not have driver loaded yet. In this case /sys/class/.../dev
 * does not exist, but $MODALIAS is set to needed module's name
 * (actually, an alias to it) by kernel. This rule instructs mdev
 * to load the module and exit:
 *    $MODALIAS=.* 0:0 660 @modprobe "$MODALIAS"
 * The kernel will generate another hotplug event when /sys/class/.../dev
 * file appears.
 *
 * When line matches, the device node is created, chmod'ed and chown'ed,
 * moved to path, and if >path, a symlink to moved node is created,
 * all this if /sys/class/.../dev exists.
 *    Examples:
 *    =loop/      - moves to /dev/loop
 *    >disk/sda%1 - moves to /dev/disk/sdaN, makes /dev/sdaN a symlink
 *
 * Then "command args..." is executed (via sh -c 'command args...').
 * @:execute on creation, $:on deletion, *:on both.
 * This happens regardless of /sys/class/.../dev existence.
 */

/* Kernel's hotplug environment constantly changes.
 * Here are new cases I observed on 3.1.0:
 *
 * Case with $DEVNAME and $DEVICE, not just $DEVPATH:
 * ACTION=add
 * BUSNUM=001
 * DEVICE=/proc/bus/usb/001/003
 * DEVNAME=bus/usb/001/003
 * DEVNUM=003
 * DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-5
 * DEVTYPE=usb_device
 * MAJOR=189
 * MINOR=2
 * PRODUCT=18d1/4e12/227
 * SUBSYSTEM=usb
 * TYPE=0/0/0
 *
 * Case with $DEVICE, but no $DEVNAME - apparenty, usb iface notification?
 * "Please load me a module" thing?
 * ACTION=add
 * DEVICE=/proc/bus/usb/001/003
 * DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-5/1-5:1.0
 * DEVTYPE=usb_interface
 * INTERFACE=8/6/80
 * MODALIAS=usb:v18D1p4E12d0227dc00dsc00dp00ic08isc06ip50
 * PRODUCT=18d1/4e12/227
 * SUBSYSTEM=usb
 * TYPE=0/0/0
 *
 * ACTION=add
 * DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-5/1-5:1.0/host5
 * DEVTYPE=scsi_host
 * SUBSYSTEM=scsi
 *
 * ACTION=add
 * DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-5/1-5:1.0/host5/scsi_host/host5
 * SUBSYSTEM=scsi_host
 *
 * ACTION=add
 * DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-5/1-5:1.0/host5/target5:0:0
 * DEVTYPE=scsi_target
 * SUBSYSTEM=scsi
 *
 * Case with strange $MODALIAS:
 * ACTION=add
 * DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-5/1-5:1.0/host5/target5:0:0/5:0:0:0
 * DEVTYPE=scsi_device
 * MODALIAS=scsi:t-0x00
 * SUBSYSTEM=scsi
 *
 * ACTION=add
 * DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-5/1-5:1.0/host5/target5:0:0/5:0:0:0/scsi_disk/5:0:0:0
 * SUBSYSTEM=scsi_disk
 *
 * ACTION=add
 * DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-5/1-5:1.0/host5/target5:0:0/5:0:0:0/scsi_device/5:0:0:0
 * SUBSYSTEM=scsi_device
 *
 * Case with explicit $MAJOR/$MINOR (no need to read /sys/$DEVPATH/dev?):
 * ACTION=add
 * DEVNAME=bsg/5:0:0:0
 * DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-5/1-5:1.0/host5/target5:0:0/5:0:0:0/bsg/5:0:0:0
 * MAJOR=253
 * MINOR=1
 * SUBSYSTEM=bsg
 *
 * ACTION=add
 * DEVPATH=/devices/virtual/bdi/8:16
 * SUBSYSTEM=bdi
 *
 * ACTION=add
 * DEVNAME=sdb
 * DEVPATH=/block/sdb
 * DEVTYPE=disk
 * MAJOR=8
 * MINOR=16
 * SUBSYSTEM=block
 *
 * Case with ACTION=change:
 * ACTION=change
 * DEVNAME=sdb
 * DEVPATH=/block/sdb
 * DEVTYPE=disk
 * DISK_MEDIA_CHANGE=1
 * MAJOR=8
 * MINOR=16
 * SUBSYSTEM=block
 */

#define DEBUG_LVL 2

#if DEBUG_LVL >= 1
# define dbg1(...) do { if (G.verbose) bb_error_msg(__VA_ARGS__); } while(0)
#else
# define dbg1(...) ((void)0)
#endif
#if DEBUG_LVL >= 2
# define dbg2(...) do { if (G.verbose >= 2) bb_error_msg(__VA_ARGS__); } while(0)
#else
# define dbg2(...) ((void)0)
#endif
#if DEBUG_LVL >= 3
# define dbg3(...) do { if (G.verbose >= 3) bb_error_msg(__VA_ARGS__); } while(0)
#else
# define dbg3(...) ((void)0)
#endif


#ifndef SO_RCVBUFFORCE
#define SO_RCVBUFFORCE 33
#endif
static const char keywords[] ALIGN1 = "add\0remove\0"; // "change\0"
enum { OP_add, OP_remove };

struct envmatch {
	struct envmatch *next;
	char *envname;
	regex_t match;
};

struct rule {
	bool keep_matching;
	bool regex_compiled;
	mode_t mode;
	int maj, min0, min1;
	struct bb_uidgid_t ugid;
	char *envvar;
	char *ren_mov;
	IF_FEATURE_MDEV_EXEC(char *r_cmd;)
	regex_t match;
	struct envmatch *envmatch;
};

struct globals {
	int root_major, root_minor;
	smallint verbose;
	char *subsystem;
	char *subsys_env; /* for putenv("SUBSYSTEM=subsystem") */
#if ENABLE_FEATURE_MDEV_CONF
	const char *filename;
	parser_t *parser;
	struct rule **rule_vec;
	unsigned rule_idx;
#endif
	struct rule cur_rule;
	char timestr[sizeof("HH:MM:SS.123456")];
} FIX_ALIASING;
#define G (*(struct globals*)bb_common_bufsiz1)
#define INIT_G() do { \
	setup_common_bufsiz(); \
	IF_NOT_FEATURE_MDEV_CONF(G.cur_rule.maj = -1;) \
	IF_NOT_FEATURE_MDEV_CONF(G.cur_rule.mode = 0660;) \
} while (0)


/* Prevent infinite loops in /sys symlinks */
#define MAX_SYSFS_DEPTH 3

/* We use additional bytes in make_device() */
#define SCRATCH_SIZE 128

#if ENABLE_FEATURE_MDEV_CONF

static void make_default_cur_rule(void)
{
	memset(&G.cur_rule, 0, sizeof(G.cur_rule));
	G.cur_rule.maj = -1; /* "not a @major,minor rule" */
	G.cur_rule.mode = 0660;
}

static void clean_up_cur_rule(void)
{
	struct envmatch *e;

	free(G.cur_rule.envvar);
	free(G.cur_rule.ren_mov);
	if (G.cur_rule.regex_compiled)
		regfree(&G.cur_rule.match);
	IF_FEATURE_MDEV_EXEC(free(G.cur_rule.r_cmd);)
	e = G.cur_rule.envmatch;
	while (e) {
		free(e->envname);
		regfree(&e->match);
		e = e->next;
	}
	make_default_cur_rule();
}

static char *parse_envmatch_pfx(char *val)
{
	struct envmatch **nextp = &G.cur_rule.envmatch;

	for (;;) {
		struct envmatch *e;
		char *semicolon;
		char *eq = strchr(val, '=');
		if (!eq /* || eq == val? */)
			return val;
		if (endofname(val) != eq)
			return val;
		semicolon = strchr(eq, ';');
		if (!semicolon)
			return val;
		/* ENVVAR=regex;... */
		*nextp = e = xzalloc(sizeof(*e));
		nextp = &e->next;
		e->envname = xstrndup(val, eq - val);
		*semicolon = '\0';
		xregcomp(&e->match, eq + 1, REG_EXTENDED);
		*semicolon = ';';
		val = semicolon + 1;
	}
}

static void parse_next_rule(void)
{
	/* Note: on entry, G.cur_rule is set to default */
	while (1) {
		char *tokens[4];
		char *val;

		/* No PARSE_EOL_COMMENTS, because command may contain '#' chars */
		if (!config_read(G.parser, tokens, 4, 3, "# \t", PARSE_NORMAL & ~PARSE_EOL_COMMENTS))
			break;

		/* Fields: [-]regex uid:gid mode [alias] [cmd] */
		dbg3("token1:'%s'", tokens[1]);

		/* 1st field */
		val = tokens[0];
		G.cur_rule.keep_matching = ('-' == val[0]);
		val += G.cur_rule.keep_matching; /* swallow leading dash */
		val = parse_envmatch_pfx(val);
		if (val[0] == '@') {
			/* @major,minor[-minor2] */
			/* (useful when name is ambiguous:
			 * "/sys/class/usb/lp0" and
			 * "/sys/class/printer/lp0")
			 */
			int sc = sscanf(val, "@%u,%u-%u", &G.cur_rule.maj, &G.cur_rule.min0, &G.cur_rule.min1);
			if (sc < 2 || G.cur_rule.maj < 0) {
				bb_error_msg("bad @maj,min on line %d", G.parser->lineno);
				goto next_rule;
			}
			if (sc == 2)
				G.cur_rule.min1 = G.cur_rule.min0;
		} else {
			char *eq = strchr(val, '=');
			if (val[0] == '$') {
				/* $ENVVAR=regex ... */
				val++;
				if (!eq) {
					bb_error_msg("bad $envvar=regex on line %d", G.parser->lineno);
					goto next_rule;
				}
				G.cur_rule.envvar = xstrndup(val, eq - val);
				val = eq + 1;
			}
			xregcomp(&G.cur_rule.match, val, REG_EXTENDED);
			G.cur_rule.regex_compiled = 1;
		}

		/* 2nd field: uid:gid - device ownership */
		if (get_uidgid(&G.cur_rule.ugid, tokens[1]) == 0) {
			bb_error_msg("unknown user/group '%s' on line %d", tokens[1], G.parser->lineno);
			goto next_rule;
		}

		/* 3rd field: mode - device permissions */
		G.cur_rule.mode = bb_parse_mode(tokens[2], G.cur_rule.mode);

		/* 4th field (opt): ">|=alias" or "!" to not create the node */
		val = tokens[3];
		if (ENABLE_FEATURE_MDEV_RENAME && val && strchr(">=!", val[0])) {
			char *s = skip_non_whitespace(val);
			G.cur_rule.ren_mov = xstrndup(val, s - val);
			val = skip_whitespace(s);
		}

		if (ENABLE_FEATURE_MDEV_EXEC && val && val[0]) {
			const char *s = "$@*";
			const char *s2 = strchr(s, val[0]);
			if (!s2) {
				bb_error_msg("bad line %u", G.parser->lineno);
				goto next_rule;
			}
			IF_FEATURE_MDEV_EXEC(G.cur_rule.r_cmd = xstrdup(val);)
		}

		return;
 next_rule:
		clean_up_cur_rule();
	} /* while (config_read) */

	dbg3("config_close(G.parser)");
	config_close(G.parser);
	G.parser = NULL;

	return;
}

/* If mdev -s, we remember rules in G.rule_vec[].
 * Otherwise, there is no point in doing it, and we just
 * save only one parsed rule in G.cur_rule.
 */
static const struct rule *next_rule(void)
{
	struct rule *rule;

	/* Open conf file if we didn't do it yet */
	if (!G.parser && G.filename) {
		dbg3("config_open('%s')", G.filename);
		G.parser = config_open2(G.filename, fopen_for_read);
		G.filename = NULL;
	}

	if (G.rule_vec) {
		/* mdev -s */
		/* Do we have rule parsed already? */
		if (G.rule_vec[G.rule_idx]) {
			dbg3("< G.rule_vec[G.rule_idx:%d]=%p", G.rule_idx, G.rule_vec[G.rule_idx]);
			return G.rule_vec[G.rule_idx++];
		}
		make_default_cur_rule();
	} else {
		/* not mdev -s */
		clean_up_cur_rule();
	}

	/* Parse one more rule if file isn't fully read */
	rule = &G.cur_rule;
	if (G.parser) {
		parse_next_rule();
		if (G.rule_vec) { /* mdev -s */
			rule = xmemdup(&G.cur_rule, sizeof(G.cur_rule));
			G.rule_vec = xrealloc_vector(G.rule_vec, 4, G.rule_idx);
			G.rule_vec[G.rule_idx++] = rule;
			dbg3("> G.rule_vec[G.rule_idx:%d]=%p", G.rule_idx, G.rule_vec[G.rule_idx]);
		}
	}

	return rule;
}

static int env_matches(struct envmatch *e)
{
	while (e) {
		int r;
		char *val = getenv(e->envname);
		if (!val)
			return 0;
		r = regexec(&e->match, val, /*size*/ 0, /*range[]*/ NULL, /*eflags*/ 0);
		if (r != 0) /* no match */
			return 0;
		e = e->next;
	}
	return 1;
}

#else

# define next_rule() (&G.cur_rule)

#endif

static void mkdir_recursive(char *name)
{
	/* if name has many levels ("dir1/dir2"),
	 * bb_make_directory() will create dir1 according to umask,
	 * not according to its "mode" parameter.
	 * Since we run with umask=0, need to temporarily switch it.
	 */
	umask(022); /* "dir1" (if any) will be 0755 too */
	bb_make_directory(name, 0755, FILEUTILS_RECUR);
	umask(0);
}

/* Builds an alias path.
 * This function potentionally reallocates the alias parameter.
 * Only used for ENABLE_FEATURE_MDEV_RENAME
 */
static char *build_alias(char *alias, const char *device_name)
{
	char *dest;

	/* ">bar/": rename to bar/device_name */
	/* ">bar[/]baz": rename to bar[/]baz */
	dest = strrchr(alias, '/');
	if (dest) { /* ">bar/[baz]" ? */
		*dest = '\0'; /* mkdir bar */
		mkdir_recursive(alias);
		*dest = '/';
		if (dest[1] == '\0') { /* ">bar/" => ">bar/device_name" */
			dest = alias;
			alias = concat_path_file(alias, device_name);
			free(dest);
		}
	}

	return alias;
}

/* mknod in /dev based on a path like "/sys/block/hda/hda1"
 * NB1: path parameter needs to have SCRATCH_SIZE scratch bytes
 * after NUL, but we promise to not mangle it (IOW: to restore NUL if needed).
 * NB2: "mdev -s" may call us many times, do not leak memory/fds!
 *
 * device_name = $DEVNAME (may be NULL)
 * path        = /sys/$DEVPATH
 */
static void make_device(char *device_name, char *path, int operation)
{
	int major, minor, type, len;
	char *path_end = path + strlen(path);

	/* Try to read major/minor string.  Note that the kernel puts \n after
	 * the data, so we don't need to worry about null terminating the string
	 * because sscanf() will stop at the first nondigit, which \n is.
	 * We also depend on path having writeable space after it.
	 */
	major = -1;
	if (operation == OP_add) {
		strcpy(path_end, "/dev");
		len = open_read_close(path, path_end + 1, SCRATCH_SIZE - 1);
		*path_end = '\0';
		if (len < 1) {
			if (!ENABLE_FEATURE_MDEV_EXEC)
				return;
			/* no "dev" file, but we can still run scripts
			 * based on device name */
		} else if (sscanf(path_end + 1, "%u:%u", &major, &minor) == 2) {
			dbg1("dev %u,%u", major, minor);
		} else {
			major = -1;
		}
	}
	/* else: for delete, -1 still deletes the node, but < -1 suppresses that */

	/* Determine device name */
	if (!device_name) {
		/*
		 * There was no $DEVNAME envvar (for example, mdev -s never has).
		 * But it is very useful: it contains the *path*, not only basename,
		 * Thankfully, uevent file has it.
		 * Example of .../sound/card0/controlC0/uevent file on Linux-3.7.7:
		 * MAJOR=116
		 * MINOR=7
		 * DEVNAME=snd/controlC0
		 */
		strcpy(path_end, "/uevent");
		len = open_read_close(path, path_end + 1, SCRATCH_SIZE - 1);
		if (len < 0)
			len = 0;
		*path_end = '\0';
		path_end[1 + len] = '\0';
		device_name = strstr(path_end + 1, "\nDEVNAME=");
		if (device_name) {
			device_name += sizeof("\nDEVNAME=")-1;
			strchrnul(device_name, '\n')[0] = '\0';
		} else {
			/* Fall back to just basename */
			device_name = (char*) bb_basename(path);
		}
	}
	/* Determine device type */
	/*
	 * http://kernel.org/doc/pending/hotplug.txt says that only
	 * "/sys/block/..." is for block devices. "/sys/bus" etc is not.
	 * But since 2.6.25 block devices are also in /sys/class/block.
	 * We use strstr("/block/") to forestall future surprises.
	 */
	type = S_IFCHR;
	if (strstr(path, "/block/") || (G.subsystem && is_prefixed_with(G.subsystem, "block")))
		type = S_IFBLK;

#if ENABLE_FEATURE_MDEV_CONF
	G.rule_idx = 0; /* restart from the beginning (think mdev -s) */
#endif
	for (;;) {
		const char *str_to_match;
		regmatch_t off[1 + 9 * ENABLE_FEATURE_MDEV_RENAME_REGEXP];
		char *command;
		char *alias;
		char aliaslink = aliaslink; /* for compiler */
		char *node_name;
		const struct rule *rule;

		str_to_match = device_name;

		rule = next_rule();

#if ENABLE_FEATURE_MDEV_CONF
		if (!env_matches(rule->envmatch))
			continue;
		if (rule->maj >= 0) {  /* @maj,min rule */
			if (major != rule->maj)
				continue;
			if (minor < rule->min0 || minor > rule->min1)
				continue;
			memset(off, 0, sizeof(off));
			goto rule_matches;
		}
		if (rule->envvar) { /* $envvar=regex rule */
			str_to_match = getenv(rule->envvar);
			dbg3("getenv('%s'):'%s'", rule->envvar, str_to_match);
			if (!str_to_match)
				continue;
		}
		/* else: str_to_match = device_name */

		if (rule->regex_compiled) {
			int regex_match = regexec(&rule->match, str_to_match, ARRAY_SIZE(off), off, 0);
			dbg3("regex_match for '%s':%d", str_to_match, regex_match);
			//bb_error_msg("matches:");
			//for (int i = 0; i < ARRAY_SIZE(off); i++) {
			//	if (off[i].rm_so < 0) continue;
			//	bb_error_msg("match %d: '%.*s'\n", i,
			//		(int)(off[i].rm_eo - off[i].rm_so),
			//		device_name + off[i].rm_so);
			//}

			if (regex_match != 0
			/* regexec returns whole pattern as "range" 0 */
			 || off[0].rm_so != 0
			 || (int)off[0].rm_eo != (int)strlen(str_to_match)
			) {
				continue; /* this rule doesn't match */
			}
		}
		/* else: it's final implicit "match-all" rule */
 rule_matches:
		dbg2("rule matched, line %d", G.parser ? G.parser->lineno : -1);
#endif
		/* Build alias name */
		alias = NULL;
		if (ENABLE_FEATURE_MDEV_RENAME && rule->ren_mov) {
			aliaslink = rule->ren_mov[0];
			if (aliaslink == '!') {
				/* "!": suppress node creation/deletion */
				major = -2;
			}
			else if (aliaslink == '>' || aliaslink == '=') {
				if (ENABLE_FEATURE_MDEV_RENAME_REGEXP) {
					char *s;
					char *p;
					unsigned n;

					/* substitute %1..9 with off[1..9], if any */
					n = 0;
					s = rule->ren_mov;
					while (*s)
						if (*s++ == '%')
							n++;

					p = alias = xzalloc(strlen(rule->ren_mov) + n * strlen(str_to_match));
					s = rule->ren_mov + 1;
					while (*s) {
						*p = *s;
						if ('%' == *s) {
							unsigned i = (s[1] - '0');
							if (i <= 9 && off[i].rm_so >= 0) {
								n = off[i].rm_eo - off[i].rm_so;
								strncpy(p, str_to_match + off[i].rm_so, n);
								p += n - 1;
								s++;
							}
						}
						p++;
						s++;
					}
				} else {
					alias = xstrdup(rule->ren_mov + 1);
				}
			}
		}
		dbg3("alias:'%s'", alias);

		command = NULL;
		IF_FEATURE_MDEV_EXEC(command = rule->r_cmd;)
		if (command) {
			/* Are we running this command now?
			 * Run @cmd on create, $cmd on delete, *cmd on any
			 */
			if ((command[0] == '@' && operation == OP_add)
			 || (command[0] == '$' && operation == OP_remove)
			 || (command[0] == '*')
			) {
				command++;
			} else {
				command = NULL;
			}
		}
		dbg3("command:'%s'", command);

		/* "Execute" the line we found */
		node_name = device_name;
		if (ENABLE_FEATURE_MDEV_RENAME && alias) {
			node_name = alias = build_alias(alias, device_name);
			dbg3("alias2:'%s'", alias);
		}

		if (operation == OP_add && major >= 0) {
			char *slash = strrchr(node_name, '/');
			if (slash) {
				*slash = '\0';
				mkdir_recursive(node_name);
				*slash = '/';
			}
			if (ENABLE_FEATURE_MDEV_CONF) {
				dbg1("mknod %s (%d,%d) %o"
					" %u:%u",
					node_name, major, minor, rule->mode | type,
					rule->ugid.uid, rule->ugid.gid
				);
			} else {
				dbg1("mknod %s (%d,%d) %o",
					node_name, major, minor, rule->mode | type
				);
			}
			if (mknod(node_name, rule->mode | type, makedev(major, minor)) && errno != EEXIST)
				bb_perror_msg("can't create '%s'", node_name);
			if (ENABLE_FEATURE_MDEV_CONF) {
				chmod(node_name, rule->mode);
				chown(node_name, rule->ugid.uid, rule->ugid.gid);
			}
			if (major == G.root_major && minor == G.root_minor)
				symlink(node_name, "root");
			if (ENABLE_FEATURE_MDEV_RENAME && alias) {
				if (aliaslink == '>') {
//TODO: on devtmpfs, device_name already exists and symlink() fails.
//End result is that instead of symlink, we have two nodes.
//What should be done?
					dbg1("symlink: %s", device_name);
					symlink(node_name, device_name);
				}
			}
		}

		if (ENABLE_FEATURE_MDEV_EXEC && command) {
			/* setenv will leak memory, use putenv/unsetenv/free */
			char *s = xasprintf("%s=%s", "MDEV", node_name);
			putenv(s);
			dbg1("running: %s", command);
			if (system(command) == -1)
				bb_perror_msg("can't run '%s'", command);
			bb_unsetenv_and_free(s);
		}

		if (operation == OP_remove && major >= -1) {
			if (ENABLE_FEATURE_MDEV_RENAME && alias) {
				if (aliaslink == '>') {
					dbg1("unlink: %s", device_name);
					unlink(device_name);
				}
			}
			dbg1("unlink: %s", node_name);
			unlink(node_name);
		}

		if (ENABLE_FEATURE_MDEV_RENAME)
			free(alias);

		/* We found matching line.
		 * Stop unless it was prefixed with '-'
		 */
		if (!ENABLE_FEATURE_MDEV_CONF || !rule->keep_matching)
			break;
	} /* for (;;) */
}

static ssize_t readlink2(char *buf, size_t bufsize)
{
	// Grr... gcc 8.1.1:
	// "passing argument 2 to restrict-qualified parameter aliases with argument 1"
	// dance around that...
	char *obuf FIX_ALIASING;
	obuf = buf;
	return readlink(buf, obuf, bufsize);
}

/* File callback for /sys/ traversal.
 * We act only on "/sys/.../dev" (pseudo)file
 */
static int FAST_FUNC fileAction(const char *fileName,
		struct stat *statbuf UNUSED_PARAM,
		void *userData,
		int depth UNUSED_PARAM)
{
	size_t len = strlen(fileName) - 4; /* can't underflow */
	char *path = userData;	/* char array[PATH_MAX + SCRATCH_SIZE] */
	char subsys[PATH_MAX];
	int res;

	/* Is it a ".../dev" file? (len check is for paranoid reasons) */
	if (strcmp(fileName + len, "/dev") != 0 || len >= PATH_MAX - 32)
		return FALSE; /* not .../dev */

	strcpy(path, fileName);
	path[len] = '\0';

	/* Read ".../subsystem" symlink in the same directory where ".../dev" is */
	strcpy(subsys, path);
	strcpy(subsys + len, "/subsystem");
	res = readlink2(subsys, sizeof(subsys)-1);
	if (res > 0) {
		subsys[res] = '\0';
		free(G.subsystem);
		if (G.subsys_env) {
			bb_unsetenv_and_free(G.subsys_env);
			G.subsys_env = NULL;
		}
		/* Set G.subsystem and $SUBSYSTEM from symlink's last component */
		G.subsystem = strrchr(subsys, '/');
		if (G.subsystem) {
			G.subsystem = xstrdup(G.subsystem + 1);
			G.subsys_env = xasprintf("%s=%s", "SUBSYSTEM", G.subsystem);
			putenv(G.subsys_env);
		}
	}

	make_device(/*DEVNAME:*/ NULL, path, OP_add);

	return TRUE;
}

/* Directory callback for /sys/ traversal */
static int FAST_FUNC dirAction(const char *fileName UNUSED_PARAM,
		struct stat *statbuf UNUSED_PARAM,
		void *userData UNUSED_PARAM,
		int depth)
{
	return (depth >= MAX_SYSFS_DEPTH ? SKIP : TRUE);
}

/* For the full gory details, see linux/Documentation/firmware_class/README
 *
 * Firmware loading works like this:
 * - kernel sets FIRMWARE env var
 * - userspace checks /lib/firmware/$FIRMWARE
 * - userspace waits for /sys/$DEVPATH/loading to appear
 * - userspace writes "1" to /sys/$DEVPATH/loading
 * - userspace copies /lib/firmware/$FIRMWARE into /sys/$DEVPATH/data
 * - userspace writes "0" (worked) or "-1" (failed) to /sys/$DEVPATH/loading
 * - kernel loads firmware into device
 */
static void load_firmware(const char *firmware, const char *sysfs_path)
{
	int cnt;
	int firmware_fd, loading_fd;

	/* check for /lib/firmware/$FIRMWARE */
	firmware_fd = -1;
	if (chdir("/lib/firmware") == 0)
		firmware_fd = open(firmware, O_RDONLY); /* can fail */

	/* check for /sys/$DEVPATH/loading ... give 30 seconds to appear */
	xchdir(sysfs_path);
	for (cnt = 0; cnt < 30; ++cnt) {
		loading_fd = open("loading", O_WRONLY);
		if (loading_fd >= 0)
			goto loading;
		sleep(1);
	}
	goto out;

 loading:
	cnt = 0;
	if (firmware_fd >= 0) {
		int data_fd;

		/* tell kernel we're loading by "echo 1 > /sys/$DEVPATH/loading" */
		if (full_write(loading_fd, "1", 1) != 1)
			goto out;

		/* load firmware into /sys/$DEVPATH/data */
		data_fd = open("data", O_WRONLY);
		if (data_fd < 0)
			goto out;
		cnt = bb_copyfd_eof(firmware_fd, data_fd);
		if (ENABLE_FEATURE_CLEAN_UP)
			close(data_fd);
	}

	/* Tell kernel result by "echo [0|-1] > /sys/$DEVPATH/loading"
	 * Note: we emit -1 also if firmware file wasn't found.
	 * There are cases when otherwise kernel would wait for minutes
	 * before timing out.
	 */
	if (cnt > 0)
		full_write(loading_fd, "0", 1);
	else
		full_write(loading_fd, "-1", 2);

 out:
	xchdir("/dev");
	if (ENABLE_FEATURE_CLEAN_UP) {
		close(firmware_fd);
		close(loading_fd);
	}
}

static char *curtime(void)
{
	struct timeval tv;
	gettimeofday(&tv, NULL);
	sprintf(
		strftime_HHMMSS(G.timestr, sizeof(G.timestr), &tv.tv_sec),
		".%06u",
		(unsigned)tv.tv_usec
	);
	return G.timestr;
}

static void open_mdev_log(const char *seq, unsigned my_pid)
{
	int logfd = open("mdev.log", O_WRONLY | O_APPEND);
	if (logfd >= 0) {
		xmove_fd(logfd, STDERR_FILENO);
		G.verbose = 2;
		applet_name = xasprintf("%s[%s]", applet_name, seq ? seq : utoa(my_pid));
	}
}

/* If it exists, does /dev/mdev.seq match $SEQNUM?
 * If it does not match, earlier mdev is running
 * in parallel, and we need to wait.
 * Active mdev pokes us with SIGCHLD to check the new file.
 */
static int
wait_for_seqfile(unsigned expected_seq)
{
	/* We time out after 2 sec */
	static const struct timespec ts = { 0, 32*1000*1000 };
	int timeout = 2000 / 32;
	int seq_fd = -1;
	int do_once = 1;
	sigset_t set_CHLD;

	sigemptyset(&set_CHLD);
	sigaddset(&set_CHLD, SIGCHLD);
	sigprocmask(SIG_BLOCK, &set_CHLD, NULL);

	for (;;) {
		int seqlen;
		char seqbuf[sizeof(long)*3 + 2];
		unsigned seqbufnum;

		if (seq_fd < 0) {
			seq_fd = open("mdev.seq", O_RDWR);
			if (seq_fd < 0)
				break;
			close_on_exec_on(seq_fd);
		}
		seqlen = pread(seq_fd, seqbuf, sizeof(seqbuf) - 1, 0);
		if (seqlen < 0) {
			close(seq_fd);
			seq_fd = -1;
			break;
		}
		seqbuf[seqlen] = '\0';
		if (seqbuf[0] == '\n' || seqbuf[0] == '\0') {
			/* seed file: write out seq ASAP */
			xwrite_str(seq_fd, utoa(expected_seq));
			xlseek(seq_fd, 0, SEEK_SET);
			dbg2("first seq written");
			break;
		}
		seqbufnum = atoll(seqbuf);
		if (seqbufnum == expected_seq) {
			/* correct idx */
			break;
		}
		if (seqbufnum > expected_seq) {
			/* a later mdev runs already (this was seen by users to happen) */
			/* do not overwrite seqfile on exit */
			close(seq_fd);
			seq_fd = -1;
			break;
		}
		if (do_once) {
			dbg2("%s mdev.seq='%s', need '%u'", curtime(), seqbuf, expected_seq);
			do_once = 0;
		}
		if (sigtimedwait(&set_CHLD, NULL, &ts) >= 0) {
			dbg3("woken up");
			continue; /* don't decrement timeout! */
		}
		if (--timeout == 0) {
			dbg1("%s mdev.seq='%s'", "timed out", seqbuf);
			break;
		}
	}
	sigprocmask(SIG_UNBLOCK, &set_CHLD, NULL);
	return seq_fd;
}

static void signal_mdevs(unsigned my_pid)
{
	procps_status_t* p = NULL;
	while ((p = procps_scan(p, PSSCAN_ARGV0)) != NULL) {
		if (p->pid != my_pid
		 && p->argv0
		 && strcmp(bb_basename(p->argv0), "mdev") == 0
		) {
			kill(p->pid, SIGCHLD);
		}
	}
}

static void process_action(char *temp, unsigned my_pid)
{
	char *fw;
	char *seq;
	char *action;
	char *env_devname;
	char *env_devpath;
	unsigned seqnum = seqnum; /* for compiler */
	int seq_fd;
	smalluint op;

	/* Hotplug:
	 * env ACTION=... DEVPATH=... SUBSYSTEM=... [SEQNUM=...] mdev
	 * ACTION can be "add", "remove", "change"
	 * DEVPATH is like "/block/sda" or "/class/input/mice"
	 */
	env_devname = getenv("DEVNAME"); /* can be NULL */
	G.subsystem = getenv("SUBSYSTEM");
	action = getenv("ACTION");
	env_devpath = getenv("DEVPATH");
	if (!action || !env_devpath /*|| !G.subsystem*/)
		bb_show_usage();
	fw = getenv("FIRMWARE");
	seq = getenv("SEQNUM");
	op = index_in_strings(keywords, action);

	if (my_pid)
		open_mdev_log(seq, my_pid);

	seq_fd = -1;
	if (my_pid && seq) {
		seqnum = atoll(seq);
		seq_fd = wait_for_seqfile(seqnum);
	}

	dbg1("%s "
		"ACTION:%s SEQNUM:%s SUBSYSTEM:%s DEVNAME:%s DEVPATH:%s"
		"%s%s",
		curtime(),
		action, seq, G.subsystem, env_devname, env_devpath,
		fw ? " FW:" : "", fw ? fw : ""
	);

	snprintf(temp, PATH_MAX, "/sys%s", env_devpath);
	if (op == OP_remove) {
		/* Ignoring "remove firmware". It was reported
		 * to happen and to cause erroneous deletion
		 * of device nodes. */
		if (!fw)
			make_device(env_devname, temp, op);
	}
	else {
		make_device(env_devname, temp, op);
		if (ENABLE_FEATURE_MDEV_LOAD_FIRMWARE) {
			if (op == OP_add && fw)
				load_firmware(fw, temp);
		}
	}

	if (seq_fd >= 0) {
		xwrite_str(seq_fd, utoa(seqnum + 1));
		signal_mdevs(my_pid);
	}
}

static void initial_scan(char *temp)
{
	struct stat st;

	xstat("/", &st);
	G.root_major = major(st.st_dev);
	G.root_minor = minor(st.st_dev);

	putenv((char*)"ACTION=add");

	/* Create all devices from /sys/dev hierarchy */
	recursive_action("/sys/dev",
			 ACTION_RECURSE | ACTION_FOLLOWLINKS,
			 fileAction, dirAction, temp, 0);
}

#if ENABLE_FEATURE_MDEV_DAEMON

/* uevent applet uses 16k buffer, and mmaps it before every read */
# define BUFFER_SIZE (2 * 1024)
# define RCVBUF (2 * 1024 * 1024)
# define MAX_ENV 32

static void daemon_loop(char *temp, int fd)
{
	for (;;) {
		char netbuf[BUFFER_SIZE];
		char *env[MAX_ENV];
		char *s, *end;
		ssize_t len;
		int idx;

		len = safe_read(fd, netbuf, sizeof(netbuf) - 1);
		if (len < 0) {
			bb_perror_msg_and_die("read");
		}
		end = netbuf + len;
		*end = '\0';

		idx = 0;
		s = netbuf;
		while (s < end && idx < MAX_ENV) {
			if (endofname(s)[0] == '=') {
				env[idx++] = s;
				putenv(s);
			}
			s += strlen(s) + 1;
		}

		process_action(temp, 0);

		while (idx)
			bb_unsetenv(env[--idx]);
	}
}
#endif

int mdev_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int mdev_main(int argc UNUSED_PARAM, char **argv)
{
	enum {
		MDEV_OPT_SCAN       = 1 << 0,
		MDEV_OPT_DAEMON     = 1 << 1,
		MDEV_OPT_FOREGROUND = 1 << 2,
	};
	int opt;
	RESERVE_CONFIG_BUFFER(temp, PATH_MAX + SCRATCH_SIZE);

	INIT_G();

	/* We can be called as hotplug helper */
	/* Kernel cannot provide suitable stdio fds for us, do it ourself */
	bb_sanitize_stdio();

	/* Force the configuration file settings exactly */
	umask(0);

	xchdir("/dev");

	opt = getopt32(argv, "s" IF_FEATURE_MDEV_DAEMON("df"));

#if ENABLE_FEATURE_MDEV_CONF
	G.filename = "/etc/mdev.conf";
	if (opt & (MDEV_OPT_SCAN|MDEV_OPT_DAEMON)) {
		/* Same as xrealloc_vector(NULL, 4, 0): */
		G.rule_vec = xzalloc((1 << 4) * sizeof(*G.rule_vec));
	}
#endif

#if ENABLE_FEATURE_MDEV_DAEMON
	if (opt & MDEV_OPT_DAEMON) {
		/*
		 * Daemon mode listening on uevent netlink socket.
		 */
		struct sockaddr_nl sa;
		int fd;

//TODO: reuse same code in uevent
		// Subscribe for UEVENT kernel messages
		sa.nl_family = AF_NETLINK;
		sa.nl_pad = 0;
		sa.nl_pid = getpid();
		sa.nl_groups = 1 << 0;
		fd = xsocket(AF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT);
		xbind(fd, (struct sockaddr *) &sa, sizeof(sa));
		close_on_exec_on(fd);

		// Without a sufficiently big RCVBUF, a ton of simultaneous events
		// can trigger ENOBUFS on read, which is unrecoverable.
		// Reproducer:
		//	mdev -d
		// 	find /sys -name uevent -exec sh -c 'echo add >"{}"' ';'
		//
		// SO_RCVBUFFORCE (root only) can go above net.core.rmem_max sysctl
		setsockopt_SOL_SOCKET_int(fd, SO_RCVBUF,      RCVBUF);
		setsockopt_SOL_SOCKET_int(fd, SO_RCVBUFFORCE, RCVBUF);

		/*
		 * Make inital scan after the uevent socket is alive and
		 * _before_ we fork away.
		 */
		initial_scan(temp);

		if (!(opt & MDEV_OPT_FOREGROUND))
			bb_daemonize_or_rexec(0, argv);

		open_mdev_log(NULL, getpid());

		daemon_loop(temp, fd);
	}
#endif
	if (opt & MDEV_OPT_SCAN) {
		/*
		 * Scan: mdev -s
		 */
		initial_scan(temp);
	} else {
		process_action(temp, getpid());

		dbg1("%s exiting", curtime());
	}

	if (ENABLE_FEATURE_CLEAN_UP)
		RELEASE_CONFIG_BUFFER(temp);

	return EXIT_SUCCESS;
}