aboutsummaryrefslogtreecommitdiff
path: root/drivers/tty/sysrq.c
blob: ed27fda13387bf56ee7ff0d0309cb4fbf7b56218 (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
/*
 *	Linux Magic System Request Key Hacks
 *
 *	(c) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
 *	based on ideas by Pavel Machek <pavel@atrey.karlin.mff.cuni.cz>
 *
 *	(c) 2000 Crutcher Dunnavant <crutcher+kernel@datastacks.com>
 *	overhauled to use key registration
 *	based upon discusions in irc://irc.openprojects.net/#kernelnewbies
 *
 *	Copyright (c) 2010 Dmitry Torokhov
 *	Input handler conversion
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/sched.h>
#include <linux/sched/rt.h>
#include <linux/interrupt.h>
#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/kdev_t.h>
#include <linux/major.h>
#include <linux/reboot.h>
#include <linux/sysrq.h>
#include <linux/kbd_kern.h>
#include <linux/proc_fs.h>
#include <linux/nmi.h>
#include <linux/quotaops.h>
#include <linux/perf_event.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/suspend.h>
#include <linux/writeback.h>
#include <linux/swap.h>
#include <linux/spinlock.h>
#include <linux/vt_kern.h>
#include <linux/workqueue.h>
#include <linux/hrtimer.h>
#include <linux/oom.h>
#include <linux/slab.h>
#include <linux/input.h>
#include <linux/uaccess.h>
#include <linux/moduleparam.h>
#include <linux/jiffies.h>
#include <linux/syscalls.h>
#include <linux/of.h>
#include <linux/rcupdate.h>

#include <asm/ptrace.h>
#include <asm/irq_regs.h>

/* Whether we react on sysrq keys or just ignore them */
static int __read_mostly sysrq_enabled = CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE;
static bool __read_mostly sysrq_always_enabled;

static bool sysrq_on(void)
{
	return sysrq_enabled || sysrq_always_enabled;
}

/*
 * A value of 1 means 'all', other nonzero values are an op mask:
 */
static bool sysrq_on_mask(int mask)
{
	return sysrq_always_enabled ||
	       sysrq_enabled == 1 ||
	       (sysrq_enabled & mask);
}

static int __init sysrq_always_enabled_setup(char *str)
{
	sysrq_always_enabled = true;
	pr_info("sysrq always enabled.\n");

	return 1;
}

__setup("sysrq_always_enabled", sysrq_always_enabled_setup);


static void sysrq_handle_loglevel(int key)
{
	int i;

	i = key - '0';
	console_loglevel = CONSOLE_LOGLEVEL_DEFAULT;
	pr_info("Loglevel set to %d\n", i);
	console_loglevel = i;
}
static struct sysrq_key_op sysrq_loglevel_op = {
	.handler	= sysrq_handle_loglevel,
	.help_msg	= "loglevel(0-9)",
	.action_msg	= "Changing Loglevel",
	.enable_mask	= SYSRQ_ENABLE_LOG,
};

#ifdef CONFIG_VT
static void sysrq_handle_SAK(int key)
{
	struct work_struct *SAK_work = &vc_cons[fg_console].SAK_work;
	schedule_work(SAK_work);
}
static struct sysrq_key_op sysrq_SAK_op = {
	.handler	= sysrq_handle_SAK,
	.help_msg	= "sak(k)",
	.action_msg	= "SAK",
	.enable_mask	= SYSRQ_ENABLE_KEYBOARD,
};
#else
#define sysrq_SAK_op (*(struct sysrq_key_op *)NULL)
#endif

#ifdef CONFIG_VT
static void sysrq_handle_unraw(int key)
{
	vt_reset_unicode(fg_console);
}

static struct sysrq_key_op sysrq_unraw_op = {
	.handler	= sysrq_handle_unraw,
	.help_msg	= "unraw(r)",
	.action_msg	= "Keyboard mode set to system default",
	.enable_mask	= SYSRQ_ENABLE_KEYBOARD,
};
#else
#define sysrq_unraw_op (*(struct sysrq_key_op *)NULL)
#endif /* CONFIG_VT */

static void sysrq_handle_crash(int key)
{
	char *killer = NULL;

	/* we need to release the RCU read lock here,
	 * otherwise we get an annoying
	 * 'BUG: sleeping function called from invalid context'
	 * complaint from the kernel before the panic.
	 */
	rcu_read_unlock();
	panic_on_oops = 1;	/* force panic */
	wmb();
	*killer = 1;
}
static struct sysrq_key_op sysrq_crash_op = {
	.handler	= sysrq_handle_crash,
	.help_msg	= "crash(c)",
	.action_msg	= "Trigger a crash",
	.enable_mask	= SYSRQ_ENABLE_DUMP,
};

static void sysrq_handle_reboot(int key)
{
	lockdep_off();
	local_irq_enable();
	emergency_restart();
}
static struct sysrq_key_op sysrq_reboot_op = {
	.handler	= sysrq_handle_reboot,
	.help_msg	= "reboot(b)",
	.action_msg	= "Resetting",
	.enable_mask	= SYSRQ_ENABLE_BOOT,
};

static void sysrq_handle_sync(int key)
{
	emergency_sync();
}
static struct sysrq_key_op sysrq_sync_op = {
	.handler	= sysrq_handle_sync,
	.help_msg	= "sync(s)",
	.action_msg	= "Emergency Sync",
	.enable_mask	= SYSRQ_ENABLE_SYNC,
};

static void sysrq_handle_show_timers(int key)
{
	sysrq_timer_list_show();
}

static struct sysrq_key_op sysrq_show_timers_op = {
	.handler	= sysrq_handle_show_timers,
	.help_msg	= "show-all-timers(q)",
	.action_msg	= "Show clockevent devices & pending hrtimers (no others)",
};

static void sysrq_handle_mountro(int key)
{
	emergency_remount();
}
static struct sysrq_key_op sysrq_mountro_op = {
	.handler	= sysrq_handle_mountro,
	.help_msg	= "unmount(u)",
	.action_msg	= "Emergency Remount R/O",
	.enable_mask	= SYSRQ_ENABLE_REMOUNT,
};

#ifdef CONFIG_LOCKDEP
static void sysrq_handle_showlocks(int key)
{
	debug_show_all_locks();
}

static struct sysrq_key_op sysrq_showlocks_op = {
	.handler	= sysrq_handle_showlocks,
	.help_msg	= "show-all-locks(d)",
	.action_msg	= "Show Locks Held",
};
#else
#define sysrq_showlocks_op (*(struct sysrq_key_op *)NULL)
#endif

#ifdef CONFIG_SMP
static DEFINE_SPINLOCK(show_lock);

static void showacpu(void *dummy)
{
	unsigned long flags;

	/* Idle CPUs have no interesting backtrace. */
	if (idle_cpu(smp_processor_id()))
		return;

	spin_lock_irqsave(&show_lock, flags);
	pr_info("CPU%d:\n", smp_processor_id());
	show_stack(NULL, NULL);
	spin_unlock_irqrestore(&show_lock, flags);
}

static void sysrq_showregs_othercpus(struct work_struct *dummy)
{
	smp_call_function(showacpu, NULL, 0);
}

static DECLARE_WORK(sysrq_showallcpus, sysrq_showregs_othercpus);

static void sysrq_handle_showallcpus(int key)
{
	/*
	 * Fall back to the workqueue based printing if the
	 * backtrace printing did not succeed or the
	 * architecture has no support for it:
	 */
	if (!trigger_all_cpu_backtrace()) {
		struct pt_regs *regs = NULL;

		if (in_irq())
			regs = get_irq_regs();
		if (regs) {
			pr_info("CPU%d:\n", smp_processor_id());
			show_regs(regs);
		}
		schedule_work(&sysrq_showallcpus);
	}
}

static struct sysrq_key_op sysrq_showallcpus_op = {
	.handler	= sysrq_handle_showallcpus,
	.help_msg	= "show-backtrace-all-active-cpus(l)",
	.action_msg	= "Show backtrace of all active CPUs",
	.enable_mask	= SYSRQ_ENABLE_DUMP,
};
#endif

static void sysrq_handle_showregs(int key)
{
	struct pt_regs *regs = NULL;

	if (in_irq())
		regs = get_irq_regs();
	if (regs)
		show_regs(regs);
	perf_event_print_debug();
}
static struct sysrq_key_op sysrq_showregs_op = {
	.handler	= sysrq_handle_showregs,
	.help_msg	= "show-registers(p)",
	.action_msg	= "Show Regs",
	.enable_mask	= SYSRQ_ENABLE_DUMP,
};

static void sysrq_handle_showstate(int key)
{
	show_state();
	show_workqueue_state();
}
static struct sysrq_key_op sysrq_showstate_op = {
	.handler	= sysrq_handle_showstate,
	.help_msg	= "show-task-states(t)",
	.action_msg	= "Show State",
	.enable_mask	= SYSRQ_ENABLE_DUMP,
};

static void sysrq_handle_showstate_blocked(int key)
{
	show_state_filter(TASK_UNINTERRUPTIBLE);
}
static struct sysrq_key_op sysrq_showstate_blocked_op = {
	.handler	= sysrq_handle_showstate_blocked,
	.help_msg	= "show-blocked-tasks(w)",
	.action_msg	= "Show Blocked State",
	.enable_mask	= SYSRQ_ENABLE_DUMP,
};

#ifdef CONFIG_TRACING
#include <linux/ftrace.h>

static void sysrq_ftrace_dump(int key)
{
	ftrace_dump(DUMP_ALL);
}
static struct sysrq_key_op sysrq_ftrace_dump_op = {
	.handler	= sysrq_ftrace_dump,
	.help_msg	= "dump-ftrace-buffer(z)",
	.action_msg	= "Dump ftrace buffer",
	.enable_mask	= SYSRQ_ENABLE_DUMP,
};
#else
#define sysrq_ftrace_dump_op (*(struct sysrq_key_op *)NULL)
#endif

static void sysrq_handle_showmem(int key)
{
	show_mem(0);
}
static struct sysrq_key_op sysrq_showmem_op = {
	.handler	= sysrq_handle_showmem,
	.help_msg	= "show-memory-usage(m)",
	.action_msg	= "Show Memory",
	.enable_mask	= SYSRQ_ENABLE_DUMP,
};

/*
 * Signal sysrq helper function.  Sends a signal to all user processes.
 */
static void send_sig_all(int sig)
{
	struct task_struct *p;

	read_lock(&tasklist_lock);
	for_each_process(p) {
		if (p->flags & PF_KTHREAD)
			continue;
		if (is_global_init(p))
			continue;

		do_send_sig_info(sig, SEND_SIG_FORCED, p, true);
	}
	read_unlock(&tasklist_lock);
}

static void sysrq_handle_term(int key)
{
	send_sig_all(SIGTERM);
	console_loglevel = CONSOLE_LOGLEVEL_DEBUG;
}
static struct sysrq_key_op sysrq_term_op = {
	.handler	= sysrq_handle_term,
	.help_msg	= "terminate-all-tasks(e)",
	.action_msg	= "Terminate All Tasks",
	.enable_mask	= SYSRQ_ENABLE_SIGNAL,
};

static void moom_callback(struct work_struct *ignored)
{
	const gfp_t gfp_mask = GFP_KERNEL;
	struct oom_control oc = {
		.zonelist = node_zonelist(first_memory_node, gfp_mask),
		.nodemask = NULL,
		.gfp_mask = gfp_mask,
		.order = -1,
	};

	mutex_lock(&oom_lock);
	if (!out_of_memory(&oc))
		pr_info("OOM request ignored because killer is disabled\n");
	mutex_unlock(&oom_lock);
}

static DECLARE_WORK(moom_work, moom_callback);

static void sysrq_handle_moom(int key)
{
	schedule_work(&moom_work);
}
static struct sysrq_key_op sysrq_moom_op = {
	.handler	= sysrq_handle_moom,
	.help_msg	= "memory-full-oom-kill(f)",
	.action_msg	= "Manual OOM execution",
	.enable_mask	= SYSRQ_ENABLE_SIGNAL,
};

#ifdef CONFIG_BLOCK
static void sysrq_handle_thaw(int key)
{
	emergency_thaw_all();
}
static struct sysrq_key_op sysrq_thaw_op = {
	.handler	= sysrq_handle_thaw,
	.help_msg	= "thaw-filesystems(j)",
	.action_msg	= "Emergency Thaw of all frozen filesystems",
	.enable_mask	= SYSRQ_ENABLE_SIGNAL,
};
#endif

static void sysrq_handle_kill(int key)
{
	send_sig_all(SIGKILL);
	console_loglevel = CONSOLE_LOGLEVEL_DEBUG;
}
static struct sysrq_key_op sysrq_kill_op = {
	.handler	= sysrq_handle_kill,
	.help_msg	= "kill-all-tasks(i)",
	.action_msg	= "Kill All Tasks",
	.enable_mask	= SYSRQ_ENABLE_SIGNAL,
};

static void sysrq_handle_unrt(int key)
{
	normalize_rt_tasks();
}
static struct sysrq_key_op sysrq_unrt_op = {
	.handler	= sysrq_handle_unrt,
	.help_msg	= "nice-all-RT-tasks(n)",
	.action_msg	= "Nice All RT Tasks",
	.enable_mask	= SYSRQ_ENABLE_RTNICE,
};

/* Key Operations table and lock */
static DEFINE_SPINLOCK(sysrq_key_table_lock);

static struct sysrq_key_op *sysrq_key_table[36] = {
	&sysrq_loglevel_op,		/* 0 */
	&sysrq_loglevel_op,		/* 1 */
	&sysrq_loglevel_op,		/* 2 */
	&sysrq_loglevel_op,		/* 3 */
	&sysrq_loglevel_op,		/* 4 */
	&sysrq_loglevel_op,		/* 5 */
	&sysrq_loglevel_op,		/* 6 */
	&sysrq_loglevel_op,		/* 7 */
	&sysrq_loglevel_op,		/* 8 */
	&sysrq_loglevel_op,		/* 9 */

	/*
	 * a: Don't use for system provided sysrqs, it is handled specially on
	 * sparc and will never arrive.
	 */
	NULL,				/* a */
	&sysrq_reboot_op,		/* b */
	&sysrq_crash_op,		/* c & ibm_emac driver debug */
	&sysrq_showlocks_op,		/* d */
	&sysrq_term_op,			/* e */
	&sysrq_moom_op,			/* f */
	/* g: May be registered for the kernel debugger */
	NULL,				/* g */
	NULL,				/* h - reserved for help */
	&sysrq_kill_op,			/* i */
#ifdef CONFIG_BLOCK
	&sysrq_thaw_op,			/* j */
#else
	NULL,				/* j */
#endif
	&sysrq_SAK_op,			/* k */
#ifdef CONFIG_SMP
	&sysrq_showallcpus_op,		/* l */
#else
	NULL,				/* l */
#endif
	&sysrq_showmem_op,		/* m */
	&sysrq_unrt_op,			/* n */
	/* o: This will often be registered as 'Off' at init time */
	NULL,				/* o */
	&sysrq_showregs_op,		/* p */
	&sysrq_show_timers_op,		/* q */
	&sysrq_unraw_op,		/* r */
	&sysrq_sync_op,			/* s */
	&sysrq_showstate_op,		/* t */
	&sysrq_mountro_op,		/* u */
	/* v: May be registered for frame buffer console restore */
	NULL,				/* v */
	&sysrq_showstate_blocked_op,	/* w */
	/* x: May be registered on mips for TLB dump */
	/* x: May be registered on ppc/powerpc for xmon */
	/* x: May be registered on sparc64 for global PMU dump */
	NULL,				/* x */
	/* y: May be registered on sparc64 for global register dump */
	NULL,				/* y */
	&sysrq_ftrace_dump_op,		/* z */
};

/* key2index calculation, -1 on invalid index */
static int sysrq_key_table_key2index(int key)
{
	int retval;

	if ((key >= '0') && (key <= '9'))
		retval = key - '0';
	else if ((key >= 'a') && (key <= 'z'))
		retval = key + 10 - 'a';
	else
		retval = -1;
	return retval;
}

/*
 * get and put functions for the table, exposed to modules.
 */
struct sysrq_key_op *__sysrq_get_key_op(int key)
{
        struct sysrq_key_op *op_p = NULL;
        int i;

	i = sysrq_key_table_key2index(key);
	if (i != -1)
	        op_p = sysrq_key_table[i];

        return op_p;
}

static void __sysrq_put_key_op(int key, struct sysrq_key_op *op_p)
{
        int i = sysrq_key_table_key2index(key);

        if (i != -1)
                sysrq_key_table[i] = op_p;
}

void __handle_sysrq(int key, bool check_mask)
{
	struct sysrq_key_op *op_p;
	int orig_log_level;
	int i;

	rcu_sysrq_start();
	rcu_read_lock();
	/*
	 * Raise the apparent loglevel to maximum so that the sysrq header
	 * is shown to provide the user with positive feedback.  We do not
	 * simply emit this at KERN_EMERG as that would change message
	 * routing in the consumers of /proc/kmsg.
	 */
	orig_log_level = console_loglevel;
	console_loglevel = CONSOLE_LOGLEVEL_DEFAULT;
	pr_info("SysRq : ");

        op_p = __sysrq_get_key_op(key);
        if (op_p) {
		/*
		 * Should we check for enabled operations (/proc/sysrq-trigger
		 * should not) and is the invoked operation enabled?
		 */
		if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
			pr_cont("%s\n", op_p->action_msg);
			console_loglevel = orig_log_level;
			op_p->handler(key);
		} else {
			pr_cont("This sysrq operation is disabled.\n");
		}
	} else {
		pr_cont("HELP : ");
		/* Only print the help msg once per handler */
		for (i = 0; i < ARRAY_SIZE(sysrq_key_table); i++) {
			if (sysrq_key_table[i]) {
				int j;

				for (j = 0; sysrq_key_table[i] !=
						sysrq_key_table[j]; j++)
					;
				if (j != i)
					continue;
				pr_cont("%s ", sysrq_key_table[i]->help_msg);
			}
		}
		pr_cont("\n");
		console_loglevel = orig_log_level;
	}
	rcu_read_unlock();
	rcu_sysrq_end();
}

void handle_sysrq(int key)
{
	if (sysrq_on())
		__handle_sysrq(key, true);
}
EXPORT_SYMBOL(handle_sysrq);

#ifdef CONFIG_INPUT
static int sysrq_reset_downtime_ms;

/* Simple translation table for the SysRq keys */
static const unsigned char sysrq_xlate[KEY_CNT] =
        "\000\0331234567890-=\177\t"                    /* 0x00 - 0x0f */
        "qwertyuiop[]\r\000as"                          /* 0x10 - 0x1f */
        "dfghjkl;'`\000\\zxcv"                          /* 0x20 - 0x2f */
        "bnm,./\000*\000 \000\201\202\203\204\205"      /* 0x30 - 0x3f */
        "\206\207\210\211\212\000\000789-456+1"         /* 0x40 - 0x4f */
        "230\177\000\000\213\214\000\000\000\000\000\000\000\000\000\000" /* 0x50 - 0x5f */
        "\r\000/";                                      /* 0x60 - 0x6f */

struct sysrq_state {
	struct input_handle handle;
	struct work_struct reinject_work;
	unsigned long key_down[BITS_TO_LONGS(KEY_CNT)];
	unsigned int alt;
	unsigned int alt_use;
	bool active;
	bool need_reinject;
	bool reinjecting;

	/* reset sequence handling */
	bool reset_canceled;
	bool reset_requested;
	unsigned long reset_keybit[BITS_TO_LONGS(KEY_CNT)];
	int reset_seq_len;
	int reset_seq_cnt;
	int reset_seq_version;
	struct timer_list keyreset_timer;
};

#define SYSRQ_KEY_RESET_MAX	20 /* Should be plenty */
static unsigned short sysrq_reset_seq[SYSRQ_KEY_RESET_MAX];
static unsigned int sysrq_reset_seq_len;
static unsigned int sysrq_reset_seq_version = 1;

static void sysrq_parse_reset_sequence(struct sysrq_state *state)
{
	int i;
	unsigned short key;

	state->reset_seq_cnt = 0;

	for (i = 0; i < sysrq_reset_seq_len; i++) {
		key = sysrq_reset_seq[i];

		if (key == KEY_RESERVED || key > KEY_MAX)
			break;

		__set_bit(key, state->reset_keybit);
		state->reset_seq_len++;

		if (test_bit(key, state->key_down))
			state->reset_seq_cnt++;
	}

	/* Disable reset until old keys are not released */
	state->reset_canceled = state->reset_seq_cnt != 0;

	state->reset_seq_version = sysrq_reset_seq_version;
}

static void sysrq_do_reset(unsigned long _state)
{
	struct sysrq_state *state = (struct sysrq_state *) _state;

	state->reset_requested = true;

	sys_sync();
	kernel_restart(NULL);
}

static void sysrq_handle_reset_request(struct sysrq_state *state)
{
	if (state->reset_requested)
		__handle_sysrq(sysrq_xlate[KEY_B], false);

	if (sysrq_reset_downtime_ms)
		mod_timer(&state->keyreset_timer,
			jiffies + msecs_to_jiffies(sysrq_reset_downtime_ms));
	else
		sysrq_do_reset((unsigned long)state);
}

static void sysrq_detect_reset_sequence(struct sysrq_state *state,
					unsigned int code, int value)
{
	if (!test_bit(code, state->reset_keybit)) {
		/*
		 * Pressing any key _not_ in reset sequence cancels
		 * the reset sequence.  Also cancelling the timer in
		 * case additional keys were pressed after a reset
		 * has been requested.
		 */
		if (value && state->reset_seq_cnt) {
			state->reset_canceled = true;
			del_timer(&state->keyreset_timer);
		}
	} else if (value == 0) {
		/*
		 * Key release - all keys in the reset sequence need
		 * to be pressed and held for the reset timeout
		 * to hold.
		 */
		del_timer(&state->keyreset_timer);

		if (--state->reset_seq_cnt == 0)
			state->reset_canceled = false;
	} else if (value == 1) {
		/* key press, not autorepeat */
		if (++state->reset_seq_cnt == state->reset_seq_len &&
		    !state->reset_canceled) {
			sysrq_handle_reset_request(state);
		}
	}
}

#ifdef CONFIG_OF
static void sysrq_of_get_keyreset_config(void)
{
	u32 key;
	struct device_node *np;
	struct property *prop;
	const __be32 *p;

	np = of_find_node_by_path("/chosen/linux,sysrq-reset-seq");
	if (!np) {
		pr_debug("No sysrq node found");
		return;
	}

	/* Reset in case a __weak definition was present */
	sysrq_reset_seq_len = 0;

	of_property_for_each_u32(np, "keyset", prop, p, key) {
		if (key == KEY_RESERVED || key > KEY_MAX ||
		    sysrq_reset_seq_len == SYSRQ_KEY_RESET_MAX)
			break;

		sysrq_reset_seq[sysrq_reset_seq_len++] = (unsigned short)key;
	}

	/* Get reset timeout if any. */
	of_property_read_u32(np, "timeout-ms", &sysrq_reset_downtime_ms);
}
#else
static void sysrq_of_get_keyreset_config(void)
{
}
#endif

static void sysrq_reinject_alt_sysrq(struct work_struct *work)
{
	struct sysrq_state *sysrq =
			container_of(work, struct sysrq_state, reinject_work);
	struct input_handle *handle = &sysrq->handle;
	unsigned int alt_code = sysrq->alt_use;

	if (sysrq->need_reinject) {
		/* we do not want the assignment to be reordered */
		sysrq->reinjecting = true;
		mb();

		/* Simulate press and release of Alt + SysRq */
		input_inject_event(handle, EV_KEY, alt_code, 1);
		input_inject_event(handle, EV_KEY, KEY_SYSRQ, 1);
		input_inject_event(handle, EV_SYN, SYN_REPORT, 1);

		input_inject_event(handle, EV_KEY, KEY_SYSRQ, 0);
		input_inject_event(handle, EV_KEY, alt_code, 0);
		input_inject_event(handle, EV_SYN, SYN_REPORT, 1);

		mb();
		sysrq->reinjecting = false;
	}
}

static bool sysrq_handle_keypress(struct sysrq_state *sysrq,
				  unsigned int code, int value)
{
	bool was_active = sysrq->active;
	bool suppress;

	switch (code) {

	case KEY_LEFTALT:
	case KEY_RIGHTALT:
		if (!value) {
			/* One of ALTs is being released */
			if (sysrq->active && code == sysrq->alt_use)
				sysrq->active = false;

			sysrq->alt = KEY_RESERVED;

		} else if (value != 2) {
			sysrq->alt = code;
			sysrq->need_reinject = false;
		}
		break;

	case KEY_SYSRQ:
		if (value == 1 && sysrq->alt != KEY_RESERVED) {
			sysrq->active = true;
			sysrq->alt_use = sysrq->alt;
			/*
			 * If nothing else will be pressed we'll need
			 * to re-inject Alt-SysRq keysroke.
			 */
			sysrq->need_reinject = true;
		}

		/*
		 * Pretend that sysrq was never pressed at all. This
		 * is needed to properly handle KGDB which will try
		 * to release all keys after exiting debugger. If we
		 * do not clear key bit it KGDB will end up sending
		 * release events for Alt and SysRq, potentially
		 * triggering print screen function.
		 */
		if (sysrq->active)
			clear_bit(KEY_SYSRQ, sysrq->handle.dev->key);

		break;

	default:
		if (sysrq->active && value && value != 2) {
			sysrq->need_reinject = false;
			__handle_sysrq(sysrq_xlate[code], true);
		}
		break;
	}

	suppress = sysrq->active;

	if (!sysrq->active) {

		/*
		 * See if reset sequence has changed since the last time.
		 */
		if (sysrq->reset_seq_version != sysrq_reset_seq_version)
			sysrq_parse_reset_sequence(sysrq);

		/*
		 * If we are not suppressing key presses keep track of
		 * keyboard state so we can release keys that have been
		 * pressed before entering SysRq mode.
		 */
		if (value)
			set_bit(code, sysrq->key_down);
		else
			clear_bit(code, sysrq->key_down);

		if (was_active)
			schedule_work(&sysrq->reinject_work);

		/* Check for reset sequence */
		sysrq_detect_reset_sequence(sysrq, code, value);

	} else if (value == 0 && test_and_clear_bit(code, sysrq->key_down)) {
		/*
		 * Pass on release events for keys that was pressed before
		 * entering SysRq mode.
		 */
		suppress = false;
	}

	return suppress;
}

static bool sysrq_filter(struct input_handle *handle,
			 unsigned int type, unsigned int code, int value)
{
	struct sysrq_state *sysrq = handle->private;
	bool suppress;

	/*
	 * Do not filter anything if we are in the process of re-injecting
	 * Alt+SysRq combination.
	 */
	if (sysrq->reinjecting)
		return false;

	switch (type) {

	case EV_SYN:
		suppress = false;
		break;

	case EV_KEY:
		suppress = sysrq_handle_keypress(sysrq, code, value);
		break;

	default:
		suppress = sysrq->active;
		break;
	}

	return suppress;
}

static int sysrq_connect(struct input_handler *handler,
			 struct input_dev *dev,
			 const struct input_device_id *id)
{
	struct sysrq_state *sysrq;
	int error;

	sysrq = kzalloc(sizeof(struct sysrq_state), GFP_KERNEL);
	if (!sysrq)
		return -ENOMEM;

	INIT_WORK(&sysrq->reinject_work, sysrq_reinject_alt_sysrq);

	sysrq->handle.dev = dev;
	sysrq->handle.handler = handler;
	sysrq->handle.name = "sysrq";
	sysrq->handle.private = sysrq;
	setup_timer(&sysrq->keyreset_timer,
		    sysrq_do_reset, (unsigned long)sysrq);

	error = input_register_handle(&sysrq->handle);
	if (error) {
		pr_err("Failed to register input sysrq handler, error %d\n",
			error);
		goto err_free;
	}

	error = input_open_device(&sysrq->handle);
	if (error) {
		pr_err("Failed to open input device, error %d\n", error);
		goto err_unregister;
	}

	return 0;

 err_unregister:
	input_unregister_handle(&sysrq->handle);
 err_free:
	kfree(sysrq);
	return error;
}

static void sysrq_disconnect(struct input_handle *handle)
{
	struct sysrq_state *sysrq = handle->private;

	input_close_device(handle);
	cancel_work_sync(&sysrq->reinject_work);
	del_timer_sync(&sysrq->keyreset_timer);
	input_unregister_handle(handle);
	kfree(sysrq);
}

/*
 * We are matching on KEY_LEFTALT instead of KEY_SYSRQ because not all
 * keyboards have SysRq key predefined and so user may add it to keymap
 * later, but we expect all such keyboards to have left alt.
 */
static const struct input_device_id sysrq_ids[] = {
	{
		.flags = INPUT_DEVICE_ID_MATCH_EVBIT |
				INPUT_DEVICE_ID_MATCH_KEYBIT,
		.evbit = { [BIT_WORD(EV_KEY)] = BIT_MASK(EV_KEY) },
		.keybit = { [BIT_WORD(KEY_LEFTALT)] = BIT_MASK(KEY_LEFTALT) },
	},
	{ },
};

static struct input_handler sysrq_handler = {
	.filter		= sysrq_filter,
	.connect	= sysrq_connect,
	.disconnect	= sysrq_disconnect,
	.name		= "sysrq",
	.id_table	= sysrq_ids,
};

static bool sysrq_handler_registered;

static inline void sysrq_register_handler(void)
{
	int error;

	sysrq_of_get_keyreset_config();

	error = input_register_handler(&sysrq_handler);
	if (error)
		pr_err("Failed to register input handler, error %d", error);
	else
		sysrq_handler_registered = true;
}

static inline void sysrq_unregister_handler(void)
{
	if (sysrq_handler_registered) {
		input_unregister_handler(&sysrq_handler);
		sysrq_handler_registered = false;
	}
}

static int sysrq_reset_seq_param_set(const char *buffer,
				     const struct kernel_param *kp)
{
	unsigned long val;
	int error;

	error = kstrtoul(buffer, 0, &val);
	if (error < 0)
		return error;

	if (val > KEY_MAX)
		return -EINVAL;

	*((unsigned short *)kp->arg) = val;
	sysrq_reset_seq_version++;

	return 0;
}

static const struct kernel_param_ops param_ops_sysrq_reset_seq = {
	.get	= param_get_ushort,
	.set	= sysrq_reset_seq_param_set,
};

#define param_check_sysrq_reset_seq(name, p)	\
	__param_check(name, p, unsigned short)

/*
 * not really modular, but the easiest way to keep compat with existing
 * bootargs behaviour is to continue using module_param here.
 */
module_param_array_named(reset_seq, sysrq_reset_seq, sysrq_reset_seq,
			 &sysrq_reset_seq_len, 0644);

module_param_named(sysrq_downtime_ms, sysrq_reset_downtime_ms, int, 0644);

#else

static inline void sysrq_register_handler(void)
{
}

static inline void sysrq_unregister_handler(void)
{
}

#endif /* CONFIG_INPUT */

int sysrq_toggle_support(int enable_mask)
{
	bool was_enabled = sysrq_on();

	sysrq_enabled = enable_mask;

	if (was_enabled != sysrq_on()) {
		if (sysrq_on())
			sysrq_register_handler();
		else
			sysrq_unregister_handler();
	}

	return 0;
}

static int __sysrq_swap_key_ops(int key, struct sysrq_key_op *insert_op_p,
                                struct sysrq_key_op *remove_op_p)
{
	int retval;

	spin_lock(&sysrq_key_table_lock);
	if (__sysrq_get_key_op(key) == remove_op_p) {
		__sysrq_put_key_op(key, insert_op_p);
		retval = 0;
	} else {
		retval = -1;
	}
	spin_unlock(&sysrq_key_table_lock);

	/*
	 * A concurrent __handle_sysrq either got the old op or the new op.
	 * Wait for it to go away before returning, so the code for an old
	 * op is not freed (eg. on module unload) while it is in use.
	 */
	synchronize_rcu();

	return retval;
}

int register_sysrq_key(int key, struct sysrq_key_op *op_p)
{
	return __sysrq_swap_key_ops(key, op_p, NULL);
}
EXPORT_SYMBOL(register_sysrq_key);

int unregister_sysrq_key(int key, struct sysrq_key_op *op_p)
{
	return __sysrq_swap_key_ops(key, NULL, op_p);
}
EXPORT_SYMBOL(unregister_sysrq_key);

#ifdef CONFIG_PROC_FS
/*
 * writing 'C' to /proc/sysrq-trigger is like sysrq-C
 */
static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf,
				   size_t count, loff_t *ppos)
{
	if (count) {
		char c;

		if (get_user(c, buf))
			return -EFAULT;
		__handle_sysrq(c, false);
	}

	return count;
}

static const struct file_operations proc_sysrq_trigger_operations = {
	.write		= write_sysrq_trigger,
	.llseek		= noop_llseek,
};

static void sysrq_init_procfs(void)
{
	if (!proc_create("sysrq-trigger", S_IWUSR, NULL,
			 &proc_sysrq_trigger_operations))
		pr_err("Failed to register proc interface\n");
}

#else

static inline void sysrq_init_procfs(void)
{
}

#endif /* CONFIG_PROC_FS */

static int __init sysrq_init(void)
{
	sysrq_init_procfs();

	if (sysrq_on())
		sysrq_register_handler();

	return 0;
}
device_initcall(sysrq_init);