sysrq: Properly check for kernel threads
[linux-2.6.git] / drivers / tty / sysrq.c
1 /*
2  *      Linux Magic System Request Key Hacks
3  *
4  *      (c) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
5  *      based on ideas by Pavel Machek <pavel@atrey.karlin.mff.cuni.cz>
6  *
7  *      (c) 2000 Crutcher Dunnavant <crutcher+kernel@datastacks.com>
8  *      overhauled to use key registration
9  *      based upon discusions in irc://irc.openprojects.net/#kernelnewbies
10  *
11  *      Copyright (c) 2010 Dmitry Torokhov
12  *      Input handler conversion
13  */
14
15 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
16
17 #include <linux/sched.h>
18 #include <linux/interrupt.h>
19 #include <linux/mm.h>
20 #include <linux/fs.h>
21 #include <linux/mount.h>
22 #include <linux/kdev_t.h>
23 #include <linux/major.h>
24 #include <linux/reboot.h>
25 #include <linux/sysrq.h>
26 #include <linux/kbd_kern.h>
27 #include <linux/proc_fs.h>
28 #include <linux/nmi.h>
29 #include <linux/quotaops.h>
30 #include <linux/perf_event.h>
31 #include <linux/kernel.h>
32 #include <linux/module.h>
33 #include <linux/suspend.h>
34 #include <linux/writeback.h>
35 #include <linux/swap.h>
36 #include <linux/spinlock.h>
37 #include <linux/vt_kern.h>
38 #include <linux/workqueue.h>
39 #include <linux/hrtimer.h>
40 #include <linux/oom.h>
41 #include <linux/slab.h>
42 #include <linux/input.h>
43 #include <linux/uaccess.h>
44
45 #include <asm/ptrace.h>
46 #include <asm/irq_regs.h>
47
48 /* Whether we react on sysrq keys or just ignore them */
49 static int __read_mostly sysrq_enabled = SYSRQ_DEFAULT_ENABLE;
50 static bool __read_mostly sysrq_always_enabled;
51
52 static bool sysrq_on(void)
53 {
54         return sysrq_enabled || sysrq_always_enabled;
55 }
56
57 /*
58  * A value of 1 means 'all', other nonzero values are an op mask:
59  */
60 static bool sysrq_on_mask(int mask)
61 {
62         return sysrq_always_enabled ||
63                sysrq_enabled == 1 ||
64                (sysrq_enabled & mask);
65 }
66
67 static int __init sysrq_always_enabled_setup(char *str)
68 {
69         sysrq_always_enabled = true;
70         pr_info("sysrq always enabled.\n");
71
72         return 1;
73 }
74
75 __setup("sysrq_always_enabled", sysrq_always_enabled_setup);
76
77
78 static void sysrq_handle_loglevel(int key)
79 {
80         int i;
81
82         i = key - '0';
83         console_loglevel = 7;
84         printk("Loglevel set to %d\n", i);
85         console_loglevel = i;
86 }
87 static struct sysrq_key_op sysrq_loglevel_op = {
88         .handler        = sysrq_handle_loglevel,
89         .help_msg       = "loglevel(0-9)",
90         .action_msg     = "Changing Loglevel",
91         .enable_mask    = SYSRQ_ENABLE_LOG,
92 };
93
94 #ifdef CONFIG_VT
95 static void sysrq_handle_SAK(int key)
96 {
97         struct work_struct *SAK_work = &vc_cons[fg_console].SAK_work;
98         schedule_work(SAK_work);
99 }
100 static struct sysrq_key_op sysrq_SAK_op = {
101         .handler        = sysrq_handle_SAK,
102         .help_msg       = "saK",
103         .action_msg     = "SAK",
104         .enable_mask    = SYSRQ_ENABLE_KEYBOARD,
105 };
106 #else
107 #define sysrq_SAK_op (*(struct sysrq_key_op *)NULL)
108 #endif
109
110 #ifdef CONFIG_VT
111 static void sysrq_handle_unraw(int key)
112 {
113         struct kbd_struct *kbd = &kbd_table[fg_console];
114
115         if (kbd)
116                 kbd->kbdmode = default_utf8 ? VC_UNICODE : VC_XLATE;
117 }
118 static struct sysrq_key_op sysrq_unraw_op = {
119         .handler        = sysrq_handle_unraw,
120         .help_msg       = "unRaw",
121         .action_msg     = "Keyboard mode set to system default",
122         .enable_mask    = SYSRQ_ENABLE_KEYBOARD,
123 };
124 #else
125 #define sysrq_unraw_op (*(struct sysrq_key_op *)NULL)
126 #endif /* CONFIG_VT */
127
128 static void sysrq_handle_crash(int key)
129 {
130         char *killer = NULL;
131
132         panic_on_oops = 1;      /* force panic */
133         wmb();
134         *killer = 1;
135 }
136 static struct sysrq_key_op sysrq_crash_op = {
137         .handler        = sysrq_handle_crash,
138         .help_msg       = "Crash",
139         .action_msg     = "Trigger a crash",
140         .enable_mask    = SYSRQ_ENABLE_DUMP,
141 };
142
143 static void sysrq_handle_reboot(int key)
144 {
145         lockdep_off();
146         local_irq_enable();
147         emergency_restart();
148 }
149 static struct sysrq_key_op sysrq_reboot_op = {
150         .handler        = sysrq_handle_reboot,
151         .help_msg       = "reBoot",
152         .action_msg     = "Resetting",
153         .enable_mask    = SYSRQ_ENABLE_BOOT,
154 };
155
156 static void sysrq_handle_sync(int key)
157 {
158         emergency_sync();
159 }
160 static struct sysrq_key_op sysrq_sync_op = {
161         .handler        = sysrq_handle_sync,
162         .help_msg       = "Sync",
163         .action_msg     = "Emergency Sync",
164         .enable_mask    = SYSRQ_ENABLE_SYNC,
165 };
166
167 static void sysrq_handle_show_timers(int key)
168 {
169         sysrq_timer_list_show();
170 }
171
172 static struct sysrq_key_op sysrq_show_timers_op = {
173         .handler        = sysrq_handle_show_timers,
174         .help_msg       = "show-all-timers(Q)",
175         .action_msg     = "Show clockevent devices & pending hrtimers (no others)",
176 };
177
178 static void sysrq_handle_mountro(int key)
179 {
180         emergency_remount();
181 }
182 static struct sysrq_key_op sysrq_mountro_op = {
183         .handler        = sysrq_handle_mountro,
184         .help_msg       = "Unmount",
185         .action_msg     = "Emergency Remount R/O",
186         .enable_mask    = SYSRQ_ENABLE_REMOUNT,
187 };
188
189 #ifdef CONFIG_LOCKDEP
190 static void sysrq_handle_showlocks(int key)
191 {
192         debug_show_all_locks();
193 }
194
195 static struct sysrq_key_op sysrq_showlocks_op = {
196         .handler        = sysrq_handle_showlocks,
197         .help_msg       = "show-all-locks(D)",
198         .action_msg     = "Show Locks Held",
199 };
200 #else
201 #define sysrq_showlocks_op (*(struct sysrq_key_op *)NULL)
202 #endif
203
204 #ifdef CONFIG_SMP
205 static DEFINE_SPINLOCK(show_lock);
206
207 static void showacpu(void *dummy)
208 {
209         unsigned long flags;
210
211         /* Idle CPUs have no interesting backtrace. */
212         if (idle_cpu(smp_processor_id()))
213                 return;
214
215         spin_lock_irqsave(&show_lock, flags);
216         printk(KERN_INFO "CPU%d:\n", smp_processor_id());
217         show_stack(NULL, NULL);
218         spin_unlock_irqrestore(&show_lock, flags);
219 }
220
221 static void sysrq_showregs_othercpus(struct work_struct *dummy)
222 {
223         smp_call_function(showacpu, NULL, 0);
224 }
225
226 static DECLARE_WORK(sysrq_showallcpus, sysrq_showregs_othercpus);
227
228 static void sysrq_handle_showallcpus(int key)
229 {
230         /*
231          * Fall back to the workqueue based printing if the
232          * backtrace printing did not succeed or the
233          * architecture has no support for it:
234          */
235         if (!trigger_all_cpu_backtrace()) {
236                 struct pt_regs *regs = get_irq_regs();
237
238                 if (regs) {
239                         printk(KERN_INFO "CPU%d:\n", smp_processor_id());
240                         show_regs(regs);
241                 }
242                 schedule_work(&sysrq_showallcpus);
243         }
244 }
245
246 static struct sysrq_key_op sysrq_showallcpus_op = {
247         .handler        = sysrq_handle_showallcpus,
248         .help_msg       = "show-backtrace-all-active-cpus(L)",
249         .action_msg     = "Show backtrace of all active CPUs",
250         .enable_mask    = SYSRQ_ENABLE_DUMP,
251 };
252 #endif
253
254 static void sysrq_handle_showregs(int key)
255 {
256         struct pt_regs *regs = get_irq_regs();
257         if (regs)
258                 show_regs(regs);
259         perf_event_print_debug();
260 }
261 static struct sysrq_key_op sysrq_showregs_op = {
262         .handler        = sysrq_handle_showregs,
263         .help_msg       = "show-registers(P)",
264         .action_msg     = "Show Regs",
265         .enable_mask    = SYSRQ_ENABLE_DUMP,
266 };
267
268 static void sysrq_handle_showstate(int key)
269 {
270         show_state();
271 }
272 static struct sysrq_key_op sysrq_showstate_op = {
273         .handler        = sysrq_handle_showstate,
274         .help_msg       = "show-task-states(T)",
275         .action_msg     = "Show State",
276         .enable_mask    = SYSRQ_ENABLE_DUMP,
277 };
278
279 static void sysrq_handle_showstate_blocked(int key)
280 {
281         show_state_filter(TASK_UNINTERRUPTIBLE);
282 }
283 static struct sysrq_key_op sysrq_showstate_blocked_op = {
284         .handler        = sysrq_handle_showstate_blocked,
285         .help_msg       = "show-blocked-tasks(W)",
286         .action_msg     = "Show Blocked State",
287         .enable_mask    = SYSRQ_ENABLE_DUMP,
288 };
289
290 #ifdef CONFIG_TRACING
291 #include <linux/ftrace.h>
292
293 static void sysrq_ftrace_dump(int key)
294 {
295         ftrace_dump(DUMP_ALL);
296 }
297 static struct sysrq_key_op sysrq_ftrace_dump_op = {
298         .handler        = sysrq_ftrace_dump,
299         .help_msg       = "dump-ftrace-buffer(Z)",
300         .action_msg     = "Dump ftrace buffer",
301         .enable_mask    = SYSRQ_ENABLE_DUMP,
302 };
303 #else
304 #define sysrq_ftrace_dump_op (*(struct sysrq_key_op *)NULL)
305 #endif
306
307 static void sysrq_handle_showmem(int key)
308 {
309         show_mem(0);
310 }
311 static struct sysrq_key_op sysrq_showmem_op = {
312         .handler        = sysrq_handle_showmem,
313         .help_msg       = "show-memory-usage(M)",
314         .action_msg     = "Show Memory",
315         .enable_mask    = SYSRQ_ENABLE_DUMP,
316 };
317
318 /*
319  * Signal sysrq helper function.  Sends a signal to all user processes.
320  */
321 static void send_sig_all(int sig)
322 {
323         struct task_struct *p;
324
325         read_lock(&tasklist_lock);
326         for_each_process(p) {
327                 if (p->flags & PF_KTHREAD)
328                         continue;
329                 if (is_global_init(p))
330                         continue;
331
332                 force_sig(sig, p);
333         }
334         read_unlock(&tasklist_lock);
335 }
336
337 static void sysrq_handle_term(int key)
338 {
339         send_sig_all(SIGTERM);
340         console_loglevel = 8;
341 }
342 static struct sysrq_key_op sysrq_term_op = {
343         .handler        = sysrq_handle_term,
344         .help_msg       = "terminate-all-tasks(E)",
345         .action_msg     = "Terminate All Tasks",
346         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
347 };
348
349 static void moom_callback(struct work_struct *ignored)
350 {
351         out_of_memory(node_zonelist(0, GFP_KERNEL), GFP_KERNEL, 0, NULL);
352 }
353
354 static DECLARE_WORK(moom_work, moom_callback);
355
356 static void sysrq_handle_moom(int key)
357 {
358         schedule_work(&moom_work);
359 }
360 static struct sysrq_key_op sysrq_moom_op = {
361         .handler        = sysrq_handle_moom,
362         .help_msg       = "memory-full-oom-kill(F)",
363         .action_msg     = "Manual OOM execution",
364         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
365 };
366
367 #ifdef CONFIG_BLOCK
368 static void sysrq_handle_thaw(int key)
369 {
370         emergency_thaw_all();
371 }
372 static struct sysrq_key_op sysrq_thaw_op = {
373         .handler        = sysrq_handle_thaw,
374         .help_msg       = "thaw-filesystems(J)",
375         .action_msg     = "Emergency Thaw of all frozen filesystems",
376         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
377 };
378 #endif
379
380 static void sysrq_handle_kill(int key)
381 {
382         send_sig_all(SIGKILL);
383         console_loglevel = 8;
384 }
385 static struct sysrq_key_op sysrq_kill_op = {
386         .handler        = sysrq_handle_kill,
387         .help_msg       = "kill-all-tasks(I)",
388         .action_msg     = "Kill All Tasks",
389         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
390 };
391
392 static void sysrq_handle_unrt(int key)
393 {
394         normalize_rt_tasks();
395 }
396 static struct sysrq_key_op sysrq_unrt_op = {
397         .handler        = sysrq_handle_unrt,
398         .help_msg       = "nice-all-RT-tasks(N)",
399         .action_msg     = "Nice All RT Tasks",
400         .enable_mask    = SYSRQ_ENABLE_RTNICE,
401 };
402
403 /* Key Operations table and lock */
404 static DEFINE_SPINLOCK(sysrq_key_table_lock);
405
406 static struct sysrq_key_op *sysrq_key_table[36] = {
407         &sysrq_loglevel_op,             /* 0 */
408         &sysrq_loglevel_op,             /* 1 */
409         &sysrq_loglevel_op,             /* 2 */
410         &sysrq_loglevel_op,             /* 3 */
411         &sysrq_loglevel_op,             /* 4 */
412         &sysrq_loglevel_op,             /* 5 */
413         &sysrq_loglevel_op,             /* 6 */
414         &sysrq_loglevel_op,             /* 7 */
415         &sysrq_loglevel_op,             /* 8 */
416         &sysrq_loglevel_op,             /* 9 */
417
418         /*
419          * a: Don't use for system provided sysrqs, it is handled specially on
420          * sparc and will never arrive.
421          */
422         NULL,                           /* a */
423         &sysrq_reboot_op,               /* b */
424         &sysrq_crash_op,                /* c & ibm_emac driver debug */
425         &sysrq_showlocks_op,            /* d */
426         &sysrq_term_op,                 /* e */
427         &sysrq_moom_op,                 /* f */
428         /* g: May be registered for the kernel debugger */
429         NULL,                           /* g */
430         NULL,                           /* h - reserved for help */
431         &sysrq_kill_op,                 /* i */
432 #ifdef CONFIG_BLOCK
433         &sysrq_thaw_op,                 /* j */
434 #else
435         NULL,                           /* j */
436 #endif
437         &sysrq_SAK_op,                  /* k */
438 #ifdef CONFIG_SMP
439         &sysrq_showallcpus_op,          /* l */
440 #else
441         NULL,                           /* l */
442 #endif
443         &sysrq_showmem_op,              /* m */
444         &sysrq_unrt_op,                 /* n */
445         /* o: This will often be registered as 'Off' at init time */
446         NULL,                           /* o */
447         &sysrq_showregs_op,             /* p */
448         &sysrq_show_timers_op,          /* q */
449         &sysrq_unraw_op,                /* r */
450         &sysrq_sync_op,                 /* s */
451         &sysrq_showstate_op,            /* t */
452         &sysrq_mountro_op,              /* u */
453         /* v: May be registered for frame buffer console restore */
454         NULL,                           /* v */
455         &sysrq_showstate_blocked_op,    /* w */
456         /* x: May be registered on ppc/powerpc for xmon */
457         NULL,                           /* x */
458         /* y: May be registered on sparc64 for global register dump */
459         NULL,                           /* y */
460         &sysrq_ftrace_dump_op,          /* z */
461 };
462
463 /* key2index calculation, -1 on invalid index */
464 static int sysrq_key_table_key2index(int key)
465 {
466         int retval;
467
468         if ((key >= '0') && (key <= '9'))
469                 retval = key - '0';
470         else if ((key >= 'a') && (key <= 'z'))
471                 retval = key + 10 - 'a';
472         else
473                 retval = -1;
474         return retval;
475 }
476
477 /*
478  * get and put functions for the table, exposed to modules.
479  */
480 struct sysrq_key_op *__sysrq_get_key_op(int key)
481 {
482         struct sysrq_key_op *op_p = NULL;
483         int i;
484
485         i = sysrq_key_table_key2index(key);
486         if (i != -1)
487                 op_p = sysrq_key_table[i];
488
489         return op_p;
490 }
491
492 static void __sysrq_put_key_op(int key, struct sysrq_key_op *op_p)
493 {
494         int i = sysrq_key_table_key2index(key);
495
496         if (i != -1)
497                 sysrq_key_table[i] = op_p;
498 }
499
500 void __handle_sysrq(int key, bool check_mask)
501 {
502         struct sysrq_key_op *op_p;
503         int orig_log_level;
504         int i;
505         unsigned long flags;
506
507         spin_lock_irqsave(&sysrq_key_table_lock, flags);
508         /*
509          * Raise the apparent loglevel to maximum so that the sysrq header
510          * is shown to provide the user with positive feedback.  We do not
511          * simply emit this at KERN_EMERG as that would change message
512          * routing in the consumers of /proc/kmsg.
513          */
514         orig_log_level = console_loglevel;
515         console_loglevel = 7;
516         printk(KERN_INFO "SysRq : ");
517
518         op_p = __sysrq_get_key_op(key);
519         if (op_p) {
520                 /*
521                  * Should we check for enabled operations (/proc/sysrq-trigger
522                  * should not) and is the invoked operation enabled?
523                  */
524                 if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
525                         printk("%s\n", op_p->action_msg);
526                         console_loglevel = orig_log_level;
527                         op_p->handler(key);
528                 } else {
529                         printk("This sysrq operation is disabled.\n");
530                 }
531         } else {
532                 printk("HELP : ");
533                 /* Only print the help msg once per handler */
534                 for (i = 0; i < ARRAY_SIZE(sysrq_key_table); i++) {
535                         if (sysrq_key_table[i]) {
536                                 int j;
537
538                                 for (j = 0; sysrq_key_table[i] !=
539                                                 sysrq_key_table[j]; j++)
540                                         ;
541                                 if (j != i)
542                                         continue;
543                                 printk("%s ", sysrq_key_table[i]->help_msg);
544                         }
545                 }
546                 printk("\n");
547                 console_loglevel = orig_log_level;
548         }
549         spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
550 }
551
552 void handle_sysrq(int key)
553 {
554         if (sysrq_on())
555                 __handle_sysrq(key, true);
556 }
557 EXPORT_SYMBOL(handle_sysrq);
558
559 #ifdef CONFIG_INPUT
560
561 /* Simple translation table for the SysRq keys */
562 static const unsigned char sysrq_xlate[KEY_CNT] =
563         "\000\0331234567890-=\177\t"                    /* 0x00 - 0x0f */
564         "qwertyuiop[]\r\000as"                          /* 0x10 - 0x1f */
565         "dfghjkl;'`\000\\zxcv"                          /* 0x20 - 0x2f */
566         "bnm,./\000*\000 \000\201\202\203\204\205"      /* 0x30 - 0x3f */
567         "\206\207\210\211\212\000\000789-456+1"         /* 0x40 - 0x4f */
568         "230\177\000\000\213\214\000\000\000\000\000\000\000\000\000\000" /* 0x50 - 0x5f */
569         "\r\000/";                                      /* 0x60 - 0x6f */
570
571 struct sysrq_state {
572         struct input_handle handle;
573         struct work_struct reinject_work;
574         unsigned long key_down[BITS_TO_LONGS(KEY_CNT)];
575         unsigned int alt;
576         unsigned int alt_use;
577         bool active;
578         bool need_reinject;
579         bool reinjecting;
580 };
581
582 static void sysrq_reinject_alt_sysrq(struct work_struct *work)
583 {
584         struct sysrq_state *sysrq =
585                         container_of(work, struct sysrq_state, reinject_work);
586         struct input_handle *handle = &sysrq->handle;
587         unsigned int alt_code = sysrq->alt_use;
588
589         if (sysrq->need_reinject) {
590                 /* we do not want the assignment to be reordered */
591                 sysrq->reinjecting = true;
592                 mb();
593
594                 /* Simulate press and release of Alt + SysRq */
595                 input_inject_event(handle, EV_KEY, alt_code, 1);
596                 input_inject_event(handle, EV_KEY, KEY_SYSRQ, 1);
597                 input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
598
599                 input_inject_event(handle, EV_KEY, KEY_SYSRQ, 0);
600                 input_inject_event(handle, EV_KEY, alt_code, 0);
601                 input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
602
603                 mb();
604                 sysrq->reinjecting = false;
605         }
606 }
607
608 static bool sysrq_filter(struct input_handle *handle,
609                          unsigned int type, unsigned int code, int value)
610 {
611         struct sysrq_state *sysrq = handle->private;
612         bool was_active = sysrq->active;
613         bool suppress;
614
615         /*
616          * Do not filter anything if we are in the process of re-injecting
617          * Alt+SysRq combination.
618          */
619         if (sysrq->reinjecting)
620                 return false;
621
622         switch (type) {
623
624         case EV_SYN:
625                 suppress = false;
626                 break;
627
628         case EV_KEY:
629                 switch (code) {
630
631                 case KEY_LEFTALT:
632                 case KEY_RIGHTALT:
633                         if (!value) {
634                                 /* One of ALTs is being released */
635                                 if (sysrq->active && code == sysrq->alt_use)
636                                         sysrq->active = false;
637
638                                 sysrq->alt = KEY_RESERVED;
639
640                         } else if (value != 2) {
641                                 sysrq->alt = code;
642                                 sysrq->need_reinject = false;
643                         }
644                         break;
645
646                 case KEY_SYSRQ:
647                         if (value == 1 && sysrq->alt != KEY_RESERVED) {
648                                 sysrq->active = true;
649                                 sysrq->alt_use = sysrq->alt;
650                                 /*
651                                  * If nothing else will be pressed we'll need
652                                  * to re-inject Alt-SysRq keysroke.
653                                  */
654                                 sysrq->need_reinject = true;
655                         }
656
657                         /*
658                          * Pretend that sysrq was never pressed at all. This
659                          * is needed to properly handle KGDB which will try
660                          * to release all keys after exiting debugger. If we
661                          * do not clear key bit it KGDB will end up sending
662                          * release events for Alt and SysRq, potentially
663                          * triggering print screen function.
664                          */
665                         if (sysrq->active)
666                                 clear_bit(KEY_SYSRQ, handle->dev->key);
667
668                         break;
669
670                 default:
671                         if (sysrq->active && value && value != 2) {
672                                 sysrq->need_reinject = false;
673                                 __handle_sysrq(sysrq_xlate[code], true);
674                         }
675                         break;
676                 }
677
678                 suppress = sysrq->active;
679
680                 if (!sysrq->active) {
681                         /*
682                          * If we are not suppressing key presses keep track of
683                          * keyboard state so we can release keys that have been
684                          * pressed before entering SysRq mode.
685                          */
686                         if (value)
687                                 set_bit(code, sysrq->key_down);
688                         else
689                                 clear_bit(code, sysrq->key_down);
690
691                         if (was_active)
692                                 schedule_work(&sysrq->reinject_work);
693
694                 } else if (value == 0 &&
695                            test_and_clear_bit(code, sysrq->key_down)) {
696                         /*
697                          * Pass on release events for keys that was pressed before
698                          * entering SysRq mode.
699                          */
700                         suppress = false;
701                 }
702                 break;
703
704         default:
705                 suppress = sysrq->active;
706                 break;
707         }
708
709         return suppress;
710 }
711
712 static int sysrq_connect(struct input_handler *handler,
713                          struct input_dev *dev,
714                          const struct input_device_id *id)
715 {
716         struct sysrq_state *sysrq;
717         int error;
718
719         sysrq = kzalloc(sizeof(struct sysrq_state), GFP_KERNEL);
720         if (!sysrq)
721                 return -ENOMEM;
722
723         INIT_WORK(&sysrq->reinject_work, sysrq_reinject_alt_sysrq);
724
725         sysrq->handle.dev = dev;
726         sysrq->handle.handler = handler;
727         sysrq->handle.name = "sysrq";
728         sysrq->handle.private = sysrq;
729
730         error = input_register_handle(&sysrq->handle);
731         if (error) {
732                 pr_err("Failed to register input sysrq handler, error %d\n",
733                         error);
734                 goto err_free;
735         }
736
737         error = input_open_device(&sysrq->handle);
738         if (error) {
739                 pr_err("Failed to open input device, error %d\n", error);
740                 goto err_unregister;
741         }
742
743         return 0;
744
745  err_unregister:
746         input_unregister_handle(&sysrq->handle);
747  err_free:
748         kfree(sysrq);
749         return error;
750 }
751
752 static void sysrq_disconnect(struct input_handle *handle)
753 {
754         struct sysrq_state *sysrq = handle->private;
755
756         input_close_device(handle);
757         cancel_work_sync(&sysrq->reinject_work);
758         input_unregister_handle(handle);
759         kfree(sysrq);
760 }
761
762 /*
763  * We are matching on KEY_LEFTALT instead of KEY_SYSRQ because not all
764  * keyboards have SysRq key predefined and so user may add it to keymap
765  * later, but we expect all such keyboards to have left alt.
766  */
767 static const struct input_device_id sysrq_ids[] = {
768         {
769                 .flags = INPUT_DEVICE_ID_MATCH_EVBIT |
770                                 INPUT_DEVICE_ID_MATCH_KEYBIT,
771                 .evbit = { BIT_MASK(EV_KEY) },
772                 .keybit = { BIT_MASK(KEY_LEFTALT) },
773         },
774         { },
775 };
776
777 static struct input_handler sysrq_handler = {
778         .filter         = sysrq_filter,
779         .connect        = sysrq_connect,
780         .disconnect     = sysrq_disconnect,
781         .name           = "sysrq",
782         .id_table       = sysrq_ids,
783 };
784
785 static bool sysrq_handler_registered;
786
787 static inline void sysrq_register_handler(void)
788 {
789         int error;
790
791         error = input_register_handler(&sysrq_handler);
792         if (error)
793                 pr_err("Failed to register input handler, error %d", error);
794         else
795                 sysrq_handler_registered = true;
796 }
797
798 static inline void sysrq_unregister_handler(void)
799 {
800         if (sysrq_handler_registered) {
801                 input_unregister_handler(&sysrq_handler);
802                 sysrq_handler_registered = false;
803         }
804 }
805
806 #else
807
808 static inline void sysrq_register_handler(void)
809 {
810 }
811
812 static inline void sysrq_unregister_handler(void)
813 {
814 }
815
816 #endif /* CONFIG_INPUT */
817
818 int sysrq_toggle_support(int enable_mask)
819 {
820         bool was_enabled = sysrq_on();
821
822         sysrq_enabled = enable_mask;
823
824         if (was_enabled != sysrq_on()) {
825                 if (sysrq_on())
826                         sysrq_register_handler();
827                 else
828                         sysrq_unregister_handler();
829         }
830
831         return 0;
832 }
833
834 static int __sysrq_swap_key_ops(int key, struct sysrq_key_op *insert_op_p,
835                                 struct sysrq_key_op *remove_op_p)
836 {
837         int retval;
838         unsigned long flags;
839
840         spin_lock_irqsave(&sysrq_key_table_lock, flags);
841         if (__sysrq_get_key_op(key) == remove_op_p) {
842                 __sysrq_put_key_op(key, insert_op_p);
843                 retval = 0;
844         } else {
845                 retval = -1;
846         }
847         spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
848         return retval;
849 }
850
851 int register_sysrq_key(int key, struct sysrq_key_op *op_p)
852 {
853         return __sysrq_swap_key_ops(key, op_p, NULL);
854 }
855 EXPORT_SYMBOL(register_sysrq_key);
856
857 int unregister_sysrq_key(int key, struct sysrq_key_op *op_p)
858 {
859         return __sysrq_swap_key_ops(key, NULL, op_p);
860 }
861 EXPORT_SYMBOL(unregister_sysrq_key);
862
863 #ifdef CONFIG_PROC_FS
864 /*
865  * writing 'C' to /proc/sysrq-trigger is like sysrq-C
866  */
867 static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf,
868                                    size_t count, loff_t *ppos)
869 {
870         if (count) {
871                 char c;
872
873                 if (get_user(c, buf))
874                         return -EFAULT;
875                 __handle_sysrq(c, false);
876         }
877
878         return count;
879 }
880
881 static const struct file_operations proc_sysrq_trigger_operations = {
882         .write          = write_sysrq_trigger,
883         .llseek         = noop_llseek,
884 };
885
886 static void sysrq_init_procfs(void)
887 {
888         if (!proc_create("sysrq-trigger", S_IWUSR, NULL,
889                          &proc_sysrq_trigger_operations))
890                 pr_err("Failed to register proc interface\n");
891 }
892
893 #else
894
895 static inline void sysrq_init_procfs(void)
896 {
897 }
898
899 #endif /* CONFIG_PROC_FS */
900
901 static int __init sysrq_init(void)
902 {
903         sysrq_init_procfs();
904
905         if (sysrq_on())
906                 sysrq_register_handler();
907
908         return 0;
909 }
910 module_init(sysrq_init);