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

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