release/src-rt-6.x.4708/linux/linux-2.6.36/drivers/char/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/buffer_head.h>          /* for fsync_bdev() */
  36 #include <linux/swap.h>
  37 #include <linux/spinlock.h>
  38 #include <linux/vt_kern.h>
  39 #include <linux/workqueue.h>
  40 #include <linux/hrtimer.h>
  41 #include <linux/oom.h>
  42 #include <linux/slab.h>
  43 #include <linux/input.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 = 1;
  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();
 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         for_each_process(p) {
 326                 if (p->mm && !is_global_init(p))
 327                         /* Not swapper, init nor kernel thread */
 328                         force_sig(sig, p);
 329         }
 330 }
 331
 332 static void sysrq_handle_term(int key)
 333 {
 334         send_sig_all(SIGTERM);
 335         console_loglevel = 8;
 336 }
 337 static struct sysrq_key_op sysrq_term_op = {
 338         .handler        = sysrq_handle_term,
 339         .help_msg       = "terminate-all-tasks(E)",
 340         .action_msg     = "Terminate All Tasks",
 341         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
 342 };
 343
 344 static void moom_callback(struct work_struct *ignored)
 345 {
 346         out_of_memory(node_zonelist(0, GFP_KERNEL), GFP_KERNEL, 0, NULL);
 347 }
 348
 349 static DECLARE_WORK(moom_work, moom_callback);
 350
 351 static void sysrq_handle_moom(int key)
 352 {
 353         schedule_work(&moom_work);
 354 }
 355 static struct sysrq_key_op sysrq_moom_op = {
 356         .handler        = sysrq_handle_moom,
 357         .help_msg       = "memory-full-oom-kill(F)",
 358         .action_msg     = "Manual OOM execution",
 359         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
 360 };
 361
 362 #ifdef CONFIG_BLOCK
 363 static void sysrq_handle_thaw(int key)
 364 {
 365         emergency_thaw_all();
 366 }
 367 static struct sysrq_key_op sysrq_thaw_op = {
 368         .handler        = sysrq_handle_thaw,
 369         .help_msg       = "thaw-filesystems(J)",
 370         .action_msg     = "Emergency Thaw of all frozen filesystems",
 371         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
 372 };
 373 #endif
 374
 375 static void sysrq_handle_kill(int key)
 376 {
 377         send_sig_all(SIGKILL);
 378         console_loglevel = 8;
 379 }
 380 static struct sysrq_key_op sysrq_kill_op = {
 381         .handler        = sysrq_handle_kill,
 382         .help_msg       = "kill-all-tasks(I)",
 383         .action_msg     = "Kill All Tasks",
 384         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
 385 };
 386
 387 static void sysrq_handle_unrt(int key)
 388 {
 389         normalize_rt_tasks();
 390 }
 391 static struct sysrq_key_op sysrq_unrt_op = {
 392         .handler        = sysrq_handle_unrt,
 393         .help_msg       = "nice-all-RT-tasks(N)",
 394         .action_msg     = "Nice All RT Tasks",
 395         .enable_mask    = SYSRQ_ENABLE_RTNICE,
 396 };
 397
 398 /* Key Operations table and lock */
 399 static DEFINE_SPINLOCK(sysrq_key_table_lock);
 400
 401 static struct sysrq_key_op *sysrq_key_table[36] = {
 402         &sysrq_loglevel_op,             /* 0 */
 403         &sysrq_loglevel_op,             /* 1 */
 404         &sysrq_loglevel_op,             /* 2 */
 405         &sysrq_loglevel_op,             /* 3 */
 406         &sysrq_loglevel_op,             /* 4 */
 407         &sysrq_loglevel_op,             /* 5 */
 408         &sysrq_loglevel_op,             /* 6 */
 409         &sysrq_loglevel_op,             /* 7 */
 410         &sysrq_loglevel_op,             /* 8 */
 411         &sysrq_loglevel_op,             /* 9 */
 412
 413         /*
 414          * a: Don't use for system provided sysrqs, it is handled specially on
 415          * sparc and will never arrive.
 416          */
 417         NULL,                           /* a */
 418         &sysrq_reboot_op,               /* b */
 419         &sysrq_crash_op,                /* c & ibm_emac driver debug */
 420         &sysrq_showlocks_op,            /* d */
 421         &sysrq_term_op,                 /* e */
 422         &sysrq_moom_op,                 /* f */
 423         /* g: May be registered for the kernel debugger */
 424         NULL,                           /* g */
 425         NULL,                           /* h - reserved for help */
 426         &sysrq_kill_op,                 /* i */
 427 #ifdef CONFIG_BLOCK
 428         &sysrq_thaw_op,                 /* j */
 429 #else
 430         NULL,                           /* j */
 431 #endif
 432         &sysrq_SAK_op,                  /* k */
 433 #ifdef CONFIG_SMP
 434         &sysrq_showallcpus_op,          /* l */
 435 #else
 436         NULL,                           /* l */
 437 #endif
 438         &sysrq_showmem_op,              /* m */
 439         &sysrq_unrt_op,                 /* n */
 440         /* o: This will often be registered as 'Off' at init time */
 441         NULL,                           /* o */
 442         &sysrq_showregs_op,             /* p */
 443         &sysrq_show_timers_op,          /* q */
 444         &sysrq_unraw_op,                /* r */
 445         &sysrq_sync_op,                 /* s */
 446         &sysrq_showstate_op,            /* t */
 447         &sysrq_mountro_op,              /* u */
 448         /* v: May be registered for frame buffer console restore */
 449         NULL,                           /* v */
 450         &sysrq_showstate_blocked_op,    /* w */
 451         /* x: May be registered on ppc/powerpc for xmon */
 452         NULL,                           /* x */
 453         /* y: May be registered on sparc64 for global register dump */
 454         NULL,                           /* y */
 455         &sysrq_ftrace_dump_op,          /* z */
 456 };
 457
 458 /* key2index calculation, -1 on invalid index */
 459 static int sysrq_key_table_key2index(int key)
 460 {
 461         int retval;
 462
 463         if ((key >= '0') && (key <= '9'))
 464                 retval = key - '0';
 465         else if ((key >= 'a') && (key <= 'z'))
 466                 retval = key + 10 - 'a';
 467         else
 468                 retval = -1;
 469         return retval;
 470 }
 471
 472 /*
 473  * get and put functions for the table, exposed to modules.
 474  */
 475 struct sysrq_key_op *__sysrq_get_key_op(int key)
 476 {
 477         struct sysrq_key_op *op_p = NULL;
 478         int i;
 479
 480         i = sysrq_key_table_key2index(key);
 481         if (i != -1)
 482                 op_p = sysrq_key_table[i];
 483
 484         return op_p;
 485 }
 486
 487 static void __sysrq_put_key_op(int key, struct sysrq_key_op *op_p)
 488 {
 489         int i = sysrq_key_table_key2index(key);
 490
 491         if (i != -1)
 492                 sysrq_key_table[i] = op_p;
 493 }
 494
 495 void __handle_sysrq(int key, bool check_mask)
 496 {
 497         struct sysrq_key_op *op_p;
 498         int orig_log_level;
 499         int i;
 500         unsigned long flags;
 501
 502         spin_lock_irqsave(&sysrq_key_table_lock, flags);
 503         /*
 504          * Raise the apparent loglevel to maximum so that the sysrq header
 505          * is shown to provide the user with positive feedback.  We do not
 506          * simply emit this at KERN_EMERG as that would change message
 507          * routing in the consumers of /proc/kmsg.
 508          */
 509         orig_log_level = console_loglevel;
 510         console_loglevel = 7;
 511         printk(KERN_INFO "SysRq : ");
 512
 513         op_p = __sysrq_get_key_op(key);
 514         if (op_p) {
 515                 /*
 516                  * Should we check for enabled operations (/proc/sysrq-trigger
 517                  * should not) and is the invoked operation enabled?
 518                  */
 519                 if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
 520                         printk("%s\n", op_p->action_msg);
 521                         console_loglevel = orig_log_level;
 522                         op_p->handler(key);
 523                 } else {
 524                         printk("This sysrq operation is disabled.\n");
 525                 }
 526         } else {
 527                 printk("HELP : ");
 528                 /* Only print the help msg once per handler */
 529                 for (i = 0; i < ARRAY_SIZE(sysrq_key_table); i++) {
 530                         if (sysrq_key_table[i]) {
 531                                 int j;
 532
 533                                 for (j = 0; sysrq_key_table[i] !=
 534                                                 sysrq_key_table[j]; j++)
 535                                         ;
 536                                 if (j != i)
 537                                         continue;
 538                                 printk("%s ", sysrq_key_table[i]->help_msg);
 539                         }
 540                 }
 541                 printk("\n");
 542                 console_loglevel = orig_log_level;
 543         }
 544         spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
 545 }
 546
 547 void handle_sysrq(int key)
 548 {
 549         if (sysrq_on())
 550                 __handle_sysrq(key, true);
 551 }
 552 EXPORT_SYMBOL(handle_sysrq);
 553
 554 #ifdef CONFIG_INPUT
 555
 556 /* Simple translation table for the SysRq keys */
 557 static const unsigned char sysrq_xlate[KEY_MAX + 1] =
 558         "\000\0331234567890-=\177\t"                    /* 0x00 - 0x0f */
 559         "qwertyuiop[]\r\000as"                          /* 0x10 - 0x1f */
 560         "dfghjkl;'`\000\\zxcv"                          /* 0x20 - 0x2f */
 561         "bnm,./\000*\000 \000\201\202\203\204\205"      /* 0x30 - 0x3f */
 562         "\206\207\210\211\212\000\000789-456+1"         /* 0x40 - 0x4f */
 563         "230\177\000\000\213\214\000\000\000\000\000\000\000\000\000\000" /* 0x50 - 0x5f */
 564         "\r\000/";                                      /* 0x60 - 0x6f */
 565
 566 static bool sysrq_down;
 567 static int sysrq_alt_use;
 568 static int sysrq_alt;
 569
 570 static bool sysrq_filter(struct input_handle *handle, unsigned int type,
 571                          unsigned int code, int value)
 572 {
 573         if (type != EV_KEY)
 574                 goto out;
 575
 576         switch (code) {
 577
 578         case KEY_LEFTALT:
 579         case KEY_RIGHTALT:
 580                 if (value)
 581                         sysrq_alt = code;
 582                 else {
 583                         if (sysrq_down && code == sysrq_alt_use)
 584                                 sysrq_down = false;
 585
 586                         sysrq_alt = 0;
 587                 }
 588                 break;
 589
 590         case KEY_SYSRQ:
 591                 if (value == 1 && sysrq_alt) {
 592                         sysrq_down = true;
 593                         sysrq_alt_use = sysrq_alt;
 594                 }
 595                 break;
 596
 597         default:
 598                 if (sysrq_down && value && value != 2)
 599                         __handle_sysrq(sysrq_xlate[code], true);
 600                 break;
 601         }
 602
 603 out:
 604         return sysrq_down;
 605 }
 606
 607 static int sysrq_connect(struct input_handler *handler,
 608                          struct input_dev *dev,
 609                          const struct input_device_id *id)
 610 {
 611         struct input_handle *handle;
 612         int error;
 613
 614         sysrq_down = false;
 615         sysrq_alt = 0;
 616
 617         handle = kzalloc(sizeof(struct input_handle), GFP_KERNEL);
 618         if (!handle)
 619                 return -ENOMEM;
 620
 621         handle->dev = dev;
 622         handle->handler = handler;
 623         handle->name = "sysrq";
 624
 625         error = input_register_handle(handle);
 626         if (error) {
 627                 pr_err("Failed to register input sysrq handler, error %d\n",
 628                         error);
 629                 goto err_free;
 630         }
 631
 632         error = input_open_device(handle);
 633         if (error) {
 634                 pr_err("Failed to open input device, error %d\n", error);
 635                 goto err_unregister;
 636         }
 637
 638         return 0;
 639
 640  err_unregister:
 641         input_unregister_handle(handle);
 642  err_free:
 643         kfree(handle);
 644         return error;
 645 }
 646
 647 static void sysrq_disconnect(struct input_handle *handle)
 648 {
 649         input_close_device(handle);
 650         input_unregister_handle(handle);
 651         kfree(handle);
 652 }
 653
 654 /*
 655  * We are matching on KEY_LEFTALT insteard of KEY_SYSRQ because not all
 656  * keyboards have SysRq ikey predefined and so user may add it to keymap
 657  * later, but we expect all such keyboards to have left alt.
 658  */
 659 static const struct input_device_id sysrq_ids[] = {
 660         {
 661                 .flags = INPUT_DEVICE_ID_MATCH_EVBIT |
 662                                 INPUT_DEVICE_ID_MATCH_KEYBIT,
 663                 .evbit = { BIT_MASK(EV_KEY) },
 664                 .keybit = { BIT_MASK(KEY_LEFTALT) },
 665         },
 666         { },
 667 };
 668
 669 static struct input_handler sysrq_handler = {
 670         .filter         = sysrq_filter,
 671         .connect        = sysrq_connect,
 672         .disconnect     = sysrq_disconnect,
 673         .name           = "sysrq",
 674         .id_table       = sysrq_ids,
 675 };
 676
 677 static bool sysrq_handler_registered;
 678
 679 static inline void sysrq_register_handler(void)
 680 {
 681         int error;
 682
 683         error = input_register_handler(&sysrq_handler);
 684         if (error)
 685                 pr_err("Failed to register input handler, error %d", error);
 686         else
 687                 sysrq_handler_registered = true;
 688 }
 689
 690 static inline void sysrq_unregister_handler(void)
 691 {
 692         if (sysrq_handler_registered) {
 693                 input_unregister_handler(&sysrq_handler);
 694                 sysrq_handler_registered = false;
 695         }
 696 }
 697
 698 #else
 699
 700 static inline void sysrq_register_handler(void)
 701 {
 702 }
 703
 704 static inline void sysrq_unregister_handler(void)
 705 {
 706 }
 707
 708 #endif /* CONFIG_INPUT */
 709
 710 int sysrq_toggle_support(int enable_mask)
 711 {
 712         bool was_enabled = sysrq_on();
 713
 714         sysrq_enabled = enable_mask;
 715
 716         if (was_enabled != sysrq_on()) {
 717                 if (sysrq_on())
 718                         sysrq_register_handler();
 719                 else
 720                         sysrq_unregister_handler();
 721         }
 722
 723         return 0;
 724 }
 725
 726 static int __sysrq_swap_key_ops(int key, struct sysrq_key_op *insert_op_p,
 727                                 struct sysrq_key_op *remove_op_p)
 728 {
 729         int retval;
 730         unsigned long flags;
 731
 732         spin_lock_irqsave(&sysrq_key_table_lock, flags);
 733         if (__sysrq_get_key_op(key) == remove_op_p) {
 734                 __sysrq_put_key_op(key, insert_op_p);
 735                 retval = 0;
 736         } else {
 737                 retval = -1;
 738         }
 739         spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
 740         return retval;
 741 }
 742
 743 int register_sysrq_key(int key, struct sysrq_key_op *op_p)
 744 {
 745         return __sysrq_swap_key_ops(key, op_p, NULL);
 746 }
 747 EXPORT_SYMBOL(register_sysrq_key);
 748
 749 int unregister_sysrq_key(int key, struct sysrq_key_op *op_p)
 750 {
 751         return __sysrq_swap_key_ops(key, NULL, op_p);
 752 }
 753 EXPORT_SYMBOL(unregister_sysrq_key);
 754
 755 #ifdef CONFIG_PROC_FS
 756 /*
 757  * writing 'C' to /proc/sysrq-trigger is like sysrq-C
 758  */
 759 static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf,
 760                                    size_t count, loff_t *ppos)
 761 {
 762         if (count) {
 763                 char c;
 764
 765                 if (get_user(c, buf))
 766                         return -EFAULT;
 767                 __handle_sysrq(c, false);
 768         }
 769
 770         return count;
 771 }
 772
 773 static const struct file_operations proc_sysrq_trigger_operations = {
 774         .write          = write_sysrq_trigger,
 775 };
 776
 777 static void sysrq_init_procfs(void)
 778 {
 779         if (!proc_create("sysrq-trigger", S_IWUSR, NULL,
 780                          &proc_sysrq_trigger_operations))
 781                 pr_err("Failed to register proc interface\n");
 782 }
 783
 784 #else
 785
 786 static inline void sysrq_init_procfs(void)
 787 {
 788 }
 789
 790 #endif /* CONFIG_PROC_FS */
 791
 792 static int __init sysrq_init(void)
 793 {
 794         sysrq_init_procfs();
 795
 796         if (sysrq_on())
 797                 sysrq_register_handler();
 798
 799         return 0;
 800 }
 801 module_init(sysrq_init);