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 */ 49static int __read_mostly sysrq_enabled = 1; 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 struct kbd_struct *kbd = &kbd_table[fg_console]; 114 115 if (kbd) 116 kbd->kbdmode = default_utf8 ? VC_UNICODE : VC_XLATE; 117} 118static 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 128static 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} 136static 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 143static void sysrq_handle_reboot(int key) 144{ 145 lockdep_off(); 146 local_irq_enable(); 147 emergency_restart(); 148} 149static 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 156static void sysrq_handle_sync(int key) 157{ 158 emergency_sync(); 159} 160static 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 167static void sysrq_handle_show_timers(int key) 168{ 169 sysrq_timer_list_show(); 170} 171 172static 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 178static void sysrq_handle_mountro(int key) 179{ 180 emergency_remount(); 181} 182static 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 190static void sysrq_handle_showlocks(int key) 191{ 192 debug_show_all_locks(); 193} 194 195static 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 205static DEFINE_SPINLOCK(show_lock); 206 207static 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 221static void sysrq_showregs_othercpus(struct work_struct *dummy) 222{ 223 smp_call_function(showacpu, NULL, 0); 224} 225 226static DECLARE_WORK(sysrq_showallcpus, sysrq_showregs_othercpus); 227 228static 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 246static 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 254static 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} 261static 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 268static void sysrq_handle_showstate(int key) 269{ 270 show_state(); 271} 272static 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 279static void sysrq_handle_showstate_blocked(int key) 280{ 281 show_state_filter(TASK_UNINTERRUPTIBLE); 282} 283static 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 293static void sysrq_ftrace_dump(int key) 294{ 295 ftrace_dump(DUMP_ALL); 296} 297static 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 307static void sysrq_handle_showmem(int key) 308{ 309 show_mem(); 310} 311static 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 */ 321static 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 332static void sysrq_handle_term(int key) 333{ 334 send_sig_all(SIGTERM); 335 console_loglevel = 8; 336} 337static 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 344static void moom_callback(struct work_struct *ignored) 345{ 346 out_of_memory(node_zonelist(0, GFP_KERNEL), GFP_KERNEL, 0, NULL); 347} 348 349static DECLARE_WORK(moom_work, moom_callback); 350 351static void sysrq_handle_moom(int key) 352{ 353 schedule_work(&moom_work); 354} 355static 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 363static void sysrq_handle_thaw(int key) 364{ 365 emergency_thaw_all(); 366} 367static 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 375static void sysrq_handle_kill(int key) 376{ 377 send_sig_all(SIGKILL); 378 console_loglevel = 8; 379} 380static 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 387static void sysrq_handle_unrt(int key) 388{ 389 normalize_rt_tasks(); 390} 391static 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 */ 399static DEFINE_SPINLOCK(sysrq_key_table_lock); 400 401static 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 */ 459static 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 */ 475struct 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 487static 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 495void __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 547void handle_sysrq(int key) 548{ 549 if (sysrq_on()) 550 __handle_sysrq(key, true); 551} 552EXPORT_SYMBOL(handle_sysrq); 553 554#ifdef CONFIG_INPUT 555 556/* Simple translation table for the SysRq keys */ 557static 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 566static bool sysrq_down; 567static int sysrq_alt_use; 568static int sysrq_alt; 569 570static 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 603out: 604 return sysrq_down; 605} 606 607static 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 647static 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 */ 659static 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 669static 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 677static bool sysrq_handler_registered; 678 679static 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 690static 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 700static inline void sysrq_register_handler(void) 701{ 702} 703 704static inline void sysrq_unregister_handler(void) 705{ 706} 707 708#endif /* CONFIG_INPUT */ 709 710int 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 726static 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 743int register_sysrq_key(int key, struct sysrq_key_op *op_p) 744{ 745 return __sysrq_swap_key_ops(key, op_p, NULL); 746} 747EXPORT_SYMBOL(register_sysrq_key); 748 749int unregister_sysrq_key(int key, struct sysrq_key_op *op_p) 750{ 751 return __sysrq_swap_key_ops(key, NULL, op_p); 752} 753EXPORT_SYMBOL(unregister_sysrq_key); 754 755#ifdef CONFIG_PROC_FS 756/* 757 * writing 'C' to /proc/sysrq-trigger is like sysrq-C 758 */ 759static 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 773static const struct file_operations proc_sysrq_trigger_operations = { 774 .write = write_sysrq_trigger, 775}; 776 777static 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 786static inline void sysrq_init_procfs(void) 787{ 788} 789 790#endif /* CONFIG_PROC_FS */ 791 792static int __init sysrq_init(void) 793{ 794 sysrq_init_procfs(); 795 796 if (sysrq_on()) 797 sysrq_register_handler(); 798 799 return 0; 800} 801module_init(sysrq_init); 802