/*
   *	Linux Magic System Request Key Hacks
   *
   *	(c) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
   *	based on ideas by Pavel Machek <pavel@atrey.karlin.mff.cuni.cz>
   *
   *	(c) 2000 Crutcher Dunnavant <crutcher+kernel@datastacks.com>
   *	overhauled to use key registration
   *	based upon discusions in irc://irc.openprojects.net/#kernelnewbies
   *
   *	Copyright (c) 2010 Dmitry Torokhov
   *	Input handler conversion
   */
  
  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  
  #include <linux/sched.h>
  #include <linux/sched/rt.h>
  #include <linux/interrupt.h>
  #include <linux/mm.h>
  #include <linux/fs.h>
  #include <linux/mount.h>
  #include <linux/kdev_t.h>
  #include <linux/major.h>
  #include <linux/reboot.h>
  #include <linux/sysrq.h>
  #include <linux/kbd_kern.h>
  #include <linux/proc_fs.h>
  #include <linux/nmi.h>
  #include <linux/quotaops.h>
  #include <linux/perf_event.h>
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/suspend.h>
  #include <linux/writeback.h>
  #include <linux/swap.h>
  #include <linux/spinlock.h>
  #include <linux/vt_kern.h>
  #include <linux/workqueue.h>
  #include <linux/hrtimer.h>
  #include <linux/oom.h>
  #include <linux/slab.h>
  #include <linux/input.h>
  #include <linux/uaccess.h>
  #include <linux/moduleparam.h>
  #include <linux/jiffies.h>
  #include <linux/syscalls.h>
  #include <linux/of.h>
  
  #include <asm/ptrace.h>
  #include <asm/irq_regs.h>
  
  /* Whether we react on sysrq keys or just ignore them */
  static int __read_mostly sysrq_enabled = CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE;
  static bool __read_mostly sysrq_always_enabled;
  
  unsigned short platform_sysrq_reset_seq[] __weak = { KEY_RESERVED };
  int sysrq_reset_downtime_ms __weak;
  
  static bool sysrq_on(void)
  {
  	return sysrq_enabled || sysrq_always_enabled;
  }
  
  /*
   * A value of 1 means 'all', other nonzero values are an op mask:
   */
  static bool sysrq_on_mask(int mask)
  {
  	return sysrq_always_enabled ||
  	       sysrq_enabled == 1 ||
  	       (sysrq_enabled & mask);
  }
  
  static int __init sysrq_always_enabled_setup(char *str)
  {
  	sysrq_always_enabled = true;
  	pr_info("sysrq always enabled.
  ");
  
  	return 1;
  }
  
  __setup("sysrq_always_enabled", sysrq_always_enabled_setup);
  
  
  static void sysrq_handle_loglevel(int key)
  {
  	int i;
  
  	i = key - '0';
  	console_loglevel = 7;
  	printk("Loglevel set to %d
  ", i);
  	console_loglevel = i;
  }
  static struct sysrq_key_op sysrq_loglevel_op = {
  	.handler	= sysrq_handle_loglevel,
  	.help_msg	= "loglevel(0-9)",
  	.action_msg	= "Changing Loglevel",
  	.enable_mask	= SYSRQ_ENABLE_LOG,
  };
  
  #ifdef CONFIG_VT
  static void sysrq_handle_SAK(int key)
  {
  	struct work_struct *SAK_work = &vc_cons[fg_console].SAK_work;
  	schedule_work(SAK_work);
  }
  static struct sysrq_key_op sysrq_SAK_op = {
  	.handler	= sysrq_handle_SAK,
  	.help_msg	= "sak(k)",
  	.action_msg	= "SAK",
  	.enable_mask	= SYSRQ_ENABLE_KEYBOARD,
  };
  #else
  #define sysrq_SAK_op (*(struct sysrq_key_op *)NULL)
  #endif
  
  #ifdef CONFIG_VT
  static void sysrq_handle_unraw(int key)
  {
  	vt_reset_unicode(fg_console);
  }
  
  static struct sysrq_key_op sysrq_unraw_op = {
  	.handler	= sysrq_handle_unraw,
  	.help_msg	= "unraw(r)",
  	.action_msg	= "Keyboard mode set to system default",
  	.enable_mask	= SYSRQ_ENABLE_KEYBOARD,
  };
  #else
  #define sysrq_unraw_op (*(struct sysrq_key_op *)NULL)
  #endif /* CONFIG_VT */
  
  static void sysrq_handle_crash(int key)
  {
  	char *killer = NULL;
  
  	panic_on_oops = 1;	/* force panic */
  	wmb();
  	*killer = 1;
  }
  static struct sysrq_key_op sysrq_crash_op = {
  	.handler	= sysrq_handle_crash,
  	.help_msg	= "crash(c)",
  	.action_msg	= "Trigger a crash",
  	.enable_mask	= SYSRQ_ENABLE_DUMP,
  };
  
  static void sysrq_handle_reboot(int key)
  {
  	lockdep_off();
  	local_irq_enable();
  	emergency_restart();
  }
  static struct sysrq_key_op sysrq_reboot_op = {
  	.handler	= sysrq_handle_reboot,
  	.help_msg	= "reboot(b)",
  	.action_msg	= "Resetting",
  	.enable_mask	= SYSRQ_ENABLE_BOOT,
  };
  
  static void sysrq_handle_sync(int key)
  {
  	emergency_sync();
  }
  static struct sysrq_key_op sysrq_sync_op = {
  	.handler	= sysrq_handle_sync,
  	.help_msg	= "sync(s)",
  	.action_msg	= "Emergency Sync",
  	.enable_mask	= SYSRQ_ENABLE_SYNC,
  };
  
  static void sysrq_handle_show_timers(int key)
  {
  	sysrq_timer_list_show();
  }
  
  static struct sysrq_key_op sysrq_show_timers_op = {
  	.handler	= sysrq_handle_show_timers,
  	.help_msg	= "show-all-timers(q)",
  	.action_msg	= "Show clockevent devices & pending hrtimers (no others)",
  };
  
  static void sysrq_handle_mountro(int key)
  {
  	emergency_remount();
  }
  static struct sysrq_key_op sysrq_mountro_op = {
  	.handler	= sysrq_handle_mountro,
  	.help_msg	= "unmount(u)",
  	.action_msg	= "Emergency Remount R/O",
  	.enable_mask	= SYSRQ_ENABLE_REMOUNT,
  };
  
  #ifdef CONFIG_LOCKDEP
  static void sysrq_handle_showlocks(int key)
  {
  	debug_show_all_locks();
  }
  
  static struct sysrq_key_op sysrq_showlocks_op = {
  	.handler	= sysrq_handle_showlocks,
  	.help_msg	= "show-all-locks(d)",
  	.action_msg	= "Show Locks Held",
  };
  #else
  #define sysrq_showlocks_op (*(struct sysrq_key_op *)NULL)
  #endif
  
  #ifdef CONFIG_SMP
  static DEFINE_SPINLOCK(show_lock);
  
  static void showacpu(void *dummy)
  {
  	unsigned long flags;
  
  	/* Idle CPUs have no interesting backtrace. */
  	if (idle_cpu(smp_processor_id()))
  		return;
  
  	spin_lock_irqsave(&show_lock, flags);
  	printk(KERN_INFO "CPU%d:
  ", smp_processor_id());
  	show_stack(NULL, NULL);
  	spin_unlock_irqrestore(&show_lock, flags);
  }
  
  static void sysrq_showregs_othercpus(struct work_struct *dummy)
  {
  	smp_call_function(showacpu, NULL, 0);
  }
  
  static DECLARE_WORK(sysrq_showallcpus, sysrq_showregs_othercpus);
  
  static void sysrq_handle_showallcpus(int key)
  {
  	/*
  	 * Fall back to the workqueue based printing if the
  	 * backtrace printing did not succeed or the
  	 * architecture has no support for it:
  	 */
  	if (!trigger_all_cpu_backtrace()) {
  		struct pt_regs *regs = get_irq_regs();
  
  		if (regs) {
  			printk(KERN_INFO "CPU%d:
  ", smp_processor_id());
  			show_regs(regs);
  		}
  		schedule_work(&sysrq_showallcpus);
  	}
  }
  
  static struct sysrq_key_op sysrq_showallcpus_op = {
  	.handler	= sysrq_handle_showallcpus,
  	.help_msg	= "show-backtrace-all-active-cpus(l)",
  	.action_msg	= "Show backtrace of all active CPUs",
  	.enable_mask	= SYSRQ_ENABLE_DUMP,
  };
  #endif
  
  static void sysrq_handle_showregs(int key)
  {
  	struct pt_regs *regs = get_irq_regs();
  	if (regs)
  		show_regs(regs);
  	perf_event_print_debug();
  }
  static struct sysrq_key_op sysrq_showregs_op = {
  	.handler	= sysrq_handle_showregs,
  	.help_msg	= "show-registers(p)",
  	.action_msg	= "Show Regs",
  	.enable_mask	= SYSRQ_ENABLE_DUMP,
  };
  
  static void sysrq_handle_showstate(int key)
  {
  	show_state();
  }
  static struct sysrq_key_op sysrq_showstate_op = {
  	.handler	= sysrq_handle_showstate,
  	.help_msg	= "show-task-states(t)",
  	.action_msg	= "Show State",
  	.enable_mask	= SYSRQ_ENABLE_DUMP,
  };
  
  static void sysrq_handle_showstate_blocked(int key)
  {
  	show_state_filter(TASK_UNINTERRUPTIBLE);
  }
  static struct sysrq_key_op sysrq_showstate_blocked_op = {
  	.handler	= sysrq_handle_showstate_blocked,
  	.help_msg	= "show-blocked-tasks(w)",
  	.action_msg	= "Show Blocked State",
  	.enable_mask	= SYSRQ_ENABLE_DUMP,
  };
  
  #ifdef CONFIG_TRACING
  #include <linux/ftrace.h>
  
  static void sysrq_ftrace_dump(int key)
  {
  	ftrace_dump(DUMP_ALL);
  }
  static struct sysrq_key_op sysrq_ftrace_dump_op = {
  	.handler	= sysrq_ftrace_dump,
  	.help_msg	= "dump-ftrace-buffer(z)",
  	.action_msg	= "Dump ftrace buffer",
  	.enable_mask	= SYSRQ_ENABLE_DUMP,
  };
  #else
  #define sysrq_ftrace_dump_op (*(struct sysrq_key_op *)NULL)
  #endif
  
  static void sysrq_handle_showmem(int key)
  {
  	show_mem(0);
  }
  static struct sysrq_key_op sysrq_showmem_op = {
  	.handler	= sysrq_handle_showmem,
  	.help_msg	= "show-memory-usage(m)",
  	.action_msg	= "Show Memory",
  	.enable_mask	= SYSRQ_ENABLE_DUMP,
  };
  
  /*
   * Signal sysrq helper function.  Sends a signal to all user processes.
   */
  static void send_sig_all(int sig)
  {
  	struct task_struct *p;
  
  	read_lock(&tasklist_lock);
  	for_each_process(p) {
  		if (p->flags & PF_KTHREAD)
  			continue;
  		if (is_global_init(p))
  			continue;
  
  		do_send_sig_info(sig, SEND_SIG_FORCED, p, true);
  	}
  	read_unlock(&tasklist_lock);
  }
  
  static void sysrq_handle_term(int key)
  {
  	send_sig_all(SIGTERM);
  	console_loglevel = 8;
  }
  static struct sysrq_key_op sysrq_term_op = {
  	.handler	= sysrq_handle_term,
  	.help_msg	= "terminate-all-tasks(e)",
  	.action_msg	= "Terminate All Tasks",
  	.enable_mask	= SYSRQ_ENABLE_SIGNAL,
  };
  
  static void moom_callback(struct work_struct *ignored)
  {
  	out_of_memory(node_zonelist(first_online_node, GFP_KERNEL), GFP_KERNEL,
  		      0, NULL, true);
  }
  
  static DECLARE_WORK(moom_work, moom_callback);
  
  static void sysrq_handle_moom(int key)
  {
  	schedule_work(&moom_work);
  }
  static struct sysrq_key_op sysrq_moom_op = {
  	.handler	= sysrq_handle_moom,
  	.help_msg	= "memory-full-oom-kill(f)",
  	.action_msg	= "Manual OOM execution",
  	.enable_mask	= SYSRQ_ENABLE_SIGNAL,
  };
  
  #ifdef CONFIG_BLOCK
  static void sysrq_handle_thaw(int key)
  {
  	emergency_thaw_all();
  }
  static struct sysrq_key_op sysrq_thaw_op = {
  	.handler	= sysrq_handle_thaw,
  	.help_msg	= "thaw-filesystems(j)",
  	.action_msg	= "Emergency Thaw of all frozen filesystems",
  	.enable_mask	= SYSRQ_ENABLE_SIGNAL,
  };
  #endif
  
  static void sysrq_handle_kill(int key)
  {
  	send_sig_all(SIGKILL);
  	console_loglevel = 8;
  }
  static struct sysrq_key_op sysrq_kill_op = {
  	.handler	= sysrq_handle_kill,
  	.help_msg	= "kill-all-tasks(i)",
  	.action_msg	= "Kill All Tasks",
  	.enable_mask	= SYSRQ_ENABLE_SIGNAL,
  };
  
  static void sysrq_handle_unrt(int key)
  {
  	normalize_rt_tasks();
  }
  static struct sysrq_key_op sysrq_unrt_op = {
  	.handler	= sysrq_handle_unrt,
  	.help_msg	= "nice-all-RT-tasks(n)",
  	.action_msg	= "Nice All RT Tasks",
  	.enable_mask	= SYSRQ_ENABLE_RTNICE,
  };
  
  /* Key Operations table and lock */
  static DEFINE_SPINLOCK(sysrq_key_table_lock);
  
  static struct sysrq_key_op *sysrq_key_table[36] = {
  	&sysrq_loglevel_op,		/* 0 */
  	&sysrq_loglevel_op,		/* 1 */
  	&sysrq_loglevel_op,		/* 2 */
  	&sysrq_loglevel_op,		/* 3 */
  	&sysrq_loglevel_op,		/* 4 */
  	&sysrq_loglevel_op,		/* 5 */
  	&sysrq_loglevel_op,		/* 6 */
  	&sysrq_loglevel_op,		/* 7 */
  	&sysrq_loglevel_op,		/* 8 */
  	&sysrq_loglevel_op,		/* 9 */
  
  	/*
  	 * a: Don't use for system provided sysrqs, it is handled specially on
  	 * sparc and will never arrive.
  	 */
  	NULL,				/* a */
  	&sysrq_reboot_op,		/* b */
  	&sysrq_crash_op,		/* c & ibm_emac driver debug */
  	&sysrq_showlocks_op,		/* d */
  	&sysrq_term_op,			/* e */
  	&sysrq_moom_op,			/* f */
  	/* g: May be registered for the kernel debugger */
  	NULL,				/* g */
  	NULL,				/* h - reserved for help */
  	&sysrq_kill_op,			/* i */
  #ifdef CONFIG_BLOCK
  	&sysrq_thaw_op,			/* j */
  #else
  	NULL,				/* j */
  #endif
  	&sysrq_SAK_op,			/* k */
  #ifdef CONFIG_SMP
  	&sysrq_showallcpus_op,		/* l */
  #else
  	NULL,				/* l */
  #endif
  	&sysrq_showmem_op,		/* m */
  	&sysrq_unrt_op,			/* n */
  	/* o: This will often be registered as 'Off' at init time */
  	NULL,				/* o */
  	&sysrq_showregs_op,		/* p */
  	&sysrq_show_timers_op,		/* q */
  	&sysrq_unraw_op,		/* r */
  	&sysrq_sync_op,			/* s */
  	&sysrq_showstate_op,		/* t */
  	&sysrq_mountro_op,		/* u */
  	/* v: May be registered for frame buffer console restore */
  	NULL,				/* v */
  	&sysrq_showstate_blocked_op,	/* w */
  	/* x: May be registered on ppc/powerpc for xmon */
  	/* x: May be registered on sparc64 for global PMU dump */
  	NULL,				/* x */
  	/* y: May be registered on sparc64 for global register dump */
  	NULL,				/* y */
  	&sysrq_ftrace_dump_op,		/* z */
  };
  
  /* key2index calculation, -1 on invalid index */
  static int sysrq_key_table_key2index(int key)
  {
  	int retval;
  
  	if ((key >= '0') && (key <= '9'))
  		retval = key - '0';
  	else if ((key >= 'a') && (key <= 'z'))
  		retval = key + 10 - 'a';
  	else
  		retval = -1;
  	return retval;
  }
  
  /*
   * get and put functions for the table, exposed to modules.
   */
  struct sysrq_key_op *__sysrq_get_key_op(int key)
  {
          struct sysrq_key_op *op_p = NULL;
          int i;
  
  	i = sysrq_key_table_key2index(key);
  	if (i != -1)
  	        op_p = sysrq_key_table[i];
  
          return op_p;
  }
  
  static void __sysrq_put_key_op(int key, struct sysrq_key_op *op_p)
  {
          int i = sysrq_key_table_key2index(key);
  
          if (i != -1)
                  sysrq_key_table[i] = op_p;
  }
  
  void __handle_sysrq(int key, bool check_mask)
  {
  	struct sysrq_key_op *op_p;
  	int orig_log_level;
  	int i;
  	unsigned long flags;
  
  	spin_lock_irqsave(&sysrq_key_table_lock, flags);
  	/*
  	 * Raise the apparent loglevel to maximum so that the sysrq header
  	 * is shown to provide the user with positive feedback.  We do not
  	 * simply emit this at KERN_EMERG as that would change message
  	 * routing in the consumers of /proc/kmsg.
  	 */
  	orig_log_level = console_loglevel;
  	console_loglevel = 7;
  	printk(KERN_INFO "SysRq : ");
  
          op_p = __sysrq_get_key_op(key);
          if (op_p) {
  		/*
  		 * Should we check for enabled operations (/proc/sysrq-trigger
  		 * should not) and is the invoked operation enabled?
  		 */
  		if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
  			printk("%s
  ", op_p->action_msg);
  			console_loglevel = orig_log_level;
  			op_p->handler(key);
  		} else {
  			printk("This sysrq operation is disabled.
  ");
  		}
  	} else {
  		printk("HELP : ");
  		/* Only print the help msg once per handler */
  		for (i = 0; i < ARRAY_SIZE(sysrq_key_table); i++) {
  			if (sysrq_key_table[i]) {
  				int j;
  
  				for (j = 0; sysrq_key_table[i] !=
  						sysrq_key_table[j]; j++)
  					;
  				if (j != i)
  					continue;
  				printk("%s ", sysrq_key_table[i]->help_msg);
  			}
  		}
  		printk("
  ");
  		console_loglevel = orig_log_level;
  	}
  	spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
  }
  
  void handle_sysrq(int key)
  {
  	if (sysrq_on())
  		__handle_sysrq(key, true);
  }
  EXPORT_SYMBOL(handle_sysrq);
  
  #ifdef CONFIG_INPUT
  
  /* Simple translation table for the SysRq keys */
  static const unsigned char sysrq_xlate[KEY_CNT] =
          "\000\0331234567890-=\177\t"                    /* 0x00 - 0x0f */
          "qwertyuiop[]\r\000as"                          /* 0x10 - 0x1f */
          "dfghjkl;'`\000\\zxcv"                          /* 0x20 - 0x2f */
          "bnm,./\000*\000 \000\201\202\203\204\205"      /* 0x30 - 0x3f */
          "\206\207\210\211\212\000\000789-456+1"         /* 0x40 - 0x4f */
          "230\177\000\000\213\214\000\000\000\000\000\000\000\000\000\000" /* 0x50 - 0x5f */
          "\r\000/";                                      /* 0x60 - 0x6f */
  
  struct sysrq_state {
  	struct input_handle handle;
  	struct work_struct reinject_work;
  	unsigned long key_down[BITS_TO_LONGS(KEY_CNT)];
  	unsigned int alt;
  	unsigned int alt_use;
  	bool active;
  	bool need_reinject;
  	bool reinjecting;
  
  	/* reset sequence handling */
  	bool reset_canceled;
  	bool reset_requested;
  	unsigned long reset_keybit[BITS_TO_LONGS(KEY_CNT)];
  	int reset_seq_len;
  	int reset_seq_cnt;
  	int reset_seq_version;
  	struct timer_list keyreset_timer;
  };
  
  #define SYSRQ_KEY_RESET_MAX	20 /* Should be plenty */
  static unsigned short sysrq_reset_seq[SYSRQ_KEY_RESET_MAX];
  static unsigned int sysrq_reset_seq_len;
  static unsigned int sysrq_reset_seq_version = 1;
  
  static void sysrq_parse_reset_sequence(struct sysrq_state *state)
  {
  	int i;
  	unsigned short key;
  
  	state->reset_seq_cnt = 0;
  
  	for (i = 0; i < sysrq_reset_seq_len; i++) {
  		key = sysrq_reset_seq[i];
  
  		if (key == KEY_RESERVED || key > KEY_MAX)
  			break;
  
  		__set_bit(key, state->reset_keybit);
  		state->reset_seq_len++;
  
  		if (test_bit(key, state->key_down))
  			state->reset_seq_cnt++;
  	}
  
  	/* Disable reset until old keys are not released */
  	state->reset_canceled = state->reset_seq_cnt != 0;
  
  	state->reset_seq_version = sysrq_reset_seq_version;
  }
  
  static void sysrq_do_reset(unsigned long _state)
  {
  	struct sysrq_state *state = (struct sysrq_state *) _state;
  
  	state->reset_requested = true;
  
  	sys_sync();
  	kernel_restart(NULL);
  }
  
  static void sysrq_handle_reset_request(struct sysrq_state *state)
  {
  	if (state->reset_requested)
  		__handle_sysrq(sysrq_xlate[KEY_B], false);
  
  	if (sysrq_reset_downtime_ms)
  		mod_timer(&state->keyreset_timer,
  			jiffies + msecs_to_jiffies(sysrq_reset_downtime_ms));
  	else
  		sysrq_do_reset((unsigned long)state);
  }
  
  static void sysrq_detect_reset_sequence(struct sysrq_state *state,
  					unsigned int code, int value)
  {
  	if (!test_bit(code, state->reset_keybit)) {
  		/*
  		 * Pressing any key _not_ in reset sequence cancels
  		 * the reset sequence.  Also cancelling the timer in
  		 * case additional keys were pressed after a reset
  		 * has been requested.
  		 */
  		if (value && state->reset_seq_cnt) {
  			state->reset_canceled = true;
  			del_timer(&state->keyreset_timer);
  		}
  	} else if (value == 0) {
  		/*
  		 * Key release - all keys in the reset sequence need
  		 * to be pressed and held for the reset timeout
  		 * to hold.
  		 */
  		del_timer(&state->keyreset_timer);
  
  		if (--state->reset_seq_cnt == 0)
  			state->reset_canceled = false;
  	} else if (value == 1) {
  		/* key press, not autorepeat */
  		if (++state->reset_seq_cnt == state->reset_seq_len &&
  		    !state->reset_canceled) {
  			sysrq_handle_reset_request(state);
  		}
  	}
  }
  
  #ifdef CONFIG_OF
  static void sysrq_of_get_keyreset_config(void)
  {
  	u32 key;
  	struct device_node *np;
  	struct property *prop;
  	const __be32 *p;
  
  	np = of_find_node_by_path("/chosen/linux,sysrq-reset-seq");
  	if (!np) {
  		pr_debug("No sysrq node found");
  		return;
  	}
  
  	/* Reset in case a __weak definition was present */
  	sysrq_reset_seq_len = 0;
  
  	of_property_for_each_u32(np, "keyset", prop, p, key) {
  		if (key == KEY_RESERVED || key > KEY_MAX ||
  		    sysrq_reset_seq_len == SYSRQ_KEY_RESET_MAX)
  			break;
  
  		sysrq_reset_seq[sysrq_reset_seq_len++] = (unsigned short)key;
  	}
  
  	/* Get reset timeout if any. */
  	of_property_read_u32(np, "timeout-ms", &sysrq_reset_downtime_ms);
  }
  #else
  static void sysrq_of_get_keyreset_config(void)
  {
  }
  #endif
  
  static void sysrq_reinject_alt_sysrq(struct work_struct *work)
  {
  	struct sysrq_state *sysrq =
  			container_of(work, struct sysrq_state, reinject_work);
  	struct input_handle *handle = &sysrq->handle;
  	unsigned int alt_code = sysrq->alt_use;
  
  	if (sysrq->need_reinject) {
  		/* we do not want the assignment to be reordered */
  		sysrq->reinjecting = true;
  		mb();
  
  		/* Simulate press and release of Alt + SysRq */
  		input_inject_event(handle, EV_KEY, alt_code, 1);
  		input_inject_event(handle, EV_KEY, KEY_SYSRQ, 1);
  		input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
  
  		input_inject_event(handle, EV_KEY, KEY_SYSRQ, 0);
  		input_inject_event(handle, EV_KEY, alt_code, 0);
  		input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
  
  		mb();
  		sysrq->reinjecting = false;
  	}
  }
  
  static bool sysrq_handle_keypress(struct sysrq_state *sysrq,
  				  unsigned int code, int value)
  {
  	bool was_active = sysrq->active;
  	bool suppress;
  
  	switch (code) {
  
  	case KEY_LEFTALT:
  	case KEY_RIGHTALT:
  		if (!value) {
  			/* One of ALTs is being released */
  			if (sysrq->active && code == sysrq->alt_use)
  				sysrq->active = false;
  
  			sysrq->alt = KEY_RESERVED;
  
  		} else if (value != 2) {
  			sysrq->alt = code;
  			sysrq->need_reinject = false;
  		}
  		break;
  
  	case KEY_SYSRQ:
  		if (value == 1 && sysrq->alt != KEY_RESERVED) {
  			sysrq->active = true;
  			sysrq->alt_use = sysrq->alt;
  			/*
  			 * If nothing else will be pressed we'll need
  			 * to re-inject Alt-SysRq keysroke.
  			 */
  			sysrq->need_reinject = true;
  		}
  
  		/*
  		 * Pretend that sysrq was never pressed at all. This
  		 * is needed to properly handle KGDB which will try
  		 * to release all keys after exiting debugger. If we
  		 * do not clear key bit it KGDB will end up sending
  		 * release events for Alt and SysRq, potentially
  		 * triggering print screen function.
  		 */
  		if (sysrq->active)
  			clear_bit(KEY_SYSRQ, sysrq->handle.dev->key);
  
  		break;
  
  	default:
  		if (sysrq->active && value && value != 2) {
  			sysrq->need_reinject = false;
  			__handle_sysrq(sysrq_xlate[code], true);
  		}
  		break;
  	}
  
  	suppress = sysrq->active;
  
  	if (!sysrq->active) {
  
  		/*
  		 * See if reset sequence has changed since the last time.
  		 */
  		if (sysrq->reset_seq_version != sysrq_reset_seq_version)
  			sysrq_parse_reset_sequence(sysrq);
  
  		/*
  		 * If we are not suppressing key presses keep track of
  		 * keyboard state so we can release keys that have been
  		 * pressed before entering SysRq mode.
  		 */
  		if (value)
  			set_bit(code, sysrq->key_down);
  		else
  			clear_bit(code, sysrq->key_down);
  
  		if (was_active)
  			schedule_work(&sysrq->reinject_work);
  
  		/* Check for reset sequence */
  		sysrq_detect_reset_sequence(sysrq, code, value);
  
  	} else if (value == 0 && test_and_clear_bit(code, sysrq->key_down)) {
  		/*
  		 * Pass on release events for keys that was pressed before
  		 * entering SysRq mode.
  		 */
  		suppress = false;
  	}
  
  	return suppress;
  }
  
  static bool sysrq_filter(struct input_handle *handle,
  			 unsigned int type, unsigned int code, int value)
  {
  	struct sysrq_state *sysrq = handle->private;
  	bool suppress;
  
  	/*
  	 * Do not filter anything if we are in the process of re-injecting
  	 * Alt+SysRq combination.
  	 */
  	if (sysrq->reinjecting)
  		return false;
  
  	switch (type) {
  
  	case EV_SYN:
  		suppress = false;
  		break;
  
  	case EV_KEY:
  		suppress = sysrq_handle_keypress(sysrq, code, value);
  		break;
  
  	default:
  		suppress = sysrq->active;
  		break;
  	}
  
  	return suppress;
  }
  
  static int sysrq_connect(struct input_handler *handler,
  			 struct input_dev *dev,
  			 const struct input_device_id *id)
  {
  	struct sysrq_state *sysrq;
  	int error;
  
  	sysrq = kzalloc(sizeof(struct sysrq_state), GFP_KERNEL);
  	if (!sysrq)
  		return -ENOMEM;
  
  	INIT_WORK(&sysrq->reinject_work, sysrq_reinject_alt_sysrq);
  
  	sysrq->handle.dev = dev;
  	sysrq->handle.handler = handler;
  	sysrq->handle.name = "sysrq";
  	sysrq->handle.private = sysrq;
  	setup_timer(&sysrq->keyreset_timer,
  		    sysrq_do_reset, (unsigned long)sysrq);
  
  	error = input_register_handle(&sysrq->handle);
  	if (error) {
  		pr_err("Failed to register input sysrq handler, error %d
  ",
  			error);
  		goto err_free;
  	}
  
  	error = input_open_device(&sysrq->handle);
  	if (error) {
  		pr_err("Failed to open input device, error %d
  ", error);
  		goto err_unregister;
  	}
  
  	return 0;
  
   err_unregister:
  	input_unregister_handle(&sysrq->handle);
   err_free:
  	kfree(sysrq);
  	return error;
  }
  
  static void sysrq_disconnect(struct input_handle *handle)
  {
  	struct sysrq_state *sysrq = handle->private;
  
  	input_close_device(handle);
  	cancel_work_sync(&sysrq->reinject_work);
  	del_timer_sync(&sysrq->keyreset_timer);
  	input_unregister_handle(handle);
  	kfree(sysrq);
  }
  
  /*
   * We are matching on KEY_LEFTALT instead of KEY_SYSRQ because not all
   * keyboards have SysRq key predefined and so user may add it to keymap
   * later, but we expect all such keyboards to have left alt.
   */
  static const struct input_device_id sysrq_ids[] = {
  	{
  		.flags = INPUT_DEVICE_ID_MATCH_EVBIT |
  				INPUT_DEVICE_ID_MATCH_KEYBIT,
  		.evbit = { BIT_MASK(EV_KEY) },
  		.keybit = { BIT_MASK(KEY_LEFTALT) },
  	},
  	{ },
  };
  
  static struct input_handler sysrq_handler = {
  	.filter		= sysrq_filter,
  	.connect	= sysrq_connect,
  	.disconnect	= sysrq_disconnect,
  	.name		= "sysrq",
  	.id_table	= sysrq_ids,
  };
  
  static bool sysrq_handler_registered;
  
  static inline void sysrq_register_handler(void)
  {
  	unsigned short key;
  	int error;
  	int i;
  
  	/* First check if a __weak interface was instantiated. */
  	for (i = 0; i < ARRAY_SIZE(sysrq_reset_seq); i++) {
  		key = platform_sysrq_reset_seq[i];
  		if (key == KEY_RESERVED || key > KEY_MAX)
  			break;
  
  		sysrq_reset_seq[sysrq_reset_seq_len++] = key;
  	}
  
  	/*
  	 * DT configuration takes precedence over anything that would
  	 * have been defined via the __weak interface.
  	 */
  	sysrq_of_get_keyreset_config();
  
  	error = input_register_handler(&sysrq_handler);
  	if (error)
  		pr_err("Failed to register input handler, error %d", error);
  	else
  		sysrq_handler_registered = true;
  }
  
  static inline void sysrq_unregister_handler(void)
  {
  	if (sysrq_handler_registered) {
  		input_unregister_handler(&sysrq_handler);
  		sysrq_handler_registered = false;
  	}
  }
  
  static int sysrq_reset_seq_param_set(const char *buffer,
  				     const struct kernel_param *kp)
  {
  	unsigned long val;
  	int error;
  
  	error = kstrtoul(buffer, 0, &val);
  	if (error < 0)
  		return error;
  
  	if (val > KEY_MAX)
  		return -EINVAL;
  
  	*((unsigned short *)kp->arg) = val;
  	sysrq_reset_seq_version++;
  
  	return 0;
  }
  
  static struct kernel_param_ops param_ops_sysrq_reset_seq = {
  	.get	= param_get_ushort,
  	.set	= sysrq_reset_seq_param_set,
  };
  
  #define param_check_sysrq_reset_seq(name, p)	\
  	__param_check(name, p, unsigned short)
  
  module_param_array_named(reset_seq, sysrq_reset_seq, sysrq_reset_seq,
  			 &sysrq_reset_seq_len, 0644);
  
  module_param_named(sysrq_downtime_ms, sysrq_reset_downtime_ms, int, 0644);
  
  #else
  
  static inline void sysrq_register_handler(void)
  {
  }
  
  static inline void sysrq_unregister_handler(void)
  {
  }
  
  #endif /* CONFIG_INPUT */
  
  int sysrq_toggle_support(int enable_mask)
  {
  	bool was_enabled = sysrq_on();
  
  	sysrq_enabled = enable_mask;
  
  	if (was_enabled != sysrq_on()) {
  		if (sysrq_on())
  			sysrq_register_handler();
  		else
  			sysrq_unregister_handler();
  	}
  
  	return 0;
  }
  
  static int __sysrq_swap_key_ops(int key, struct sysrq_key_op *insert_op_p,
                                  struct sysrq_key_op *remove_op_p)
  {
  	int retval;
  	unsigned long flags;
  
  	spin_lock_irqsave(&sysrq_key_table_lock, flags);
  	if (__sysrq_get_key_op(key) == remove_op_p) {
  		__sysrq_put_key_op(key, insert_op_p);
  		retval = 0;
  	} else {
  		retval = -1;
  	}
  	spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
  	return retval;
  }
  
  int register_sysrq_key(int key, struct sysrq_key_op *op_p)
  {
  	return __sysrq_swap_key_ops(key, op_p, NULL);
  }
  EXPORT_SYMBOL(register_sysrq_key);
  
  int unregister_sysrq_key(int key, struct sysrq_key_op *op_p)
  {
  	return __sysrq_swap_key_ops(key, NULL, op_p);
  }
  EXPORT_SYMBOL(unregister_sysrq_key);
  
  #ifdef CONFIG_PROC_FS
  /*
   * writing 'C' to /proc/sysrq-trigger is like sysrq-C
   */
  static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf,
  				   size_t count, loff_t *ppos)
  {
  	if (count) {
  		char c;
  
  		if (get_user(c, buf))
  			return -EFAULT;
  		__handle_sysrq(c, false);
  	}
  
  	return count;
  }
  
  static const struct file_operations proc_sysrq_trigger_operations = {
  	.write		= write_sysrq_trigger,
  	.llseek		= noop_llseek,
  };
  
  static void sysrq_init_procfs(void)
  {
  	if (!proc_create("sysrq-trigger", S_IWUSR, NULL,
  			 &proc_sysrq_trigger_operations))
  		pr_err("Failed to register proc interface
  ");
  }
  
  #else
  
  static inline void sysrq_init_procfs(void)
  {
  }
  
  #endif /* CONFIG_PROC_FS */
  
  static int __init sysrq_init(void)
  {
  	sysrq_init_procfs();
  
  	if (sysrq_on())
  		sysrq_register_handler();
  
  	return 0;
  }
  module_init(sysrq_init);