/*
 *      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/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 <asm/ptrace.h>
#include <asm/irq_regs.h>

/* Whether we react on sysrq keys or just ignore them */
static int __read_mostly sysrq_enabled = SYSRQ_DEFAULT_ENABLE;
static bool __read_mostly sysrq_always_enabled;

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.\n");

        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\n", 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",
        .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",
        .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",
        .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",
        .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",
        .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",
        .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:\n", 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:\n", 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(0, 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 */
        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\n", op_p->action_msg);
                        console_loglevel = orig_log_level;
                        op_p->handler(key);
                } else {
                        printk("This sysrq operation is disabled.\n");
                }
        } 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("\n");
                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;
};

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_filter(struct input_handle *handle,
                         unsigned int type, unsigned int code, int value)
{
        struct sysrq_state *sysrq = handle->private;
        bool was_active = sysrq->active;
        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:
                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, 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) {
                        /*
                         * 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);

                } 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;
                }
                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;

        error = input_register_handle(&sysrq->handle);
        if (error) {
                pr_err("Failed to register input sysrq handler, error %d\n",
                        error);
                goto err_free;
        }

        error = input_open_device(&sysrq->handle);
        if (error) {
                pr_err("Failed to open input device, error %d\n", 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);
        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)
{
        int error;

        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;
        }
}

#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\n");
}

#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);