TTY: create drivers/tty and move the tty core files there

The tty code should be in its own subdirectory and not in the char
driver with all of the cruft that is currently there.

Based on work done by Arnd Bergmann <arnd@arndb.de>

Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 811 insertions, 0 deletions

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
new file mode 100644
index 000000000000..eaa5d3efa79d
--- /dev/null
+++ b/drivers/tty/sysrq.c
@@ -0,0 +1,811 @@
+/*
+ *      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/buffer_head.h>          /* for fsync_bdev() */
+#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 <asm/ptrace.h>
+#include <asm/irq_regs.h>
+
+/* Whether we react on sysrq keys or just ignore them */
+static int __read_mostly sysrq_enabled = 1;
+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)
+{
+        struct kbd_struct *kbd = &kbd_table[fg_console];
+
+        if (kbd)
+                kbd->kbdmode = default_utf8 ? VC_UNICODE : VC_XLATE;
+}
+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();
+}
+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;
+
+        for_each_process(p) {
+                if (p->mm && !is_global_init(p))
+                        /* Not swapper, init nor kernel thread */
+                        force_sig(sig, p);
+        }
+}
+
+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);
+}
+
+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_MAX + 1] =
+        "\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 */
+
+static bool sysrq_down;
+static int sysrq_alt_use;
+static int sysrq_alt;
+static DEFINE_SPINLOCK(sysrq_event_lock);
+
+static bool sysrq_filter(struct input_handle *handle, unsigned int type,
+                         unsigned int code, int value)
+{
+        bool suppress;
+
+        /* We are called with interrupts disabled, just take the lock */
+        spin_lock(&sysrq_event_lock);
+
+        if (type != EV_KEY)
+                goto out;
+
+        switch (code) {
+
+        case KEY_LEFTALT:
+        case KEY_RIGHTALT:
+                if (value)
+                        sysrq_alt = code;
+                else {
+                        if (sysrq_down && code == sysrq_alt_use)
+                                sysrq_down = false;
+
+                        sysrq_alt = 0;
+                }
+                break;
+
+        case KEY_SYSRQ:
+                if (value == 1 && sysrq_alt) {
+                        sysrq_down = true;
+                        sysrq_alt_use = sysrq_alt;
+                }
+                break;
+
+        default:
+                if (sysrq_down && value && value != 2)
+                        __handle_sysrq(sysrq_xlate[code], true);
+                break;
+        }
+
+out:
+        suppress = sysrq_down;
+        spin_unlock(&sysrq_event_lock);
+
+        return suppress;
+}
+
+static int sysrq_connect(struct input_handler *handler,
+                         struct input_dev *dev,
+                         const struct input_device_id *id)
+{
+        struct input_handle *handle;
+        int error;
+
+        sysrq_down = false;
+        sysrq_alt = 0;
+
+        handle = kzalloc(sizeof(struct input_handle), GFP_KERNEL);
+        if (!handle)
+                return -ENOMEM;
+
+        handle->dev = dev;
+        handle->handler = handler;
+        handle->name = "sysrq";
+
+        error = input_register_handle(handle);
+        if (error) {
+                pr_err("Failed to register input sysrq handler, error %d\n",
+                        error);
+                goto err_free;
+        }
+
+        error = input_open_device(handle);
+        if (error) {
+                pr_err("Failed to open input device, error %d\n", error);
+                goto err_unregister;
+        }
+
+        return 0;
+
+ err_unregister:
+        input_unregister_handle(handle);
+ err_free:
+        kfree(handle);
+        return error;
+}
+
+static void sysrq_disconnect(struct input_handle *handle)
+{
+        input_close_device(handle);
+        input_unregister_handle(handle);
+        kfree(handle);
+}
+
+/*
+ * 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);