printf: Remove unused 'bprintf'

[drm/drm-misc.git] / include / linux / console.h

/*
 *  linux/include/linux/console.h
 *
 *  Copyright (C) 1993        Hamish Macdonald
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file COPYING in the main directory of this archive
 * for more details.
 *
 * Changed:
 * 10-Mar-94: Arno Griffioen: Conversion for vt100 emulator port from PC LINUX
 */

#ifndef _LINUX_CONSOLE_H_
#define _LINUX_CONSOLE_H_ 1

#include <linux/atomic.h>
#include <linux/bits.h>
#include <linux/irq_work.h>
#include <linux/rculist.h>
#include <linux/rcuwait.h>
#include <linux/types.h>
#include <linux/vesa.h>

struct vc_data;
struct console_font_op;
struct console_font;
struct module;
struct tty_struct;
struct notifier_block;

enum con_scroll {
        SM_UP,
        SM_DOWN,
};

enum vc_intensity;

/**
 * struct consw - callbacks for consoles
 *
 * @owner:      the module to get references of when this console is used
 * @con_startup: set up the console and return its name (like VGA, EGA, ...)
 * @con_init:   initialize the console on @vc. @init is true for the very first
 *              call on this @vc.
 * @con_deinit: deinitialize the console from @vc.
 * @con_clear:  erase @count characters at [@x, @y] on @vc. @count >= 1.
 * @con_putc:   emit one character with attributes @ca to [@x, @y] on @vc.
 *              (optional -- @con_putcs would be called instead)
 * @con_putcs:  emit @count characters with attributes @s to [@x, @y] on @vc.
 * @con_cursor: enable/disable cursor depending on @enable
 * @con_scroll: move lines from @top to @bottom in direction @dir by @lines.
 *              Return true if no generic handling should be done.
 *              Invoked by csi_M and printing to the console.
 * @con_switch: notifier about the console switch; it is supposed to return
 *              true if a redraw is needed.
 * @con_blank:  blank/unblank the console. The target mode is passed in @blank.
 *              @mode_switch is set if changing from/to text/graphics. The hook
 *              is supposed to return true if a redraw is needed.
 * @con_font_set: set console @vc font to @font with height @vpitch. @flags can
 *              be %KD_FONT_FLAG_DONT_RECALC. (optional)
 * @con_font_get: fetch the current font on @vc of height @vpitch into @font.
 *              (optional)
 * @con_font_default: set default font on @vc. @name can be %NULL or font name
 *              to search for. @font can be filled back. (optional)
 * @con_resize: resize the @vc console to @width x @height. @from_user is true
 *              when this change comes from the user space.
 * @con_set_palette: sets the palette of the console @vc to @table (optional)
 * @con_scrolldelta: the contents of the console should be scrolled by @lines.
 *                   Invoked by user. (optional)
 * @con_set_origin: set origin (see &vc_data::vc_origin) of the @vc. If not
 *              provided or returns false, the origin is set to
 *              @vc->vc_screenbuf. (optional)
 * @con_save_screen: save screen content into @vc->vc_screenbuf. Called e.g.
 *              upon entering graphics. (optional)
 * @con_build_attr: build attributes based on @color, @intensity and other
 *              parameters. The result is used for both normal and erase
 *              characters. (optional)
 * @con_invert_region: invert a region of length @count on @vc starting at @p.
 *              (optional)
 * @con_debug_enter: prepare the console for the debugger. This includes, but
 *              is not limited to, unblanking the console, loading an
 *              appropriate palette, and allowing debugger generated output.
 *              (optional)
 * @con_debug_leave: restore the console to its pre-debug state as closely as
 *              possible. (optional)
 */
struct consw {
        struct module *owner;
        const char *(*con_startup)(void);
        void    (*con_init)(struct vc_data *vc, bool init);
        void    (*con_deinit)(struct vc_data *vc);
        void    (*con_clear)(struct vc_data *vc, unsigned int y,
                             unsigned int x, unsigned int count);
        void    (*con_putc)(struct vc_data *vc, u16 ca, unsigned int y,
                            unsigned int x);
        void    (*con_putcs)(struct vc_data *vc, const u16 *s,
                             unsigned int count, unsigned int ypos,
                             unsigned int xpos);
        void    (*con_cursor)(struct vc_data *vc, bool enable);
        bool    (*con_scroll)(struct vc_data *vc, unsigned int top,
                        unsigned int bottom, enum con_scroll dir,
                        unsigned int lines);
        bool    (*con_switch)(struct vc_data *vc);
        bool    (*con_blank)(struct vc_data *vc, enum vesa_blank_mode blank,
                             bool mode_switch);
        int     (*con_font_set)(struct vc_data *vc,
                                const struct console_font *font,
                                unsigned int vpitch, unsigned int flags);
        int     (*con_font_get)(struct vc_data *vc, struct console_font *font,
                        unsigned int vpitch);
        int     (*con_font_default)(struct vc_data *vc,
                        struct console_font *font, const char *name);
        int     (*con_resize)(struct vc_data *vc, unsigned int width,
                              unsigned int height, bool from_user);
        void    (*con_set_palette)(struct vc_data *vc,
                        const unsigned char *table);
        void    (*con_scrolldelta)(struct vc_data *vc, int lines);
        bool    (*con_set_origin)(struct vc_data *vc);
        void    (*con_save_screen)(struct vc_data *vc);
        u8      (*con_build_attr)(struct vc_data *vc, u8 color,
                        enum vc_intensity intensity,
                        bool blink, bool underline, bool reverse, bool italic);
        void    (*con_invert_region)(struct vc_data *vc, u16 *p, int count);
        void    (*con_debug_enter)(struct vc_data *vc);
        void    (*con_debug_leave)(struct vc_data *vc);
};

extern const struct consw *conswitchp;

extern const struct consw dummy_con;    /* dummy console buffer */
extern const struct consw vga_con;      /* VGA text console */
extern const struct consw newport_con;  /* SGI Newport console  */

struct screen_info;
#ifdef CONFIG_VGA_CONSOLE
void vgacon_register_screen(struct screen_info *si);
#else
static inline void vgacon_register_screen(struct screen_info *si) { }
#endif

int con_is_bound(const struct consw *csw);
int do_unregister_con_driver(const struct consw *csw);
int do_take_over_console(const struct consw *sw, int first, int last, int deflt);
void give_up_console(const struct consw *sw);
#ifdef CONFIG_VT
void con_debug_enter(struct vc_data *vc);
void con_debug_leave(void);
#else
static inline void con_debug_enter(struct vc_data *vc) { }
static inline void con_debug_leave(void) { }
#endif

/*
 * The interface for a console, or any other device that wants to capture
 * console messages (printer driver?)
 */

/**
 * enum cons_flags - General console flags
 * @CON_PRINTBUFFER:    Used by newly registered consoles to avoid duplicate
 *                      output of messages that were already shown by boot
 *                      consoles or read by userspace via syslog() syscall.
 * @CON_CONSDEV:        Indicates that the console driver is backing
 *                      /dev/console.
 * @CON_ENABLED:        Indicates if a console is allowed to print records. If
 *                      false, the console also will not advance to later
 *                      records.
 * @CON_BOOT:           Marks the console driver as early console driver which
 *                      is used during boot before the real driver becomes
 *                      available. It will be automatically unregistered
 *                      when the real console driver is registered unless
 *                      "keep_bootcon" parameter is used.
 * @CON_ANYTIME:        A misnomed historical flag which tells the core code
 *                      that the legacy @console::write callback can be invoked
 *                      on a CPU which is marked OFFLINE. That is misleading as
 *                      it suggests that there is no contextual limit for
 *                      invoking the callback. The original motivation was
 *                      readiness of the per-CPU areas.
 * @CON_BRL:            Indicates a braille device which is exempt from
 *                      receiving the printk spam for obvious reasons.
 * @CON_EXTENDED:       The console supports the extended output format of
 *                      /dev/kmesg which requires a larger output buffer.
 * @CON_SUSPENDED:      Indicates if a console is suspended. If true, the
 *                      printing callbacks must not be called.
 * @CON_NBCON:          Console can operate outside of the legacy style console_lock
 *                      constraints.
 */
enum cons_flags {
        CON_PRINTBUFFER         = BIT(0),
        CON_CONSDEV             = BIT(1),
        CON_ENABLED             = BIT(2),
        CON_BOOT                = BIT(3),
        CON_ANYTIME             = BIT(4),
        CON_BRL                 = BIT(5),
        CON_EXTENDED            = BIT(6),
        CON_SUSPENDED           = BIT(7),
        CON_NBCON               = BIT(8),
};

/**
 * struct nbcon_state - console state for nbcon consoles
 * @atom:       Compound of the state fields for atomic operations
 *
 * @req_prio:           The priority of a handover request
 * @prio:               The priority of the current owner
 * @unsafe:             Console is busy in a non takeover region
 * @unsafe_takeover:    A hostile takeover in an unsafe state happened in the
 *                      past. The console cannot be safe until re-initialized.
 * @cpu:                The CPU on which the owner runs
 *
 * To be used for reading and preparing of the value stored in the nbcon
 * state variable @console::nbcon_state.
 *
 * The @prio and @req_prio fields are particularly important to allow
 * spin-waiting to timeout and give up without the risk of a waiter being
 * assigned the lock after giving up.
 */
struct nbcon_state {
        union {
                unsigned int    atom;
                struct {
                        unsigned int prio               :  2;
                        unsigned int req_prio           :  2;
                        unsigned int unsafe             :  1;
                        unsigned int unsafe_takeover    :  1;
                        unsigned int cpu                : 24;
                };
        };
};

/*
 * The nbcon_state struct is used to easily create and interpret values that
 * are stored in the @console::nbcon_state variable. Ensure this struct stays
 * within the size boundaries of the atomic variable's underlying type in
 * order to avoid any accidental truncation.
 */
static_assert(sizeof(struct nbcon_state) <= sizeof(int));

/**
 * enum nbcon_prio - console owner priority for nbcon consoles
 * @NBCON_PRIO_NONE:            Unused
 * @NBCON_PRIO_NORMAL:          Normal (non-emergency) usage
 * @NBCON_PRIO_EMERGENCY:       Emergency output (WARN/OOPS...)
 * @NBCON_PRIO_PANIC:           Panic output
 * @NBCON_PRIO_MAX:             The number of priority levels
 *
 * A higher priority context can takeover the console when it is
 * in the safe state. The final attempt to flush consoles in panic()
 * can be allowed to do so even in an unsafe state (Hope and pray).
 */
enum nbcon_prio {
        NBCON_PRIO_NONE = 0,
        NBCON_PRIO_NORMAL,
        NBCON_PRIO_EMERGENCY,
        NBCON_PRIO_PANIC,
        NBCON_PRIO_MAX,
};

struct console;
struct printk_buffers;

/**
 * struct nbcon_context - Context for console acquire/release
 * @console:                    The associated console
 * @spinwait_max_us:            Limit for spin-wait acquire
 * @prio:                       Priority of the context
 * @allow_unsafe_takeover:      Allow performing takeover even if unsafe. Can
 *                              be used only with NBCON_PRIO_PANIC @prio. It
 *                              might cause a system freeze when the console
 *                              is used later.
 * @backlog:                    Ringbuffer has pending records
 * @pbufs:                      Pointer to the text buffer for this context
 * @seq:                        The sequence number to print for this context
 */
struct nbcon_context {
        /* members set by caller */
        struct console          *console;
        unsigned int            spinwait_max_us;
        enum nbcon_prio         prio;
        unsigned int            allow_unsafe_takeover   : 1;

        /* members set by emit */
        unsigned int            backlog                 : 1;

        /* members set by acquire */
        struct printk_buffers   *pbufs;
        u64                     seq;
};

/**
 * struct nbcon_write_context - Context handed to the nbcon write callbacks
 * @ctxt:               The core console context
 * @outbuf:             Pointer to the text buffer for output
 * @len:                Length to write
 * @unsafe_takeover:    If a hostile takeover in an unsafe state has occurred
 */
struct nbcon_write_context {
        struct nbcon_context    __private ctxt;
        char                    *outbuf;
        unsigned int            len;
        bool                    unsafe_takeover;
};

/**
 * struct console - The console descriptor structure
 * @name:               The name of the console driver
 * @write:              Legacy write callback to output messages (Optional)
 * @read:               Read callback for console input (Optional)
 * @device:             The underlying TTY device driver (Optional)
 * @unblank:            Callback to unblank the console (Optional)
 * @setup:              Callback for initializing the console (Optional)
 * @exit:               Callback for teardown of the console (Optional)
 * @match:              Callback for matching a console (Optional)
 * @flags:              Console flags. See enum cons_flags
 * @index:              Console index, e.g. port number
 * @cflag:              TTY control mode flags
 * @ispeed:             TTY input speed
 * @ospeed:             TTY output speed
 * @seq:                Sequence number of the next ringbuffer record to print
 * @dropped:            Number of unreported dropped ringbuffer records
 * @data:               Driver private data
 * @node:               hlist node for the console list
 *
 * @nbcon_state:        State for nbcon consoles
 * @nbcon_seq:          Sequence number of the next record for nbcon to print
 * @nbcon_device_ctxt:  Context available for non-printing operations
 * @nbcon_prev_seq:     Seq num the previous nbcon owner was assigned to print
 * @pbufs:              Pointer to nbcon private buffer
 * @kthread:            Printer kthread for this console
 * @rcuwait:            RCU-safe wait object for @kthread waking
 * @irq_work:           Defer @kthread waking to IRQ work context
 */
struct console {
        char                    name[16];
        void                    (*write)(struct console *co, const char *s, unsigned int count);
        int                     (*read)(struct console *co, char *s, unsigned int count);
        struct tty_driver       *(*device)(struct console *co, int *index);
        void                    (*unblank)(void);
        int                     (*setup)(struct console *co, char *options);
        int                     (*exit)(struct console *co);
        int                     (*match)(struct console *co, char *name, int idx, char *options);
        short                   flags;
        short                   index;
        int                     cflag;
        uint                    ispeed;
        uint                    ospeed;
        u64                     seq;
        unsigned long           dropped;
        void                    *data;
        struct hlist_node       node;

        /* nbcon console specific members */

        /**
         * @write_atomic:
         *
         * NBCON callback to write out text in any context. (Optional)
         *
         * This callback is called with the console already acquired. However,
         * a higher priority context is allowed to take it over by default.
         *
         * The callback must call nbcon_enter_unsafe() and nbcon_exit_unsafe()
         * around any code where the takeover is not safe, for example, when
         * manipulating the serial port registers.
         *
         * nbcon_enter_unsafe() will fail if the context has lost the console
         * ownership in the meantime. In this case, the callback is no longer
         * allowed to go forward. It must back out immediately and carefully.
         * The buffer content is also no longer trusted since it no longer
         * belongs to the context.
         *
         * The callback should allow the takeover whenever it is safe. It
         * increases the chance to see messages when the system is in trouble.
         * If the driver must reacquire ownership in order to finalize or
         * revert hardware changes, nbcon_reacquire_nobuf() can be used.
         * However, on reacquire the buffer content is no longer available. A
         * reacquire cannot be used to resume printing.
         *
         * The callback can be called from any context (including NMI).
         * Therefore it must avoid usage of any locking and instead rely
         * on the console ownership for synchronization.
         */
        void (*write_atomic)(struct console *con, struct nbcon_write_context *wctxt);

        /**
         * @write_thread:
         *
         * NBCON callback to write out text in task context.
         *
         * This callback must be called only in task context with both
         * device_lock() and the nbcon console acquired with
         * NBCON_PRIO_NORMAL.
         *
         * The same rules for console ownership verification and unsafe
         * sections handling applies as with write_atomic().
         *
         * The console ownership handling is necessary for synchronization
         * against write_atomic() which is synchronized only via the context.
         *
         * The device_lock() provides the primary serialization for operations
         * on the device. It might be as relaxed (mutex)[*] or as tight
         * (disabled preemption and interrupts) as needed. It allows
         * the kthread to operate in the least restrictive mode[**].
         *
         * [*] Standalone nbcon_context_try_acquire() is not safe with
         *     the preemption enabled, see nbcon_owner_matches(). But it
         *     can be safe when always called in the preemptive context
         *     under the device_lock().
         *
         * [**] The device_lock() makes sure that nbcon_context_try_acquire()
         *      would never need to spin which is important especially with
         *      PREEMPT_RT.
         */
        void (*write_thread)(struct console *con, struct nbcon_write_context *wctxt);

        /**
         * @device_lock:
         *
         * NBCON callback to begin synchronization with driver code.
         *
         * Console drivers typically must deal with access to the hardware
         * via user input/output (such as an interactive login shell) and
         * output of kernel messages via printk() calls. This callback is
         * called by the printk-subsystem whenever it needs to synchronize
         * with hardware access by the driver. It should be implemented to
         * use whatever synchronization mechanism the driver is using for
         * itself (for example, the port lock for uart serial consoles).
         *
         * The callback is always called from task context. It may use any
         * synchronization method required by the driver.
         *
         * IMPORTANT: The callback MUST disable migration. The console driver
         *      may be using a synchronization mechanism that already takes
         *      care of this (such as spinlocks). Otherwise this function must
         *      explicitly call migrate_disable().
         *
         * The flags argument is provided as a convenience to the driver. It
         * will be passed again to device_unlock(). It can be ignored if the
         * driver does not need it.
         */
        void (*device_lock)(struct console *con, unsigned long *flags);

        /**
         * @device_unlock:
         *
         * NBCON callback to finish synchronization with driver code.
         *
         * It is the counterpart to device_lock().
         *
         * This callback is always called from task context. It must
         * appropriately re-enable migration (depending on how device_lock()
         * disabled migration).
         *
         * The flags argument is the value of the same variable that was
         * passed to device_lock().
         */
        void (*device_unlock)(struct console *con, unsigned long flags);

        atomic_t                __private nbcon_state;
        atomic_long_t           __private nbcon_seq;
        struct nbcon_context    __private nbcon_device_ctxt;
        atomic_long_t           __private nbcon_prev_seq;

        struct printk_buffers   *pbufs;
        struct task_struct      *kthread;
        struct rcuwait          rcuwait;
        struct irq_work         irq_work;
};

#ifdef CONFIG_LOCKDEP
extern void lockdep_assert_console_list_lock_held(void);
#else
static inline void lockdep_assert_console_list_lock_held(void)
{
}
#endif

#ifdef CONFIG_DEBUG_LOCK_ALLOC
extern bool console_srcu_read_lock_is_held(void);
#else
static inline bool console_srcu_read_lock_is_held(void)
{
        return 1;
}
#endif

extern int console_srcu_read_lock(void);
extern void console_srcu_read_unlock(int cookie);

extern void console_list_lock(void) __acquires(console_mutex);
extern void console_list_unlock(void) __releases(console_mutex);

extern struct hlist_head console_list;

/**
 * console_srcu_read_flags - Locklessly read flags of a possibly registered
 *                              console
 * @con:        struct console pointer of console to read flags from
 *
 * Locklessly reading @con->flags provides a consistent read value because
 * there is at most one CPU modifying @con->flags and that CPU is using only
 * read-modify-write operations to do so.
 *
 * Requires console_srcu_read_lock to be held, which implies that @con might
 * be a registered console. The purpose of holding console_srcu_read_lock is
 * to guarantee that the console state is valid (CON_SUSPENDED/CON_ENABLED)
 * and that no exit/cleanup routines will run if the console is currently
 * undergoing unregistration.
 *
 * If the caller is holding the console_list_lock or it is _certain_ that
 * @con is not and will not become registered, the caller may read
 * @con->flags directly instead.
 *
 * Context: Any context.
 * Return: The current value of the @con->flags field.
 */
static inline short console_srcu_read_flags(const struct console *con)
{
        WARN_ON_ONCE(!console_srcu_read_lock_is_held());

        /*
         * The READ_ONCE() matches the WRITE_ONCE() when @flags are modified
         * for registered consoles with console_srcu_write_flags().
         */
        return data_race(READ_ONCE(con->flags));
}

/**
 * console_srcu_write_flags - Write flags for a registered console
 * @con:        struct console pointer of console to write flags to
 * @flags:      new flags value to write
 *
 * Only use this function to write flags for registered consoles. It
 * requires holding the console_list_lock.
 *
 * Context: Any context.
 */
static inline void console_srcu_write_flags(struct console *con, short flags)
{
        lockdep_assert_console_list_lock_held();

        /* This matches the READ_ONCE() in console_srcu_read_flags(). */
        WRITE_ONCE(con->flags, flags);
}

/* Variant of console_is_registered() when the console_list_lock is held. */
static inline bool console_is_registered_locked(const struct console *con)
{
        lockdep_assert_console_list_lock_held();
        return !hlist_unhashed(&con->node);
}

/*
 * console_is_registered - Check if the console is registered
 * @con:        struct console pointer of console to check
 *
 * Context: Process context. May sleep while acquiring console list lock.
 * Return: true if the console is in the console list, otherwise false.
 *
 * If false is returned for a console that was previously registered, it
 * can be assumed that the console's unregistration is fully completed,
 * including the exit() callback after console list removal.
 */
static inline bool console_is_registered(const struct console *con)
{
        bool ret;

        console_list_lock();
        ret = console_is_registered_locked(con);
        console_list_unlock();
        return ret;
}

/**
 * for_each_console_srcu() - Iterator over registered consoles
 * @con:        struct console pointer used as loop cursor
 *
 * Although SRCU guarantees the console list will be consistent, the
 * struct console fields may be updated by other CPUs while iterating.
 *
 * Requires console_srcu_read_lock to be held. Can be invoked from
 * any context.
 */
#define for_each_console_srcu(con)                                      \
        hlist_for_each_entry_srcu(con, &console_list, node,             \
                                  console_srcu_read_lock_is_held())

/**
 * for_each_console() - Iterator over registered consoles
 * @con:        struct console pointer used as loop cursor
 *
 * The console list and the &console.flags are immutable while iterating.
 *
 * Requires console_list_lock to be held.
 */
#define for_each_console(con)                                           \
        lockdep_assert_console_list_lock_held();                        \
        hlist_for_each_entry(con, &console_list, node)

#ifdef CONFIG_PRINTK
extern void nbcon_cpu_emergency_enter(void);
extern void nbcon_cpu_emergency_exit(void);
extern bool nbcon_can_proceed(struct nbcon_write_context *wctxt);
extern bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt);
extern bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt);
extern void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt);
#else
static inline void nbcon_cpu_emergency_enter(void) { }
static inline void nbcon_cpu_emergency_exit(void) { }
static inline bool nbcon_can_proceed(struct nbcon_write_context *wctxt) { return false; }
static inline bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) { return false; }
static inline bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { return false; }
static inline void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt) { }
#endif

extern int console_set_on_cmdline;
extern struct console *early_console;

enum con_flush_mode {
        CONSOLE_FLUSH_PENDING,
        CONSOLE_REPLAY_ALL,
};

extern int add_preferred_console(const char *name, const short idx, char *options);
extern void console_force_preferred_locked(struct console *con);
extern void register_console(struct console *);
extern int unregister_console(struct console *);
extern void console_lock(void);
extern int console_trylock(void);
extern void console_unlock(void);
extern void console_conditional_schedule(void);
extern void console_unblank(void);
extern void console_flush_on_panic(enum con_flush_mode mode);
extern struct tty_driver *console_device(int *);
extern void console_stop(struct console *);
extern void console_start(struct console *);
extern int is_console_locked(void);
extern int braille_register_console(struct console *, int index,
                char *console_options, char *braille_options);
extern int braille_unregister_console(struct console *);
#ifdef CONFIG_TTY
extern void console_sysfs_notify(void);
#else
static inline void console_sysfs_notify(void)
{ }
#endif
extern bool console_suspend_enabled;

/* Suspend and resume console messages over PM events */
extern void suspend_console(void);
extern void resume_console(void);

int mda_console_init(void);

void vcs_make_sysfs(int index);
void vcs_remove_sysfs(int index);

/* Some debug stub to catch some of the obvious races in the VT code */
#define WARN_CONSOLE_UNLOCKED()                                         \
        WARN_ON(!atomic_read(&ignore_console_lock_warning) &&           \
                !is_console_locked() && !oops_in_progress)
/*
 * Increment ignore_console_lock_warning if you need to quiet
 * WARN_CONSOLE_UNLOCKED() for debugging purposes.
 */
extern atomic_t ignore_console_lock_warning;

extern void console_init(void);

/* For deferred console takeover */
void dummycon_register_output_notifier(struct notifier_block *nb);
void dummycon_unregister_output_notifier(struct notifier_block *nb);

#endif /* _LINUX_CONSOLE_H */