text: #ifndef _LINUX_TTY_H
  #define _LINUX_TTY_H
  
  #include <linux/fs.h>
  #include <linux/major.h>
  #include <linux/termios.h>
  #include <linux/workqueue.h>
  #include <linux/tty_driver.h>
  #include <linux/tty_ldisc.h>
  #include <linux/mutex.h>
  #include <linux/tty_flags.h>
  #include <uapi/linux/tty.h>
  #include <linux/rwsem.h>
  #include <linux/llist.h>
  
  
  /*
   * Lock subclasses for tty locks
   *
   * TTY_LOCK_NORMAL is for normal ttys and master ptys.
   * TTY_LOCK_SLAVE is for slave ptys only.
   *
   * Lock subclasses are necessary for handling nested locking with pty pairs.
   * tty locks which use nested locking:
   *
   * legacy_mutex - Nested tty locks are necessary for releasing pty pairs.
   *		  The stable lock order is master pty first, then slave pty.
   * termios_rwsem - The stable lock order is tty_buffer lock->termios_rwsem.
   *		   Subclassing this lock enables the slave pty to hold its
   *		   termios_rwsem when claiming the master tty_buffer lock.
   * tty_buffer lock - slave ptys can claim nested buffer lock when handling
   *		     signal chars. The stable lock order is slave pty, then
   *		     master.
   */
  
  enum {
  	TTY_LOCK_NORMAL = 0,
  	TTY_LOCK_SLAVE,
  };
  
  /*
   * (Note: the *_driver.minor_start values 1, 64, 128, 192 are
   * hardcoded at present.)
   */
  #define NR_UNIX98_PTY_DEFAULT	4096      /* Default maximum for Unix98 ptys */
  #define NR_UNIX98_PTY_RESERVE	1024	  /* Default reserve for main devpts */
  #define NR_UNIX98_PTY_MAX	(1 << MINORBITS) /* Absolute limit */
  
  /*
   * This character is the same as _POSIX_VDISABLE: it cannot be used as
   * a c_cc[] character, but indicates that a particular special character
   * isn't in use (eg VINTR has no character etc)
   */
  #define __DISABLED_CHAR '\0'
  
  struct tty_buffer {
  	union {
  		struct tty_buffer *next;
  		struct llist_node free;
  	};
  	int used;
  	int size;
  	int commit;
  	int read;
  	int flags;
  	/* Data points here */
  	unsigned long data[0];
  };
  
  /* Values for .flags field of tty_buffer */
  #define TTYB_NORMAL	1	/* buffer has no flags buffer */
  
  static inline unsigned char *char_buf_ptr(struct tty_buffer *b, int ofs)
  {
  	return ((unsigned char *)b->data) + ofs;
  }
  
  static inline char *flag_buf_ptr(struct tty_buffer *b, int ofs)
  {
  	return (char *)char_buf_ptr(b, ofs) + b->size;
  }
  
  struct tty_bufhead {
  	struct tty_buffer *head;	/* Queue head */
  	struct work_struct work;
  	struct mutex	   lock;
  	atomic_t	   priority;
  	struct tty_buffer sentinel;
  	struct llist_head free;		/* Free queue head */
  	atomic_t	   mem_used;    /* In-use buffers excluding free list */
  	int		   mem_limit;
  	struct tty_buffer *tail;	/* Active buffer */
  };
  /*
   * When a break, frame error, or parity error happens, these codes are
   * stuffed into the flags buffer.
   */
  #define TTY_NORMAL	0
  #define TTY_BREAK	1
  #define TTY_FRAME	2
  #define TTY_PARITY	3
  #define TTY_OVERRUN	4
  
  #define INTR_CHAR(tty) ((tty)->termios.c_cc[VINTR])
  #define QUIT_CHAR(tty) ((tty)->termios.c_cc[VQUIT])
  #define ERASE_CHAR(tty) ((tty)->termios.c_cc[VERASE])
  #define KILL_CHAR(tty) ((tty)->termios.c_cc[VKILL])
  #define EOF_CHAR(tty) ((tty)->termios.c_cc[VEOF])
  #define TIME_CHAR(tty) ((tty)->termios.c_cc[VTIME])
  #define MIN_CHAR(tty) ((tty)->termios.c_cc[VMIN])
  #define SWTC_CHAR(tty) ((tty)->termios.c_cc[VSWTC])
  #define START_CHAR(tty) ((tty)->termios.c_cc[VSTART])
  #define STOP_CHAR(tty) ((tty)->termios.c_cc[VSTOP])
  #define SUSP_CHAR(tty) ((tty)->termios.c_cc[VSUSP])
  #define EOL_CHAR(tty) ((tty)->termios.c_cc[VEOL])
  #define REPRINT_CHAR(tty) ((tty)->termios.c_cc[VREPRINT])
  #define DISCARD_CHAR(tty) ((tty)->termios.c_cc[VDISCARD])
  #define WERASE_CHAR(tty) ((tty)->termios.c_cc[VWERASE])
  #define LNEXT_CHAR(tty)	((tty)->termios.c_cc[VLNEXT])
  #define EOL2_CHAR(tty) ((tty)->termios.c_cc[VEOL2])
  
  #define _I_FLAG(tty, f)	((tty)->termios.c_iflag & (f))
  #define _O_FLAG(tty, f)	((tty)->termios.c_oflag & (f))
  #define _C_FLAG(tty, f)	((tty)->termios.c_cflag & (f))
  #define _L_FLAG(tty, f)	((tty)->termios.c_lflag & (f))
  
  #define I_IGNBRK(tty)	_I_FLAG((tty), IGNBRK)
  #define I_BRKINT(tty)	_I_FLAG((tty), BRKINT)
  #define I_IGNPAR(tty)	_I_FLAG((tty), IGNPAR)
  #define I_PARMRK(tty)	_I_FLAG((tty), PARMRK)
  #define I_INPCK(tty)	_I_FLAG((tty), INPCK)
  #define I_ISTRIP(tty)	_I_FLAG((tty), ISTRIP)
  #define I_INLCR(tty)	_I_FLAG((tty), INLCR)
  #define I_IGNCR(tty)	_I_FLAG((tty), IGNCR)
  #define I_ICRNL(tty)	_I_FLAG((tty), ICRNL)
  #define I_IUCLC(tty)	_I_FLAG((tty), IUCLC)
  #define I_IXON(tty)	_I_FLAG((tty), IXON)
  #define I_IXANY(tty)	_I_FLAG((tty), IXANY)
  #define I_IXOFF(tty)	_I_FLAG((tty), IXOFF)
  #define I_IMAXBEL(tty)	_I_FLAG((tty), IMAXBEL)
  #define I_IUTF8(tty)	_I_FLAG((tty), IUTF8)
  
  #define O_OPOST(tty)	_O_FLAG((tty), OPOST)
  #define O_OLCUC(tty)	_O_FLAG((tty), OLCUC)
  #define O_ONLCR(tty)	_O_FLAG((tty), ONLCR)
  #define O_OCRNL(tty)	_O_FLAG((tty), OCRNL)
  #define O_ONOCR(tty)	_O_FLAG((tty), ONOCR)
  #define O_ONLRET(tty)	_O_FLAG((tty), ONLRET)
  #define O_OFILL(tty)	_O_FLAG((tty), OFILL)
  #define O_OFDEL(tty)	_O_FLAG((tty), OFDEL)
  #define O_NLDLY(tty)	_O_FLAG((tty), NLDLY)
  #define O_CRDLY(tty)	_O_FLAG((tty), CRDLY)
  #define O_TABDLY(tty)	_O_FLAG((tty), TABDLY)
  #define O_BSDLY(tty)	_O_FLAG((tty), BSDLY)
  #define O_VTDLY(tty)	_O_FLAG((tty), VTDLY)
  #define O_FFDLY(tty)	_O_FLAG((tty), FFDLY)
  
  #define C_BAUD(tty)	_C_FLAG((tty), CBAUD)
  #define C_CSIZE(tty)	_C_FLAG((tty), CSIZE)
  #define C_CSTOPB(tty)	_C_FLAG((tty), CSTOPB)
  #define C_CREAD(tty)	_C_FLAG((tty), CREAD)
  #define C_PARENB(tty)	_C_FLAG((tty), PARENB)
  #define C_PARODD(tty)	_C_FLAG((tty), PARODD)
  #define C_HUPCL(tty)	_C_FLAG((tty), HUPCL)
  #define C_CLOCAL(tty)	_C_FLAG((tty), CLOCAL)
  #define C_CIBAUD(tty)	_C_FLAG((tty), CIBAUD)
  #define C_CRTSCTS(tty)	_C_FLAG((tty), CRTSCTS)
  #define C_CMSPAR(tty)	_C_FLAG((tty), CMSPAR)
  
  #define L_ISIG(tty)	_L_FLAG((tty), ISIG)
  #define L_ICANON(tty)	_L_FLAG((tty), ICANON)
  #define L_XCASE(tty)	_L_FLAG((tty), XCASE)
  #define L_ECHO(tty)	_L_FLAG((tty), ECHO)
  #define L_ECHOE(tty)	_L_FLAG((tty), ECHOE)
  #define L_ECHOK(tty)	_L_FLAG((tty), ECHOK)
  #define L_ECHONL(tty)	_L_FLAG((tty), ECHONL)
  #define L_NOFLSH(tty)	_L_FLAG((tty), NOFLSH)
  #define L_TOSTOP(tty)	_L_FLAG((tty), TOSTOP)
  #define L_ECHOCTL(tty)	_L_FLAG((tty), ECHOCTL)
  #define L_ECHOPRT(tty)	_L_FLAG((tty), ECHOPRT)
  #define L_ECHOKE(tty)	_L_FLAG((tty), ECHOKE)
  #define L_FLUSHO(tty)	_L_FLAG((tty), FLUSHO)
  #define L_PENDIN(tty)	_L_FLAG((tty), PENDIN)
  #define L_IEXTEN(tty)	_L_FLAG((tty), IEXTEN)
  #define L_EXTPROC(tty)	_L_FLAG((tty), EXTPROC)
  
  struct device;
  struct signal_struct;
  
  /*
   * Port level information. Each device keeps its own port level information
   * so provide a common structure for those ports wanting to use common support
   * routines.
   *
   * The tty port has a different lifetime to the tty so must be kept apart.
   * In addition be careful as tty -> port mappings are valid for the life
   * of the tty object but in many cases port -> tty mappings are valid only
   * until a hangup so don't use the wrong path.
   */
  
  struct tty_port;
  
  struct tty_port_operations {
  	/* Return 1 if the carrier is raised */
  	int (*carrier_raised)(struct tty_port *port);
  	/* Control the DTR line */
  	void (*dtr_rts)(struct tty_port *port, int raise);
  	/* Called when the last close completes or a hangup finishes
  	   IFF the port was initialized. Do not use to free resources. Called
  	   under the port mutex to serialize against activate/shutdowns */
  	void (*shutdown)(struct tty_port *port);
  	/* Called under the port mutex from tty_port_open, serialized using
  	   the port mutex */
          /* FIXME: long term getting the tty argument *out* of this would be
             good for consoles */
  	int (*activate)(struct tty_port *port, struct tty_struct *tty);
  	/* Called on the final put of a port */
  	void (*destruct)(struct tty_port *port);
  };
  	
  struct tty_port {
  	struct tty_bufhead	buf;		/* Locked internally */
  	struct tty_struct	*tty;		/* Back pointer */
  	struct tty_struct	*itty;		/* internal back ptr */
  	const struct tty_port_operations *ops;	/* Port operations */
  	spinlock_t		lock;		/* Lock protecting tty field */
  	int			blocked_open;	/* Waiting to open */
  	int			count;		/* Usage count */
  	wait_queue_head_t	open_wait;	/* Open waiters */
  	wait_queue_head_t	close_wait;	/* Close waiters */
  	wait_queue_head_t	delta_msr_wait;	/* Modem status change */
  	unsigned long		flags;		/* TTY flags ASY_*/
  	unsigned char		console:1,	/* port is a console */
  				low_latency:1;	/* optional: tune for latency */
  	struct mutex		mutex;		/* Locking */
  	struct mutex		buf_mutex;	/* Buffer alloc lock */
  	unsigned char		*xmit_buf;	/* Optional buffer */
  	unsigned int		close_delay;	/* Close port delay */
  	unsigned int		closing_wait;	/* Delay for output */
  	int			drain_delay;	/* Set to zero if no pure time
  						   based drain is needed else
  						   set to size of fifo */
  	struct kref		kref;		/* Ref counter */
  };
  
  /*
   * Where all of the state associated with a tty is kept while the tty
   * is open.  Since the termios state should be kept even if the tty
   * has been closed --- for things like the baud rate, etc --- it is
   * not stored here, but rather a pointer to the real state is stored
   * here.  Possible the winsize structure should have the same
   * treatment, but (1) the default 80x24 is usually right and (2) it's
   * most often used by a windowing system, which will set the correct
   * size each time the window is created or resized anyway.
   * 						- TYT, 9/14/92
   */
  
  struct tty_operations;
  
  struct tty_struct {
  	int	magic;
  	struct kref kref;
  	struct device *dev;
  	struct tty_driver *driver;
  	const struct tty_operations *ops;
  	int index;
  
  	/* Protects ldisc changes: Lock tty not pty */
  	struct ld_semaphore ldisc_sem;
  	struct tty_ldisc *ldisc;
  
  	struct mutex atomic_write_lock;
  	struct mutex legacy_mutex;
  	struct mutex throttle_mutex;
  	struct rw_semaphore termios_rwsem;
  	struct mutex winsize_mutex;
  	spinlock_t ctrl_lock;
  	spinlock_t flow_lock;
  	/* Termios values are protected by the termios rwsem */
  	struct ktermios termios, termios_locked;
  	struct termiox *termiox;	/* May be NULL for unsupported */
  	char name[64];
  	struct pid *pgrp;		/* Protected by ctrl lock */
  	struct pid *session;
  	unsigned long flags;
  	int count;
  	struct winsize winsize;		/* winsize_mutex */
  	unsigned long stopped:1,	/* flow_lock */
  		      flow_stopped:1,
  		      unused:BITS_PER_LONG - 2;
  	int hw_stopped;
  	unsigned long ctrl_status:8,	/* ctrl_lock */
  		      packet:1,
  		      unused_ctrl:BITS_PER_LONG - 9;
  	unsigned int receive_room;	/* Bytes free for queue */
  	int flow_change;
  
  	struct tty_struct *link;
  	struct fasync_struct *fasync;
  	int alt_speed;		/* For magic substitution of 38400 bps */
  	wait_queue_head_t write_wait;
  	wait_queue_head_t read_wait;
  	struct work_struct hangup_work;
  	void *disc_data;
  	void *driver_data;
  	struct list_head tty_files;
  
  #define N_TTY_BUF_SIZE 4096
  
  	int closing;
  	unsigned char *write_buf;
  	int write_cnt;
  	/* If the tty has a pending do_SAK, queue it here - akpm */
  	struct work_struct SAK_work;
  	struct tty_port *port;
  };
  
  /* Each of a tty's open files has private_data pointing to tty_file_private */
  struct tty_file_private {
  	struct tty_struct *tty;
  	struct file *file;
  	struct list_head list;
  };
  
  /* tty magic number */
  #define TTY_MAGIC		0x5401
  
  /*
   * These bits are used in the flags field of the tty structure.
   *
   * So that interrupts won't be able to mess up the queues,
   * copy_to_cooked must be atomic with respect to itself, as must
   * tty->write.  Thus, you must use the inline functions set_bit() and
   * clear_bit() to make things atomic.
   */
  #define TTY_THROTTLED 		0	/* Call unthrottle() at threshold min */
  #define TTY_IO_ERROR 		1	/* Cause an I/O error (may be no ldisc too) */
  #define TTY_OTHER_CLOSED 	2	/* Other side (if any) has closed */
  #define TTY_EXCLUSIVE 		3	/* Exclusive open mode */
  #define TTY_DEBUG 		4	/* Debugging */
  #define TTY_DO_WRITE_WAKEUP 	5	/* Call write_wakeup after queuing new */
  #define TTY_LDISC_OPEN	 	11	/* Line discipline is open */
  #define TTY_PTY_LOCK 		16	/* pty private */
  #define TTY_NO_WRITE_SPLIT 	17	/* Preserve write boundaries to driver */
  #define TTY_HUPPED 		18	/* Post driver->hangup() */
  #define TTY_LDISC_HALTED	22	/* Line discipline is halted */
  
  #define TTY_WRITE_FLUSH(tty) tty_write_flush((tty))
  
  /* Values for tty->flow_change */
  #define TTY_THROTTLE_SAFE 1
  #define TTY_UNTHROTTLE_SAFE 2
  
  static inline void __tty_set_flow_change(struct tty_struct *tty, int val)
  {
  	tty->flow_change = val;
  }
  
  static inline void tty_set_flow_change(struct tty_struct *tty, int val)
  {
  	tty->flow_change = val;
  	smp_mb();
  }
  
  #ifdef CONFIG_TTY
  extern void console_init(void);
  extern void tty_kref_put(struct tty_struct *tty);
  extern struct pid *tty_get_pgrp(struct tty_struct *tty);
  extern void tty_vhangup_self(void);
  extern void disassociate_ctty(int priv);
  extern dev_t tty_devnum(struct tty_struct *tty);
  extern void proc_clear_tty(struct task_struct *p);
  extern struct tty_struct *get_current_tty(void);
  /* tty_io.c */
  extern int __init tty_init(void);
  #else
  static inline void console_init(void)
  { }
  static inline void tty_kref_put(struct tty_struct *tty)
  { }
  static inline struct pid *tty_get_pgrp(struct tty_struct *tty)
  { return NULL; }
  static inline void tty_vhangup_self(void)
  { }
  static inline void disassociate_ctty(int priv)
  { }
  static inline dev_t tty_devnum(struct tty_struct *tty)
  { return 0; }
  static inline void proc_clear_tty(struct task_struct *p)
  { }
  static inline struct tty_struct *get_current_tty(void)
  { return NULL; }
  /* tty_io.c */
  static inline int __init tty_init(void)
  { return 0; }
  #endif
  
  extern void tty_write_flush(struct tty_struct *);
  
  extern struct ktermios tty_std_termios;
  
  extern int vcs_init(void);
  
  extern struct class *tty_class;
  
  /**
   *	tty_kref_get		-	get a tty reference
   *	@tty: tty device
   *
   *	Return a new reference to a tty object. The caller must hold
   *	sufficient locks/counts to ensure that their existing reference cannot
   *	go away
   */
  
  static inline struct tty_struct *tty_kref_get(struct tty_struct *tty)
  {
  	if (tty)
  		kref_get(&tty->kref);
  	return tty;
  }
  
  extern int tty_paranoia_check(struct tty_struct *tty, struct inode *inode,
  			      const char *routine);
  extern char *tty_name(struct tty_struct *tty, char *buf);
  extern void tty_wait_until_sent(struct tty_struct *tty, long timeout);
  extern int tty_check_change(struct tty_struct *tty);
  extern void __stop_tty(struct tty_struct *tty);
  extern void stop_tty(struct tty_struct *tty);
  extern void __start_tty(struct tty_struct *tty);
  extern void start_tty(struct tty_struct *tty);
  extern int tty_register_driver(struct tty_driver *driver);
  extern int tty_unregister_driver(struct tty_driver *driver);
  extern struct device *tty_register_device(struct tty_driver *driver,
  					  unsigned index, struct device *dev);
  extern struct device *tty_register_device_attr(struct tty_driver *driver,
  				unsigned index, struct device *device,
  				void *drvdata,
  				const struct attribute_group **attr_grp);
  extern void tty_unregister_device(struct tty_driver *driver, unsigned index);
  extern int tty_read_raw_data(struct tty_struct *tty, unsigned char *bufp,
  			     int buflen);
  extern void tty_write_message(struct tty_struct *tty, char *msg);
  extern int tty_send_xchar(struct tty_struct *tty, char ch);
  extern int tty_put_char(struct tty_struct *tty, unsigned char c);
  extern int tty_chars_in_buffer(struct tty_struct *tty);
  extern int tty_write_room(struct tty_struct *tty);
  extern void tty_driver_flush_buffer(struct tty_struct *tty);
  extern void tty_throttle(struct tty_struct *tty);
  extern void tty_unthrottle(struct tty_struct *tty);
  extern int tty_throttle_safe(struct tty_struct *tty);
  extern int tty_unthrottle_safe(struct tty_struct *tty);
  extern int tty_do_resize(struct tty_struct *tty, struct winsize *ws);
  extern void tty_driver_remove_tty(struct tty_driver *driver,
  				  struct tty_struct *tty);
  extern void tty_free_termios(struct tty_struct *tty);
  extern int is_current_pgrp_orphaned(void);
  extern int is_ignored(int sig);
  extern int tty_signal(int sig, struct tty_struct *tty);
  extern void tty_hangup(struct tty_struct *tty);
  extern void tty_vhangup(struct tty_struct *tty);
  extern int tty_hung_up_p(struct file *filp);
  extern void do_SAK(struct tty_struct *tty);
  extern void __do_SAK(struct tty_struct *tty);
  extern void no_tty(void);
  extern void tty_flush_to_ldisc(struct tty_struct *tty);
  extern void tty_buffer_free_all(struct tty_port *port);
  extern void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld);
  extern void tty_buffer_init(struct tty_port *port);
  extern void tty_buffer_set_lock_subclass(struct tty_port *port);
  extern speed_t tty_termios_baud_rate(struct ktermios *termios);
  extern speed_t tty_termios_input_baud_rate(struct ktermios *termios);
  extern void tty_termios_encode_baud_rate(struct ktermios *termios,
  						speed_t ibaud, speed_t obaud);
  extern void tty_encode_baud_rate(struct tty_struct *tty,
  						speed_t ibaud, speed_t obaud);
  
  /**
   *	tty_get_baud_rate	-	get tty bit rates
   *	@tty: tty to query
   *
   *	Returns the baud rate as an integer for this terminal. The
   *	termios lock must be held by the caller and the terminal bit
   *	flags may be updated.
   *
   *	Locking: none
   */
  static inline speed_t tty_get_baud_rate(struct tty_struct *tty)
  {
  	return tty_termios_baud_rate(&tty->termios);
  }
  
  extern void tty_termios_copy_hw(struct ktermios *new, struct ktermios *old);
  extern int tty_termios_hw_change(struct ktermios *a, struct ktermios *b);
  
  extern struct tty_ldisc *tty_ldisc_ref(struct tty_struct *);
  extern void tty_ldisc_deref(struct tty_ldisc *);
  extern struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *);
  extern void tty_ldisc_hangup(struct tty_struct *tty);
  extern const struct file_operations tty_ldiscs_proc_fops;
  
  extern void tty_wakeup(struct tty_struct *tty);
  extern void tty_ldisc_flush(struct tty_struct *tty);
  
  extern long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
  extern int tty_mode_ioctl(struct tty_struct *tty, struct file *file,
  			unsigned int cmd, unsigned long arg);
  extern int tty_perform_flush(struct tty_struct *tty, unsigned long arg);
  extern void tty_default_fops(struct file_operations *fops);
  extern struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx);
  extern int tty_alloc_file(struct file *file);
  extern void tty_add_file(struct tty_struct *tty, struct file *file);
  extern void tty_free_file(struct file *file);
  extern void free_tty_struct(struct tty_struct *tty);
  extern void deinitialize_tty_struct(struct tty_struct *tty);
  extern struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx);
  extern int tty_release(struct inode *inode, struct file *filp);
  extern int tty_init_termios(struct tty_struct *tty);
  extern int tty_standard_install(struct tty_driver *driver,
  		struct tty_struct *tty);
  
  extern struct mutex tty_mutex;
  extern spinlock_t tty_files_lock;
  
  #define tty_is_writelocked(tty)  (mutex_is_locked(&tty->atomic_write_lock))
  
  extern void tty_port_init(struct tty_port *port);
  extern void tty_port_link_device(struct tty_port *port,
  		struct tty_driver *driver, unsigned index);
  extern struct device *tty_port_register_device(struct tty_port *port,
  		struct tty_driver *driver, unsigned index,
  		struct device *device);
  extern struct device *tty_port_register_device_attr(struct tty_port *port,
  		struct tty_driver *driver, unsigned index,
  		struct device *device, void *drvdata,
  		const struct attribute_group **attr_grp);
  extern int tty_port_alloc_xmit_buf(struct tty_port *port);
  extern void tty_port_free_xmit_buf(struct tty_port *port);
  extern void tty_port_destroy(struct tty_port *port);
  extern void tty_port_put(struct tty_port *port);
  
  static inline struct tty_port *tty_port_get(struct tty_port *port)
  {
  	if (port && kref_get_unless_zero(&port->kref))
  		return port;
  	return NULL;
  }
  
  /* If the cts flow control is enabled, return true. */
  static inline bool tty_port_cts_enabled(struct tty_port *port)
  {
  	return port->flags & ASYNC_CTS_FLOW;
  }
  
  extern struct tty_struct *tty_port_tty_get(struct tty_port *port);
  extern void tty_port_tty_set(struct tty_port *port, struct tty_struct *tty);
  extern int tty_port_carrier_raised(struct tty_port *port);
  extern void tty_port_raise_dtr_rts(struct tty_port *port);
  extern void tty_port_lower_dtr_rts(struct tty_port *port);
  extern void tty_port_hangup(struct tty_port *port);
  extern void tty_port_tty_hangup(struct tty_port *port, bool check_clocal);
  extern void tty_port_tty_wakeup(struct tty_port *port);
  extern int tty_port_block_til_ready(struct tty_port *port,
  				struct tty_struct *tty, struct file *filp);
  extern int tty_port_close_start(struct tty_port *port,
  				struct tty_struct *tty, struct file *filp);
  extern void tty_port_close_end(struct tty_port *port, struct tty_struct *tty);
  extern void tty_port_close(struct tty_port *port,
  				struct tty_struct *tty, struct file *filp);
  extern int tty_port_install(struct tty_port *port, struct tty_driver *driver,
  				struct tty_struct *tty);
  extern int tty_port_open(struct tty_port *port,
  				struct tty_struct *tty, struct file *filp);
  static inline int tty_port_users(struct tty_port *port)
  {
  	return port->count + port->blocked_open;
  }
  
  extern int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc);
  extern int tty_unregister_ldisc(int disc);
  extern int tty_set_ldisc(struct tty_struct *tty, int ldisc);
  extern int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty);
  extern void tty_ldisc_release(struct tty_struct *tty);
  extern void tty_ldisc_init(struct tty_struct *tty);
  extern void tty_ldisc_deinit(struct tty_struct *tty);
  extern void tty_ldisc_begin(void);
  
  static inline int tty_ldisc_receive_buf(struct tty_ldisc *ld, unsigned char *p,
  					char *f, int count)
  {
  	if (ld->ops->receive_buf2)
  		count = ld->ops->receive_buf2(ld->tty, p, f, count);
  	else {
  		count = min_t(int, count, ld->tty->receive_room);
  		if (count)
  			ld->ops->receive_buf(ld->tty, p, f, count);
  	}
  	return count;
  }
  
  
  /* n_tty.c */
  extern struct tty_ldisc_ops tty_ldisc_N_TTY;
  extern void n_tty_inherit_ops(struct tty_ldisc_ops *ops);
  
  /* tty_audit.c */
  #ifdef CONFIG_AUDIT
  extern void tty_audit_add_data(struct tty_struct *tty, unsigned char *data,
  			       size_t size, unsigned icanon);
  extern void tty_audit_exit(void);
  extern void tty_audit_fork(struct signal_struct *sig);
  extern void tty_audit_tiocsti(struct tty_struct *tty, char ch);
  extern void tty_audit_push(struct tty_struct *tty);
  extern int tty_audit_push_current(void);
  #else
  static inline void tty_audit_add_data(struct tty_struct *tty,
  		unsigned char *data, size_t size, unsigned icanon)
  {
  }
  static inline void tty_audit_tiocsti(struct tty_struct *tty, char ch)
  {
  }
  static inline void tty_audit_exit(void)
  {
  }
  static inline void tty_audit_fork(struct signal_struct *sig)
  {
  }
  static inline void tty_audit_push(struct tty_struct *tty)
  {
  }
  static inline int tty_audit_push_current(void)
  {
  	return 0;
  }
  #endif
  
  /* tty_ioctl.c */
  extern int n_tty_ioctl_helper(struct tty_struct *tty, struct file *file,
  		       unsigned int cmd, unsigned long arg);
  extern long n_tty_compat_ioctl_helper(struct tty_struct *tty, struct file *file,
  		       unsigned int cmd, unsigned long arg);
  
  /* vt.c */
  
  extern int vt_ioctl(struct tty_struct *tty,
  		    unsigned int cmd, unsigned long arg);
  
  extern long vt_compat_ioctl(struct tty_struct *tty,
  		     unsigned int cmd, unsigned long arg);
  
  /* tty_mutex.c */
  /* functions for preparation of BKL removal */
  extern void __lockfunc tty_lock(struct tty_struct *tty);
  extern void __lockfunc tty_unlock(struct tty_struct *tty);
  extern void __lockfunc tty_lock_slave(struct tty_struct *tty);
  extern void __lockfunc tty_unlock_slave(struct tty_struct *tty);
  extern void tty_set_lock_subclass(struct tty_struct *tty);
  /*
   * this shall be called only from where BTM is held (like close)
   *
   * We need this to ensure nobody waits for us to finish while we are waiting.
   * Without this we were encountering system stalls.
   *
   * This should be indeed removed with BTM removal later.
   *
   * Locking: BTM required. Nobody is allowed to hold port->mutex.
   */
  static inline void tty_wait_until_sent_from_close(struct tty_struct *tty,
  		long timeout)
  {
  	tty_unlock(tty); /* tty->ops->close holds the BTM, drop it while waiting */
  	tty_wait_until_sent(tty, timeout);
  	tty_lock(tty);
  }
  
  /*
   * wait_event_interruptible_tty -- wait for a condition with the tty lock held
   *
   * The condition we are waiting for might take a long time to
   * become true, or might depend on another thread taking the
   * BTM. In either case, we need to drop the BTM to guarantee
   * forward progress. This is a leftover from the conversion
   * from the BKL and should eventually get removed as the BTM
   * falls out of use.
   *
   * Do not use in new code.
   */
  #define wait_event_interruptible_tty(tty, wq, condition)		\
  ({									\
  	int __ret = 0;							\
  	if (!(condition))						\
  		__ret = __wait_event_interruptible_tty(tty, wq,		\
  						       condition);	\
  	__ret;								\
  })
  
  #define __wait_event_interruptible_tty(tty, wq, condition)		\
  	___wait_event(wq, condition, TASK_INTERRUPTIBLE, 0, 0,		\
  			tty_unlock(tty);				\
  			schedule();					\
  			tty_lock(tty))
  
  #ifdef CONFIG_PROC_FS
  extern void proc_tty_register_driver(struct tty_driver *);
  extern void proc_tty_unregister_driver(struct tty_driver *);
  #else
  static inline void proc_tty_register_driver(struct tty_driver *d) {}
  static inline void proc_tty_unregister_driver(struct tty_driver *d) {}
  #endif
  
  #endif
  