#ifndef _LINUX_TTY_LDISC_H
  #define _LINUX_TTY_LDISC_H
  
  /*
   * This structure defines the interface between the tty line discipline
   * implementation and the tty routines.  The following routines can be
   * defined; unless noted otherwise, they are optional, and can be
   * filled in with a null pointer.
   *
   * int	(*open)(struct tty_struct *);
   *
   *	This function is called when the line discipline is associated
   *	with the tty.  The line discipline can use this as an
   *	opportunity to initialize any state needed by the ldisc routines.
   *
   * void	(*close)(struct tty_struct *);
   *
   *	This function is called when the line discipline is being
   *	shutdown, either because the tty is being closed or because
   *	the tty is being changed to use a new line discipline
   *
   * void	(*flush_buffer)(struct tty_struct *tty);
   *
   *	This function instructs the line discipline to clear its
   *	buffers of any input characters it may have queued to be
   *	delivered to the user mode process.
   *
   * ssize_t (*chars_in_buffer)(struct tty_struct *tty);
   *
   *	This function returns the number of input characters the line
   *	discipline may have queued up to be delivered to the user mode
   *	process.
   *
   * ssize_t (*read)(struct tty_struct * tty, struct file * file,
   *		   unsigned char * buf, size_t nr);
   *
   *	This function is called when the user requests to read from
   *	the tty.  The line discipline will return whatever characters
   *	it has buffered up for the user.  If this function is not
   *	defined, the user will receive an EIO error.
   *
   * ssize_t (*write)(struct tty_struct * tty, struct file * file,
   *		    const unsigned char * buf, size_t nr);
   *
   *	This function is called when the user requests to write to the
   *	tty.  The line discipline will deliver the characters to the
   *	low-level tty device for transmission, optionally performing
   *	some processing on the characters first.  If this function is
   *	not defined, the user will receive an EIO error.
   *
   * int	(*ioctl)(struct tty_struct * tty, struct file * file,
   *		 unsigned int cmd, unsigned long arg);
   *
   *	This function is called when the user requests an ioctl which
   *	is not handled by the tty layer or the low-level tty driver.
   *	It is intended for ioctls which affect line discpline
   *	operation.  Note that the search order for ioctls is (1) tty
   *	layer, (2) tty low-level driver, (3) line discpline.  So a
   *	low-level driver can "grab" an ioctl request before the line
   *	discpline has a chance to see it.
   *
   * long	(*compat_ioctl)(struct tty_struct * tty, struct file * file,
   *		        unsigned int cmd, unsigned long arg);
   *
   *	Process ioctl calls from 32-bit process on 64-bit system
   *
   * void	(*set_termios)(struct tty_struct *tty, struct ktermios * old);
   *
   *	This function notifies the line discpline that a change has
   *	been made to the termios structure.
   *
   * int	(*poll)(struct tty_struct * tty, struct file * file,
   *		  poll_table *wait);
   *
   *	This function is called when a user attempts to select/poll on a
   *	tty device.  It is solely the responsibility of the line
   *	discipline to handle poll requests.
   *
   * void	(*receive_buf)(struct tty_struct *, const unsigned char *cp,
   *		       char *fp, int count);
   *
   *	This function is called by the low-level tty driver to send
   *	characters received by the hardware to the line discpline for
   *	processing.  <cp> is a pointer to the buffer of input
   *	character received by the device.  <fp> is a pointer to a
   *	pointer of flag bytes which indicate whether a character was
   *	received with a parity error, etc. <fp> may be NULL to indicate
   *	all data received is TTY_NORMAL.
   *
   * void	(*write_wakeup)(struct tty_struct *);
   *
   *	This function is called by the low-level tty driver to signal
   *	that line discpline should try to send more characters to the
   *	low-level driver for transmission.  If the line discpline does
   *	not have any more data to send, it can just return.
   *
   * int (*hangup)(struct tty_struct *)
   *
   *	Called on a hangup. Tells the discipline that it should
   *	cease I/O to the tty driver. Can sleep. The driver should
   *	seek to perform this action quickly but should wait until
   *	any pending driver I/O is completed.
   *
   * void (*fasync)(struct tty_struct *, int on)
   *
   *	Notify line discipline when signal-driven I/O is enabled or
   *	disabled.
   *
   * void (*dcd_change)(struct tty_struct *tty, unsigned int status)
   *
   *	Tells the discipline that the DCD pin has changed its status.
   *	Used exclusively by the N_PPS (Pulse-Per-Second) line discipline.
   *
   * int	(*receive_buf2)(struct tty_struct *, const unsigned char *cp,
   *			char *fp, int count);
   *
   *	This function is called by the low-level tty driver to send
   *	characters received by the hardware to the line discpline for
   *	processing.  <cp> is a pointer to the buffer of input
   *	character received by the device.  <fp> is a pointer to a
   *	pointer of flag bytes which indicate whether a character was
   *	received with a parity error, etc. <fp> may be NULL to indicate
   *	all data received is TTY_NORMAL.
   *	If assigned, prefer this function for automatic flow control.
   */
  
  #include <linux/fs.h>
  #include <linux/wait.h>
  #include <linux/wait.h>
  
  
  /*
   * the semaphore definition
   */
  struct ld_semaphore {
  	long			count;
  	raw_spinlock_t		wait_lock;
  	unsigned int		wait_readers;
  	struct list_head	read_wait;
  	struct list_head	write_wait;
  #ifdef CONFIG_DEBUG_LOCK_ALLOC
  	struct lockdep_map	dep_map;
  #endif
  };
  
  extern void __init_ldsem(struct ld_semaphore *sem, const char *name,
  			 struct lock_class_key *key);
  
  #define init_ldsem(sem)						\
  do {								\
  	static struct lock_class_key __key;			\
  								\
  	__init_ldsem((sem), #sem, &__key);			\
  } while (0)
  
  
  extern int ldsem_down_read(struct ld_semaphore *sem, long timeout);
  extern int ldsem_down_read_trylock(struct ld_semaphore *sem);
  extern int ldsem_down_write(struct ld_semaphore *sem, long timeout);
  extern int ldsem_down_write_trylock(struct ld_semaphore *sem);
  extern void ldsem_up_read(struct ld_semaphore *sem);
  extern void ldsem_up_write(struct ld_semaphore *sem);
  
  #ifdef CONFIG_DEBUG_LOCK_ALLOC
  extern int ldsem_down_read_nested(struct ld_semaphore *sem, int subclass,
  				  long timeout);
  extern int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
  				   long timeout);
  #else
  # define ldsem_down_read_nested(sem, subclass, timeout)		\
  		ldsem_down_read(sem, timeout)
  # define ldsem_down_write_nested(sem, subclass, timeout)	\
  		ldsem_down_write(sem, timeout)
  #endif
  
  
  struct tty_ldisc_ops {
  	int	magic;
  	char	*name;
  	int	num;
  	int	flags;
  
  	/*
  	 * The following routines are called from above.
  	 */
  	int	(*open)(struct tty_struct *);
  	void	(*close)(struct tty_struct *);
  	void	(*flush_buffer)(struct tty_struct *tty);
  	ssize_t	(*chars_in_buffer)(struct tty_struct *tty);
  	ssize_t	(*read)(struct tty_struct *tty, struct file *file,
  			unsigned char __user *buf, size_t nr);
  	ssize_t	(*write)(struct tty_struct *tty, struct file *file,
  			 const unsigned char *buf, size_t nr);
  	int	(*ioctl)(struct tty_struct *tty, struct file *file,
  			 unsigned int cmd, unsigned long arg);
  	long	(*compat_ioctl)(struct tty_struct *tty, struct file *file,
  				unsigned int cmd, unsigned long arg);
  	void	(*set_termios)(struct tty_struct *tty, struct ktermios *old);
  	unsigned int (*poll)(struct tty_struct *, struct file *,
  			     struct poll_table_struct *);
  	int	(*hangup)(struct tty_struct *tty);
  
  	/*
  	 * The following routines are called from below.
  	 */
  	void	(*receive_buf)(struct tty_struct *, const unsigned char *cp,
  			       char *fp, int count);
  	void	(*write_wakeup)(struct tty_struct *);
  	void	(*dcd_change)(struct tty_struct *, unsigned int);
  	void	(*fasync)(struct tty_struct *tty, int on);
  	int	(*receive_buf2)(struct tty_struct *, const unsigned char *cp,
  				char *fp, int count);
  
  	struct  module *owner;
  
  	int refcount;
  };
  
  struct tty_ldisc {
  	struct tty_ldisc_ops *ops;
  	struct tty_struct *tty;
  };
  
  #define TTY_LDISC_MAGIC	0x5403
  
  #define LDISC_FLAG_DEFINED	0x00000001
  
  #define MODULE_ALIAS_LDISC(ldisc) \
  	MODULE_ALIAS("tty-ldisc-" __stringify(ldisc))
  
  #endif /* _LINUX_TTY_LDISC_H */