text: #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.
   *
   * 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 (*dcd_change)(struct tty_struct *tty, unsigned int status,
   *			struct pps_event_time *ts)
   *
   *	Tells the discipline that the DCD pin has changed its status and
   *	the relative timestamp. Pointer ts cannot be NULL.
   */
  
  #include <linux/fs.h>
  #include <linux/wait.h>
  #include <linux/pps_kernel.h>
  
  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,
  				struct pps_event_time *);
  
  	struct  module *owner;
  
  	int refcount;
  };
  
  struct tty_ldisc {
  	struct tty_ldisc_ops *ops;
  	atomic_t users;
  };
  
  #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 */
  