text: /* SPDX-License-Identifier: GPL-2.0 */
  #ifndef _LINUX_TTY_DRIVER_H
  #define _LINUX_TTY_DRIVER_H
  
  /*
   * This structure defines the interface between the low-level tty
   * driver 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.
   *
   * struct tty_struct * (*lookup)(struct tty_driver *self, struct file *, int idx)
   *
   *	Return the tty device corresponding to idx, NULL if there is not
   *	one currently in use and an ERR_PTR value on error. Called under
   *	tty_mutex (for now!)
   *
   *	Optional method. Default behaviour is to use the ttys array
   *
   * int (*install)(struct tty_driver *self, struct tty_struct *tty)
   *
   *	Install a new tty into the tty driver internal tables. Used in
   *	conjunction with lookup and remove methods.
   *
   *	Optional method. Default behaviour is to use the ttys array
   *
   * void (*remove)(struct tty_driver *self, struct tty_struct *tty)
   *
   *	Remove a closed tty from the tty driver internal tables. Used in
   *	conjunction with lookup and remove methods.
   *
   *	Optional method. Default behaviour is to use the ttys array
   *
   * int  (*open)(struct tty_struct * tty, struct file * filp);
   *
   * 	This routine is called when a particular tty device is opened.
   * 	This routine is mandatory; if this routine is not filled in,
   * 	the attempted open will fail with ENODEV.
   *
   *	Required method. Called with tty lock held.
   *
   * void (*close)(struct tty_struct * tty, struct file * filp);
   *
   * 	This routine is called when a particular tty device is closed.
   *	Note: called even if the corresponding open() failed.
   *
   *	Required method. Called with tty lock held.
   *
   * void (*shutdown)(struct tty_struct * tty);
   *
   * 	This routine is called under the tty lock when a particular tty device
   *	is closed for the last time. It executes before the tty resources
   *	are freed so may execute while another function holds a tty kref.
   *
   * void (*cleanup)(struct tty_struct * tty);
   *
   *	This routine is called asynchronously when a particular tty device
   *	is closed for the last time freeing up the resources. This is
   *	actually the second part of shutdown for routines that might sleep.
   *
   *
   * int (*write)(struct tty_struct * tty,
   * 		 const unsigned char *buf, int count);
   *
   * 	This routine is called by the kernel to write a series of
   * 	characters to the tty device.  The characters may come from
   * 	user space or kernel space.  This routine will return the
   *	number of characters actually accepted for writing.
   *
   *	Optional: Required for writable devices.
   *
   * int (*put_char)(struct tty_struct *tty, unsigned char ch);
   *
   * 	This routine is called by the kernel to write a single
   * 	character to the tty device.  If the kernel uses this routine,
   * 	it must call the flush_chars() routine (if defined) when it is
   * 	done stuffing characters into the driver.  If there is no room
   * 	in the queue, the character is ignored.
   *
   *	Optional: Kernel will use the write method if not provided.
   *
   *	Note: Do not call this function directly, call tty_put_char
   *
   * void (*flush_chars)(struct tty_struct *tty);
   *
   * 	This routine is called by the kernel after it has written a
   * 	series of characters to the tty device using put_char().  
   *
   *	Optional:
   *
   *	Note: Do not call this function directly, call tty_driver_flush_chars
   * 
   * int  (*write_room)(struct tty_struct *tty);
   *
   * 	This routine returns the numbers of characters the tty driver
   * 	will accept for queuing to be written.  This number is subject
   * 	to change as output buffers get emptied, or if the output flow
   *	control is acted.
   *
   *	Required if write method is provided else not needed.
   *
   *	Note: Do not call this function directly, call tty_write_room
   * 
   * int  (*ioctl)(struct tty_struct *tty, unsigned int cmd, unsigned long arg);
   *
   * 	This routine allows the tty driver to implement
   *	device-specific ioctls.  If the ioctl number passed in cmd
   * 	is not recognized by the driver, it should return ENOIOCTLCMD.
   *
   *	Optional
   *
   * long (*compat_ioctl)(struct tty_struct *tty,,
   * 	                unsigned int cmd, unsigned long arg);
   *
   * 	implement ioctl processing for 32 bit process on 64 bit system
   *
   *	Optional
   * 
   * void (*set_termios)(struct tty_struct *tty, struct ktermios * old);
   *
   * 	This routine allows the tty driver to be notified when
   * 	device's termios settings have changed.
   *
   *	Optional: Called under the termios lock
   *
   *
   * void (*set_ldisc)(struct tty_struct *tty);
   *
   * 	This routine allows the tty driver to be notified when the
   * 	device's termios settings have changed.
   *
   *	Optional: Called under BKL (currently)
   * 
   * void (*throttle)(struct tty_struct * tty);
   *
   * 	This routine notifies the tty driver that input buffers for
   * 	the line discipline are close to full, and it should somehow
   * 	signal that no more characters should be sent to the tty.
   *
   *	Optional: Always invoke via tty_throttle(), called under the
   *	termios lock.
   * 
   * void (*unthrottle)(struct tty_struct * tty);
   *
   * 	This routine notifies the tty drivers that it should signals
   * 	that characters can now be sent to the tty without fear of
   * 	overrunning the input buffers of the line disciplines.
   * 
   *	Optional: Always invoke via tty_unthrottle(), called under the
   *	termios lock.
   *
   * void (*stop)(struct tty_struct *tty);
   *
   * 	This routine notifies the tty driver that it should stop
   * 	outputting characters to the tty device.  
   *
   *	Called with ->flow_lock held. Serialized with start() method.
   *
   *	Optional:
   *
   *	Note: Call stop_tty not this method.
   * 
   * void (*start)(struct tty_struct *tty);
   *
   * 	This routine notifies the tty driver that it resume sending
   *	characters to the tty device.
   *
   *	Called with ->flow_lock held. Serialized with stop() method.
   *
   *	Optional:
   *
   *	Note: Call start_tty not this method.
   * 
   * void (*hangup)(struct tty_struct *tty);
   *
   * 	This routine notifies the tty driver that it should hang up the
   * 	tty device.
   *
   *	Optional:
   *
   *	Called with tty lock held.
   *
   * int (*break_ctl)(struct tty_struct *tty, int state);
   *
   * 	This optional routine requests the tty driver to turn on or
   * 	off BREAK status on the RS-232 port.  If state is -1,
   * 	then the BREAK status should be turned on; if state is 0, then
   * 	BREAK should be turned off.
   *
   * 	If this routine is implemented, the high-level tty driver will
   * 	handle the following ioctls: TCSBRK, TCSBRKP, TIOCSBRK,
   * 	TIOCCBRK.
   *
   *	If the driver sets TTY_DRIVER_HARDWARE_BREAK then the interface
   *	will also be called with actual times and the hardware is expected
   *	to do the delay work itself. 0 and -1 are still used for on/off.
   *
   *	Optional: Required for TCSBRK/BRKP/etc handling.
   *
   * void (*wait_until_sent)(struct tty_struct *tty, int timeout);
   * 
   * 	This routine waits until the device has written out all of the
   * 	characters in its transmitter FIFO.
   *
   *	Optional: If not provided the device is assumed to have no FIFO
   *
   *	Note: Usually correct to call tty_wait_until_sent
   *
   * void (*send_xchar)(struct tty_struct *tty, char ch);
   *
   * 	This routine is used to send a high-priority XON/XOFF
   * 	character to the device.
   *
   *	Optional: If not provided then the write method is called under
   *	the atomic write lock to keep it serialized with the ldisc.
   *
   * int (*resize)(struct tty_struct *tty, struct winsize *ws)
   *
   *	Called when a termios request is issued which changes the
   *	requested terminal geometry.
   *
   *	Optional: the default action is to update the termios structure
   *	without error. This is usually the correct behaviour. Drivers should
   *	not force errors here if they are not resizable objects (eg a serial
   *	line). See tty_do_resize() if you need to wrap the standard method
   *	in your own logic - the usual case.
   *
   * void (*set_termiox)(struct tty_struct *tty, struct termiox *new);
   *
   *	Called when the device receives a termiox based ioctl. Passes down
   *	the requested data from user space. This method will not be invoked
   *	unless the tty also has a valid tty->termiox pointer.
   *
   *	Optional: Called under the termios lock
   *
   * int (*get_icount)(struct tty_struct *tty, struct serial_icounter *icount);
   *
   *	Called when the device receives a TIOCGICOUNT ioctl. Passed a kernel
   *	structure to complete. This method is optional and will only be called
   *	if provided (otherwise EINVAL will be returned).
   */
  
  #include <linux/export.h>
  #include <linux/fs.h>
  #include <linux/list.h>
  #include <linux/cdev.h>
  #include <linux/termios.h>
  #include <linux/seq_file.h>
  
  struct tty_struct;
  struct tty_driver;
  struct serial_icounter_struct;
  struct serial_struct;
  
  struct tty_operations {
  	struct tty_struct * (*lookup)(struct tty_driver *driver,
  			struct file *filp, int idx);
  	int  (*install)(struct tty_driver *driver, struct tty_struct *tty);
  	void (*remove)(struct tty_driver *driver, struct tty_struct *tty);
  	int  (*open)(struct tty_struct * tty, struct file * filp);
  	void (*close)(struct tty_struct * tty, struct file * filp);
  	void (*shutdown)(struct tty_struct *tty);
  	void (*cleanup)(struct tty_struct *tty);
  	int  (*write)(struct tty_struct * tty,
  		      const unsigned char *buf, int count);
  	int  (*put_char)(struct tty_struct *tty, unsigned char ch);
  	void (*flush_chars)(struct tty_struct *tty);
  	int  (*write_room)(struct tty_struct *tty);
  	int  (*chars_in_buffer)(struct tty_struct *tty);
  	int  (*ioctl)(struct tty_struct *tty,
  		    unsigned int cmd, unsigned long arg);
  	long (*compat_ioctl)(struct tty_struct *tty,
  			     unsigned int cmd, unsigned long arg);
  	void (*set_termios)(struct tty_struct *tty, struct ktermios * old);
  	void (*throttle)(struct tty_struct * tty);
  	void (*unthrottle)(struct tty_struct * tty);
  	void (*stop)(struct tty_struct *tty);
  	void (*start)(struct tty_struct *tty);
  	void (*hangup)(struct tty_struct *tty);
  	int (*break_ctl)(struct tty_struct *tty, int state);
  	void (*flush_buffer)(struct tty_struct *tty);
  	void (*set_ldisc)(struct tty_struct *tty);
  	void (*wait_until_sent)(struct tty_struct *tty, int timeout);
  	void (*send_xchar)(struct tty_struct *tty, char ch);
  	int (*tiocmget)(struct tty_struct *tty);
  	int (*tiocmset)(struct tty_struct *tty,
  			unsigned int set, unsigned int clear);
  	int (*resize)(struct tty_struct *tty, struct winsize *ws);
  	int (*set_termiox)(struct tty_struct *tty, struct termiox *tnew);
  	int (*get_icount)(struct tty_struct *tty,
  				struct serial_icounter_struct *icount);
  	int  (*get_serial)(struct tty_struct *tty, struct serial_struct *p);
  	int  (*set_serial)(struct tty_struct *tty, struct serial_struct *p);
  	void (*show_fdinfo)(struct tty_struct *tty, struct seq_file *m);
  #ifdef CONFIG_CONSOLE_POLL
  	int (*poll_init)(struct tty_driver *driver, int line, char *options);
  	int (*poll_get_char)(struct tty_driver *driver, int line);
  	void (*poll_put_char)(struct tty_driver *driver, int line, char ch);
  #endif
  	int (*proc_show)(struct seq_file *, void *);
  } __randomize_layout;
  
  struct tty_driver {
  	int	magic;		/* magic number for this structure */
  	struct kref kref;	/* Reference management */
  	struct cdev **cdevs;
  	struct module	*owner;
  	const char	*driver_name;
  	const char	*name;
  	int	name_base;	/* offset of printed name */
  	int	major;		/* major device number */
  	int	minor_start;	/* start of minor device number */
  	unsigned int	num;	/* number of devices allocated */
  	short	type;		/* type of tty driver */
  	short	subtype;	/* subtype of tty driver */
  	struct ktermios init_termios; /* Initial termios */
  	unsigned long	flags;		/* tty driver flags */
  	struct proc_dir_entry *proc_entry; /* /proc fs entry */
  	struct tty_driver *other; /* only used for the PTY driver */
  
  	/*
  	 * Pointer to the tty data structures
  	 */
  	struct tty_struct **ttys;
  	struct tty_port **ports;
  	struct ktermios **termios;
  	void *driver_state;
  
  	/*
  	 * Driver methods
  	 */
  
  	const struct tty_operations *ops;
  	struct list_head tty_drivers;
  } __randomize_layout;
  
  extern struct list_head tty_drivers;
  
  extern struct tty_driver *__tty_alloc_driver(unsigned int lines,
  		struct module *owner, unsigned long flags);
  extern void put_tty_driver(struct tty_driver *driver);
  extern void tty_set_operations(struct tty_driver *driver,
  			const struct tty_operations *op);
  extern struct tty_driver *tty_find_polling_driver(char *name, int *line);
  
  extern void tty_driver_kref_put(struct tty_driver *driver);
  
  /* Use TTY_DRIVER_* flags below */
  #define tty_alloc_driver(lines, flags) \
  		__tty_alloc_driver(lines, THIS_MODULE, flags)
  
  /*
   * DEPRECATED Do not use this in new code, use tty_alloc_driver instead.
   * (And change the return value checks.)
   */
  static inline struct tty_driver *alloc_tty_driver(unsigned int lines)
  {
  	struct tty_driver *ret = tty_alloc_driver(lines, 0);
  	if (IS_ERR(ret))
  		return NULL;
  	return ret;
  }
  
  static inline struct tty_driver *tty_driver_kref_get(struct tty_driver *d)
  {
  	kref_get(&d->kref);
  	return d;
  }
  
  /* tty driver magic number */
  #define TTY_DRIVER_MAGIC		0x5402
  
  /*
   * tty driver flags
   * 
   * TTY_DRIVER_RESET_TERMIOS --- requests the tty layer to reset the
   * 	termios setting when the last process has closed the device.
   * 	Used for PTY's, in particular.
   * 
   * TTY_DRIVER_REAL_RAW --- if set, indicates that the driver will
   * 	guarantee never not to set any special character handling
   * 	flags if ((IGNBRK || (!BRKINT && !PARMRK)) && (IGNPAR ||
   * 	!INPCK)).  That is, if there is no reason for the driver to
   * 	send notifications of parity and break characters up to the
   * 	line driver, it won't do so.  This allows the line driver to
   *	optimize for this case if this flag is set.  (Note that there
   * 	is also a promise, if the above case is true, not to signal
   * 	overruns, either.)
   *
   * TTY_DRIVER_DYNAMIC_DEV --- if set, the individual tty devices need
   *	to be registered with a call to tty_register_device() when the
   *	device is found in the system and unregistered with a call to
   *	tty_unregister_device() so the devices will be show up
   *	properly in sysfs.  If not set, driver->num entries will be
   *	created by the tty core in sysfs when tty_register_driver() is
   *	called.  This is to be used by drivers that have tty devices
   *	that can appear and disappear while the main tty driver is
   *	registered with the tty core.
   *
   * TTY_DRIVER_DEVPTS_MEM -- don't use the standard arrays, instead
   *	use dynamic memory keyed through the devpts filesystem.  This
   *	is only applicable to the pty driver.
   *
   * TTY_DRIVER_HARDWARE_BREAK -- hardware handles break signals. Pass
   *	the requested timeout to the caller instead of using a simple
   *	on/off interface.
   *
   * TTY_DRIVER_DYNAMIC_ALLOC -- do not allocate structures which are
   *	needed per line for this driver as it would waste memory.
   *	The driver will take care.
   *
   * TTY_DRIVER_UNNUMBERED_NODE -- do not create numbered /dev nodes. In
   *	other words create /dev/ttyprintk and not /dev/ttyprintk0.
   *	Applicable only when a driver for a single tty device is
   *	being allocated.
   */
  #define TTY_DRIVER_INSTALLED		0x0001
  #define TTY_DRIVER_RESET_TERMIOS	0x0002
  #define TTY_DRIVER_REAL_RAW		0x0004
  #define TTY_DRIVER_DYNAMIC_DEV		0x0008
  #define TTY_DRIVER_DEVPTS_MEM		0x0010
  #define TTY_DRIVER_HARDWARE_BREAK	0x0020
  #define TTY_DRIVER_DYNAMIC_ALLOC	0x0040
  #define TTY_DRIVER_UNNUMBERED_NODE	0x0080
  
  /* tty driver types */
  #define TTY_DRIVER_TYPE_SYSTEM		0x0001
  #define TTY_DRIVER_TYPE_CONSOLE		0x0002
  #define TTY_DRIVER_TYPE_SERIAL		0x0003
  #define TTY_DRIVER_TYPE_PTY		0x0004
  #define TTY_DRIVER_TYPE_SCC		0x0005	/* scc driver */
  #define TTY_DRIVER_TYPE_SYSCONS		0x0006
  
  /* system subtypes (magic, used by tty_io.c) */
  #define SYSTEM_TYPE_TTY			0x0001
  #define SYSTEM_TYPE_CONSOLE		0x0002
  #define SYSTEM_TYPE_SYSCONS		0x0003
  #define SYSTEM_TYPE_SYSPTMX		0x0004
  
  /* pty subtypes (magic, used by tty_io.c) */
  #define PTY_TYPE_MASTER			0x0001
  #define PTY_TYPE_SLAVE			0x0002
  
  /* serial subtype definitions */
  #define SERIAL_TYPE_NORMAL	1
  
  #endif /* #ifdef _LINUX_TTY_DRIVER_H */
  