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Filename : tty_driver.h
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/* 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 ENOTTY 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 */