TTY Struct¶
struct tty_struct
is allocated by the TTY layer upon the first open of the TTY
device and released after the last close. The TTY layer passes this structure
to most of struct tty_operation’s hooks. Members of tty_struct are documented
in TTY Struct Reference at the bottom.
Initialization¶
-
void
tty_init_termios
(struct tty_struct *tty)¶ helper for termios setup
Parameters
struct tty_struct *tty
- the tty to set up
Description
Initialise the termios structure for this tty. This runs under the
tty_mutex
currently so we can be relaxed about ordering.
Name¶
-
const char *
tty_name
(const struct tty_struct *tty)¶ return tty naming
Parameters
const struct tty_struct *tty
- tty structure
Description
Convert a tty structure into a name. The name reflects the kernel naming policy and if udev is in use may not reflect user space
Locking: none
Reference counting¶
-
struct tty_struct *
tty_kref_get
(struct tty_struct *tty)¶ get a tty reference
Parameters
struct tty_struct *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
-
void
tty_kref_put
(struct tty_struct *tty)¶ release a tty kref
Parameters
struct tty_struct *tty
- tty device
Description
Release a reference to the tty device and if need be let the kref layer destruct the object for us.
Install¶
-
int
tty_standard_install
(struct tty_driver *driver, struct tty_struct *tty)¶ usual tty->ops->install
Parameters
struct tty_driver *driver
- the driver for the tty
struct tty_struct *tty
- the tty
Description
If the driver overrides tty->ops->install, it still can call this function to perform the standard install operations.
Read & Write¶
-
int
tty_put_char
(struct tty_struct *tty, unsigned char ch)¶ write one character to a tty
Parameters
struct tty_struct *tty
- tty
unsigned char ch
- character to write
Description
Write one byte to the tty using the provided tty->ops->put_char() method if present.
Note
the specific put_char operation in the driver layer may go away soon. Don’t call it directly, use this method
Return
the number of characters successfully output.
Start & Stop¶
-
void
stop_tty
(struct tty_struct *tty)¶ propagate flow control
Parameters
struct tty_struct *tty
- tty to stop
Description
Perform flow control to the driver. May be called on an already stopped
device and will not re-call the tty_driver->stop()
method.
This functionality is used by both the line disciplines for halting incoming
flow and by the driver. It may therefore be called from any context, may be
under the tty atomic_write_lock
but not always.
- Locking:
- flow.lock
-
void
start_tty
(struct tty_struct *tty)¶ propagate flow control
Parameters
struct tty_struct *tty
- tty to start
Description
Start a tty that has been stopped if at all possible. If tty was previously
stopped and is now being started, the tty_driver->start()
method is invoked
and the line discipline woken.
- Locking:
- flow.lock
Wakeup¶
-
void
tty_wakeup
(struct tty_struct *tty)¶ request more data
Parameters
struct tty_struct *tty
- terminal
Description
Internal and external helper for wakeups of tty. This function informs the line discipline if present that the driver is ready to receive more output data.
Hangup¶
-
void
tty_hangup
(struct tty_struct *tty)¶ trigger a hangup event
Parameters
struct tty_struct *tty
- tty to hangup
Description
A carrier loss (virtual or otherwise) has occurred on tty. Schedule a hangup sequence to run after this event.
-
void
tty_vhangup
(struct tty_struct *tty)¶ process vhangup
Parameters
struct tty_struct *tty
- tty to hangup
Description
The user has asked via system call for the terminal to be hung up. We do this synchronously so that when the syscall returns the process is complete. That guarantee is necessary for security reasons.
-
int
tty_hung_up_p
(struct file *filp)¶ was tty hung up
Parameters
struct file *filp
- file pointer of tty
Return
true if the tty has been subject to a vhangup or a carrier loss
Misc¶
-
int
tty_do_resize
(struct tty_struct *tty, struct winsize *ws)¶ resize event
Parameters
struct tty_struct *tty
- tty being resized
struct winsize *ws
- new dimensions
Description
Update the termios variables and send the necessary signals to peform a terminal resize correctly.
TTY Struct Flags¶
These bits are used in the tty_struct.flags
field.
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.
- TTY_THROTTLED
- Driver input is throttled. The ldisc should call
tty_driver.unthrottle()
in order to resume reception when it is ready to process more data (at threshold min). - TTY_IO_ERROR
- If set, causes all subsequent userspace read/write calls on the tty to
fail, returning -
EIO
. (May be no ldisc too.) - TTY_OTHER_CLOSED
- Device is a pty and the other side has closed.
- TTY_EXCLUSIVE
- Exclusive open mode (a single opener).
- TTY_DO_WRITE_WAKEUP
- If set, causes the driver to call the
tty_ldisc_ops.write_wakeup()
method in order to resume transmission when it can accept more data to transmit. - TTY_LDISC_OPEN
- Indicates that a line discipline is open. For debugging purposes only.
- TTY_PTY_LOCK
- A flag private to pty code to implement
TIOCSPTLCK
/TIOCGPTLCK
logic. - TTY_NO_WRITE_SPLIT
- Prevent driver from splitting up writes into smaller chunks (preserve write boundaries to driver).
- TTY_HUPPED
- The TTY was hung up. This is set post
tty_driver.hangup()
. - TTY_HUPPING
- The TTY is in the process of hanging up to abort potential readers.
- TTY_LDISC_CHANGING
- Line discipline for this TTY is being changed. I/O should not block when this is set. Use tty_io_nonblock() to check.
- TTY_LDISC_HALTED
- Line discipline for this TTY was stopped. No work should be queued to this ldisc.
TTY Struct Reference¶
-
struct
tty_struct
¶ state associated with a tty while open
Definition
struct tty_struct {
int magic;
struct kref kref;
struct device *dev;
struct tty_driver *driver;
const struct tty_operations *ops;
int index;
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;
struct ktermios termios, termios_locked;
char name[64];
unsigned long flags;
int count;
struct winsize winsize;
struct {
spinlock_t lock;
bool stopped;
bool tco_stopped;
unsigned long unused[0];
} flow;
struct {
spinlock_t lock;
struct pid *pgrp;
struct pid *session;
unsigned char pktstatus;
bool packet;
unsigned long unused[0];
} ctrl;
int hw_stopped;
unsigned int receive_room;
int flow_change;
struct tty_struct *link;
struct fasync_struct *fasync;
wait_queue_head_t write_wait;
wait_queue_head_t read_wait;
struct work_struct hangup_work;
void *disc_data;
void *driver_data;
spinlock_t files_lock;
struct list_head tty_files;
#define N_TTY_BUF_SIZE 4096;
int closing;
unsigned char *write_buf;
int write_cnt;
struct work_struct SAK_work;
struct tty_port *port;
};
Members
magic
- magic value set early in alloc_tty_struct to
TTY_MAGIC
, for debugging purposes kref
- reference counting by
tty_kref_get()
andtty_kref_put()
, reaching zero frees the structure dev
- class device or
NULL
(e.g. ptys, serdev) driver
struct tty_driver
operating this ttyops
struct tty_operations
of driver for this tty (open, close, etc.)index
- index of this tty (e.g. to construct name like tty12)
ldisc_sem
- protects line discipline changes (ldisc) – lock tty not pty
ldisc
- the current line discipline for this tty (n_tty by default)
atomic_write_lock
- protects against concurrent writers, i.e. locks write_cnt, write_buf and similar
legacy_mutex
- leftover from history (BKL -> BTM -> legacy_mutex), protecting several operations on this tty
throttle_mutex
- protects against concurrent tty_throttle_safe() and tty_unthrottle_safe() (but not tty_unthrottle())
termios_rwsem
- protects termios and termios_locked
winsize_mutex
- protects winsize
termios
- termios for the current tty, copied from/to driver.termios
termios_locked
- locked termios (by
TIOCGLCKTRMIOS
andTIOCSLCKTRMIOS
ioctls) name
- name of the tty constructed by
tty_line_name()
(e.g. ttyS3) flags
- bitwise OR of
TTY_THROTTLED
,TTY_IO_ERROR
, … count
- count of open processes, reaching zero cancels all the work for this tty and drops a kref too (but does not free this tty)
winsize
- size of the terminal “window” (cf. winsize_mutex)
flow
- flow settings grouped together, see also flow.unused
flow.lock
- lock for flow members
flow.stopped
- tty stopped/started by
stop_tty()
/start_tty()
flow.tco_stopped
- tty stopped/started by
TCOOFF
/TCOON
ioctls (it has precedence over flow.stopped) flow.unused
- alignment for Alpha, so that no members other than flow.* are modified by the same 64b word store. The flow’s __aligned is there for the very same reason.
ctrl
- control settings grouped together, see also ctrl.unused
ctrl.lock
- lock for ctrl members
ctrl.pgrp
- process group of this tty (setpgrp(2))
ctrl.session
- session of this tty (setsid(2)). Writes are protected by both ctrl.lock and legacy_mutex, readers must use at least one of them.
ctrl.pktstatus
- packet mode status (bitwise OR of
TIOCPKT_
constants) ctrl.packet
- packet mode enabled
ctrl.unused
- alignment for Alpha, see flow.unused for explanation
hw_stopped
- not controlled by the tty layer, under driver’s control for CTS handling
receive_room
- bytes permitted to feed to ldisc without any being lost
flow_change
- controls behavior of throttling, see tty_throttle_safe() and tty_unthrottle_safe()
link
- link to another pty (master -> slave and vice versa)
fasync
- state for
O_ASYNC
(forSIGIO
); managed by fasync_helper() write_wait
- concurrent writers are waiting in this queue until they are allowed to write
read_wait
- readers wait for data in this queue
hangup_work
- normally a work to perform a hangup (do_tty_hangup()); while
freeing the tty, (re)used to
release_one_tty()
disc_data
- pointer to ldisc’s private data (e.g. to
struct n_tty_data
) driver_data
- pointer to driver’s private data (e.g.
struct uart_state
) files_lock
- protects tty_files list
tty_files
- list of (re)openers of this tty (i.e. linked
struct tty_file_private
) closing
- when set during close, n_tty processes only START & STOP chars
write_buf
- temporary buffer used during
tty_write()
to copy user data to write_cnt
- count of bytes written in
tty_write()
to write_buf SAK_work
- if the tty has a pending do_SAK, it is queued here
port
- persistent storage for this device (i.e.
struct tty_port
)
Description
All of the state associated with a tty while the tty is open. Persistent
storage for tty devices is referenced here as port and is documented in
struct tty_port
.