NAME
tty —
general terminal interface
SYNOPSIS
#include <sys/ioctl.h>
DESCRIPTION
This section describes the interface to the terminal drivers in the system.
Terminal Special Files
Each hardware terminal port on the system usually has two terminal special
device files associated with it in the directory
/dev/ (for
example,
/dev/tty03 and
/dev/dty03).
The
/dev/ttyXX special file is used for dial-in modems and
terminals. When a user logs into the system on one of these hardware terminal
ports, the system has already opened the associated device and prepared the
line for normal interactive use (see
getty(8)).
The
/dev/dtyXX special file is a SunOS-compatible dial-out
device. Unlike the dial-in device, opening the dial-out device never blocks.
If the corresponding dial-in device is already opened (not blocked in the open
waiting for carrier), then the dial-out open will fail immediately; otherwise
it will succeed immediately. While the dial-out device is open, the dial-in
device may not be opened. If the dial-in open is blocking, it will wait until
the dial-out device is closed (and carrier is detected); otherwise it will
fail immediately.
There is also a special case of a terminal file that connects not to a hardware
terminal port, but to another program on the other side. These special
terminal devices are called
ptys (pseudo terminals) and
provide the mechanism necessary to give users the same interface to the system
when logging in over a network (using
rlogin(1), or
telnet(1) for example.) Even in
these cases the details of how the terminal file was opened and set up is
already handled by special software in the system. Thus, users do not normally
need to worry about the details of how these lines are opened or used. Also,
these lines are often used for dialing out of a system (through an out-calling
modem), but again the system provides programs that hide the details of
accessing these terminal special files (see
tip(1)).
When an interactive user logs in, the system prepares the line to behave in a
certain way (called a
line discipline), the particular
details of which is described in
stty(1) at the command level, and
in
termios(4) at the
programming level. A user may be concerned with changing settings associated
with his particular login terminal and should refer to the preceding man pages
for the common cases. The remainder of this man page is concerned with
describing details of using and controlling terminal devices at a low level,
such as that possibly required by a program wishing to provide features
similar to those provided by the system.
Line disciplines
A terminal file is used like any other file in the system in that it can be
opened, read, and written to using standard system calls. For each existing
terminal file, there is a software processing module called a
line discipline associated with it. The
line
discipline essentially glues the low level device driver code with the
high level generic interface routines (such as
read(2) and
write(2)), and is responsible for
implementing the semantics associated with the device. When a terminal file is
first opened by a program, the default
line discipline
called the
termios
line discipline is associated with
the file. This is the primary line discipline that is used in most cases and
provides the semantics that users normally associate with a terminal. When the
termios
line discipline is in effect, the terminal
file behaves and is operated according to the rules described in
termios(4). Please refer to
that man page for a full description of the terminal semantics. The operations
described here generally represent features common across all
line disciplines, however some of these calls may not make
sense in conjunction with a line discipline other than
termios
, and some may not be supported by the
underlying hardware (or lack thereof, as in the case of ptys).
Terminal File Operations
All of the following operations are invoked using the
ioctl(2) system call. Refer to
that man page for a description of the
request and
argp parameters. In addition to the ioctl
requests defined here, the specific line discipline in
effect will define other
requests specific to it (actually
termios(4) defines them as
function calls, not ioctl
requests.) The following section
lists the available ioctl requests. The name of the request, a description of
its purpose, and the typed
argp parameter (if any) are
listed. For example, the first entry says
TIOCSLINED char name[32]
and would be called on the terminal associated with file descriptor zero by the
following code fragment:
ioctl(0, TIOCSLINED, "termios");
Terminal File Request
Descriptions
-
-
TIOCSLINED
char name[32]
- Change to the new line discipline called
name.
-
-
TIOCGLINED
char name[32]
- Return the current line discipline in the string pointed to
by name.
-
-
TIOCSBRK
void
- Set the terminal hardware into BREAK condition.
-
-
TIOCCBRK
void
- Clear the terminal hardware BREAK condition.
-
-
TIOCSDTR
void
- Assert data terminal ready (DTR).
-
-
TIOCCDTR
void
- Clear data terminal ready (DTR).
-
-
TIOCGPGRP
int *tpgrp
- Return the current process group the terminal is associated
with in the integer pointed to by tpgrp. This is the
underlying call that implements the
tcgetpgrp(3) call.
-
-
TIOCSPGRP
int *tpgrp
- Associate the terminal with the process group (as an
integer) pointed to by tpgrp. This is the underlying
call that implements the
tcsetpgrp(3) call.
-
-
TIOCGETA
struct termios *term
- Place the current value of the termios state associated
with the device in the termios structure pointed to by
term. This is the underlying call that implements
the tcgetattr(3)
call.
-
-
TIOCSETA
struct termios *term
- Set the termios state associated with the device
immediately. This is the underlying call that implements the
tcsetattr(3) call with
the
TCSANOW
option.
-
-
TIOCSETAW
struct termios *term
- First wait for any output to complete, then set the termios
state associated with the device. This is the underlying call that
implements the
tcsetattr(3) call with
the
TCSADRAIN
option.
-
-
TIOCSETAF
struct termios *term
- First wait for any output to complete, clear any pending
input, then set the termios state associated with the device. This is the
underlying call that implements the
tcsetattr(3) call with
the
TCSAFLUSH
option.
-
-
TIOCOUTQ
int *num
- Place the current number of characters in the output queue
in the integer pointed to by num.
-
-
TIOCSTI
char *cp
- Simulate typed input. Pretend as if the terminal received
the character pointed to by cp.
-
-
TIOCNOTTY
void
- This call is obsolete but left for compatibility. In the
past, when a process that didn't have a controlling terminal (see
The Controlling Terminal in
termios(4)) first opened a
terminal device, it acquired that terminal as its controlling terminal.
For some programs this was a hazard as they didn't want a controlling
terminal in the first place, and this provided a mechanism to disassociate
the controlling terminal from the calling process. It
must be called by opening the file
/dev/tty and calling
TIOCNOTTY
on that file descriptor.
The current system does not allocate a controlling terminal to a process on
an open() call: there is a specific ioctl called
TIOCSCTTY
to make a terminal the controlling
terminal. In addition, a program can fork() and call the
setsid() system call which will place the process into
its own session - which has the effect of disassociating it from the
controlling terminal. This is the new and preferred method for programs to
lose their controlling terminal.
-
-
TIOCSTOP
void
- Stop output on the terminal (like typing ^S at the
keyboard).
-
-
TIOCSTART
void
- Start output on the terminal (like typing ^Q at the
keyboard).
-
-
TIOCSCTTY
void
- Make the terminal the controlling terminal for the process
(the process must not currently have a controlling terminal).
-
-
TIOCDRAIN
void
- Wait until all output is drained.
-
-
TIOCEXCL
void
- Set exclusive use on the terminal. No further opens are
permitted except by root. Of course, this means that programs that are run
by root (or setuid) will not obey the exclusive setting - which limits the
usefulness of this feature.
-
-
TIOCNXCL
void
- Clear exclusive use of the terminal. Further opens are
permitted.
-
-
TIOCFLUSH
int *what
- If the value of the int pointed to by
what contains the
FREAD
bit
as defined in <sys/fcntl.h>,
then all characters in the input queue are cleared. If it contains the
FWRITE
bit, then all characters in the output
queue are cleared. If the value of the integer is zero, then it behaves as
if both the FREAD
and
FWRITE
bits were set (i.e. clears both
queues).
-
-
TIOCGWINSZ
struct winsize *ws
- Put the window size information associated with the
terminal in the winsize structure pointed to by
ws. The window size structure contains the number of
rows and columns (and pixels if appropriate) of the devices attached to
the terminal. It is set by user software and is the means by which most
full-screen oriented programs determine the screen size. The
winsize structure is defined in
<sys/ioctl.h>.
-
-
TIOCSWINSZ
struct winsize *ws
- Set the window size associated with the terminal to be the
value in the winsize structure pointed to by
ws (see above).
-
-
TIOCGQSIZE
int *qsize
- Get the current size of the tty input and output
queues.
-
-
TIOCSQSIZE
int *qsize
- Set the size of the tty input and output queues. Valid
sizes are between
1024
and
65536
and input values are converted to a power of
two. All pending input and output is dropped.
-
-
TIOCCONS
int *on
- If on points to a non-zero integer,
redirect kernel console output (kernel printf's) to this terminal. If
on points to a zero integer, redirect kernel console
output back to the normal console. This is usually used on workstations to
redirect kernel messages to a particular window.
-
-
TIOCMSET
int *state
- The integer pointed to by state
contains bits that correspond to modem state. Following is a list of
defined variables and the modem state they represent:
- TIOCM_LE
- Line Enable.
- TIOCM_DTR
- Data Terminal Ready.
- TIOCM_RTS
- Request To Send.
- TIOCM_ST
- Secondary Transmit.
- TIOCM_SR
- Secondary Receive.
- TIOCM_CTS
- Clear To Send.
- TIOCM_CAR
- Carrier Detect.
- TIOCM_CD
- Carrier Detect (synonym).
- TIOCM_RNG
- Ring Indication.
- TIOCM_RI
- Ring Indication (synonym).
- TIOCM_DSR
- Data Set Ready.
This call sets the terminal modem state to that represented by
state. Not all terminals may support this.
-
-
TIOCMGET
int *state
- Return the current state of the terminal modem lines as
represented above in the integer pointed to by
state.
-
-
TIOCMBIS
int *state
- The bits in the integer pointed to by
state represent modem state as described above,
however the state is OR-ed in with the current state.
-
-
TIOCMBIC
int *state
- The bits in the integer pointed to by
state represent modem state as described above,
however each bit which is on in state is cleared in
the terminal.
-
-
TIOCSFLAGS
int *state
- The bits in the integer pointed to by
state contain bits that correspond to serial port
state. Following is a list of defined flag values and the serial port
state they represent:
- TIOCFLAG_SOFTCAR
- Ignore hardware carrier.
- TIOCFLAG_CLOCAL
- Set the
termios(4)
CLOCAL
flag on open.
- TIOCFLAG_CRTSCTS
- Set the
termios(4)
CRTSCTS
flag on open.
- TIOCFLAG_MDMBUF
- Set the
termios(4)
MDMBUF
flag on open.
This call sets the serial port state to that represented by
state. Not all serial ports may support this.
-
-
TIOCGFLAGS
int *state
- Return the current state of the serial port as represented
above in the integer pointed to by state.
COMPATIBILITY
Two ioctls are maintained for backwards compatibility. They provide methods to
get and set the current line discipline, but are not extensible.
-
-
TIOCSETD
int *ldisc
- Change to the new line discipline pointed to by
ldisc. The old list of available line disciplines
are listed in <sys/ttycom.h> and
are:
- TTYDISC
- Termios interactive line discipline.
- TABLDISC
- Tablet line discipline.
- SLIPDISC
- Serial IP line discipline.
- PPPDISC
- Point to Point Protocol line discipline.
- STRIPDISC
- Starmode Radio IP line discipline.
-
-
TIOCGETD
int *ldisc
- Return the current line discipline in the integer pointed
to by ldisc.
SEE ALSO
stty(1),
ioctl(2),
tcgetattr(3),
tcsetattr(3),
ttyaction(3),
pty(4),
termios(4),
ttys(5),
getty(8),
linedisc(9)
HISTORY
Separate dial-out device files were implemented in SunOS 4. They were cloned by
Charles M. Hannum for
NetBSD
1.4.