tty - general terminal interface
#include <sys/ioctl.h>
This section describes the interface to the terminal drivers
in the system.
Terminal Special Files [Toc] [Back]
Each hardware terminal port on the system usually has a terminal special
device file associated with it in the directory /dev/ (for
example,
/dev/tty03). 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)).
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 and provide the mechanism
necessary to
give users the same interface to the system when logging in
over a network
(using ssh(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.
For hardware terminal ports, dial-out is supported through
matching device
nodes called calling units. For instance, the terminal
called
/dev/tty03 would have a matching calling unit called
/dev/cua03. These
two devices are normally differentiated by creating the
calling unit device
node with a minor number 128 greater than the dial-in
device node.
Whereas the dial-in device (the tty) normally requires a
hardware signal
to indicate to the system that it is active, the dial-out
device (the
cua) does not, and hence can communicate unimpeded with a
device such as
a modem. This means that a process like getty(8) will wait
on a dial-in
device until a connection is established. Meanwhile, a dial-out connection
can be established on the dial-out device (for the very
same hardware
terminal port) without disturbing anything else on the
system. The
getty(8) process does not even notice that anything is happening on the
terminal port. If a connecting call comes in after the dial-out connection
has finished, the getty(8) process will deal with it
properly, without
having noticed the intervening dial-out action. For
more information
on dial-out, see tip(1), and cu(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 are 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 [Toc] [Back]
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, although 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 [Toc] [Back]
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
TIOCSETD int *ldisc
and would be called on the terminal associated with file descriptor zero
by the following code fragment:
int ldisc;
ldisc = TTYDISC;
ioctl(0, TIOCSETD, &ldisc);
Terminal File Request Descriptions [Toc] [Back]
TIOCSETD int *ldisc
Change to the new line discipline pointed to by
ldisc. The
available line disciplines are listed in
<sys/ttycom.h> and
currently 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.
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 termios(4)
tcgetattr() 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 termios(4) tcsetattr() 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
termios(4)
tcgetattr() call.
TIOCSETA struct termios *term
Set the termios state associated with the device
immediately.
This is the underlying call that implements the
termios(4)
tcsetattr() 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 termios(4) tcsetattr()
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
termios(4)
tcsetattr() 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 fullscreen
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).
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
variables and the serial port state they
represent:
TIOCFLAG_SOFTCAR Ignore hardware carrier.
TIOCFLAG_CLOCAL Set clocal on open.
TIOCFLAG_CRTSCTS Set crtscts on open.
TIOCFLAG_MDMBUF Set mdmbuf 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.
/dev/tty controlling terminal, if any
stty(1), tty(1), ioctl(2), pty(4), termios(4), ttys(5), getty(8)
The cua support is inspired by similar support in SunOS.
OpenBSD 3.6 August 14, 1992
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