TTY(4) | Device Drivers Manual | TTY(4) |
tty
— general
terminal interface
#include
<sys/ioctl.h>
This section describes the interface to the terminal drivers in the system.
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.
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).
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
and would be called on the terminal associated with file descriptor zero by the following code fragment:
ioctl(0, TIOCSLINED, "termios");
TIOCSLINED
char name[32]TIOCGLINED
char name[32]TIOCSBRK
voidTIOCCBRK
voidTIOCSDTR
voidTIOCCDTR
voidTIOCGPGRP
int *tpgrpTIOCSPGRP
int *tpgrpTIOCGETA
struct termios *termTIOCSETA
struct termios *termTCSANOW
option.TIOCSETAW
struct termios *termTCSADRAIN
option.TIOCSETAF
struct termios *termTCSAFLUSH
option.TIOCOUTQ
int *numTIOCSTI
char *cpTIOCNOTTY
voidTIOCNOTTY
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
voidTIOCSTART
voidTIOCSCTTY
voidTIOCDRAIN
voidTIOCEXCL
voidTIOCNXCL
voidTIOCFLUSH
int *whatFREAD
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<sys/ioctl.h>
.TIOCSWINSZ
struct winsize *wsTIOCGQSIZE
int *qsizeTIOCSQSIZE
int *qsize1024
and 65536
and input
values are converted to a power of two. All pending input and output is
dropped.TIOCCONS
int *onTIOCMSET
int *stateThis call sets the terminal modem state to that represented by state. Not all terminals may support this.
TIOCMGET
int *stateTIOCMBIS
int *stateTIOCMBIC
int *stateTIOCSFLAGS
int *stateCLOCAL
flag on open.CRTSCTS
flag on open.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 *stateTwo ioctls are maintained for backwards compatibility. They provide methods to get and set the current line discipline, but are not extensible.
TIOCSETD
int *ldisc<sys/ttycom.h>
and are:
TIOCGETD
int *ldiscstty(1), ioctl(2), tcgetattr(3), tcsetattr(3), ttyaction(3), pty(4), termios(4), ttys(5), getty(8), linedisc(9)
A console typewriter device /dev/tty and asynchronous communication interfaces /dev/tty[0-5] first appeared in Version 1 AT&T UNIX. Separate dial-out device files were implemented in SunOS 4. They were cloned by Charles M. Hannum for NetBSD 1.4.
September 7, 2019 | NetBSD 10.99 |