NAME
tels, telm — STREAMS Telnet slave (pseudo-terminal) driver, STREAMS Telnet master driver (used by telnetd only), respectively
SYNOPSIS
#include <sys/termios.h>
#include <sys/strtio.h>
int open("/dev/pts/
tN
", O_RDWR);
DESCRIPTION
A Telnet pseudo-terminal consists of a tightly-coupled pair of character
devices, called the master device and slave device. The master and
slave device drivers work together to provide a Telnet connection on the
server side where
the master provides a connection to
telnetd
and
the slave provides a terminal device special file access for the Telnet
application processes, as depicted below:
--------------------------
| Pseudo terminal functions|
Application <--> |--------------------------| <--> telnetd
Processes | Slave | Master |
| (tels) | (telm) |
--------------------------
The slave driver,
tels
with
ptem
(STREAMS pty emulation module)
and
ldterm
(STREAMS line discipline module)
pushed on top (not shown for simplicity), provides a terminal interface
as described in
termio(7).
Whereas devices that provide the terminal interface described in
termio(7)
have a hardware device behind them; in contrast, the slave device has
telnetd
manipulating it through the master side of the Telnet pseudo terminal.
There are no nodes in
the file system for each individual master device.
Rather, the master driver is set up as a STREAMS
clone(7)
driver with its major device number set to the major for the clone driver
and its minor device number set to the major for the
telm
driver. The master driver is opened by telnetd using the
open(2)
system call with
/dev/telnetm
as the device file parameter. The clone open finds the next available minor
number for the master device. The master device is available only if it
and its corresponding slave device are not already opened.
In order to use the STREAMS Telnet subsystem, a node for the
master driver
/dev/telnetm
and
N
number of Telnet slave devices must be installed.
The number of slave devices is set by a kernel
tunable parameter called
nstrtel.
This can be
modified using SAM; its default and minimum value
is 60. The value of
nstrtel
is the upper limit
of the number of telnet sessions that can be opened.
Multiple opens
are allowed on the Telnet slave device.
The master and slave drivers pass all STREAMS messages to their adjacent
drivers.
When the connection is closed from the Telnet client side, an
M_HANGUP
message is sent
to the corresponding slave device which will render that slave device
unusable. The process on the slave side gets the errno
ENXIO
when attempting a
write(2)
system call to the slave device file but it will be able to
read any data remaining in the slave stream. Finally, when all the
data has been read, the
read(2)
system call will return 0, indicating that the slave can no longer be used.
AUTHOR
tels()
and
telm()
were developed by HP.
FILES
- /dev/telnetm
Streams Telnet master clone device
- /dev/pts/tN
Streams slave devices where
N
is the minor number of the slave device and 0 <
N
<
nstrtel.
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