ldterm(7) Miscellaneous Information Manual ldterm(7)
NAME
ldterm - standard STREAMS terminal line discipline module
SYNOPSIS
DESCRIPTION
is a STREAMS module that supplies the line discipline for streams-based terminal or pseudo-terminal device drivers. This module provides
most of the functions of the general terminal interface described in termio(7). However, it does not perform the low-level device control
functions specified by the word defined by the POSIX structure or the System V structure (defined in and respectively). Also, some opera-
tions require the cooperation of the modules and drivers pushed below the module in a tty or pty (slave) stream. This man page only covers
specific interface here and refers to the readers to termio(7) for the detail terminal interface.
Internally, the module uses the Extended UNIX Code (EUC) character encoding scheme. This encoding scheme enables the module to process
multibyte characters as well as simple 8-bit characters. It correctly handles backspacing, word erasing, and tab expansion for multibyte
EUC characters.
The module provides standard terminal operation consistent with the behavior specified by POSIX 1003.1 and System V Interface Definition
(SVID) Third Edition. It also provides compatibility with the behavior of the BSD 4.3 line discipline. Notice that on other STREAMS sys-
tems, the BSD 4.3 compatibility feature is usually provided by a separate STREAMS module called Hence, applications on HP-UX need not push
on top of to get BSD 4.3 compatibility. In fact, the module is not provided on the HP-UX system at all.
The module normally sits above either a STREAMS tty driver or a STREAMS pty slave driver. The user issues an ioctl(2) system call to push
onto the stream once the STREAMS tty or STREAMS pty slave device is opened.
STREAMS Messages
The module processes various types of STREAMS messages. The line discipline will act on any of the following message types. Any others
that the module receives, however, are passed onto the next module on the stream.
Read-side Behavior
processes the following STREAMS messages on its input stream:
If is set, the read put routine flushes the read queue, discards characters in the input message buffers, and discards any partially
buffered multibyte EUC characters. Then, it forwards the message upstream.
The read put routine processes the message according to POSIX rules for
processing events, parity errors, and framing errors and signal generation (see termio(7) for detail). If there is no data in
the message, the message is assumed to represent an input event, which is represented by a framing error with a character value
of 0 (zero). If there is data in the message, the data value is an integer that indicates the occurrence of an input event, or a
character received with a parity or framing error. The low-order 8 bits of the data value is the byte that was read. If the
flag is set in the higher-order bits of this integer, then a parity error was detected. If the flag is set in the higher-order
bits of this integer, a framing error was detected.
After reading the data value, the read put routine discards the message.
The read put routine processes the message according to the
POSIX 1003.1 specification, using multibyte processing for backspacing, word erasing, and tab expansion as appropriate.
It generates echo characters and places them in the output buffer to be sent downstream to the write queue. While processing
incoming data, it scans for and characters and sends messages downstream to the write queue, if needed.
If the total number of buffered input characters is more than the high-water mark and is set, the read put routine sends an mes-
sage downstream. When the queue reduces its backlog below the low water mark, it sends an message downstream.
If the number of buffered input characters reaches and the flag is set, the read put routine discards new input characters and
sends a character (downstream. If is not set, it flushes the input queue.
If the flag is set, the read put routine sends messages upstream when the appropriate signal characters are encountered. Then it
discards the characters.
If a character matching is encountered, and the flag is set, the read put routine sends an message upstream to flush all write
queues. The message is reflected by the stream head and sent downstream through all the write queues.
If the character signifies the logical termination of input, the read put routine sends the currently buffered characters
upstream to the stream head.
Logical termination of input depends on the state of the flag. If is set, the module is in canonical input mode. In that case,
the read put routine logically terminates input at the end of a line of input. Canonical line termination characters are and If
is clear, the discipline module is in noncanonical or raw input mode. In that case, the read put routine terminates input when
at least bytes are present in the input message buffer or the timer specified by expires (see termio(7) for more details).
If the message acknowledges the POSIX
command, the read put routine copies the and speeds information, which is sent by the console driver downstream, from the message
into the internal POSIX structure. Then it copies the internal POSIX structure into the message.
If the message acknowledges one of the POSIX set commands (i.e. and the read put routine copies all of the data from the message
into the internal POSIX structure.
After this processing is done, the read put routine determines if the I/O control command was originally a BSD 4.3 or System V
I/O control command that was converted to a POSIX command by the write service routine. If so, it restores the original data so
that the message acknowledges the original I/O control command. Then it forwards the message upstream.
This message was sent by the driver to make special requests to
The structure of messages is the same as that of messages. The message block points to a message buffer containing an data
structure (defined in The member of this structure contains a command, just as it does in an message. The member of the message
block contains a pointer to an message block, which contains data associated with the message.
The read put routine processes messages containing the following commands:
Turn off input processing normally performed on upstream
messages. This is for the use of modules or drivers that perform their own input processing such as pseudo-terminal (see
ptm(7) and pts(7)) in mode connected to a program that performs the input processing.
Turn on input processing normally performed on upstream
messages. This message is sent when the driver want to exit the mode.
Write-side Behavior
processes the following STREAMS messages on its output stream. Messages not listed here are simply forwarded downstream.
The write put routine flushes the write queue and discards any
buffered output data. Then, it forwards the message downstream.
The write service routine processes the data according
to the POSIX 1003.1 specification output flags. It sends the processed characters downstream to the driver when the output queue
fills up and all of the data is processed.
The write put routine validates the format of the
message and checks for known commands. If the message format is invalid, it turns the message into an message, and returns the
message upstream. If the I/O control command is not recognized, it forwards the message downstream for processing by other mod-
ules.
The write put routine determines if the command is one that must be processed in the proper sequence relative to messages. If
so, it queues the message to the write queue for later processing by the write service routine. Commands that require processing
in sequence are:
Otherwise, the module's write put routine processes the command immediately. Detailed descriptions of the preceding commands are
provided in the subsection, below.
This message is sent by the stream head to notify downstream modules when an
application has issued a read request and there is not enough data queued at the stream head to satisfy the request. The is sent
downstream normally when is operating in non-canonical input mode. If is positive, the write put routine starts an input timer.
When the timer expires, it sends all buffered input upstream. Then, it forwards the message downstream.
ioctl Commands
The module acts on two categories of commands:
o Primary terminal I/O control commands
o BSD 4.3 compatibility terminal I/O control commands
Detail descriptions on how to use these can be found on the termio(7) man page. NOTE: the documented on termio(7) are currently not sup-
ported on
Primary Terminal I/O Control Commands
The module acts on the following primary terminal I/O commands:
When the module receives any of these commands in an message, it forwards them downstream. When it receives the message in the read
queue, it copies the POSIX information from the message into the internal POSIX structure and forwards the message upstream. If
a mode change requires options at the stream head to be changed, an message is sent upstream. If the flag is turned on or off,
the read mode at the stream head is changed to message-nondiscard with read notification on or byte-stream mode with read notifi-
cation off respectively. If the flag is turned on or off, the tostop mode at the stream head is turned on or off respectively.
The module forwards the message downstream. When it receives the message in the read queue, it copies the flags and speeds from the
message into the internal POSIX structure. Then, it copies the entire structure into the message and forwards the message
upstream.
These commands set the old System V
information. The module converts the message to a POSIX message, then forwards the message with a corresponding POSIX command
(i.e. The original I/O control command and message are stored for use on
This command get the old System V
information. The module converts the message to a POSIX message, then forwards the message with the command. The original I/O
control command and message are stored to be used on When it receives the matching message, the module processes it as for a com-
mand, then converts the POSIX information into the System V information and replies.
The module forwards this command downstream to be handled by the driver so that the driver has a chance to drain the data before
sending an message upstream.
This command controls the behavior of input/output flow control.
If the argument is 0 and output is not already stopped, an message is sent downstream. If the argument is 1 and the output is
stopped, an message is sent downstream. If the argument is 2 and input is not already stopped, an message is sent downstream.
If the argument is 3 and input is stopped, an message is sent downstream.
This command flush the input or/and output streams. If the argument is 0, an
message with a flag byte of is sent downstream. This message will be reflected back upstream by the driver to flush the entire
input stream. If the argument is 1, an message with a flag byte of is sent upstream. This message will be reflected downstream
by the stream head to flush the entire output stream.
This command sets the window size variables.
The argument of this command takes a pointer to a structure. The module does not use the window size variable, but maintains it
here for any needed replies to commands. The module forwards the message downstream.
When the module receives this command, it returns the window size variable that was set by the last command. The argument of this command
takes a pointer to a structure.
This command sets the character widths and screen widths for the EUC
character sets. The argument of this command takes a pointer to an structure which contains the information for setting the
character widths and screen widths of the EUC character sets. After processing the command, forwards this message downstream to
the next module.
This command returns the character widths and screen widths for the EUC
character sets. This command takes a pointer to an structure via which the EUC character widths and screen widths information
will be returned.
This command put
to the so called mode which enable to recognize the HP15_SJIS, HP15_BIG5, HP15_CCDC, and HP15_GB character sets and process them
in such a way that they behave like EUC characters. The argument for this command takes a pointer to an integer value which
specify on of the above-mentioned four supported HP15 character sets. If the argument is set to HP15_ASCII, then will switch
back to normal ASCII processing. is mutually exclusive with
This command returns the current HP15 character that has been set via the
command. This command takes a pointer to an integer via which the result is returned. If no previous has been issued, then it
will return HP15_ASCII.
BSD 4.3 Compatible Terminal I/O Commands
The module acts on the following I/O commands, which are compatible with the BSD I/O environment:
Set `exclusive-use' mode. No further opens are permitted until the
file has been closed.
Turn off `exclusive-use' mode.
The module does nothing but reply to this command. In a BSD system, the command is used to set the current line discipline type. It
does not have much meaning in a STREAMS environment, because line discipline modules are changed by popping the current module
from the stream and pushing a different one onto the stream.
In a BSD system, this command is used to get the current line discipline
type. The command does not have much meaning in a STREAMS environment. The module replies with a value of 2 for binary compati-
bility, since supports job control.
This command flush the input or/and output streams similar to that of the
command. The argument is a pointer to an variable. If its value is zero, both the input and output streams are flushed by send-
ing the appropriate messages upstream and downstream. Otherwise, the value of the is treated as the logical of the and flags
defined by If the flag is set, the input stream is flushed. If the flag is set, the output stream is flushed. Then, acknowl-
edges the message with
This command takes a pointer to an integer and returns the number of characters
buffered up in the output buffer.
This command sets the POSIX
flag to indicate that the terminal line should be disconnected when the last file descriptor associated with that line is closed.
The module converts the command into a compatible POSIX I/O control command by sending an message containing the command with
current settings downstream.
The command restarts output. If the terminal was stopped, the
module sends an message downstream.
This command stops output. The
module sends an message downstream.
This command sets the break condition on a line.
The module sends an message containing a value of 1 as data to the driver, then replies with
This command clears the break condition on a line.
The module sends an message containing a value of 0 (zero) as data to the driver, then replies with
These commands set the
information, defined in The argument is a pointer to an structure. The module converts the message to a POSIX message. Then, it
forwards the POSIX message with a corresponding POSIX command The original I/O control command and message are stored for use on
This command
returns the information based on the interpretation of the current content of the POSIX structure maintained in The argument is a
pointer to an structure via where the information is returned.
This command sets the
information, defined in The argument is a pointer to an structure. The module converts the message to a POSIX message. Then, it
forwards the POSIX message with a corresponding POSIX command The original I/O control command and message are stored for use on
This command
returns the information based on the interpretation of the current content of the POSIX structure maintained in The argument is a
pointer to an structure via where the information is returned.
This command sets the
information defined in The module converts the message to a POSIX message. Then, it forwards the POSIX message with a corre-
sponding POSIX command The original I/O control command and message are stored for use on
The module returns the information based on the interpretation of the current content of the POSIX structure maintained in
These commands set the BSD 4.3 flags information, defined in
For and the argument is a pointer to an whose value is a mask containing flags to be set/clear. For the argument is a pointer to
an whose value is a new set of flags to be set. The module converts the message to a POSIX then forwards the POSIX message with
a corresponding POSIX command It stores the original I/O control command and message to be used on
The module returns the BSD 4.3 flags information based on the interpretation of the current content of the POSIX structure maintained
in
This command takes an argument of a pointer to a character and pretends
that the character was typed on the terminal. The user must either have the privilege or have read permission on the controlling
terminal against which the ioctl is issued. See privileges(5) for more information about privileged access on systems that sup-
port fine-grained privileges.
This command takes an argument of a pointer to an integer and returns the
number of immediately readable characters.
AUTHOR
was developed by HP and OSF.
SEE ALSO
ioctl(2), privileges(5), ptem(7), ptm(7), pts(7), streamio(7), termio(7).
ldterm(7)