LDTERM(4M) STREAMS Modules LDTERM(4M)

NAME

ldterm - standard STREAMS terminal line discipline module

SYNOPSIS

#include <sys/stream.h>


#include <sys/termios.h>


int ioctl(fd,I_PUSH,"ldterm");

DESCRIPTION

The ldterm STREAMS module provides most of the termio(4I) terminal
interface. The vis module does not perform the low-level device control
functions specified by flags in the c_cflag word of the termio/termios
structure, or by the IGNBRK, IGNPAR, PARMRK, or INPCK flags in the
c_iflag word of the termio/termios structure. Those functions must be
performed by the driver or by modules pushed below the ldterm module.
The ldterm module performs all other termio/termios functions, though
some may require the cooperation of the driver or modules pushed below
ldterm and may not be performed in some cases. These include the IXOFF
flag in the c_iflag word and the delays specified in the c_oflag word.


The ldterm module also handles single and multi-byte characters from
various codesets including both Extended Unix Code (EUC) and non-EUC
codesets.


The remainder of this section describes the processing of various STREAMS
messages on the read- and write-side.

Read-side Behavior
Various types of STREAMS messages are processed as follows:

M_BREAK
Depending on the state of the BRKINT flag, either an
interrupt signal is generated or the message is treated as if
it were an M_DATA message containing a single ASCII NUL
character when this message is received.


M_DATA
This message is normally processed using the standard termio
input processing. If the ICANON flag is set, a single input
record (``line'') is accumulated in an internal buffer and
sent upstream when a line-terminating character is received.
If the ICANON flag is not set, other input processing is
performed and the processed data are passed upstream.

If output is to be stopped or started as a result of the
arrival of characters (usually CNTRL-Q and CNTRL-S), M_STOP
and M_START messages are sent downstream. If the IXOFF flag
is set and input is to be stopped or started as a result of
flow-control considerations, M_STOPI and M_STARTI messages
are sent downstream.

M_DATA messages are sent downstream, as necessary, to perform
echoing.

If a signal is to be generated, an M_FLUSH message with a
flag byte of FLUSHR is placed on the read queue. If the
signal is also to flush output, an M_FLUSH message with a
flag byte of FLUSHW is sent downstream.


All other messages are passed upstream unchanged.

Write-side Behavior
Various types of STREAMS messages are processed as follows:

M_FLUSH
The write queue of the module is flushed of all its data
messages and the message is passed downstream.


M_IOCTL
The function of this ioctl is performed and the message is
passed downstream in most cases. The TCFLSH and TCXONC
ioctls can be performed entirely in the ldterm module, so
the reply is sent upstream and the message is not passed
downstream.


M_DATA
If the OPOST flag is set, or both the XCASE and ICANON flags
are set, output processing is performed and the processed
message is passed downstream along with any M_DELAY messages
generated. Otherwise, the message is passed downstream
without change.


M_CTL
If the size of the data buffer associated with the message
is the size of struct iocblk, ldterm will perform functional
negotiation to determine where the termio(4I) processing is
to be done. If the command field of the iocblk structure
(ioc_cmd) is set to MC_NO_CANON, the input canonical
processing normally performed on M_DATA messages is disabled
and those messages are passed upstream unmodified. (This is
for the use of modules or drivers that perform their own
input processing, such as a pseudo-terminal in TIOCREMOTE
mode connected to a program that performs this processing).
If the command is MC_DO_CANON, all input processing is
enabled. If the command is MC_PART_CANON, then an M_DATA
message containing a termios structure is expected to be
attached to the original M_CTL message. The ldterm module
will examine the iflag, oflag, and lflag fields of the
termios structure and from that point on, will process only
those flags that have not been turned ON. If none of the
above commands are found, the message is ignored. In any
case, the message is passed upstream.


M_FLUSH
The read queue of the module is flushed of all its data
messages and all data in the record being accumulated are
also flushed. The message is passed upstream.


M_IOCACK
The data contained within the message, which is to be
returned to the process, are augmented if necessary, and the
message is passed upstream.


All other messages are passed downstream unchanged.

IOCTLS

The ldterm module processes the following TRANSPARENT ioctls. All others
are passed downstream.

TCGETS/TCGETA

The message is passed downstream. If an acknowledgment is seen, the
data provided by the driver and modules downstream are augmented and
the acknowledgement is passed upstream.


TCSETS/TCSETSW/TCSETSF/TCSETA/TCSETAW/TCSETAF

The parameters that control the behavior of the ldterm module are
changed. If a mode change requires options at the stream head to be
changed, an M_SETOPTS message is sent upstream. If the ICANON flag
is turned on or off, the read mode at the stream head is changed to
message-nondiscard or byte-stream mode, respectively. If the TOSTOP
flag is turned on or off, the tostop mode at the stream head is
turned on or off, respectively. In any case, ldterm passes the ioctl
on downstream for possible additional processing.


TCFLSH

If the argument is 0, an M_FLUSH message with a flag byte of FLUSHR
is sent downstream and placed on the read queue. If the argument is
1, the write queue is flushed of all its data messages and an M_FLUSH
message with a flag byte of FLUSHW is sent upstream and downstream.
If the argument is 2, the write queue is flushed of all its data
messages and an M_FLUSH message with a flag byte of FLUSHRW is sent
downstream and placed on the read queue.


TCXONC

If the argument is 0 and output is not already stopped, an M_STOP
message is sent downstream. If the argument is 1 and output is
stopped, an M_START message is sent downstream. If the argument is 2
and input is not already stopped, an M_STOPI message is sent
downstream. If the argument is 3 and input is stopped, an M_STARTI
message is sent downstream.


TCSBRK

The message is passed downstream, so the driver has a chance to drain
the data and then send an M_IOCACK message upstream.


EUC_WSET

This call takes a pointer to an eucioc structure, and uses it to set
the EUC line discipline's local definition for the code set widths to
be used for subsequent operations. Within the stream, the line
discipline may optionally notify other modules of this setting using
M_CTL messages. When this call is received and the eucioc structure
contains valid data, the line discipline changes into EUC handling
mode once the eucioc data is completely transferred to an internal
data structure.


EUC_WGET

This call takes a pointer to an eucioc structure, and returns in it
the EUC code set widths currently in use by the EUC line discipline.
If the current codeset of the line discipline is not an EUC one, the
result is meaningless.

SEE ALSO

termios(3C), console(4D), termio(4I)


STREAMS Programming Guide

June 20, 2021 LDTERM(4M)