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ldterm(4m)
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 in‐
terface. 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 multibyte 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 inter‐
rupt signal is generated or the message is treated as if it
were an M_DATA message containing a single ASCII NUL charac‐
ter 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 ar‐
rival 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 per‐
form 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 sig‐
nal 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_DE‐
LAY 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 func‐
tional negotiation to determine where the termio(4I) pro‐
cessing is to be done. If the command field of the iocblk
structure (ioc_cmd) is set to MC_NO_CANON, the input canon‐
ical 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 pro‐
cessing is enabled. If the command is MC_PART_CANON, then
an M_DATA message containing a termios structure is ex‐
pected 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 ig‐
nored. 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 re‐
turned 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 oth‐
ers 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 acknowledgment 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 euciocdata 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 disci‐
pline. 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
HISTORY
Prior to Oracle Solaris 11.4, programs needed to push the ldterm module
onto the subsidiary side of a pseudo-terminal pair if open() was called
from a program not linked for XPG4 or later standards. If called from a
program linked with values-xpg4.o or values-xpg6.o, then open() would
automatically push ptem, ldterm, and ttcompat modules onto the sub‐
sidiary side, and callers pushing them as well would encounter unex‐
pected behavior.
Oracle Solaris 11.4 added these modules to /etc/iu.system.ap for
pts(4D) so that they are automatically pushed by autopush(8) regardless
of how the program is linked, and ensured that only one copy of each is
pushed onto each stream.
Oracle Solaris 11.4 19 Jun 2024 ldterm(4M)