ldterm(7) UNIX System V ldterm(7)
NAME
ldterm - standard STREAMS terminal line discipline module
DESCRIPTION
ldterm is a STREAMS module that provides most of the termio(7) terminal
interface. This module does not perform the low-level device control
functions specified by flags in the ccflag word of the termio/termios
structure or by the IGNBRK, IGNPAR, PARMRK, or INPCK flags in the ciflag
word of the termio/termios structure; those functions must be performed
by the driver or by modules pushed below the ldterm module. All other
termio/termios functions are performed by ldterm; some of them, however,
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
ciflag word and the delays specified in the coflag word.
ldterm also handles EUC and multi-byte characters.
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:
MBREAK
When this message is received, either an interrupt signal is
generated or the message is treated as if it were an MDATA message
containing a single ASCII NUL character, depending on the state of
the BRKINT flag.
MDATA
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), MSTOP and MSTART
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,
MSTOPI and MSTARTI messages are sent downstream.
MDATA messages are sent downstream, as necessary, to perform
echoing.
If a signal is to be generated, an MFLUSH message with a flag byte
of FLUSHR is placed on the read queue. If the signal is also to
flush output, an MFLUSH message with a flag byte of FLUSHW is sent
downstream.
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ldterm(7) UNIX System V ldterm(7)
MCTL
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(7) processing is to be done. If the
command field of the iocblk structure (ioccmd) is set to
MCNOCANON, the input canonical processing normally performed on
MDATA 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 MCDOCANON, all input processing is enabled. If the
command is MCPARTCANON, then an MDATA message containing a
termios structure is expected to be attached to the original MCTL
message. The ldterm module will examine the iflag, oflag, and lflag
fields of the termios structure and from then on will process only
those flags which 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.
MFLUSH
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.
MIOCACK
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 upstream unchanged.
Write-side Behavior
Various types of STREAMS messages are processed as follows:
MFLUSH
The write queue of the module is flushed of all its data messages
and the message is passed downstream.
MIOCTL
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.
MDATA
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 MDELAY messages generated.
Otherwise, the message is passed downstream without change.
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ldterm(7) UNIX System V ldterm(7)
All other messages are passed downstream unchanged.
IOCTLS
The following ioctls are processed by the ldterm module. All others are
passed downstream. EUCWSET and EUCWGET are ISTR ioctl calls whereas
other ioctls listed here are TRANSPARENT ioctls.
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 MSETOPTS 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.
TCFLSH
If the argument is 0, an MFLUSH 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
MFLUSH 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 MFLUSH 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 MSTOP
message is sent downstream. If the argument is 1 and output is
stopped, an MSTART message is sent downstream. If the argument is
2 and input is not already stopped, an MSTOPI message is sent
downstream. If the argument is 3 and input is stopped, an MSTARTI
message is sent downstream.
TCSBRK
The message is passed downstream, so the driver has a chance to
drain the data and then send and an MIOCACK message upstream.
EUCWSET
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 via
MCTL messages.
EUCWGET
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.
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ldterm(7) UNIX System V ldterm(7)
SEE ALSO
termios(2), console(7), ports(7), termio(7)
Programmer's Guide: STREAMS
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