LDTERM(7M)LDTERM(7M)NAMEldterm - standard STREAMS terminal line discipline module
The ldterm STREAMS module provides most of the termio(7I) terminal
interface. The vis module does not perform the low-level device con‐
trol 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 func‐
tions 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 speci‐
fied 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
The remainder of this section describes the processing of various
STREAMS messages on the read- and write-side.
Various types of STREAMS messages are processed as follows:
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 char‐
acter when this message is received.
This message is normally processed using the standard
termio input processing. If the ICANON flag is set, a sin‐
gle 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
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 per‐
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.
Various types of STREAMS messages are processed as follows:
The write queue of the module is flushed of all its data
messages and the message is passed downstream.
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
If the OPOST flag is set, or both the XCASE and ICANON
flags are set, output processing is performed and the pro‐
cessed message is passed downstream along with any M_DELAY
messages generated. Otherwise, the message is passed
downstream without change.
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(7I) pro‐
cessing 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 unmodi‐
fied. (This is for the use of modules or drivers that per‐
form 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.
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.
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.
The ldterm module processes the following TRANSPARENT ioctls. All oth‐
ers are passed downstream.
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.
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.
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.
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.
The message is passed downstream, so the driver has a chance to
drain the data and then send an M_IOCACK message upstream.
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.
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 ALSOtermios(3C), console(7D), termio(7I)
STREAMS Programming Guide
Jun 7, 1999 LDTERM(7M)