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#include <sys/stream.h>#include <sys/termios.h>int ioctl( fd, I_PUSH, "ldterm"
);

Description   ldterm is a STREAMS module that provides most of the termio(7I)
terminal interface.  This 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. ldterm performs
all other termio/termios functions; 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 c_iflag word
and the delays  specified in the c_oflag word. 
ldterm also handles Extended
Unix Code (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 BehaviorVarious types of STREAMS messages are processed as follows:
M_BREAK  When this message is received, 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.
 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.
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(7I) 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 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. 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 upstream unchanged. 
Write-side BehaviorVarious 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. All other messages
are passed downstream unchanged. 
IOCTLs ldterm 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. 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. See Alsotermios(3),
console(7D), termio(7I)