ldterm - standard STREAMS terminal line discipline module
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.
Various types of STREAMS messages are processed as follows:
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.
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.
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 downstream.
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.
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.
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 others 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 euciocstructure 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 discipline. If the current codeset of the line discipline is not an EUC one, the result is meaningless.
Prior to Oracle Solaris 11.4, programs needed to push the ldterm module onto the slave 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 slave side, and callers pushing them as well would encounter unexpected 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.