layers(M)

layers -- protocol used between host and windowing terminal under layers(C)

Syntax

#include <sys/jioctl.h>

Description

layers are asynchronous windows supported by the operating system in a windowing terminal. Communication between the UNIX system processes and terminal processes under layers(C) occurs via multiplexed channels managed by the respective operating systems using a protocol as specified in xtproto(M).

To use layers, you must have configured the xt driver. This is done using the mkdev layers script. For more information, see mkdev(ADM).

The contents of packets transferring data between a UNIX system process and a layer are asymmetric. Data sent from the UNIX system to a particular terminal process is undifferentiated and it is up to the terminal process to interpret the contents of packets.

Control information for terminal processes is sent via channel 0. Process 0 in the windowing terminal performs the designated functions on behalf of the process connected to the designated channel. These packets take the form:

command, channel

except for timeout and jagent information which take the form:

command, data...

The commands are the bottom eight bits extracted from the following ioctl(S) codes:

JBOOT

Prepare to load a new terminal program into the designated layer.

JTERM

Kill the downloaded layer program and restore the default window program.

JTIMO

Set the timeout parameters for the protocol. The data consists of two bytes: the value of the receive timeout in seconds and the value of the transmit timeout in seconds.

JTIMOM

Set the timeout parameters for the protocol. The data consists of four bytes in two groups: the value of the receive timeout in milliseconds (the low eight bits followed by the high eight bits) and the value of the transmit timeout (in the same format).

JZOMBOOT

Like JBOOT, but do not execute the program after loading.

JAGENT

Send a source byte string to the terminal agent routine and wait for a reply byte string to be returned.

The data are from a bagent structure (see jagent(M)) and consists of a one-byte size field followed by a two-byte agent command code and parameters. Two-byte integers transmitted as part of an agent command are sent with the high-order byte first. The response from the terminal is generally identical to the command packet, with the two command bytes replaced by the return code: 0 for success, -1 for failure. Note that the routines in the libwindows(S) library all send parameters in an agentrect structure. The agent command codes and their parameters are as follows:

A_NEWLAYER: followed by a two-byte channel number and a rectangle structure (four two-byte coordinates).
A_CURRENT: followed by a two-byte channel number.
A_DELETE: followed by a two-byte channel number.
A_TOP: followed by a two-byte channel number.
A_BOTTOM: followed by a two-byte channel number.
A_MOVE: followed by a two-byte channel number and a point to move to (two two-byte coordinates).
A_RESHAPE: followed by a two-byte channel number and the new rectangle (four two-byte coordinates).
A_NEW: followed by a two-byte channel number and a rectangle structure (four two-byte coordinates).
A_EXIT: no parameters needed.
A_ROMVERSION: no parameters needed. The response packet contains the size byte, two-byte return code, two unused bytes, and the parameter part of the terminal id string (for example, ``8;7;3'').

Packets from the windowing terminal to the UNIX system all take the following form:

command, data. . .

The single-byte commands are as follows:

C_SENDCHAR: Send the next byte to the UNIX system process.
C_NEW: Create a new UNIX system process group for this layer. Remember the window size parameters for this layer. The data for this command is in the form described by the jwinsize structure. The size of the window is specified by two 2-byte integers, sent low byte first.
C_UNBLK: Unblock transmission to this layer. There is no data for this command.
C_DELETE: Delete the UNIX system process group attached to this layer. There is no data for this command.
C_EXIT: Exit. Kill all UNIX system process groups associated with this terminal and terminate the session. There is no data for this command.
C_DEFUNCT: Layer program has died: send a terminate signal to the UNIX system process groups associated with this terminal. There is no data for this command.
C_SENDNCHARS: The rest of the data are characters to be passed to the UNIX system process.
C_RESHAPE: The layer has been reshaped. Change the window size parameters for this layer. The data takes the same form as for the C_NEW command.

layers(M)

Syntax

Description

See also