Linux Keystroke HOWTO
			         by
		 Zenon Fortuna (zenon@netcom.com)


Version: 1.0						May 7th '94

INDEX
	0.	What is "Keystroke-HOWTO" ?
	1.	Short description
	2.	Tools for keyboard driver modification
	3.	Modifying keytable file
	3.0	Example of keytable file modification
	3.1	Temporary modification of the keyboard setup
	3.2	Permanent modification
	4.	Example of the key_macro script
	5.	Comments
	6.	Further ideas ?

----------------------------------------------------------------------------
 0.	What is "Keystroke-HOWTO" ?

	This document is for users, who want to assign special action to some
	of keys of the keyboard. The suggested method is to use the loadkeys(1)
	or to modify the defkeymap.c file and relink the kernel.

	The method described below was tested on Linux 1.0 release, packaged
	in the Slackware 1.2.0.x distribution.


1.	Short description

	The Linux virtual terminal and keyboard drivers assume default keyboard
	mapping as defined in the drivers/char/defkeymap.c file of the kernel
	source. The 12 PC keyboard function keys may get strings assigned to
	their action. After pressing any of those function keys, perhaps
	modified with the Alt or Ctrl keys, the current virtual terminal
	adds the specific string to its input and output buffers, in effect
	emulating entry of this string as typed in from the keyboard.

	Setting an appropriate string for chosen function key, we can simplify
	execution of selected command, for example calling a Shell-script
	"/usr/local/bin/key_macro", which we can create and modify as desired.


2.	Tools for keyboard driver modification

	We may use loadkeys(1), dumpkeys(1) and showkey(1):
	  The loadkeys(1) utility helps to load new strings into the kernel
	keyboard buffers or prepares the new C-code to modify the kernel.
	  The dumpkeys(1) should be used to get the current keyboard mapping
	table for inspection or modification.
	  The showkey(1) may assist us to obtain the keycode of the selected
	function key.

	If your Linux system does not have these utilities, you may get them
	via anonymouse ftp as kbd-0.87.tar.gz package from
		sunsite.unc.edu:/pub/Linux/system/Keyboards, or
		tsx-11.mit.edu:/pub/linux/sources/system


3.	Modifying keytable file

	Linux kernel includes compiled defkeymap.c code, which is generated
	with the loadkeys(1) utility from a defkeymap.map file. Both files
	are included in the src/linux/drivers/char directory.

	We need to modify the defkeymap.map file, so let's make a local
	copy of it either by
		# cp defkeymap.map my_keytable.map
	or
		# dumpkeys > my_keytable.map

	There is also a large collection of different keytable files in the
	/usr/lib/kbd/keytables directory, from which "defkeym.map" is identical
	to the src/linux/drivers/char/defkeymap.map file.

	The method which uses the dumpkeys(1) utility is recommended, because
	it may happen, that our kernel was already modified or generated
	for us with different defkeymap.map file than the one we can find.

	Lets read the contents of our my_keytable.map file: there are more
	than 300 lines of code, and we can find 3 groups of declarations.
	The first group begins with words "keycode" or "alt keycode" or
	"control keycode" or "shift keycode".
	The second group begins with the word "string".
	The third group begins with the word "compose".

	More about the keytables(5) syntax can be read with
		% man keytables


3.0	Example of keytable file modification

	As an example of assigning a macro-string to a function key stroke,
	let's make the "Ctrl-F1" to call our "/usr/local/bin/key_macro"
	Shell-script.

	First of all we should find out what is the keycode for the F1 function
	key.
	We may use the showkey(1) utility to find the keycode with pressing F1.

	Instead we can search for the "F1" string in the "my_keytable.map" file
	to find the following line:

	keycode  59 = F1               F11              Console_13      

	This means, that the keycode for the F1 function key is 59.
	This line defines also, that after pressing the F1 key the keyboard
	driver would send out the string denoted by the string-code "F1".
	To see the contents of this string, one can search for the "string F1"
	pattern, to find

	string F1 = "\033[[A"

	This means, that after pressing the F1 key, the keyboard driver sends
	the "Esc [ [ A" (without blank spaces).

	We shouldn't change this string, because some applications depend on
	this string as default action of the F1 function key.

	However, below the "keycode  59 =..." line we may read a line defining
	the Ctrl-F1 action:

	control keycode  59 = F1

	This essentially means, that pressing "Ctrl-F1" we send the same string
	out (denoted by the string-code F1) as pressing the plain "F1" key.
	To change it we should find an unused string-code name.

	A good candidate could be the F26 string-code, which in the default
	defkeymap.map file denotes an empty string in the following line:

	F26 = ""

	Instead, let's change it in "my_keytable.map" to

	F26 = "/usr/local/bin/key_macro\n"

	Then let's change the shown above line defining Ctrl-F1 action, to

	control keycode 59 = F26

	In the summary, we made two changes to the original "my_keytable.map"
	file: we declared the new value to the F26 string and we have defined
	the Ctrl-F1 calling the F26 string.


3.1	Temporary modification of the keyboard setup

	Having properly modified "my_keytable.map" we can copy the changes
	to the kernel keyboard driver, using the loadkeys(1) utility:

	% loadkeys my_keytable.map

	The permission to modify the kernel keyboard driver is granted to
	everybody who has the read access to the "/dev/console" device.

	To verify that the intended changes were installed, we can use the
	dumpkeys(1) utility to check the F26 value, for example

	% dumpkeys | grep F26

	We may see:
	string F26 = "/usr/local/bin/key_macro\012"

	which is OK, because "\012", or LF, is equivalent to "\n".

	Now, pressing "Ctrl-F1" should call the "/usr/local/bin/key_macro"
	Shell-script, as intended. 


3.2	Permanent modification

	The changes to the kernel keyboard driver imposed by the loadkeys(1)
	last until the next reboot (or the next call to loadkeys).

	We can modify the /etc/rc.d/rc.local to call the loadkeys with our
	my_keytable.map file as an argument. Instead, we can modify the
	src/linux/drivers/char/defkeymap.c and re-link the kernel with
	new defaults.

	We should not modify the defkeymap.c manually, but rather generate
	it with the loadkeys(1) utility:

	# mv defkeymap.c defkeymap.c.ORIG
	# loadkeys --mktable my_keytable.map > defkeymap.c

	Then we should generate the new kernel, essentially changing directory
	to the root of the linux kernel source, and using the make(1).

	Finally, we should use the lilo(1) to boot with our new kernel.


4.	Example of the key_macro script

	A particularly useful script for simple-key-stroke operation may be
	a Shell-script preparing, or printing, a screen dump.
	The code below should be regarded as an example of possible
	applications:

#!/bin/sh
#
# This is an example of useful key_macro script
#

VT_NUMBER=`tty|cut -c9-`
FILE=/tmp/vt$VT_NUMBER.dump
setterm -dump $VT_NUMBER -file $FILE
echo SCREEN DUMP saved in $FILE
#
# Uncomment the line below if you want to print the resulted dump-file
# lpr $FILE

	The *problem* with the above "setterm -dump ..." call is, that
	it uses the ioctl(0,TIOCLINUX) system call, which is reserved
	for the Superuser only. This means, that the intended screen-dump
	would work only for "root". Oh, well.


5.	Comments

	There is a limit to the sum the lengths of all strings which are
	to be copied to the keyboard driver: FUNC_BUFSIZE, declared in
	the "keyboard.h" is set to 512 bytes.

	In case of attempt to assign too long strings, the loadkeys(1)
	will fail with the message: "func-buf overflow".

	The defkeymap.map and generated getkeymap.c use about 100 bytes only.


6.	Further ideas ?

	In case you find anything worth adding to this document, please send
	your comments to zenon@netcom.com -- thanks (zf)