Chip 1998 September/CHIP Eylül 1998.iso/Slackwar/docs/mini/Keystroke

Text File | 1995-05-09 | 9.4 KB | 279 lines

=================== Keystroke-HOWTO, version 2.0 ====================

            Linux Keystroke HOWTO
                     by
         Zenon Fortuna ([e-mail])


Version: 2.0                        April 4th '95

INDEX
    0.    What is "Keystroke-HOWTO" ?
    1.    History of changes
    2.    Short description
    3.    Tools for keyboard driver modification
    4.    Modifying keytable file
    4.0    Example of keytable file modification
    4.1    Temporary modification of the keyboard setup
    4.2    Permanent modification
    5.    Example of the key_macro script
    6.    Comments
    7.    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.

    This text does NOT discuss remapping of keyboard keys, e.g. Backspace
    or Delete keys. For informations about remapping of keys read the
    Backspace Mini-HOWTO written by Stephen Lee.

    The method described below was tested on Linux 1.2.1 release, packaged
    in the Slackware 2.2.0 distribution.


1.    History of changes

    April 4th '95    Version: 2.0
       Adapted for the Linux 1.2.1:
       - simple changes in suggested modification of the "my_keytable.map"
       - modified "key_macro" example with /dev/vcs* screen dumping

    May   7th '94    Version: 1.0
       The initial version of the "Keystroke-HOWTO", which worked for the
       Linux 1.0


2.    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.


3.    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 anonymous ftp as kbd-0.89.tar.gz or kbd-0.90.tar.gz package from
        sunsite.unc.edu:/pub/Linux/system/Keyboards, or
        tsx-11.mit.edu:/pub/linux/sources/system
    You should use the GNU tar to extract the needed files.


4.    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 "defkeymap.map" may be
    used as src/linux/drivers/char/defkeymap.map file on your system.

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

    Lets read the contents of the my_keytable.map file: there are more
    than 300 lines of code, and we can find 3 groups of declarations:
    The first group consists of lines with the word "keycode", maybe
    prepended with additional words like "alt", "control", etc.
    The second group consists of lines with the word "string".
    The third group consists of lines with the word "compose".

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


4.0    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

    This suggests, 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, we may define the new action for Ctrl-F1, provided it is not
    reserved by your kernel for other special actions.
    To see the mappings of the F1 key modified with the Ctrl-, Shift- or
    other modes, we may inspect the "my_keytable.map" file with

        # grep 59 my_keytable.map

    In case when there is no line with "control keycode 59" we may use
    the Ctrl-F1 without problems. (when a line with the "shift control
    keycode 59" exists it is still OK)

    Let us add a following line to the "my_keytable.map" file:

        control keycode 59 = key_symbol

    where the "key_symbol" would define the action of the Ctrl-F1 key.
    The Linux 1.2.* allows a dynamic allocation of strings, but a name
    of the "key_symbol" may be picked up only from a fixed set of names.
    Between other names the key-symbols F1-F246 are allowed.
    For "my_keytable.map" on my system the F21 was unused, but you should
    inspect your "my_keytable.map" and choose a proper key-symbol.
    So, we may end up with a line

        control keycode 59 = F21

    Now we have to define the contents of the F21, adding a line

        string F21 = "/usr/local/bin/key_macro\n"

    In the summary, we made two changes to the original "my_keytable.map"
    file: we declared the new string F21, and we have declared
    that the Ctrl-F1 key will be calling the F21 contents.


4.1    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 F21 value, for example

    % dumpkeys | grep F21

    We may see:

    keycode 59 = F1        F11    Console_13    F21

    string F21 = "/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.


4.2    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 install and boot our new kernel.


5.    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.

    This example has changed since the version 1.0 of Linux, because
    of the changes in the Linux kernel, which does not provide the
    ioctl(0,TIOCLINUX) system call anymore.

    To read the virtual console screen dumps one should prepare first
    some device files. As "root" user we may create the following files:

        # mknod /dev/vcs1  c 7 1
        # mknod /dev/vcs2  c 7 2
        ...
        # mknod /dev/vcs63 c 7 63

    Of course, it is sufficient to have only the /dev/vcs* files specific
    for the virtual consoles you are using.

    The code below should be regarded as an example of possible
    /usr/local/bin/key_macro file:

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

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


6.    Comments

    There is no practical limit on the sum the lengths of all strings
    which we would like to load to the keyboard driver. The previous fixed
    buffer of the length of FUNC_BUFSIZE (set to 512 bytes), has been
    replaced in the Linux 1.2.* by a strategy of dynamic buffer allocation
    ... in chunks of 512 bytes each.

    The most recent copy of the Keystroke-HOWTO can be found in

        ftp.netcom.com: /pub/ze/zenon/linux/howto


7.    Further ideas ?

    In case you find anything worth adding to this document, please send
    your comments to [e-mail] -- thanks (zf)