Development/Tools/Using kconf update: Difference between revisions

    From KDE TechBase
    (Initial copy from wiki.kde.org.)
     
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    What used to happen is that the application looks up both the old and the new configuration option and then decides which one to use. This method has several drawbacks:
    What used to happen is that the application looks up both the old and the new configuration option and then decides which one to use. This method has several drawbacks:
       
       
    The application may need to read more configuration files than strictly needed, resulting in a slower startup.  
    The application may need to read more configuration files than strictly needed, resulting in a slower startup. The application becomes bigger with code that will only be used once.  
    The application becomes bigger with code that will only be used once.  


    kconf_update addresses these problems by offering a framework to update configuration files without adding code to the application itself.
    kconf_update addresses these problems by offering a framework to update configuration files without adding code to the application itself.
       
       
    ==How it works==
    ==How it works==
    Applications can install so called "update files" under $KDEDIR/share/apps/kconf_update. An update file has ".upd" as extension and contains instructions for transferring/converting configuration information from one place to another.
    Applications can install so called "update files" under $KDEDIR/share/apps/kconf_update. An update file has ".upd" as extension and contains instructions for transferring/converting configuration information from one place to another.
    Updating the configuration happens automatically, either when KDE gets started or when kded detects a new update file in the above mentioned location.
       
       
    Update files are separated into sections. Each section has an Id. When a section describing a configuration change has been applied, the Id will be stored in the file "kconf_updaterc". This information is used to make sure that a configuration update is only performed once.
    Updating the configuration happens automatically, either when KDE gets started or when kded detects a new update file in the above mentioned location.
       
       
    If you overwrite an existing update file with a new version that contains a new section, only the update instructions from this extra section will be performed.
    Update files are separated into sections. Each section has an Id. When a section describing a configuration change has been applied, the Id will be stored in the file "kconf_updaterc". This information is used to make sure that a configuration update is only performed once.
       
       
    If you overwrite an existing update file with a new version that contains a new section, only the update instructions from this extra section will be performed.
       
       
    ==File format of the update file==
    ==File format of the update file==
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    All entries from <oldfile> are piped into <_script>. The output of script is used as new entries for <newfile>. Existing entries can be deleted by adding lines with "# DELETE [group]key" in the output of the script. To delete a whole group use "# DELETEGROUP [group]".
    All entries from <oldfile> are piped into <_script>. The output of script is used as new entries for <newfile>. Existing entries can be deleted by adding lines with "# DELETE [group]key" in the output of the script. To delete a whole group use "# DELETEGROUP [group]".
       
       
    <_script> should be installed into $(kde_datadir)/kconf_update, or kconf_update will not be able to find it. It is not portable to install binary applications in $kde_datadir, so you have to stick with interpreted scripts like sh or perl scripts. From KDE 3.2 onwards it's also possible to install kconf_update applications in $(kde_bindir)/kconf_update_bin, which opens the door to kconf_update applications that are written in C++ and use Qt's powerful string API instead.
    <_script> should be installed into $(kde_datadir)/kconf_update, or kconf_update will not be able to find it. It is not portable to install binary applications in $kde_datadir, so you have to stick with interpreted scripts like sh or perl scripts. From KDE 3.2 onwards it's also possible to install kconf_update applications in $(kde_bindir)/kconf_update_bin, which opens the door to kconf_update applications that are written in C++ and use Qt's powerful string API instead.
       
       
    A workaround for KDE 3.1.x and older is to install a .sh script in $(kde_datadir) that contains a simple exec:
    A workaround for KDE 3.1.x and older is to install a .sh script in $(kde_datadir) that contains a simple exec:
    Line 50: Line 47:
    If Script was issued after a "Group" command the behavior is slightly different: all entries from <oldfile>/<oldgroup> are piped into <_script>. The output of script is used as new entries for <newfile>/<newgroup>, unless a different group is specified with "[group]". Existing entries can be deleted from <oldgroup> by adding lines with "# DELETE key" in the output of the script. To delete <oldgroup> use "# DELETEGROUP".
    If Script was issued after a "Group" command the behavior is slightly different: all entries from <oldfile>/<oldgroup> are piped into <_script>. The output of script is used as new entries for <newfile>/<newgroup>, unless a different group is specified with "[group]". Existing entries can be deleted from <oldgroup> by adding lines with "# DELETE key" in the output of the script. To delete <oldgroup> use "# DELETEGROUP".
       
       
    <interpreter> can be something like "perl".
    <interpreter> can be something like "perl".
       
       
    Since KDE 3.3 it is also possible to have a Script without specifying <oldfile> or <newfile>. In that case the script is run but it will not be fed any input and its output will simply be discarded.
    Since KDE 3.3 it is also possible to have a Script without specifying <oldfile> or <newfile>. In that case the script is run but it will not be fed any input and its output will simply be discarded.
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    With this entry you can specify options that apply to the next "Script", "Key" or "AllKeys" entry (only to the first!). Possible options are:
    With this entry you can specify options that apply to the next "Script", "Key" or "AllKeys" entry (only to the first!). Possible options are:
       
       
    - "copy" Copy the configuration item instead of moving it. This means that the configuration item will not be deleted from <oldfile>/<oldgroup>.
    "copy" Copy the configuration item instead of moving it. This means that the configuration item will not be deleted from <oldfile>/<oldgroup>.
       
       
    - "overwrite" Normally, a configuration item is not moved if an item with the new name already exists. When this option is specified the old configuration item will overwrite any existing item.
    "overwrite" Normally, a configuration item is not moved if an item with the new name already exists. When this option is specified the old configuration item will overwrite any existing item.
        
        
      Key=<oldkey>,<newkey>  
      Key=<oldkey>,<newkey>  
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    Specifies that <oldkey> is removed from the selected group. This can be used to remove obsolete entries or to force a revert to default values.
    Specifies that <oldkey> is removed from the selected group. This can be used to remove obsolete entries or to force a revert to default values.
        
        
    Example update file
    <pre>Example update file
    # This is comment
    # This is comment
    Id=kde2.2
    Id=kde2.2
    Line 107: Line 104:
    RemoveGroup=KDE
    RemoveGroup=KDE
    # End of file
    # End of file
    </pre>


    The above update file extracts config information from the file "kioslaverc" and stores it into the file "kio_httprc".
    The above update file extracts config information from the file "kioslaverc" and stores it into the file "kio_httprc".

    Revision as of 17:57, 17 July 2007

    Note
    The text for this document was lifted from the source file kdelibs/kconf_update/README.kconf_update. It is reprinted here so that we have a description outside of the source code, and so we can add more example update scripts.


    What it does

    kconf_update is a tool designed to update config files. Over time applications sometimes need to rearrange the way configuration options are stored. Since such an update shouldn't influence the configuration options that the user has selected, the application must take care that the options stored in the old way will still be honored.

    What used to happen is that the application looks up both the old and the new configuration option and then decides which one to use. This method has several drawbacks:

    The application may need to read more configuration files than strictly needed, resulting in a slower startup. The application becomes bigger with code that will only be used once.

    kconf_update addresses these problems by offering a framework to update configuration files without adding code to the application itself.

    How it works

    Applications can install so called "update files" under $KDEDIR/share/apps/kconf_update. An update file has ".upd" as extension and contains instructions for transferring/converting configuration information from one place to another.

    Updating the configuration happens automatically, either when KDE gets started or when kded detects a new update file in the above mentioned location.

    Update files are separated into sections. Each section has an Id. When a section describing a configuration change has been applied, the Id will be stored in the file "kconf_updaterc". This information is used to make sure that a configuration update is only performed once.

    If you overwrite an existing update file with a new version that contains a new section, only the update instructions from this extra section will be performed.

    File format of the update file

    Empty lines or lines that start with '#' are considered comments. Commas (,) are used to seperate fields and may not occur as part of any field and all of the keywords are case-sensitive, i.e. you cannot say "key" instead of "Key" for example.

    The remainder of the file is parsed and executed sequentially from top to bottom. Each line can contain one entry. The following entries are recognized:

    Id=<id> 
    

    With <id> identifying the group of update entries that follows. Once a group of entries have been applied, their <id> is stored and this group of entries will not be applied again.

    File=<oldfile>,<newfile> 
    File=<oldfile> 
    

    Specifies that configuration information is read from <oldfile> and written to <newfile>. If you only specify <oldfile>, the information is read from as well as written to <oldfile>.

     Script=<_script>[,<interpreter>] 
    

    All entries from <oldfile> are piped into <_script>. The output of script is used as new entries for <newfile>. Existing entries can be deleted by adding lines with "# DELETE [group]key" in the output of the script. To delete a whole group use "# DELETEGROUP [group]".

    <_script> should be installed into $(kde_datadir)/kconf_update, or kconf_update will not be able to find it. It is not portable to install binary applications in $kde_datadir, so you have to stick with interpreted scripts like sh or perl scripts. From KDE 3.2 onwards it's also possible to install kconf_update applications in $(kde_bindir)/kconf_update_bin, which opens the door to kconf_update applications that are written in C++ and use Qt's powerful string API instead.

    A workaround for KDE 3.1.x and older is to install a .sh script in $(kde_datadir) that contains a simple exec:

    exec "`kde-config --prefix`/bin/kconf_update_bin/my_update_app"
    
    

    This is equivalent to what KDE 3.2 can do directly, but of course the .upd file now points to the .sh script instead of the binary application.

    If Script was issued after a "Group" command the behavior is slightly different: all entries from <oldfile>/<oldgroup> are piped into <_script>. The output of script is used as new entries for <newfile>/<newgroup>, unless a different group is specified with "[group]". Existing entries can be deleted from <oldgroup> by adding lines with "# DELETE key" in the output of the script. To delete <oldgroup> use "# DELETEGROUP".

    <interpreter> can be something like "perl".

    Since KDE 3.3 it is also possible to have a Script without specifying <oldfile> or <newfile>. In that case the script is run but it will not be fed any input and its output will simply be discarded.

    ScriptArguments=<arguments> 
    

    If specified, the arguments will be passed to <_script>. IMPORTANT: Specify the ScriptArguments _before_ the Script.

    Group=<oldgroup>,<newgroup> 
    Group=<oldgroup> 
    

    Specifies that configuration information is read from the group <oldgroup> and written to <newgroup>. If you only specify <oldgroup>, the information is read from as well as written to <oldgroup>. You can use <default> to specify keys that are not under any group.

    RemoveGroup=<oldgroup> 
    

    Specifies that <oldgroup> is removed entirely. This can be used to remove obsolete entries or to force a revert to default values.

    Options=<option1>, <option2>, .... 
    

    With this entry you can specify options that apply to the next "Script", "Key" or "AllKeys" entry (only to the first!). Possible options are:

    "copy" Copy the configuration item instead of moving it. This means that the configuration item will not be deleted from <oldfile>/<oldgroup>.

    "overwrite" Normally, a configuration item is not moved if an item with the new name already exists. When this option is specified the old configuration item will overwrite any existing item.

    Key=<oldkey>,<newkey> 
    Key=<oldkey> 
    

    Specifies that configuration information is read from the key <oldkey> and written to <newkey>. If you only specify <oldkey>, the information is read from as well as written to <oldkey>.

    AllKeys 
    

    Specifies that all configuration information in the selected group should be moved (All keys).

    AllGroups 
    

    Specifies that all configuration information from all keys in ALL groups should be moved.

    RemoveKey=<oldkey> 
    

    Specifies that <oldkey> is removed from the selected group. This can be used to remove obsolete entries or to force a revert to default values.

    Example update file
    # This is comment
    Id=kde2.2
    File=kioslaverc,kio_httprc
    Group=Proxy Settings
    Key=NoProxyFor
    Key=UseProxy
    Key=httpProxy,Proxy
    Group=Cache Settings,Cache
    Key=MaxCacheSize
    Key=UseCache
    Group=UserAgent
    AllKeys
    RemoveGroup=KDE
    # End of file
    

    The above update file extracts config information from the file "kioslaverc" and stores it into the file "kio_httprc".

    It reads the keys "NoProxyFor", "UseProxy" and "httpProxy" from the group "Proxy Settings" in the "kioslaverc" file. If any of these options are present they are written to the keys "NoProxyFor", "UseProxy" and "Proxy" (!) in the group "Proxy Settings" in the "kio_httprc" file.

    It also reads the keys "MaxCacheSize" and "UseCache" from the group "Cache Settings" in the "kioslaverc" file and writes this information to the keys "MaxCacheSize" and "UseCache" in the group "Cache" (!) in the "kio_httprc" file.

    Then it takes all keys in the "UserAgent" group of the file "kioslaverc" and moves then to the "UserAgent" group in the "kio_httprc" file.

    Finally it removes the entire "KDE" group in the kioslaverc file.

    Debugging and testing

    If you are developing a kconf_update script and want to test or debug it you need to make sure kconf_update runs again after each of your changes. There are a number of ways to achieve this.

    The easiest is to not install the kconf_update script in the first place, but manually call it through a pipe. If you want to test the update script for your application KHello's config file khellorc, you can test by using

    % cat ~/.kde/share/config/khellorc | khello_conf_update.sh
    
    

    (assuming khello_conf_update.sh is the kconf_update script and ~/.kde is your $KDEHOME). This is easier than making install every time, but has the obvious downside that you need to 'parse' your script's output yourself instead of letting kconf_update do it and check the resulting output file.

    After 'make install' the kconf_update script is run by kded, but it does so only once. This is of course the idea behind it, but while developing it can be a problem. You can increase the revision number for each subsequent run of 'make install' to force a new kconf_update run, but there's a better approach that doesn't skyrocket the version number for a mediocre debug session.

    kded doesn't really ignore scripts that it has already run right away. Instead it checks the affected config file every time a .upd file is added or changed. The reason it still doesn't run again on your config file lies in the traces kconf_update leaves behind: it adds a special config group '[$Version]' with a key 'update_info'. This key lists all kconf_update scripts that have already been run on this config file. Just remove your file's entry, 'make install', and kconf_update will happily run your script again, without you having to increase the version number.

    If you want to know what kconf_update has been up to lately, have a look at $KDEHOME/share/apps/kconf_update/update.log

    Common Problems

    kconf_update refuses to update an entry If you change the value of an entry without changing the key or file, make sure to tell kconf_update that it should overwrite the old entry by adding "Options=overwrite".

    Authors and Developers

    Original Application author and developer is Waldo Bastian (bastian at kde dot org)

    Copyright and License

    Copyright © 2001, Waldo Bastian

    This program is licensed under the terms of the GNU General Public License, Version 2.