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ELEKTRA-PLUGINS(7) ELEKTRA-PLUGINS(7)

NAME

elektra-plugins - plugins overview

Plugins can be mounted into the KDB and can access or manipulate the KeySet on every access.

Multiple plugins can be mounted into the key data base elektra-glossary.md. On every access to the key data base they are executed and thus can change the functionality.Elektra already has a wide range of different plugins. The plugin folders should contain a README.md with further information. (Or follow links below.) The plugins are:

For background information see elektra-plugins-framework(7) elektra-plugins-framework.md.

C-Interface

All plugins implement the same interface:
  • kdbOpen() calls elektraPluginOpen() of every plugin to let them do their initialisation.
  • kdbGet() requests elektraPluginGet() of every plugin in the queried backends to return a key set.
  • kdbSet() usually calls elektraPluginSet() of every plugin in the queried backends to store the configuration.
  • kdbSet() also calls elektraPluginError() for every plugin when an error happens. Because of elektraPluginError(), plugins are guaranteed to have their chance for necessary cleanups.
  • kdbClose() makes sure that plugins can finally free their own resources in elektraPluginClose().

KDB-Interface

See also

For an easy introduction, see this tutorial how to write a storage plugin /doc/tutorials/plugins.md. For more background information of the plugin framework, continue here /doc/help/plugin-framework.md. Otherwise, you can visit the the API documentation http://doc.libelektra.org/api/current/html/group__plugin.html.

Resolver

Before configuration is actually written, the file name needs to be determined (will be automatically added by kdb mount):
  • resolver resolver/ uses POSIX APIs to handle conflicts gracefully
  • wresolver wresolver/ minimalistic resolver for non-POSIX systems
  • noresolver noresolver/ does not resolve, but can act as one

and afterwards the configuration file must be synced with harddisc (recommended to add at every kdb mount):

sync sync/ uses POSIX APIs to sync configuration file with harddisc

Storage

Are responsible for reading writing the configuration to configuration files.

Read and write everything a KeySet might contain:

dump dump/ makes a dump of a KeySet in an Elektra-specific format

Read (and write) standard config files of /etc:

  • augeas augeas/ parses and generates many different configuration files using the augeas library
  • hosts hosts/ read/write hosts files
  • line line/ reads any file line by line

Using semi-structured data for config files:

Plugins that just show some functionality, (currently) not intended for productive use:

  • fstab fstab/ reads fstab files.
  • regexstore regexstore/
  • simpleini simpleini/ is ini without sections
  • csvstorage csvstorage/ for csv files

System Information

Information compiled in Elektra: - version version/ is a build-in plugin directly within the core so that it cannot give wrong version information - constants constants/ various constants, including version information

Providing information found on the system not available in persistent files:

uname uname/ information from the uname syscall.

Filter

Filter plugins process keys and their values in both directions. In one direction they undo what they do in the other direction. Most filter plugins available now encode and decode values. Storage plugins that use characters to separate key names, values or metadata will not work without them.

Encoding

Rewrite unwanted characters with different techniques:
  • ccode ccode/ using the technique from arrays in the programming language C
  • hexcode hexcode/ using hex codes

Transformations:

  • keytometa keytometa/ transforms keys to metadata
  • rename rename/ renames keys according to different rules

Doing other stuff:

  • crypto crypto/ encrypts / decrypts confidential values
  • iconv iconv/ make sure the configuration will have correct character encoding
  • hidden hidden/ hides keys whose names start with a ..
  • null null/ takes care of null values and other binary specialities

Notification and Logging

Log/Send out all changes to configuration to:
  • dbus dbus/
  • journald journald/
  • syslog syslog/
  • logchange logchange/ prints the change of every key on the console

Debug

Trace everything that happens within KDB:
  • timeofday timeofday/ print timestamps
  • tracer tracer/
  • counter counter/ count and print how often plugin is used

Checker

Copies meta data to keys:
  • glob glob/ using globbing techniques
  • struct struct/ using a defined structure (may also reject configuration not conforming to that structure)

Plugins that check if values are valid based on meta data (typically copied by another plugin just before):

  • validation validation/ by using regex
  • network network/ by using network APIs
  • path path/ by checking files on filesystem
  • type type/ using runtime type checking (CORBA types/)
  • enum enum/ compares the keyvalue against a list of valid values
  • mathcheck mathcheck/ by mathematical expressions using keysvalues as operants
  • conditionals conditionals/ by using if-then-else like statements

Interpreter

These plugins start an interpreter and allow you to use a bindings.
  • jni jni/ java plugins started by jni, works with jna plugins
  • python python/ Python 3 plugins (technical preview/)
  • python2 python2/ Python 2 plugins (technical preview, deprecated/)
  • lua lua/ Lua plugins (technical preview/)

Others

  • doc doc/ contains the documentation of the plugin interface
  • error error/ yields errors as described in metadata (handy for test purposes)
  • template template/ to be copied for new plugins
  • lineendings lineendings/ tests file for consistent line endings
  • list list/ loads other plugins
  • filecheck filecheck/ does sanity checks on a file

To add a new plugin you can copy the template plugin. Please make sure to add your plugin:

  • to this list, at least in Others
  • to cmake /cmake/ElektraCache.cmake, at least in ALL

2015-11-19