NAME

       doc_decisions_global_plugins_mdGlobal Plugins
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   Issue
       • Checker  plugins  see  only  part  of  the  configuration  and cannot check constraints between keys of
         different mountpoints

       • Notification does not happen once after final commit, but for every plugin

       • Some plugins are not implementable, e.g. global locks (that lock before any  other  plugin  and  unlock
         after  any  other),  but  also  journal  plugins that keep track of actions to be done and already done
         (latter is maybe out of scope for this decision)

   Constraints
       • Use arrays in configuration and allow arbitrary number of global plugins

       • Plugin interface should be the same. Many plugins, e.g. dbus, should work as  global  plugins  w/o  any
         significant change (e.g. only one more entry in contract)

   Assumptions
       • Global plugins to not depend on specific applications nor specific mountpoints.

       • There  is  no  plugin  that  works  as  global  plugin  but  will  not  work as mounted plugin, too (to
         investigate: locker plugins can lead to deadlocks?)

   Considered Alternatives
       • using different plugin interface (like hooks)

   Decision
       Configuration will be in arrays below the keys:

       system/elektra/globalplugins/
           prerollback
           postrollback
           preget
           postget
           preset
           setstorage
           precommit
           postcommit

       Plugins state in contract that they will work as global plugin, i.e. do not need to  work  on  individual
       config files, when following contract is present:

       infos/global

       The kdb-tool should have following list-like interface:

       kdb global-plugin-add
       kdb global-plugin-del
       kdb global-plugin-list

   Argument
       Some nice features that will be implemented as global plugins.

   Transformation
       Transformation keys which are read and transformed to be usable by the application:

       [dir/a]
       transform=/x
       transform/python=...upper()
                /lua=..

       (actually  two  plugins  are  involved: one that fetches transformation keys, the other that executes the
       transformation code)

       • preget: fetch all foreign keys (kdbGet)

       • postget: run transformation for all foreign keys

   Global lock
       simplifies threading and process locking by not having to think about recursive cases.

   Shell plugins
       Run shell code at end of all plugins, e.g. especially doing

       git add
       git commit

   Inference plugins
       The globbing would be more natural (derived from specification). Or  even  more  advanced  ways  to  copy
       information from specification to the keys, e.g. type inference

   Journalling plugins
       It  should  be  possible  to  write  plugins  which  need  all  file  names of all resolver plugins. E.g.
       journalling, global mmap.

   Implications
   Default global plugins
       Its useful to have some important global plugins, e.g. locking by default. Internal list to be used  when
       no system/elektra/global_mountpoints/ exists.

       State diagrams of plugins need to be redrawn to also include global plugin states.

   Related decisions
   Notes
   Open Points
       • How to test global plugins?

       • locker plugins can lead to deadlocks? (must be avoided by contract?)

   Implementation Hints
       • add Plugin *globalPlugins [NR_OF_PLUGINS] to _KDB

       • during  kdbOpen,  system/elektra/globalplugins/  is  read  and  plugins are constructed and placed into
         globalPlugins.

       • In kdbGet and kdbSet hooks execute one of these plugins

       • by default

         • the  plugins  are  all  the  same  list  plugins,   and   their   subplugins   are   executed,   when
           system/elektra/globalplugins/_ states they should be executed

         • a  lock  plugin  that  executes  at begin and end of kdbGet and kdbSet, respective, i.e. postrollback
           preget postget preset postcommit

         • the lock plugin contains the code currently found in resolver

Version 0.8.14                                   Mon Jul 24 2017       doc_decisions_global_plugins_md(3elektra)