Problem

Some components of kdbGet/kdbSet should be optional. We use the plugin system for that. However, some of these cases cannot be tied to a mountpoint. This was the idea of global plugins, but that idea proved problematic. In the old global plugins implementation:

Notification does not happen once after final commit, but for every plugin.
Problems in spec plugin

These problems can be traced back to the placement of the plugins. We need to clean up and simplify the placement.

Constraints

Plugin interface should be the same. Many plugins, where appropriate, e.g. dbus, should work as global plugins w/o any change in code (i.e. only changes in contract)
Global plugins might depend on specific applications or specific mount points (it should be possible to enforce global plugins for specific applications).

Assumptions

Only following plugins need hook functionality:
- mmap
- spec
- gopts
- receiving of notifications (internalnotification)
- sending of notifications (dbus, ...)
- recording of changes

Considered Alternatives

generic placements like /prerollback /rollback /postrollback /getresolver /pregetcache /pregetstorage /getstorage /postgetstorage /postgetcache /setresolver /presetstorage /setstorage /precommit /commit /postcommit which can be executed at: /init /deinit /foreach proved to be too complicated and difficult to test.

Decision

Have hooks and APIs specific for plugins listed in assumptions. These hooks are not shared, so no list plugin is needed.

Installed plugins will be used.

We'll hard code the names of the plugins. For changing those plugins symlinks will have to be used.

Rationale

allows adding more types of plugins later, also post-1.0
much clearer semantics for each type, no need to compromise
easier to implement

Implications

remove global-mount command
command for mmap/notification/... enable disable (like current kdb cache tool)
remove list plugin
remove plugins that stop working or disallow global positioning for them
call spec as needed several times
remove current global plugins mechanism
rename global to hook in contract

Related Decisions

Array
Ensure