Linking Scripts

These scripts contain all the logic for creating links between nodes. This involves, to a large extent, deciding which links to create.

Hooks

The hooks in this section are organized in 3 sub-categories. The first category includes hooks that are triggered by changes in the graph. Some of them are tasked to schedule a “rescan-for-linking” event, which is the lowest priority event and its purpose is to scan through all the linkable session items and link them to a particular target. The “rescan-for-linking” event is always scheduled to run once for all the graph changes in a cycle. This is achieved by flagging the event as already scheduled in the module-standard-event-source; this flag is then cleared by a hook that runs on this event.

Selecting a target for each linkable and linking to it is deferred to another set of hooks by pushing a “select-target” event for each linkable. This event is the highest priority event and therefore no other changes in the graph are processed while targets are being selected.

Hooks triggered by changes in the graph

Hook name	File	Triggered by	Action
linking/rescan-trigger	rescan.lua	linkable SI added|removed or metadata-changed	schedules rescan-for-linking event
linking/linkable-removed	rescan.lua	linkable SI removed	destroys links related to the removed linkable
linking/follow	move-follow.lua	metadata-changed	schedules rescan-for-linking when the configured default sources/sinks are changed by the user
linking/move	move-follow.lua	metadata-changed	schedules rescan-for-linking when node target metadata properties are changed
linking/rescan-media-role-links	rescan-media-role-links.lua	link SI added, removed or metadata-changed	activates or deactivates role-based links based on role priorities and actions

rescan-for-linking hooks, in order of execution

Hook name	File	Description
m-standard-event-source/rescan-done	module-standard-event-source.c	clears the rescan_scheduled flag
linking/rescan	rescan.lua	schedules select-target for each linkable session item

select-target hooks, in order of execution

Hook name	File	Description
linking/find-defined-target	find-defined-target.lua	Select the target that has been defined explicitly by the ‘target.object’ property or metadata
linking/find-filter-target	find-filter-target.lua	Select the target of a filter node, if the subject is a filter node
linking/find-media-role-target	find-media-role-target.lua	Select the target based on the stream’s media.role and the target’s device.intended-roles
linking/find-default-target	find-default-target.lua	Select the default source/sink as target
linking/find-best-target	find-best-target.lua	Select target based on priority.session
linking/get-filter-from-target	get-filter-from-target.lua	Translate the found target to a filter target that should be linked instead
linking/prepare-link	prepare-link.lua	Break existing link if needed, check if the target is available for linking; send error to the client if needed
linking/link-target	link-target.lua	Create si-standard-link session item to create links between the subject linkable and the selected target