Before the OCF Resource Agent API 1.1 standard introduced the reload-agent action and the reloadable parameter meta-data attribute, Pacemaker supported using the reload action with the unique attribute. Only Pacemaker agents are known to have used this extension.
Pacemaker 2.1.0 introduced support for reload-agent and deprecated support for reload. Once we no longer support rolling upgrades from <2.1.0 (see subtask), we can drop the deprecated support. See code for ra_supports_legacy_reload and PCMK_ACTION_RELOAD.