Kai Lüke
347f35cf42
Up to now we recommended to use TARGET.upholds/ symlinks to start units when an extension is loaded. However, this has some drawbacks. First, for services that should not be tried to be started all the time we have to resort to hiding them through a target that gets uphold and then uses regular .wants/ for the actual service. Second, we actually leak services on extension unload even if the unit has disappeared with the extension. Third, to affect a service through a drop-in or a config change from a confext/sysext and that service is already running, we need a way to restart/reload it instead of just starting it. Similar to EXTENSION_RELOAD_MANAGER=1, add a EXTENSION_RESTART_UNITS= and a EXTENSION_RELOAD_OR_RESTART_UNITS= setting to the extension-release metadata file, carrying a whitespace-separated list of units to restart/reload on merge/refresh/unmerge after the daemon reload. Also detect when the unit has vanished which is normally the case when the unit was part of the unmerged extension, and stop it explicitly to prevent it leaking. When the extension itself ships the binary it should use EXTENSION_RESTART_UNITS= to make sure the new binary is picked up. Since starting through this setting does not work when the extension is mounted from the initrd, extensions should still ship at least a .wants/ symlink to start at boot but can also continue to ship a .upholds/ symlink for backwards compatibility without any drawback and still benefit from the unit stopping triggered by the new setting. While there are cases where one could want to set EXTENSION_RESTART_UNITS= without requiring a daemon reload (e.g., an env var file change instead of a unit drop-in), we now do an implicit daemon reload when we have to restart units so that we know we work on the right state and we spare users remembering to set this setting in addition to prevent running into this issue.
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