[Unit]
Description=MARS per-resource trigger from /mars/resource-@{res}/systemd-trigger
Documentation=https://github.com/schoebel/mars/docu/mars-manual.pdf

## Prohibit parallelism with any daemon-reload
After=daemon-reload.service

## The per-resource trigger is the _only_ one which is allowed
## to remotely start / stop any units dealing with resources.
## Otherwise, races or conflicting start / stop operations might
## occur, leading to deadlocks / failures / etc.
##
## General rule: each *.path watcher can only start its corresponding
## *-trigger.service at most _once_ in parallel (provided that the actions
## caused by "marsadm systemd-trigger-extern" are not forking into background).
## So there is never any parallelism of _any_ unit with exactly _itself_
## (although _different_ units are allowed to run in parallel to each other,
## of course).

## Do not start both the global and any of the per-resource triggers
## in parallel.
## It could lead to various races between global and per-resource units.
## In contrast, different per-resource triggers are not mutually exclusive.
After=mars-trigger.service

[Service]
# Important for blocking parallelism with itself
Type=oneshot
RemainAfterExit=no
# Important for avoiding failures: do not send any signals
KillMode=none
# Important: the resource argument will keep remote triggers disjoint
ExecStart=/usr/bin/marsadm systemd-trigger-extern @{res}

[Install]
WantedBy=mars.service