maintenance: add support for systemd timers on Linux

The existing mechanism for scheduling background maintenance is done
through cron. On Linux systems managed by systemd, systemd provides an
alternative to schedule recurring tasks: systemd timers.

The main motivations to implement systemd timers in addition to cron
are:
* cron is optional and Linux systems running systemd might not have it
  installed.
* The execution of `crontab -l` can tell us if cron is installed but not
  if the daemon is actually running.
* With systemd, each service is run in its own cgroup and its logs are
  tagged by the service inside journald. With cron, all scheduled tasks
  are running in the cron daemon cgroup and all the logs of the
  user-scheduled tasks are pretended to belong to the system cron
  service.
  Concretely, a user that doesn’t have access to the system logs won’t
  have access to the log of their own tasks scheduled by cron whereas
  they will have access to the log of their own tasks scheduled by
  systemd timer.
  Although `cron` attempts to send email, that email may go unseen by
  the user because these days, local mailboxes are not heavily used
  anymore.

In order to schedule git maintenance, we need two unit template files:
* ~/.config/systemd/user/git-maintenance@.service
  to define the command to be started by systemd and
* ~/.config/systemd/user/git-maintenance@.timer
  to define the schedule at which the command should be run.

Those units are templates that are parameterized by the frequency.

Based on those templates, 3 timers are started:
* git-maintenance@hourly.timer
* git-maintenance@daily.timer
* git-maintenance@weekly.timer

The command launched by those three timers are the same as with the
other scheduling methods:

/path/to/git for-each-repo --exec-path=/path/to
--config=maintenance.repo maintenance run --schedule=%i

with the full path for git to ensure that the version of git launched
for the scheduled maintenance is the same as the one used to run
`maintenance start`.

The timer unit contains `Persistent=true` so that, if the computer is
powered down when a maintenance task should run, the task will be run
when the computer is back powered on.

Signed-off-by: Lénaïc Huard <lenaic@lhuard.fr>
Acked-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 61 insertions, 6 deletions

diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index b36b7f5fb0..b289cae6b9 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -20,6 +20,18 @@ test_xmllint () {
 	fi
 }
 
+test_lazy_prereq SYSTEMD_ANALYZE '
+	systemd-analyze --help >out &&
+	grep verify out
+'
+
+test_systemd_analyze_verify () {
+	if test_have_prereq SYSTEMD_ANALYZE
+	then
+		systemd-analyze verify "$@"
+	fi
+}
+
 test_expect_success 'help text' '
 	test_expect_code 129 git maintenance -h 2>err &&
 	test_i18ngrep "usage: git maintenance <subcommand>" err &&
@@ -634,15 +646,56 @@ test_expect_success 'start and stop Windows maintenance' '
 	test_cmp expect args
 '
 
+test_expect_success 'start and stop Linux/systemd maintenance' '
+	write_script print-args <<-\EOF &&
+	printf "%s\n" "$*" >>args
+	EOF
+
+	XDG_CONFIG_HOME="$PWD" &&
+	export XDG_CONFIG_HOME &&
+	rm -f args &&
+	GIT_TEST_MAINT_SCHEDULER="systemctl:./print-args" git maintenance start --scheduler=systemd-timer &&
+
+	# start registers the repo
+	git config --get --global --fixed-value maintenance.repo "$(pwd)" &&
+
+	test_systemd_analyze_verify "systemd/user/git-maintenance@.service" &&
+
+	printf -- "--user enable --now git-maintenance@%s.timer\n" hourly daily weekly >expect &&
+	test_cmp expect args &&
+
+	rm -f args &&
+	GIT_TEST_MAINT_SCHEDULER="systemctl:./print-args" git maintenance stop &&
+
+	# stop does not unregister the repo
+	git config --get --global --fixed-value maintenance.repo "$(pwd)" &&
+
+	test_path_is_missing "systemd/user/git-maintenance@.timer" &&
+	test_path_is_missing "systemd/user/git-maintenance@.service" &&
+
+	printf -- "--user disable --now git-maintenance@%s.timer\n" hourly daily weekly >expect &&
+	test_cmp expect args
+'
+
 test_expect_success 'start and stop when several schedulers are available' '
 	write_script print-args <<-\EOF &&
 	printf "%s\n" "$*" | sed "s:gui/[0-9][0-9]*:gui/[UID]:; s:\(schtasks /create .* /xml\).*:\1:;" >>args
 	EOF
 
 	rm -f args &&
-	GIT_TEST_MAINT_SCHEDULER="launchctl:./print-args launchctl,schtasks:./print-args schtasks" git maintenance start --scheduler=launchctl &&
-	printf "schtasks /delete /tn Git Maintenance (%s) /f\n" \
+	GIT_TEST_MAINT_SCHEDULER="systemctl:./print-args systemctl,launchctl:./print-args launchctl,schtasks:./print-args schtasks" git maintenance start --scheduler=systemd-timer &&
+	printf "launchctl bootout gui/[UID] $pfx/Library/LaunchAgents/org.git-scm.git.%s.plist\n" \
 		hourly daily weekly >expect &&
+	printf "schtasks /delete /tn Git Maintenance (%s) /f\n" \
+		hourly daily weekly >>expect &&
+	printf -- "systemctl --user enable --now git-maintenance@%s.timer\n" hourly daily weekly >>expect &&
+	test_cmp expect args &&
+
+	rm -f args &&
+	GIT_TEST_MAINT_SCHEDULER="systemctl:./print-args systemctl,launchctl:./print-args launchctl,schtasks:./print-args schtasks" git maintenance start --scheduler=launchctl &&
+	printf -- "systemctl --user disable --now git-maintenance@%s.timer\n" hourly daily weekly >expect &&
+	printf "schtasks /delete /tn Git Maintenance (%s) /f\n" \
+		hourly daily weekly >>expect &&
 	for frequency in hourly daily weekly
 	do
 		PLIST="$pfx/Library/LaunchAgents/org.git-scm.git.$frequency.plist" &&
@@ -652,17 +705,19 @@ test_expect_success 'start and stop when several schedulers are available' '
 	test_cmp expect args &&
 
 	rm -f args &&
-	GIT_TEST_MAINT_SCHEDULER="launchctl:./print-args launchctl,schtasks:./print-args schtasks" git maintenance start --scheduler=schtasks &&
+	GIT_TEST_MAINT_SCHEDULER="systemctl:./print-args systemctl,launchctl:./print-args launchctl,schtasks:./print-args schtasks" git maintenance start --scheduler=schtasks &&
+	printf -- "systemctl --user disable --now git-maintenance@%s.timer\n" hourly daily weekly >expect &&
 	printf "launchctl bootout gui/[UID] $pfx/Library/LaunchAgents/org.git-scm.git.%s.plist\n" \
-		hourly daily weekly >expect &&
+		hourly daily weekly >>expect &&
 	printf "schtasks /create /tn Git Maintenance (%s) /f /xml\n" \
 		hourly daily weekly >>expect &&
 	test_cmp expect args &&
 
 	rm -f args &&
-	GIT_TEST_MAINT_SCHEDULER="launchctl:./print-args launchctl,schtasks:./print-args schtasks" git maintenance stop &&
+	GIT_TEST_MAINT_SCHEDULER="systemctl:./print-args systemctl,launchctl:./print-args launchctl,schtasks:./print-args schtasks" git maintenance stop &&
+	printf -- "systemctl --user disable --now git-maintenance@%s.timer\n" hourly daily weekly >expect &&
 	printf "launchctl bootout gui/[UID] $pfx/Library/LaunchAgents/org.git-scm.git.%s.plist\n" \
-		hourly daily weekly >expect &&
+		hourly daily weekly >>expect &&
 	printf "schtasks /delete /tn Git Maintenance (%s) /f\n" \
 		hourly daily weekly >>expect &&
 	test_cmp expect args