eos-updater: Add support for OSTree sysroot autocleanup

When OSTree staged deployments are used, the old rollback deployment is
deleted during system shutdown. To keep from slowing down shutdown, the
OSTree repo is not pruned at that time. That means that even though the
deployment was deleted, the objects are still on disk. Since that may be
a significant amount of wasted disk space, the full cleanup with repo
pruning needs to be run at some time after rebooting. See
ostreedev/ostree#2510 for details.

To detect when cleanup is necessary, a systemd drop in is added to touch
the `/sysroot/.cleanup` file after `ostree-finalize-staged.service` has
finalized the new deployment. The reason to use a drop-in for
`ostree-finalize-staged.service` rather then creating the file from
`eos-updater` is to avoid the situation where an unclean shutdown occurs
and the new deployment is not finalized. In that case, cleanup would be
run unnecessarily on the next boot.

A new systemd service, `eos-updater-autocleanup.service`, is added to
run `ostree admin cleanup` when `/sysroot/.cleanup` exists and then
delete it afterwards. This adds a dependency on the `ostree` CLI but a
separate program could be provided calling the `ostree_sysroot_cleanup`
API and deleting the `/sysroot/.cleanup` file itself.

https://phabricator.endlessm.com/T5658

debian/control

@@ -39,6 +39,7 @@ Multi-arch: no
 Depends:
  gir1.2-glib-2.0,
  mogwai-scheduled,
+ ostree,
  python3-gi,
  systemd (>= 200),
  ${misc:Depends},

debian/eos-updater.install

@@ -2,12 +2,14 @@ lib/systemd/system/eos-autoupdater.service
 lib/systemd/system/eos-autoupdater.timer
 lib/systemd/system/eos-updater-avahi.path
 lib/systemd/system/eos-updater-avahi.service
+lib/systemd/system/eos-updater-autocleanup.service
 lib/systemd/system/eos-updater-flatpak-installer.service
 lib/systemd/system/eos-updater-flatpak-installer-fallback.service
 lib/systemd/system/eos-updater-flatpak-installer-fallback.timer
 lib/systemd/system/eos-updater.service
 lib/systemd/system/eos-update-server.service
 lib/systemd/system/eos-update-server.socket
+lib/systemd/system/ostree-finalize-staged.service.d/autocleanup.conf
 usr/libexec/eos-updater
 usr/libexec/eos-autoupdater
 usr/libexec/eos-updater-avahi

eos-updater/eos-updater-autocleanup.service.in

@@ -0,0 +1,37 @@
+[Unit]
+Description=Automatically cleanup after staged Endless OS Updater deployment
+Documentation=man:ostree-admin-cleanup(1) man:eos-updater(8)
+
+# Run ostree admin cleanup only if /sysroot/.cleanup is present and then
+# delete it when cleanup is successful.
+#
+# FIXME: Drop this when https://github.com/ostreedev/ostree/issues/2510
+# is resolved.
+ConditionPathExists=/sysroot/.cleanup
+
+# We want this to be triggered by multi-user.target but not block it via
+# the default After added to target units since pruning the repo can be
+# slow. See the Default Dependencies sections in systemd.service(5) and
+# systemd.target(5).
+DefaultDependencies=no
+Requires=sysinit.target
+After=sysinit.target basic.target
+Conflicts=shutdown.target
+Before=shutdown.target
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=@ostree@ admin cleanup
+ExecStart=/bin/rm -f /sysroot/.cleanup
+
+# Only /sysroot and /boot need to be written to.
+ProtectSystem=strict
+ReadWritePaths=/sysroot /boot
+
+# This will be allowed to run in the background, so try to make it less
+# disruptive while it prunes the repo.
+IOSchedulingClass=idle
+
+[Install]
+WantedBy=multi-user.target

eos-updater/finalize-autocleanup.conf.in

@@ -0,0 +1,9 @@
+# This is a drop-in file for ostree-finalize-staged.service.
+#
+# FIXME: Drop this when https://github.com/ostreedev/ostree/issues/2510
+# is resolved.
+
+[Service]
+# After finalizing the staged deployment, touch the .cleanup file so
+# that the cleanup can be completed on the next boot.
+ExecStop=-/bin/touch /sysroot/.cleanup

eos-updater/meson.build

@@ -105,6 +105,7 @@ install_data(
 # systemd files
 config = configuration_data()
 config.set('libexecdir', join_paths(get_option('prefix'), get_option('libexecdir')))
+config.set('ostree', find_program('ostree').path())
 
 configure_file(
   input: 'eos-updater.service.in',
@@ -113,6 +114,20 @@ configure_file(
   configuration: config,
 )
 
+configure_file(
+  input: 'eos-updater-autocleanup.service.in',
+  output: 'eos-updater-autocleanup.service',
+  install_dir: dependency('systemd').get_pkgconfig_variable('systemdsystemunitdir'),
+  configuration: config,
+)
+
+configure_file(
+  input: 'finalize-autocleanup.conf.in',
+  output: 'autocleanup.conf',
+  install_dir: join_paths(dependency('systemd').get_pkgconfig_variable('systemdsystemunitdir'), 'ostree-finalize-staged.service.d'),
+  configuration: config,
+)
+
 # Example configuration
 install_data(
   files('eos-updater.conf'),