os, release: reboot host if needed after reaching configured.target

Reboot the system towards the end of the configuration phase during boot
if any of the first-party components deem this necessary. The reboot is
enacted after reaching the configured.target and before reaching the
multi-user.target, so e.g. user data has been applied and bootstrap
containers have already run, but the host is not yet fully operational.

Components can hook into the new reboot-if-required.service to be able
to run at this point. They should implement a "reboot-if-required"
command to trigger a reboot if it is needed.

Currently, prairiedog is the only component hook into this service and
implement a "reboot-if-required" command. It will trigger a reboot if
boot settings have changed, i.e. if the kernel or systemd command line
arguments were changed via the user data mechanism or a bootstrap
container.

Signed-off-by: Markus Boehme <[email protected]>

packages/os/os.spec

@@ -48,6 +48,7 @@ Source116: load-kernel-modules.service.in
 Source117: cfsignal.service
 Source118: generate-network-config.service
 Source119: prepare-primary-interface.service
+Source120: reboot-if-required.service
 
 # 2xx sources: tmpfilesd configs
 Source200: migration-tmpfiles.conf
@@ -429,7 +430,7 @@ install -d %{buildroot}%{_cross_unitdir}
 install -p -m 0644 \
   %{S:100} %{S:101} %{S:102} %{S:103} %{S:105} \
   %{S:106} %{S:107} %{S:110} %{S:111} %{S:112} \
-  %{S:113} %{S:114} %{S:118} %{S:119} \
+  %{S:113} %{S:114} %{S:118} %{S:119} %{S:120} \
   %{buildroot}%{_cross_unitdir}
 
 %if %{_is_vendor_variant}
@@ -590,6 +591,7 @@ install -p -m 0644 %{S:300} %{buildroot}%{_cross_udevrulesdir}/80-ephemeral-stor
 
 %files -n %{_cross_os}prairiedog
 %{_cross_bindir}/prairiedog
+%{_cross_unitdir}/reboot-if-required.service
 
 %files -n %{_cross_os}certdog
 %{_cross_bindir}/certdog

packages/os/reboot-if-required.service

@@ -0,0 +1,11 @@
+[Unit]
+Description=Reboot system if needed for configuration changes to take effect
+# Block manual interactions for now to prevent unplanned reboots.
+RefuseManualStart=true
+RefuseManualStop=true
+After=configured.target
+
+[Service]
+Type=oneshot
+ExecStart=/usr/bin/prairiedog reboot-if-required
+StandardError=journal+console

packages/release/activate-multi-user.service

@@ -1,7 +1,7 @@
 [Unit]
 Description=Isolates multi-user.target
-After=configured.target
-Requires=configured.target
+After=configured.target reboot-if-required.service
+Requires=configured.target reboot-if-required.service
 
 [Service]
 Type=oneshot