shared/condition: add ConditionControlGroupController=v1|v2

Before, we only allowed conditionalizing on controllers, not the hierarchy.
This commit extends this to allow a simple check for v1 (i.e. classic or hybrid),
and v2 (full unified).

An alternative approach would be to add a separate Condition for this, but I'm
not too keen on that, considering that v1 is already being deprecrecated
(c.f. 82f3063218).

1 files changed, 19 insertions, 8 deletions

diff --git a/man/systemd.unit.xml b/man/systemd.unit.xml
index 333449097f..cd9437c509 100644
--- a/man/systemd.unit.xml
+++ b/man/systemd.unit.xml
@@ -1456,14 +1456,25 @@
         <varlistentry>
           <term><varname>ConditionControlGroupController=</varname></term>
 
-          <listitem><para>Verify that the given cgroup controller (eg. <literal>cpu</literal>) is available
-          for use on the system. For example, a particular controller may not be available if it was disabled
-          on the kernel command line with <varname>cgroup_disable=controller</varname>. Multiple controllers
-          may be passed with a space separating them; in this case the condition will only pass if all listed
-          controllers are available for use. Controllers unknown to systemd are ignored. Valid controllers
-          are <literal>cpu</literal>, <literal>cpuacct</literal>, <literal>io</literal>,
-          <literal>blkio</literal>, <literal>memory</literal>, <literal>devices</literal>, and
-          <literal>pids</literal>.</para>
+          <listitem><para>Check whether given cgroup controllers (eg. <literal>cpu</literal>) are available
+          for use on the system or whether the legacy v1 cgroup or the modern v2 cgroup hierarchy is used.
+          </para>
+
+          <para>Multiple controllers may be passed with a space separating them; in this case the condition
+          will only pass if all listed controllers are available for use. Controllers unknown to systemd are
+          ignored. Valid controllers are <literal>cpu</literal>, <literal>cpuacct</literal>,
+          <literal>io</literal>, <literal>blkio</literal>, <literal>memory</literal>,
+          <literal>devices</literal>, and <literal>pids</literal>. Even if available in the kernel, a
+          particular controller may not be available if it was disabled on the kernel command line with
+          <varname>cgroup_disable=controller</varname>.</para>
+
+          <para>Alternatively, two special strings <literal>v1</literal> and <literal>v2</literal> may be
+          specified (without any controller names). <literal>v2</literal> will pass if the unified v2 cgroup
+          hierachy is used, and <literal>v1</literal> will pass if the legacy v1 hierarchy or the hybrid
+          hierarchy are used (see the discussion of <varname>systemd.unified_cgroup_hierarchy</varname> and
+          <varname>systemd.legacy_systemd_cgroup_controller</varname> in
+          <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+          for more information).</para>
           </listitem>
         </varlistentry>