From 235b0f28e2d8460c1825fb74f608d2a7b3f506fb Mon Sep 17 00:00:00 2001
From: Jonathan Lebon <jonathan@jlebon.com>
Date: Mon, 25 Nov 2019 17:20:11 -0500
Subject: [PATCH] Add coreos-keep-cgroup-v1.service

In f31, the default cgroup changed to v2. However, we've decided to stay
on v1 for the time being. Thus, we don't want older nodes upgrading to
f31 to be forced into v2.

Add a tiny service which just scans the BLS configs and injects the
`systemd.unified_cgroup_hierarchy` karg as needed.

For more information, see:
https://github.com/coreos/fedora-coreos-tracker/issues/292
https://github.com/coreos/fedora-coreos-streams/issues/26#issuecomment-558361931
---
 .../lib/systemd/system-preset/40-coreos.preset  |  1 +
 .../system/coreos-keep-cgroup-v1.service        | 15 +++++++++++++++
 .../90cgroups/usr/libexec/coreos-keep-cgroup-v1 | 17 +++++++++++++++++
 3 files changed, 33 insertions(+)
 create mode 100644 overlay.d/90cgroups/usr/lib/systemd/system/coreos-keep-cgroup-v1.service
 create mode 100755 overlay.d/90cgroups/usr/libexec/coreos-keep-cgroup-v1

diff --git a/overlay.d/05core/usr/lib/systemd/system-preset/40-coreos.preset b/overlay.d/05core/usr/lib/systemd/system-preset/40-coreos.preset
index 89a4bc8d21..e9930f0b7d 100644
--- a/overlay.d/05core/usr/lib/systemd/system-preset/40-coreos.preset
+++ b/overlay.d/05core/usr/lib/systemd/system-preset/40-coreos.preset
@@ -13,3 +13,4 @@ enable afterburn-firstboot-checkin.service
 enable afterburn-sshkeys@.service
 # Update agent
 enable zincati.service
+enable coreos-keep-cgroup-v1.service
diff --git a/overlay.d/90cgroups/usr/lib/systemd/system/coreos-keep-cgroup-v1.service b/overlay.d/90cgroups/usr/lib/systemd/system/coreos-keep-cgroup-v1.service
new file mode 100644
index 0000000000..0f7ff02c86
--- /dev/null
+++ b/overlay.d/90cgroups/usr/lib/systemd/system/coreos-keep-cgroup-v1.service
@@ -0,0 +1,15 @@
+[Unit]
+Description=CoreOS Keep CGroups v1
+Documentation=https://github.com/coreos/fedora-coreos-tracker/issues/292
+RequiresMountsFor=/boot
+# Note we don't conditionalize on ConditionKernelCommandLine= here because the
+# kernel arg might've been added manually just for this boot; we still want to
+# change the BLS entries in that case.
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=/usr/libexec/coreos-keep-cgroup-v1
+
+[Install]
+WantedBy=multi-user.target
diff --git a/overlay.d/90cgroups/usr/libexec/coreos-keep-cgroup-v1 b/overlay.d/90cgroups/usr/libexec/coreos-keep-cgroup-v1
new file mode 100755
index 0000000000..2a3ba69f2d
--- /dev/null
+++ b/overlay.d/90cgroups/usr/libexec/coreos-keep-cgroup-v1
@@ -0,0 +1,17 @@
+#!/bin/bash
+set -euo pipefail
+
+for f in /boot/loader/entries/*.conf; do
+    options=$(grep '^options ' "$f" | cut -f2- -d' ')
+
+    # If it's already specified, don't touch whatever value is there. That way,
+    # users that purposely opted into v2 early keep it. It also makes this
+    # script idempotent.
+    if grep -q "systemd.unified_cgroup_hierarchy" <<< "$options"; then
+        continue
+    fi
+
+    # otherwise, make sure we stay on v1
+    sed -e "/^options / s/$/ systemd.unified_cgroup_hierarchy=0/" -i "$f"
+    echo "$(basename "$f"): injected systemd.unified_cgroup_hierarchy=0"
+done