35coreos-ignition: handle the case where booted kargs don't match des…

…ired

Today when you boot a system it's possible a value for a karg you
specified in the Ignition config matches the BLS config but not the
kargs from the current boot (in /proc/cmdline). Let's detect this and
reboot in that case too.

overlay.d/05core/usr/lib/dracut/modules.d/35coreos-ignition/coreos-kargs.sh

@@ -1,30 +1,60 @@
 #!/bin/bash
 set -euo pipefail
 
-# First check to see if the requested state is satisfied by the current boot
-/usr/bin/rdcore kargs --current --create-if-changed /run/coreos-kargs-thisboot-differ "$@"
+
+# There are a few cases we need to handle here. To illustrate this
+# we'll use scenarios below where:
+#
+# - "booted":   The kernel arguments from the currently booting system.
+# - "ignition": The kernel arguments in the Ignition configuration.
+# - "bls":      The kernel arguments currently baked into the disk
+#               image BLS configs.
+#
+# The scenarios are:
+#
+# A.
+#   - Scenario:
+#       - booted: ""
+#       - ignition: "foobar"
+#       - bls: ""
+#   - Action: -> Update BLS configs, perform reboot
+# B.
+#   - Scenario:
+#       - booted: "foobar"
+#       - ignition: "foobar"
+#       - bls: ""
+#   - Action: -> Update BLS configs, skip reboot
+# C.
+#   - Scenario:
+#       - booted: ""
+#       - ignition: "foobar"
+#       - bls: "foobar"
+#   - Action: -> Skip update of BLS configs (they match already), perform reboot
+#
+# The logic here boils down to:
+#   if "ignition" != "booted"; then needreboot=1; fi
+#   if "ignition" != "bls"; then updatebls(); fi
+
+
+
+# If the desired state isn't reflected by the current boot we'll need to reboot.
+/usr/bin/rdcore kargs --current --create-if-changed /run/coreos-kargs-reboot "$@"
+if [ -e /run/coreos-kargs-reboot ]; then
+    msg="Desired kernel arguments don't match current boot. Requesting reboot."
+    systemd-cat -t coreos-kargs <<< "$msg"
+fi
 
 if is-live-image; then
 	# If we're in a live system and the kargs don't match then we must error.
-    if [ -e /run/coreos-kargs-thisboot-differ ]; then
+    if [ -e /run/coreos-kargs-reboot ]; then
         echo "Need to modify kernel arguments, but cannot affect live system." >&2
         exit 1
     fi
 else
+    # Update the BLS configs if they need to be updated.
     /usr/bin/rdcore kargs --boot-device /dev/disk/by-label/boot --create-if-changed /run/coreos-kargs-changed "$@"
-    # If the bootloader was changed and the kernel arguments don't match this boot
-    # then we must reboot. If they do match this boot then we can skip the reboot.
-    #
-    # Note we write info messages via systemd-cat here because stdout gets swallowed
-    # by Ignition if there is no failure. This forces the info into the journal.
     if [ -e /run/coreos-kargs-changed ]; then
-        if [ -e /run/coreos-kargs-thisboot-differ ]; then
-            msg="Kernel arguments were changed. Requesting reboot."
-            systemd-cat -t coreos-kargs <<< "$msg"
-            touch /run/coreos-kargs-reboot
-        else
-            msg="Kernel arguments were changed, but they match this boot. Skipping reboot."
-            systemd-cat -t coreos-kargs <<< "$msg"
-        fi
+        msg="Kernel arguments in BLS config were updated."
+        systemd-cat -t coreos-kargs <<< "$msg"
     fi
 fi