examples: add ignition-kargs binary example

examples/ignition-kargs-helper

@@ -0,0 +1,45 @@
+#!/bin/bash
+
+set -euxo pipefail
+
+# Mount /boot. Note that we mount /boot but we don't unmount it because we
+# are run in a systemd unit with MountFlags=slave so it is unmounted for us.
+bootmnt=/mnt/boot_partition
+mkdir -p ${bootmnt}
+bootdev=/dev/disk/by-label/boot
+mount -o rw ${bootdev} ${bootmnt}
+grubcfg="${bootmnt}/grub/grub.cfg"
+
+kernelopts="$(grep kernelopts= <$grubcfg)"
+
+while [[ $# -gt 0 ]]
+do
+key="$1"
+
+case $key in
+--should-exist)
+    arg="$2"
+    # don't repeat the arg
+    if [[ ! " ${kernelopts[*]} " =~ " ${arg} " ]]; then
+        kernelopts="$kernelopts $arg "
+    fi
+    shift 2
+    ;;
+--should-not-exist)
+    arg="$2"
+    kernelopts="$(echo "$kernelopts" | sed "s|$2||g")"
+    shift 2
+    ;;
+    *)
+    echo "Unknown option"
+    exit 1
+    ;;
+esac
+done
+
+# only apply the changes & reboot if changes have been made
+if [[ ! "$kernelopts" == "$(grep kernelopts= <$grubcfg)" ]]; then
+    awk "{sub(/kernelopts=.*/,\"$kernelopts\"); print}" $grubcfg > tmp && mv tmp $grubcfg
+
+    systemctl reboot
+fi

examples/ignition-kargs.service

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+[Unit]
+Description=Ignition (kargs)
+Documentation=https://github.com/coreos/ignition
+ConditionPathExists=/etc/initrd-release
+DefaultDependencies=false
+Before=ignition-complete.target
+
+# Stage order: setup -> fetch-offline [-> fetch] [-> kargs] -> disks -> mount -> files.
+After=ignition-fetch.service
+Before=ignition-disks.service
+
+OnFailure=emergency.target
+OnFailureJobMode=isolate
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+EnvironmentFile=/run/ignition.env
+ExecStart=/usr/bin/ignition --root=/sysroot --platform=${PLATFORM_ID} --stage=kargs
+# MountFlags=slave is so the umount of /boot is guaranteed to happen.
+# /boot will only be mounted for the lifetime of the unit.
+MountFlags=slave