examples: add ignition-kargs binary example

examples/ignition-kargs-helper

@@ -0,0 +1,46 @@
+#!/bin/bash
+
+# Requires sed & awk to be present
+
+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 | sed \"s,kernelopts=,,g\")"
+
+while [[ $# -gt 0 ]]
+do
+    key="$1"
+
+    case $key in
+    --should-exist)
+        arg="$2"
+        # don't repeat the arg
+        if [[ ! " ${kernelopts[*]} " =~ " ${arg} " ]]; then
+            kernelopts="$kernelopts $arg "
+        fi
+        shift 2
+        ;;
+    --should-not-exist)
+        kernelopts="$(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=$kernelopts\"); print}" $grubcfg > /run/kargs_tmp && mv /run/kargs_tmp $grubcfg
+
+    systemctl reboot
+fi