feat: add overlay testing script

overlay.sh

@@ -0,0 +1,36 @@
+#!/bin/sh
+
+UID=$(id -u)
+GID=$(id -g)
+CURDIR=$(pwd)
+
+set -u 
+set -e
+
+echo "Umounting merge directory if it is mounted"
+if mount | grep -q "${CURDIR}.merge"; then
+  sudo umount -lf "${CURDIR}.merge"
+fi
+
+# echo "Removing old upper directory"
+# sudo rm -rf "${CURDIR}.upper"
+
+echo "Creating directories"
+sudo mkdir -p "${CURDIR}.upper"
+sudo mkdir -p "${CURDIR}.workdir"
+sudo mkdir -p "${CURDIR}.merge"
+
+echo "Setting permissions"
+sudo chown "$UID:$GID" "${CURDIR}.upper"
+sudo chown "$UID:$GID" "${CURDIR}.workdir"
+sudo chown "$UID:$GID" "${CURDIR}.merge"
+
+echo "Mounting filesystem"
+sudo mount -t overlay \
+	-o "lowerdir=${CURDIR},upperdir=${CURDIR}.upper,workdir=${CURDIR}.workdir" \
+	overlay \
+	"${CURDIR}.merge"
+
+echo "Running shell"
+cd "${CURDIR}.merge" || exit 1
+exec $SHELL