rewrite based on reference project from github

dracut-module/90netboot/mount-netboot.sh

@@ -0,0 +1,32 @@
+#!/bin/sh
+# Download and mount squashfs root with overlay
+
+. /tmp/netboot.conf
+
+info "Downloading root filesystem from http://${BOOT_SERVER}/${IMAGE_VERSION}/filesystem.squashfs"
+
+mkdir -p /run/netboot
+wget -O /run/netboot/root.squashfs \
+    "http://${BOOT_SERVER}/${IMAGE_VERSION}/filesystem.squashfs" || \
+    die "Failed to download root filesystem from $BOOT_SERVER"
+
+info "Download complete, mounting filesystems..."
+
+# Mount squashfs (read-only base)
+mkdir -p /run/rootfs/lower
+mount -t squashfs /run/netboot/root.squashfs /run/rootfs/lower || \
+    die "Failed to mount squashfs"
+
+# Create tmpfs for overlay (writable layer)
+mkdir -p /run/rootfs/upper /run/rootfs/work
+mount -t tmpfs -o size=4G tmpfs /run/rootfs/upper || \
+    die "Failed to create tmpfs overlay"
+mkdir -p /run/rootfs/upper/upper /run/rootfs/upper/work
+
+# Mount overlay (combines read-only base + writable tmpfs)
+mount -t overlay overlay \
+    -o lowerdir=/run/rootfs/lower,upperdir=/run/rootfs/upper/upper,workdir=/run/rootfs/upper/work \
+    /sysroot || \
+    die "Failed to mount overlay"
+
+info "Root filesystem mounted successfully"