# Linux Kernel Module Cheat

#### 38.15.4. rootfs_overlay

Source: rootfs_overlay.

We use this directory for:

- customized configuration files

- userland module test scripts that don’t need to be compiled.

  Contrast this with C examples that need compilation.

This directory is copied into the target filesystem by:

    ./copy-overlay
    ./build-buildroot

Source: copy-overlay

Build Buildroot is required for the same reason as described at: Section 2.2.2.2, “Your first kernel module hack”.

However, since the rootfs_overlay directory does not require compilation, unlike say kernel modules, we also make it 9P available to the guest directly even without `./copy-overlay` at:

    ls /mnt/9p/rootfs_overlay

This way you can just hack away the scripts and try them out immediately without any further operations.

- <code>out_rootfs_overlay_dir</code>