reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git/commit/?id=025756ee7b476241270dd8ccbe17cc4c473800fa
        git remote add brauner-vfs https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
        git fetch --no-tags brauner-vfs vfs-7.4.idmap
        git checkout 025756ee7b476241270dd8ccbe17cc4c473800fa
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # pip install -r Documentation/sphinx/requirements.txt
        make htmldocs