reproduce (this is a W=1 build):
        # https://github.com/riteshharjani/linux/commit/0270bb5b6bb6e0a43a4edd72e6e0087cba6ed650
        git remote add riteshharjani https://github.com/riteshharjani/linux
        git fetch --no-tags riteshharjani ext4-iomap-v3
        git checkout 0270bb5b6bb6e0a43a4edd72e6e0087cba6ed650
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash