function mo {
local directory="${1}"
local file
if [ "${directory}" ] ; then
    directory="$(realpath "${directory}")"
    file="${directory}/filesystem.squashfs"
    if mkdir 'overlay' ; then
        cd 'overlay'
        mkdir {lower,upper,work,mount}
        if mount "${file}" 'lower' ; then
            mount -t 'overlay' 'overlay' 'mount' \
-o lowerdir='lower',upperdir='upper',workdir='work'
        fi
        cd ..
    fi
else
    echo 'KO: directory?'
fi
}

function uo {
cd 'overlay'
if umount 'mount' ; then
    rmdir 'mount'
    rm --recursive 'upper' 'work'
    if umount 'lower' ; then
        rmdir 'lower'
    fi
fi
cd ..
rmdir 'overlay'
}


function mr {
for f in 'dev' 'dev/pts' 'proc' 'sys' ; do
    mount --bind "/${f}" "overlay/mount/${f}"
done
}

alias cr="\
chroot \
\"overlay/mount\" \
"

alias cru="\
chroot \
--userspec \"1000:1000\" \
\"overlay/mount\" \
"

function ur {
for f in 'sys' 'proc' 'dev/pts' 'dev' ; do
    umount --lazy "overlay/mount/${f}"
done
}


function mm {
mount --make-rslave --rbind '/deb' 'overlay/mount/deb'
}

function um {
umount --recursive 'overlay/mount/deb'
}


function ms {
local directory="${1}"
local level="${2}"
if [ "${directory}" ] ; then
    if mkdir "${directory}" ; then
        [ "${level}" ] || level='18'
        cp overlay/mount/{vmlinuz,initrd.img} "${directory}"
        mksquashfs \
'overlay/mount' "${directory}/filesystem.squashfs" \
-b '1M' \
-comp 'zstd' -Xcompression-level "${level}"
        chown --recursive 1000:1000 "${directory}"
    fi
fi
}