#!/bin/bash
#
# Copy root filesystem into an existing raspberry pi image.
# We take over the kernel modules and firmware files from
# the existing image, as those are tightly belonging to
# the kernel of this image.
#
# Note1: that we also change the uuids of the disks during this step.
#
# Note2: This way the bootloader and kernel from the existing
# image is used.
#
# Note3: We intentionally don't use the result of mktemp
# directly to reduce the risk of damaging the host filesystem.
#
output="$1"
[ "x${output}" == "x" ] && output="raspbian.img"
# download image
[ ! -f ../${output} ] && (wget --output-document=../raspbian.zip 'https://downloads.raspberrypi.org/raspbian_lite_latest' && unzip -p ../raspbian.zip > ../${output}) || true
# copy filesystem and change uuids
d=$(basename $(mktemp -d));
f=$(basename $(mktemp /tmp/XXXXXXXXXX.tar));
l=$(sudo kpartx -l ../${output} | sed -n '/loop/ s,.*/dev/\(loop[0-9]\+\).*,\1, p;q;');
[ "x${d}" != "x" ] &&
sudo kpartx -as ../${output} &&
sudo mount /dev/mapper/${l}p2 /tmp/${d} &&
sed -i "s,PARTUUID=[^ ]*\(.*vfat\),PARTUUID=$(sudo blkid /dev/mapper/${l}p1 -s PARTUUID -o value)\1," etc/fstab &&
sed -i "s,PARTUUID=[^ ]*\(.*ext4\),PARTUUID=$(sudo blkid /dev/mapper/${l}p2 -s PARTUUID -o value)\1," etc/fstab &&
(cd /tmp/${d}; sudo tar -cf /tmp/${f} {lib/firmware,lib/modules,dev}) &&
sudo rm -Rf /tmp/${d}/* &&
sudo tar -cf - . | (cd /tmp/${d}/; sudo tar -xf -) &&
(cd /tmp/${d}; sudo tar -xf /tmp/${f}) &&
sudo umount /tmp/${d} &&
sudo kpartx -d ../${output} &&
rmdir /tmp/${d};
rm /tmp/${f}
# modify command line in boot partition
d=$(basename $(mktemp -d));
l=$(sudo kpartx -l ../${output} | sed -n '/loop/ s,.*/dev/\(loop[0-9]\+\).*,\1, p;q;');
[ "x${d}" != "x" ] &&
sudo kpartx -as ../${output} &&
sudo mount /dev/mapper/${l}p1 /tmp/${d} &&
sed -i 's| init=/usr/lib/raspi-config/init_resize.sh||' /tmp/${d}/cmdline.txt &&
sed -i 's| quiet||' /tmp/${d}/cmdline.txt &&
sudo umount /tmp/${d} &&
sudo kpartx -d ../${output} &&
rmdir /tmp/${d}