# vi: ts=4 expandtab syntax=sh

# default imagesize = 2252*1024**2 = 2.2G (the current size we ship)
imagesize=${IMAGE_SIZE:-2361393152}
fs_label="${FS_LABEL:-rootfs}"

rootfs_dev_mapper=
loop_device=
loop_raw=
backing_img=

clean_loops() {
    local kpartx_ret
    local kpartx_stdout

    if [ -n "${backing_img}" ]; then
        # sync before removing loop to avoid "Device or resource busy" errors
        sync
        kpartx_ret=""
        kpartx_stdout=$(kpartx -v -d "${backing_img}") || kpartx_ret=$?
        echo "$kpartx_stdout"
        if [ -n "$kpartx_ret" ]; then
            if echo "$kpartx_stdout" | grep -q "loop deleted"; then
                echo "Suppressing kpartx returning error (#860894)"
            else
                exit $kpartx_ret
            fi
        fi
        unset backing_img
    fi

    if [ -z "${rootfs_dev_mapper}" ]; then
        return 0
    fi

    unset loop_device
    unset loop_raw
    unset rootfs_dev_mapper
}

create_empty_disk_image() {
    # Prepare an empty disk image
    dd if=/dev/zero of="$1" bs=1 count=0 seek="${imagesize}"
}

create_manifest() {
    local chroot_root=${1}
    local target_file=${2}
    echo "create_manifest chroot_root: ${chroot_root}"
    dpkg-query --show --admindir="${chroot_root}/var/lib/dpkg" > ${target_file}
    echo "create_manifest call to dpkg-query finished."
    ./config/snap-seed-parse "${chroot_root}" "${target_file}"
    echo "create_manifest call to snap_seed_parse finished."
    echo "create_manifest finished"
}

make_ext4_partition() {
    device="$1"
    label=${fs_label:+-L "${fs_label}"}
    mkfs.ext4 -F -b 4096 -i 8192 -m 0 ${label} -E resize=536870912 "$device"
}

mount_image() {
    trap clean_loops EXIT
    backing_img="$1"
    local rootpart="$2"
    kpartx_mapping="$(kpartx -s -v -a ${backing_img})"

    # Find the loop device
    loop_p1="$(echo -e ${kpartx_mapping} | head -n1 | awk '{print$3}')"
    loop_device="/dev/${loop_p1%p[0-9]*}"
    if [ ! -b ${loop_device} ]; then
        echo "unable to find loop device for ${backing_img}"
        exit 1
    fi

    # Find the rootfs location
    rootfs_dev_mapper="/dev/mapper/${loop_p1%%[0-9]}${rootpart}"
    if [ ! -b "${rootfs_dev_mapper}" ]; then
        echo "${rootfs_dev_mapper} is not a block device";
        exit 1
    fi

    # Add some information to the debug logs
    echo "Mounted disk image ${backing_img} to ${rootfs_dev_mapper}"
    blkid ${rootfs_dev_mapper}

    return 0
}

setup_mountpoint() {
    local mountpoint="$1"

    mount --rbind --make-rslave /dev "$mountpoint/dev"
    mount proc-live -t proc "$mountpoint/proc"
    mount sysfs-live -t sysfs "$mountpoint/sys"
    mount -t tmpfs none "$mountpoint/tmp"
    mount -t tmpfs none "$mountpoint/var/lib/apt"
    mount -t tmpfs none "$mountpoint/var/cache/apt"
    mv "$mountpoint/etc/resolv.conf" resolv.conf.tmp
    cp /etc/resolv.conf "$mountpoint/etc/resolv.conf"
    chroot "$mountpoint" apt-get update

}

teardown_mountpoint() {
    # Reverse the operations from setup_mountpoint
    local mountpoint="$1"

    # ensure we have exactly one trailing slash, and escape all slashes for awk
    mountpoint_match=$(echo "$mountpoint" | sed -e's,/$,,; s,/,\\/,g;')'\/'
    # sort -r ensures that deeper mountpoints are unmounted first
    for submount in $(awk </proc/self/mounts "\$2 ~ /$mountpoint_match/ \
                      { print \$2 }" | LC_ALL=C sort -r); do
        umount $submount
    done
    mv resolv.conf.tmp "$mountpoint/etc/resolv.conf"
}

mount_partition() {
    partition="$1"
    mountpoint="$2"

    mount "$partition" "$mountpoint"
    setup_mountpoint "$mountpoint"
}

mount_overlay() {
    lower="$1"
    upper="$2"
    work="$2/../work"
    path="$3"

    mkdir -p "$work"
    mount -t overlay overlay \
	-olowerdir="$lower",upperdir="$upper",workdir="$work" \
	"$path"
}

mount_disk_image() {
    local disk_image=${1}
    local mountpoint=${2}
    mount_image ${disk_image} 1
    mount_partition "${rootfs_dev_mapper}" $mountpoint

    local uefi_dev="/dev/mapper${loop_device///dev/}p15"
    if [ -b ${uefi_dev} -a -e $mountpoint/boot/efi ]; then
        mount "${uefi_dev}" $mountpoint/boot/efi
    fi

    # This is needed to allow for certain operations
    # such as updating grub and installing software
    cat > $mountpoint/usr/sbin/policy-rc.d << EOF
#!/bin/sh
# ${IMAGE_STR}
echo "All runlevel operations denied by policy" >&2
exit 101
EOF
    chmod 0755 $mountpoint/usr/sbin/policy-rc.d

}

umount_partition() {
    local mountpoint=${1}
    teardown_mountpoint $mountpoint
    umount -R $mountpoint
    udevadm settle

    if [ -n "${rootfs_dev_mapper}" -a -b "${rootfs_dev_mapper}" ]; then
        # buildd's don't have /etc/mtab symlinked
        # /etc/mtab is needed in order zerofree space for ext4 filesystems
        [ -e /etc/mtab ] || ln -s /proc/mounts /etc/mtab

        # both of these are likely overkill, but it does result in slightly
        # smaller ext4 filesystem
        e2fsck -y -E discard ${rootfs_dev_mapper}
        zerofree ${rootfs_dev_mapper}
    fi
}

umount_disk_image() {
    mountpoint="$1"

    local uefi_dev="/dev/mapper${loop_device///dev/}p15"
    if [ -e "$mountpoint/boot/efi" -a -b "$uefi_dev" ]; then
	# zero fill free space in UEFI partition
	cat < /dev/zero > "$mountpoint/boot/efi/bloat_file" 2> /dev/null || true
	rm "$mountpoint/boot/efi/bloat_file"
        umount --detach-loop "$mountpoint/boot/efi"
    fi

    if [ -e $mountpoint/usr/sbin/policy-rc.d ]; then
        rm $mountpoint/usr/sbin/policy-rc.d
    fi
    umount_partition $mountpoint
    clean_loops
}

modify_vmdk_header() {
    # Modify the VMDK headers so that both VirtualBox _and_ VMware can
    # read the vmdk and import them.

    vmdk_name="${1}"
    descriptor=$(mktemp)
    newdescriptor=$(mktemp)

    # Extract the vmdk header for manipulation
    dd if="${vmdk_name}" of="${descriptor}" bs=1 skip=512 count=1024
    echo "Cat'ing original vmdk disk descriptor to console for debugging."
    # cat header so we are aware of the original descriptor for debugging
    cat $descriptor

    # trim null bytes to treat as standard text file
    tr -d '\000' < $descriptor > $newdescriptor

    #   remove the vmdk-stream-converter comment and replace with
    #       # Disk DescriptorFile. This is needed for Virtualbox
    #   remove the comments from vmdk-stream-converter which causes
    #       VirtualBox and others to fail VMDK validation
    sed -i -e 's|# Description file.*|# Disk DescriptorFile|' \
        -e '/# Believe this is random*/d' \
        -e '/# Indicates no parent/d' \
        -e '/# The Disk Data Base/d' \
            ${newdescriptor}

    # add newline to newdescriptor
    echo "" >> $newdescriptor

    # add required tools version
    echo -n 'ddb.toolsVersion = "2147483647"' >> $newdescriptor

    echo "Cat'ing modified descriptor for debugging."
    cat $newdescriptor

    # diff original descriptor and new descriptor for debugging
    # diff exits 1 if difference. pipefail not set so piping diff
    # to cat prints diff and swallows exit 1
    echo "Printing diff of original and new descriptors."
    diff --text $descriptor $newdescriptor | cat

    # The header must be 1024 or less before padding
    if ! expr $(stat --format=%s ${newdescriptor}) \< 1025 > /dev/null 2>&1; then
        echo "descriptor is too large, VMDK will be invalid!"; 
        exit 1
    fi

    # reset newdescriptor to be 1024
    truncate --no-create --size=1K $newdescriptor

    # Overwrite the vmdk header with our new, modified one
    dd conv=notrunc,nocreat \
        if="${newdescriptor}" of="${vmdk_name}" \
        bs=1 seek=512 count=1024

    rm ${descriptor} ${newdescriptor}
}

create_vmdk() {
    # There is no real good way to create a _compressed_ VMDK using open source
    # tooling that works across multiple VMDK-capable platforms. This functions
    # uses vmdk-stream-converter and then calls modify_vmdk_header to produce a
    # compatible VMDK.

    src="$1"
    destination="$2"
    size="${3:-10240}"

    streamconverter="VMDKstream"
    scratch_d=$(mktemp -d)
    cp ${src} ${scratch_d}/resize.img

    truncate --size=${size}M ${scratch_d}/resize.img
    python -m ${streamconverter} ${scratch_d}/resize.img ${destination}
    modify_vmdk_header ${destination}

    qemu-img info ${destination}
    rm -rf ${scratch_d}
}

create_derivative() {
    # arg1 is the disk type
    # arg2 is the new name
    unset derivative_img
    case ${1} in
           uefi) disk_image="binary/boot/disk-uefi.ext4";
                 dname="${disk_image//-uefi/-$2-uefi}";;
              *) disk_image="binary/boot/disk.ext4";
                 dname="${disk_image//.ext4/-$2.ext4}";;
    esac

    if [ ! -e ${disk_image} ]; then
        echo "Did not find ${disk_image}!"; exit 1;
    fi

    cp ${disk_image} ${dname}
    export derivative_img=${dname}
}

convert_to_qcow2() {
    src="$1"
    destination="$2"
    qemu-img convert -c -O qcow2 -o compat=0.10 "$src" "$destination"
    qemu-img info "$destination"
}

replace_grub_root_with_label() {
    # When update-grub is run, it will detect the disks in the build system.
    # Instead, we want grub to use the right labelled disk
    CHROOT_ROOT="$1"

    # If boot by partuuid has been requested, don't override.
    if [ -f $CHROOT_ROOT/etc/default/grub.d/40-force-partuuid.cfg ] && \
           grep -q ^GRUB_FORCE_PARTUUID= $CHROOT_ROOT/etc/default/grub.d/40-force-partuuid.cfg
    then
        return 0
    fi
    sed -i -e "s,root=[^ ]*,root=LABEL=${fs_label}," \
        "$CHROOT_ROOT/boot/grub/grub.cfg"
}


# When running update-grub in a chroot on a build host, we don't want it to
# probe for disks or probe for other installed OSes.  Extract common
# diversion wrappers, so this isn't reinvented differently for each image.
divert_grub() {
	CHROOT_ROOT="$1"

	chroot "$CHROOT_ROOT" dpkg-divert --local \
		--rename /usr/sbin/grub-probe
	chroot "$CHROOT_ROOT" touch /usr/sbin/grub-probe
	chroot "$CHROOT_ROOT" chmod +x /usr/sbin/grub-probe

	chroot "$CHROOT_ROOT" dpkg-divert --local \
		--divert /etc/grub.d/30_os-prober.dpkg-divert \
		--rename /etc/grub.d/30_os-prober

	# Divert systemd-detect-virt; /etc/kernel/postinst.d/zz-update-grub
	# no-ops if we are in a container, and the launchpad farm runs builds
	# in lxd.  We therefore pretend that we're never in a container (by
	# exiting 1).
	chroot "$CHROOT_ROOT" dpkg-divert --local \
		--rename /usr/bin/systemd-detect-virt
	echo "exit 1" > "$CHROOT_ROOT"/usr/bin/systemd-detect-virt
	chmod +x "$CHROOT_ROOT"/usr/bin/systemd-detect-virt
}

undivert_grub() {
	CHROOT_ROOT="$1"

	chroot "$CHROOT_ROOT" rm /usr/sbin/grub-probe
	chroot "$CHROOT_ROOT" dpkg-divert --remove --local \
		--rename /usr/sbin/grub-probe

	chroot "$CHROOT_ROOT" dpkg-divert --remove --local \
		--divert /etc/grub.d/30_os-prober.dpkg-divert \
		--rename /etc/grub.d/30_os-prober

	if grep -q "^exit 1$" "$CHROOT_ROOT"/usr/bin/systemd-detect-virt; then
		rm "$CHROOT_ROOT"/usr/bin/systemd-detect-virt
	fi
	chroot "$CHROOT_ROOT" dpkg-divert --remove --local \
		--rename /usr/bin/systemd-detect-virt
}

recreate_initramfs() {
	# Regenerate the initramfs by running update-initramfs in the
	# chroot at $1 and copying the generated initramfs
	# around. Beware that this was written for a single use case
	# (live-server) and may not work in all cases without
	# tweaking...
	# config/common must be sourced before calling this function.
	CHROOT="$1"
	# Start by cargo culting bits of lb_chroot_hacks:
	if [ -n "$LB_INITRAMFS_COMPRESSION" ]; then
		echo "COMPRESS=$LB_INITRAMFS_COMPRESSION" > "$CHROOT"/etc/initramfs-tools/conf.d/livecd-rootfs.conf
	fi
	chroot "$CHROOT" sh -c "${UPDATE_INITRAMFS_OPTIONS:-} update-initramfs -k all -t -u"
	rm -rf "$CHROOT"/etc/initramfs-tools/conf.d/livecd-rootfs.conf
	# Then bits of lb_binary_linux-image:
	case "${LB_INITRAMFS}" in
		casper)
			DESTDIR="binary/casper"
			;;

		live-boot)
			DESTDIR="binary/live"
			;;

		*)
			DESTDIR="binary/boot"
			;;
	esac
	mv "$CHROOT"/boot/initrd.img-* $DESTDIR
}

release_ver() {
    # Return the release version number
    distro-info --series="$LB_DISTRIBUTION" -r | awk '{ print $1 }'
}

_snap_post_process() {
    # Look for the 'core' snap. If it is not present, assume that the image
    # contains only snaps with bases >= core18. In that case snapd is
    # preseeded. However, when 'core' is being installed and snapd has not
    # been installed by a call to 'snap_preseed' (see below) then it is
    # removed again.
    local CHROOT_ROOT=$1
    local SNAP_NAME=$2

    local seed_dir="$CHROOT_ROOT/var/lib/snapd/seed"
    local snaps_dir="$seed_dir/snaps"
    local seed_yaml="$seed_dir/seed.yaml"
    local assertions_dir="$seed_dir/assertions"
    local snapd_install_stamp="$seed_dir/.snapd-explicit-install-stamp"

    case $SNAP_NAME in
        core[0-9]*)
            # If the 'core' snap is not present, assume we are coreXX-only and
            # install the snapd snap.
            if [ ! -f ${snaps_dir}/core_[0-9]*.snap ]; then
                _snap_preseed $CHROOT_ROOT snapd stable
            fi
            ;;
        core)
            # If the snapd snap has been seeded, but not marked as explicitly
            # installed (see snap_preseed below), then remove it.
            if [ -f ${snaps_dir}/snapd_[0-9]*.snap ] && \
                    [ ! -f "$snapd_install_stamp" ]
            then
                # Remove snap, assertions and entry in seed.yaml
                rm -f ${snaps_dir}/snapd_[0-9]*.snap
                rm -f ${assertions_dir}/snapd_[0-9]*.assert
                sed -i -e'N;/name: snapd/,+2d' $seed_yaml
            fi
            ;;
        *)
            # ignore
            ;;
    esac
}

_snap_preseed() {
    # Download the snap/assertion and add to the preseed
    local CHROOT_ROOT=$1
    local SNAP=$2
    local SNAP_NAME=${SNAP%/*}
    local CHANNEL=${3:?Snap channel must be specified}

    local seed_dir="$CHROOT_ROOT/var/lib/snapd/seed"
    local snaps_dir="$seed_dir/snaps"
    local seed_yaml="$seed_dir/seed.yaml"
    local assertions_dir="$seed_dir/assertions"

    # Download the snap & assertion
    local snap_download_failed=0

    # Preseed a snap only once
    if [ -f ${snaps_dir}/${SNAP_NAME}_[0-9]*.snap ]; then
        return
    fi

    sh -c "
        set -x;
        cd \"$CHROOT_ROOT/var/lib/snapd/seed\";
        SNAPPY_STORE_NO_CDN=1 snap download \
            --cohort="${COHORT_KEY:-}" \
            --channel=\"$CHANNEL\" \"$SNAP_NAME\"" || snap_download_failed=1
    if [ $snap_download_failed = 1 ] ; then
        echo "If the channel ($CHANNEL) includes '*/ubuntu-##.##' track per "
        echo "Ubuntu policy (ex. stable/ubuntu-18.04) the publisher will need "
        echo "to temporarily create the channel/track to allow fallback during"
        echo "download (ex. stable/ubuntu-18.04 falls back to stable if the"
        echo "prior had been created in the past)."
        exit 1
    fi

    mv -v $seed_dir/*.assert $assertions_dir
    mv -v $seed_dir/*.snap $snaps_dir

    # Pre-seed snap's base
    local core_snap=""
    case $SNAP_NAME in
        snapd)
            # snapd is self-contained, ignore base
            ;;
        core|core[0-9][0-9])
            # core and core## are self-contained, ignore base
            ;;
        *)
            # Determine which core snap is needed
            local snap_info

            # snap info doesn't have --channel, so must run agains the downloaded snap
            snap_info=$(snap info --verbose ${snaps_dir}/${SNAP_NAME}_[0-9]*.snap)

            if [ $? -ne 0 ]; then
                echo "Failed to retrieve base of $SNAP_NAME!"
                exit 1
            fi

            core_snap=$(echo "$snap_info" | grep '^base:' | awk '{print $2}')

            # If snap info does not list a base use 'core'
            core_snap=${core_snap:-core}

            _snap_preseed $CHROOT_ROOT $core_snap stable
            ;;
    esac

    # Add the snap to the seed.yaml
    ! [ -e $seed_yaml ] && echo "snaps:" > $seed_yaml
    cat <<EOF >> $seed_yaml
  -
    name: ${SNAP_NAME}
    channel: ${CHANNEL}
EOF

    case ${SNAP} in */classic) echo "    classic: true" >> $seed_yaml;; esac

    echo -n "    file: " >> $seed_yaml
    (cd $snaps_dir; ls -1 ${SNAP_NAME}_*.snap) >> $seed_yaml

    _snap_post_process $CHROOT_ROOT $SNAP_NAME
}

snap_prepare_assertions() {
    # Configure basic snapd assertions
    local CHROOT_ROOT=$1
    # A colon-separated string of brand:model to be used for the image's model
    # assertion
    local CUSTOM_BRAND_MODEL=$2

    local seed_dir="$CHROOT_ROOT/var/lib/snapd/seed"
    local snaps_dir="$seed_dir/snaps"
    local assertions_dir="$seed_dir/assertions"
    local model_assertion="$assertions_dir/model"
    local account_key_assertion="$assertions_dir/account-key"
    local account_assertion="$assertions_dir/account"

    mkdir -p "$assertions_dir"
    mkdir -p "$snaps_dir"

    local brand="$(echo $CUSTOM_BRAND_MODEL | cut -d: -f 1)"
    local model="$(echo $CUSTOM_BRAND_MODEL | cut -d: -f 2)"

    if ! [ -e "$model_assertion" ] ; then
        snap known --remote model series=16 \
            model=$model brand-id=$brand \
            > "$model_assertion"
    fi

    if ! [ -e "$account_key_assertion" ] ; then
        local account_key=$(sed -n -e's/sign-key-sha3-384: //p' \
            < "$model_assertion")
        snap known --remote account-key \
            public-key-sha3-384="$account_key" \
            > "$account_key_assertion"
    fi


    if ! [ -e "$account_assertion" ] ; then
        local account=$(sed -n -e's/account-id: //p' < "$account_key_assertion")
        snap known --remote account account-id=$account \
            > "$account_assertion"
    fi
}

snap_prepare() {
    # Configure basic snapd assertions and pre-seeds the 'core' snap
    local CHROOT_ROOT=$1
    # Optional. If set, should be a colon-separated string of brand:model to be
    # used for the image's model assertion
    local CUSTOM_BRAND_MODEL=${2:-generic:generic-classic}

    local seed_dir="$CHROOT_ROOT/var/lib/snapd/seed"
    local snaps_dir="$seed_dir/snaps"

    snap_prepare_assertions "$CHROOT_ROOT" "$CUSTOM_BRAND_MODEL"
}

snap_preseed() {
    # Preseed a snap in the image
    local CHROOT_ROOT=$1
    local SNAP=$2
    local SNAP_NAME=${SNAP%/*}
    # Per Ubuntu policy, all seeded snaps (with the exception of the core
    # snap) must pull from stable/ubuntu-$(release_ver) as their channel.
    local CHANNEL=${3:-"stable/ubuntu-$(release_ver)"}

    snap_prepare $CHROOT_ROOT

    _snap_preseed $CHROOT_ROOT $SNAP $CHANNEL

    # Mark this image as having snapd installed explicitly.
    case $SNAP_NAME in
        snapd)
            touch "$CHROOT_ROOT/var/lib/snapd/seed/.snapd-explicit-install-stamp"
            ;;
    esac


    # Do basic validation of generated snapd seed.yaml, doing it here
    # means we catch all the places(tm) that snaps are added but the
    # downside is that each time a snap is added the seed must be valid,
    # i.e. snaps with bases need to add bases first etc.
    if [ -e chroot/var/lib/snapd/seed/seed.yaml ]; then
        snap debug validate-seed "$CHROOT_ROOT/var/lib/snapd/seed/seed.yaml"
    fi
}

configure_oci() {
    # configure a chroot to be a OCI/docker container
    # theses changes are taken from the current Dockerfile modifications done
    # at https://github.com/tianon/docker-brew-ubuntu-core/blob/master/update.sh

    local chroot=$1

    echo "==== Configuring OCI ===="

    # https://github.com/docker/docker/blob/9a9fc01af8fb5d98b8eec0740716226fadb3735c/contrib/mkimage/debootstrap#L40-L48
    echo '#!/bin/sh' > ${chroot}/usr/sbin/policy-rc.d
    echo 'exit 101' >> ${chroot}/usr/sbin/policy-rc.d
    Chroot ${chroot} "chmod +x /usr/sbin/policy-rc.d"

    # https://github.com/docker/docker/blob/9a9fc01af8fb5d98b8eec0740716226fadb3735c/contrib/mkimage/debootstrap#L54-L56
    Chroot ${chroot} "dpkg-divert --local --rename --add /sbin/initctl"
    cp -a ${chroot}/usr/sbin/policy-rc.d ${chroot}/sbin/initctl
    sed -i 's/^exit.*/exit 0/' ${chroot}/sbin/initctl

    # https://github.com/docker/docker/blob/9a9fc01af8fb5d98b8eec0740716226fadb3735c/contrib/mkimage/debootstrap#L71-L78
    echo 'force-unsafe-io' > ${chroot}/etc/dpkg/dpkg.cfg.d/docker-apt-speedup

    # https://github.com/docker/docker/blob/9a9fc01af8fb5d98b8eec0740716226fadb3735c/contrib/mkimage/debootstrap#L85-L105
    echo 'DPkg::Post-Invoke { "rm -f /var/cache/apt/archives/*.deb /var/cache/apt/archives/partial/*.deb /var/cache/apt/*.bin || true"; };' > ${chroot}/etc/apt/apt.conf.d/docker-clean

    echo 'APT::Update::Post-Invoke { "rm -f /var/cache/apt/archives/*.deb /var/cache/apt/archives/partial/*.deb /var/cache/apt/*.bin || true"; };' >> ${chroot}/etc/apt/apt.conf.d/docker-clean

    echo 'Dir::Cache::pkgcache ""; Dir::Cache::srcpkgcache "";' >> ${chroot}/etc/apt/apt.conf.d/docker-clean

    # https://github.com/docker/docker/blob/9a9fc01af8fb5d98b8eec0740716226fadb3735c/contrib/mkimage/debootstrap#L109-L115
    echo 'Acquire::Languages "none";' > ${chroot}/etc/apt/apt.conf.d/docker-no-languages

    # https://github.com/docker/docker/blob/9a9fc01af8fb5d98b8eec0740716226fadb3735c/contrib/mkimage/debootstrap#L118-L130
    echo 'Acquire::GzipIndexes "true"; Acquire::CompressionTypes::Order:: "gz";' > ${chroot}/etc/apt/apt.conf.d/docker-gzip-indexes

    # https://github.com/docker/docker/blob/9a9fc01af8fb5d98b8eec0740716226fadb3735c/contrib/mkimage/debootstrap#L134-L151
    echo 'Apt::AutoRemove::SuggestsImportant "false";' > ${chroot}/etc/apt/apt.conf.d/docker-autoremove-suggests

    # delete all the apt list files since they're big and get stale quickly
    rm -rf ${chroot}/var/lib/apt/lists/*

    # verify that the APT lists files do not exist
    Chroot chroot "apt-get indextargets" > indextargets.out
    [ ! -s indextargets.out ]
    rm indextargets.out
    # (see https://bugs.launchpad.net/cloud-images/+bug/1699913)

    # make systemd-detect-virt return "docker"
    # See: https://github.com/systemd/systemd/blob/aa0c34279ee40bce2f9681b496922dedbadfca19/src/basic/virt.c#L434
    mkdir -p ${chroot}/run/systemd
    echo 'docker' > ${chroot}/run/systemd/container

    rm -rf ${chroot}/var/cache/apt/*.bin
    echo "==== Configuring OCI done ===="
}

is_live_layer () {
    local pass=$1
    for livepass in $LIVE_PASSES; do
	    [ "$livepass" != "$pass" ] && continue
        return 0
    done
    return 1
}