setup-buildchroot

#!/bin/bash
#
# setup-buildchroot - set up a Debian build chroot
#
# For details, see usage() and Documentation/building-xfstests.md

set -e -u

SCRIPTNAME="$(basename "$0")"
SCRIPTDIR="$(readlink -f "$(dirname "$0")")"

INTERACTIVE=true

DEBIAN_RELEASE=
DEBIAN_RELEASE_DEFAULT=bookworm
DEBIAN_PORTS_RELEASE_DEFAULT=unstable

DEBIAN_KEYRING=
DEBIAN_KEYRING_DEFAULT=/usr/share/keyrings/debian-archive-keyring.gpg
DEBIAN_PORTS_KEYRING_DEFAULT=/usr/share/keyrings/debian-ports-archive-keyring.gpg

DEBIAN_ARCH=
case $(uname -m) in
    aarch64)   DEBIAN_ARCH_DEFAULT=arm64  ;;
    i386|i686) DEBIAN_ARCH_DEFAULT=i386   ;;
    x86_64)    DEBIAN_ARCH_DEFAULT=amd64  ;;
    *)         DEBIAN_ARCH_DEFAULT=$(uname -m) ;;
esac
DEBIAN_PORTS_ARCH_DEFAULT=x32

DEBIAN_MIRROR=
DEBIAN_MIRROR_DEFAULT=http://ftp.debian.org/debian
DEBIAN_PORTS_MIRROR_DEFAULT=http://ftp.ports.debian.org/debian-ports

CHROOT_NAME=
CHROOT_DIR=
CHROOT_FILE=
CHROOT_USER=

DO_OVERLAY=
DO_OVERLAY_DEFAULT=no

DO_CCACHE=
DO_CCACHE_DEFAULT=yes

DO_TAR=
DO_TAR_DEFAULT=no

QEMU=
BINFMT_MISC_MNT=/proc/sys/fs/binfmt_misc

SCHROOT_CONFFILE=/etc/schroot/schroot.conf
SCHROOT_CHROOT_D=/etc/schroot/chroot.d
SCHROOT_FSTAB=xfstests-bld/fstab
SCHROOT_FSTAB_FILE=/etc/schroot/$SCHROOT_FSTAB

PROXY=

if type -P zstd >& /dev/null ; then
    TAR_COMPRESS=zstd
elif type -P xz >& /dev/null; then
    TAR_COMPRESS=xz
elif type -P bzip2 >& /dev/null ; then
    TAR_COMPRESS=bz2
else
    TAR_COMPRESS=gz
fi

select_packages()
{
    # Additional packages to install in the build chroot
    BUILD_DEPENDENCIES=(
    autoconf
    autoconf2.64
    automake
    autopoint
    bison
    build-essential
    ca-certificates
    debootstrap
    e2fslibs-dev
    ed
    fakechroot
    flex
    gettext
    git
    golang-go
    libacl1-dev
    libblkid-dev
    libdbus-1-3
    libgdbm-dev
    libicu-dev
    libkeyutils-dev
    libsqlite3-dev
    libssl-dev
    libsystemd-dev
    libtool-bin
    liburcu-dev
    lsb-release
    meson
    pkg-config
    python3-setuptools
    qemu-utils
    rsync
    symlinks
    uuid-dev
    zlib1g-dev
    )
    if [ "${DO_CCACHE}" = "yes" ]; then
       BUILD_DEPENDENCIES+=(ccache)
    fi
}

die()
{
    local msg

    echo 1>&2 "ERROR: $1"
    shift
    for msg; do
	echo 1>&2 "       $msg"
    done
    exit 1
}

log()
{
    local msg

    echo "[INFO] $1"
    shift
    for msg; do
	echo "       $msg"
    done
}

run_cmd()
{
    log "Running command: $*"
    "$@"
}

usage()
{
    cat <<EOF
Usage: $SCRIPTNAME [OPTION]...

Set up a Debian chroot for building xfstests tarballs and test appliances.  Both
native and foreign chroots are supported; foreign chroots will use QEMU
user-mode emulation.  The resulting chroot is added to $SCHROOT_CONFFILE
so that it can be entered using the schroot program.  Run with no arguments to
be prompted for the various options, or specify them on the command line.

Options:
    --release=RELEASE   Debian release to use.  Default: $DEBIAN_RELEASE_DEFAULT
    --arch=ARCH         Debian architecture to use.  Default: $DEBIAN_ARCH_DEFAULT
    --mirror=MIRROR     Debian mirror to use.
			    Default: $DEBIAN_MIRROR_DEFAULT
    --keyring=KEYRING   Debian keyring to use.
			    Default: $DEBIAN_KEYRING_DEFAULT
    --chroot-dir=DIR    Chroot directory.  Default: /chroots/\$RELEASE-\$ARCH
    --chroot-file=FILE	Chroot file used if --tar is enabled.
			    Default: /tmp/\$RELEASE-\$ARCH.tar.$TAR_COMPRESS
    --chroot-name=NAME  Name of chroot.  Default: basename of \$DIR
    --chroot-user=USER  User which will be allowed to access the chroot,
                        ***including passwordless root access***.  Default:
                        value of \$SUDO_USER, if any.
    --proxy             Web proxy to use when fetching the packages.
    --use-overlay       Use the overlay file system when creating the chroot
    --no-overlay        Don't use the overlay file system in the chroot
    --ccache		Use ccache to accelerate builds in the chroot
    --no-ccache		Don't use ccache in the chroot
    --tar		Generate a compressed tar file containing the chroot
    --no-tar		Generate the chroot as a directory
    --tar-compress	Default compression format to use
			   (valid options: bz2 gz xz zstd)
    --ports		Change the defaults for debian-ports architectures.
    --noninteractive    Use the defaults rather than prompting
EOF
}

check_prerequisites()
{
    if ! type -P debootstrap >/dev/null; then
	die "debootstrap is not installed!" \
	    "On Debian-based systems, run: 'sudo apt-get install debootstrap'"
    fi

    if ! type -P schroot >/dev/null; then
	die "schroot is not installed!" \
	    "On Debian-based systems, run: 'sudo apt-get install schroot'"
    fi

    if [ ! -f "$SCHROOT_CONFFILE" ]; then
	die "$SCHROOT_CONFFILE does not exist!"
    fi

    if [ "$(id -u)" != 0 ]; then
	die "this script must be run as root!"
    fi
}

prompt_for_param()
{
    local prompt="$1"
    local param_name="$2"
    local default_value="$3"

    if [ -z "${!param_name}" ] && $INTERACTIVE; then
	echo -n "Enter $prompt (${default_value:-none}): "
	read -r "$param_name"
    fi
    if [ -z "${!param_name}" ]; then
	declare -g "$param_name=$default_value"
    fi
}

select_debian_release()
{
    prompt_for_param "Debian release" DEBIAN_RELEASE "$DEBIAN_RELEASE_DEFAULT"
}

select_debian_arch()
{
    while true; do
	prompt_for_param "Debian architecture" \
		DEBIAN_ARCH "$DEBIAN_ARCH_DEFAULT"
	local suggestion=
	case "$DEBIAN_ARCH" in
	x86|i686)
	    suggestion=i386
	    ;;
	x86_64|x86-64|x64)
	    suggestion=amd64
	    ;;
	arm|arm32|aarch32)
	    suggestion=armhf
	    ;;
	aarch64)
	    suggestion=arm64
	    ;;
	esac
	if [ -z "$suggestion" ]; then
	    break
	fi
	local msg="$DEBIAN_ARCH is not a valid Debian architecture name; did you mean $suggestion?"
	if ! $INTERACTIVE; then
	    die "$msg"
	fi
	echo "$msg"
	DEBIAN_ARCH=
    done
}

select_debian_mirror()
{
    prompt_for_param "Debian mirror" DEBIAN_MIRROR "$DEBIAN_MIRROR_DEFAULT"
}

select_debian_keyring()
{
    prompt_for_param "Debian keyring" DEBIAN_KEYRING "$DEBIAN_KEYRING_DEFAULT"
}

add_fstab_bind()
{
    if ! grep "^$SCRIPTDIR\s" $SCHROOT_FSTAB_FILE &> /dev/null; then
	echo "Adding $SCRIPTDIR bind mount to $SCHROOT_FSTAB_FILE"
	echo "$SCRIPTDIR      $SCRIPTDIR      none    rw,bind         0       0" >> $SCHROOT_FSTAB_FILE
	return 0
    fi
    return 1
}

select_chroot_name()
{
    prompt_for_param "chroot name" CHROOT_NAME \
		     "${DEBIAN_RELEASE}-${DEBIAN_ARCH}"
    prompt_for_param "yes to store the chroot in a compressed tar file" \
		     DO_TAR "$DO_TAR_DEFAULT"
    if test "$DO_TAR" = "yes" ; then
	if test -n "$CHROOT_DIR" ; then
	    die "--chroot-dir and --tar are not compatile"
	fi
	prompt_for_param "chroot file" CHROOT_FILE \
			 "/chroots/${CHROOT_NAME}.tar.${TAR_COMPRESS}"
	case "$CHROOT_FILE" in
	    *.tar.gz|*.tar.xz|*.tar.bz2|*.tar.zstd)
		: ;;
	    *)
		die "Invalid chroot file: $CHROOT_FILE"
		;;
	esac

	if [ -e "$CHROOT_FILE" ]; then
	    add_fstab_bind && exit 0
	    die "$CHROOT_FILE already exists and $SCHROOT_FSTAB_FILE up-to-date!"
	fi
	if test "$DO_OVERLAY" = "yes" ; then
	    die "Using an overay file system incompatible with a tar file"
	fi
    else
	if test -n "$CHROOT_FILE" ; then
	    die "--chroot-file and --no-tar are not compatile"
	fi
	prompt_for_param "chroot directory" CHROOT_DIR \
			 "/chroots/${CHROOT_NAME}"
	if [ -e "$CHROOT_DIR" ]; then
	    add_fstab_bind && exit 0
	    die "$CHROOT_DIR already exists and $SCHROOT_FSTAB_FILE up-to-date!"
	fi
	prompt_for_param "yes to use overlay file system" DO_OVERLAY "$DO_OVERLAY_DEFAULT"
    fi
}

select_chroot_user()
{
    prompt_for_param "chroot user" CHROOT_USER "${SUDO_USER:-}"
}

select_ccache()
{
    prompt_for_param "yes to use ccache" DO_CCACHE "$DO_CCACHE_DEFAULT"
}

select_proxy()
{
    prompt_for_param "proxy" PROXY "${PROXY}"
}

parse_options()
{
    local longopts="help"
    local options

    longopts+=",release:"
    longopts+=",arch:"
    longopts+=",mirror:"
    longopts+=",keyring:"
    longopts+=",chroot-dir:"
    longopts+=",chroot-file:"
    longopts+=",chroot-name:"
    longopts+=",chroot-user:"
    longopts+=",proxy:"
    longopts+=",use-overlay"
    longopts+=",no-overlay"
    longopts+=",ccache"
    longopts+=",no-ccache"
    longopts+=",tar"
    longopts+=",no-tar"
    longopts+=",tar-compress:"
    longopts+=",noninteractive"
    longopts+=",ports"

    if ! options=$(getopt -o "" -l "$longopts" -- "$@"); then
	usage 1>&2
	exit 2
    fi

    eval set -- "$options"
    while (( $# >= 0 )); do
	case "$1" in
	--help)
	    usage
	    exit 0
	    ;;
	--release)
	    DEBIAN_RELEASE="$2"
	    shift
	    ;;
	--arch)
	    DEBIAN_ARCH="$2"
	    shift
	    ;;
	--mirror)
	    DEBIAN_MIRROR="$2"
	    shift
	    ;;
	--keyring)
	    DEBIAN_KEYRING="$2"
	    shift
	    ;;
	--chroot-dir)
	    CHROOT_DIR="$2"
	    shift
	    ;;
	--chroot-file)
	    CHROOT_FILE="$2"
	    DO_TAR=yes
	    shift
	    ;;
	--chroot-name)
	    CHROOT_NAME="$2"
	    shift
	    ;;
	--chroot-user)
	    CHROOT_USER="$2"
	    shift
	    ;;
	--proxy)
	    PROXY="$2"
	    shift
	    ;;
	--use-overlay)
	    DO_OVERLAY=yes
	    ;;
	--no-overlay)
	    DO_OVERLAY=no
	    ;;
	--ccache)
	    DO_CCACHE=yes
	    ;;
	--no-ccache)
	    DO_CCACHE=no
	    ;;
	--tar)
	    DO_TAR=yes
	    ;;
	--no-tar)
	    DO_TAR=no
	    ;;
	--tar-compress)
	    DO_TAR=yes
	    TAR_COMPRESS="$2"
	    shift
	    case "$TAR_COMPRESS" in
		bz2)
		    if ! type -P bzip2 >& /dev/null ; then
			die "bzip2 is not available"
		    fi
		    ;;
		xz)
		    if ! type -P xz >& /dev/null ; then
			die "xz is not available"
		    fi
		    ;;
		zstd)
		    if ! type -P zstd >& /dev/null ; then
			die "zstd is not available"
		    fi
		    ;;
		gz)
		    :
		    ;;
		*)
		    die "Invalid tar compression extension $TAR_COMPRESS"
		    ;;
	    esac
	    ;;
	--ports)
	    DEBIAN_ARCH_DEFAULT="$DEBIAN_PORTS_ARCH_DEFAULT"
	    DEBIAN_KEYRING_DEFAULT="$DEBIAN_PORTS_KEYRING_DEFAULT"
	    DEBIAN_MIRROR_DEFAULT="$DEBIAN_PORTS_MIRROR_DEFAULT"
	    DEBIAN_RELEASE_DEFAULT="$DEBIAN_PORTS_RELEASE_DEFAULT"
	    ;;
	--noninteractive)
	    INTERACTIVE=false
	    ;;
	--)
	    shift
	    break
	    ;;
	*)
	    echo 1>&2 "Invalid option: \"$1\""
	    usage 1>&2
	    exit 2
	    ;;
	esac
	shift
    done
}

is_native_chroot()
{
    case "$(uname -m)" in
    x86_64)	[[ $DEBIAN_ARCH = amd64 || $DEBIAN_ARCH = i386 ||
		   $DEBIAN_ARCH = x32 ]] ;;
    aarch64)	[[ $DEBIAN_ARCH = arm64 || $DEBIAN_ARCH = armhf ]] ;;
    arm)	[[ $DEBIAN_ARCH = armhf ]] ;;
    ppc64le)	[[ $DEBIAN_ARCH = ppc64el ]] ;;
    *)		[[ $DEBIAN_ARCH = "$(uname -m)" ]] ;;
    esac
}

# Validate that binfmt_misc support for the requested architecture is enabled,
# then set $QEMU to the path to the QEMU binary that should be used.
validate_binfmt_misc()
{
    local qemu_arch binfmt binfmt_file

    case "$DEBIAN_ARCH" in
    armhf)	qemu_arch=arm ;;
    arm64)	qemu_arch=aarch64 ;;
    ppc64el)	qemu_arch=ppc64le ;;
    *)		qemu_arch="$DEBIAN_ARCH" ;;
    esac

    if [ ! -d "$BINFMT_MISC_MNT" ]; then
	die "$BINFMT_MISC_MNT doesn't exist.  To set up a chroot for a" \
	    "foreign architecture, you must enable CONFIG_BINFMT_MISC in your kernel."
    fi

    if ! mountpoint "$BINFMT_MISC_MNT" &>/dev/null; then
	die "binfmt_misc is not mounted on $BINFMT_MISC_MNT!" \
	    "If your init system isn't mounting binfmt_misc automatically" \
	    "(systemd should mount it by default), you can add to your fstab:" \
	    "" \
	    "    binfmt_misc $BINFMT_MISC_MNT binfmt_misc defaults 0 0"
    fi

    if [ "$(<"$BINFMT_MISC_MNT/status")" = "disabled" ]; then
	die "binfmt_misc is currently disabled!  To enable it, run:"
	    "    sudo sh -c 'echo 1 > $BINFMT_MISC_MNT/status'"
    fi

    binfmt="qemu-$qemu_arch"
    binfmt_file="$BINFMT_MISC_MNT/$binfmt"

    if [ ! -e "$binfmt_file" ]; then
	die "No binfmt_misc handler for $binfmt is installed!" \
	    "Make sure you've installed both the binfmt-support and qemu-user-static" \
	    "packages, e.g. on Debian-based systems:" \
	    "" \
	    "    sudo apt-get install binfmt-support qemu-user-static" \
	    "" \
	    "on some systems you must also explicitly enable and start the" \
	    "binfmt-support service:" \
	    "" \
	    "    sudo systemctl enable --now binfmt-support.service"
    fi

    QEMU=$(awk '/^interpreter/{print $2}' "$binfmt_file")

    log "Detected foreign chroot, using user-mode emulation with $QEMU"
}

# Get the schroot configuration from either schroot.conf or entries in
# the chroot.d directory
get_schroot_config()
{
    cat $SCHROOT_CONFFILE

    if test -d $SCHROOT_CHROOT_D
    then
	(cd $SCHROOT_CHROOT_D ;
	 find . -maxdepth 1 -type f |
	     grep -E '^./[a-zA-Z0-9_-][a-zA-Z0-9_.-]*$' |
	     xargs cat)
    fi
}

# Extract the schroot.conf entry, if any, for $CHROOT_NAME
extract_schroot_entry()
{
    get_schroot_config | awk '
{
    if ($0 ~ /^[[:space:]]*\[.*\][[:space:]]*$/) {
	sub(/\][[:space:]]*$/, "")
	sub(/^[[:space:]]*\[/, "")
	section=$0
    } else if (section == "'"$CHROOT_NAME"'" && $0 !~ /^[[:space:]]*(#.*)?$/) {
	print
    }
}
'
}

generate_schroot_entry()
{
    local tar="$*"

    # See `man schroot.conf`
    #
    # Note: 'setup.nssdatabases=' prevents NSS databases, such as passwd
    # entries, from being copied into the chroot.  They aren't needed anyway,
    # and there could be a large number of entries on the host system which
    # break things and/or make building things much slower.
    cat <<EOF
description=xfstests-bld chroot with Debian $DEBIAN_RELEASE ($DEBIAN_ARCH)
EOF
    if [ "$tar" = "--tar" ]; then
	cat <<EOF
type=file
file=$CHROOT_FILE
EOF
    else
	cat <<EOF
type=directory
directory=$CHROOT_DIR
EOF
    fi
    cat <<EOF
users=${CHROOT_USER:+$CHROOT_USER,}root
root-users=$CHROOT_USER
setup.fstab=$SCHROOT_FSTAB
setup.nssdatabases=
EOF
    if [ "${DO_OVERLAY}" = "yes" ]; then
	echo "union-type=overlay"
    fi
    if [ "${DO_OVERLAY}" = "yes" -o "$tar" = "--tar" ]; then
	cat <<EOF
source-users=${CHROOT_USER:+$CHROOT_USER,}root
source-root-users=$CHROOT_USER
EOF
    fi
}

check_for_conflicting_schroot_entry()
{
    if [ -z "$(extract_schroot_entry)" ]; then
	return
    fi
    if cmp -s <(extract_schroot_entry | sort) \
	      <(generate_schroot_entry | sort)
    then
	return
    fi
    log "$SCHROOT_CONFFILE already contains a different entry for [$CHROOT_NAME]"
    echo "--> Wanted:"
    generate_schroot_entry
    echo
    echo "--> Found:"
    extract_schroot_entry
    echo
    die "Please either delete the existing entry first, or fix it manually."
}

# Add an entry to schroot.conf for the chroot.
add_schroot_conf_entry()
{
    local f
    check_for_conflicting_schroot_entry
    if [ -n "$(extract_schroot_entry)" ]; then
	log "$CHROOT_NAME entry already exists in $SCHROOT_CONFFILE"
	return
    fi

    if test -d $SCHROOT_CHROOT_D
    then
	f="$SCHROOT_CHROOT_D/$CHROOT_NAME"
    else
	f="$SCHROOT_CONFFILE"
    fi
    log "Adding new entry to $f:"
    {
	echo
	echo "# entry added by $SCRIPTNAME"
	echo "[$CHROOT_NAME]"
	generate_schroot_entry
    } | tee -a "$f"
    echo
}

# Create the schroot fstab file needed by the chroot.  The fstab will contain
# the usual entries to mount sysfs, procfs, etc., as well as an entry that
# bind-mounts the xfstests-bld directory into the chroot.
#
# Note that all chroots created by this script will share the same fstab.
create_schroot_fstab()
{
    if [ -e "$SCHROOT_FSTAB_FILE" ]; then
	log "$SCHROOT_FSTAB_FILE was already created"
	add_fstab_bind || true
	return
    fi
    mkdir -p "$(dirname "$SCHROOT_FSTAB_FILE")"

    cat >"$SCHROOT_FSTAB_FILE" <<EOF
/proc           /proc           none    rw,bind         0       0
/sys            /sys            none    rw,bind         0       0
/dev            /dev            none    rw,bind         0       0
/dev/pts        /dev/pts        none    rw,bind         0       0
/home           /home           none    rw,bind         0       0
/tmp            /tmp            none    rw,bind         0       0
$SCRIPTDIR      $SCRIPTDIR      none    rw,bind         0       0
EOF
    log "Created $SCHROOT_FSTAB_FILE" \
	"(bind-mount path: $SCRIPTDIR)"
}

run_in_chroot()
{
    # Note: we execute the command in a login shell rather than execute it
    # directly because this makes the $PATH get set up correctly.
    DEBIAN_FRONTEND=noninteractive DEBCONF_NONINTERACTIVE_SEEN=true \
	LC_ALL=C LANGUAGE=C LANG=C chroot "$CHROOT_DIR" /bin/sh -l -c "$1"
}

copy_in_user()
{
    local user="$1"
    local group

    if ! group="$(id -g $user 2>/dev/null)" ; then
	return;
    fi
    if ! grep -q "^$user:" "$CHROOT_DIR/etc/passwd" ; then
	getent passwd "$user" >> "$CHROOT_DIR/etc/passwd"
    fi
    if ! grep -q "^group:" "$CHROOT_DIR/etc/group" ; then
	getent group "$(id -g "$user")" >> "$CHROOT_DIR/etc/group"
    fi
}

create_chroot()
{
    if test "${DO_TAR}" = "yes" ; then
	CHROOT_DIR=$(mktemp --tmpdir -d "${CHROOT_NAME}.XXXXXXXX")
	chmod 755 "${CHROOT_DIR}"
    fi

    mkdir -p -m0755 "$CHROOT_DIR"

    test -z "${PROXY}" || export http_proxy=${PROXY}
    if ! run_cmd debootstrap --arch "$DEBIAN_ARCH" ${QEMU:+--foreign} \
	    --keyring "$DEBIAN_KEYRING" "$DEBIAN_RELEASE" "$CHROOT_DIR" \
	    "$DEBIAN_MIRROR"
    then
	# Clean up if the first step fails since the problem may be trivial,
	# e.g. an invalid release, arch, or mirror.  But if we fail later, leave
	# the directory around so that the problem can be debugged.
	rm -rf "$CHROOT_DIR"
	exit 1
    fi

    if [ -n "$QEMU" ]; then
	log "Installing $QEMU as $CHROOT_DIR/usr/bin/$(basename "$QEMU")"
	cp "$QEMU" "$CHROOT_DIR/usr/bin/"
	mkdir  -p "$CHROOT_DIR/usr/libexec/qemu-binfmt/"
	ln -s "../../bin/aarch64-binfmt-P" "$CHROOT_DIR/usr/libexec/qemu-binfmt/aarch64-binfmt-P"

	log "Entering chroot to complete the second stage of the bootstrapping process"
	run_in_chroot "/debootstrap/debootstrap --second-stage"

	log "Entering chroot to configure the installed packages"
	run_in_chroot "dpkg --configure -a"

	log "Creating $CHROOT_DIR/etc/apt/sources.list"
	cat >"$CHROOT_DIR/etc/apt/sources.list" <<EOF
deb     $DEBIAN_MIRROR  $DEBIAN_RELEASE         main
deb-src $DEBIAN_MIRROR  $DEBIAN_RELEASE         main contrib non-free
deb     $DEBIAN_MIRROR  $DEBIAN_RELEASE-updates main
EOF

	# If on the host system /dev/shm is a symlink to /run/shm, configuring
	# the initscripts package will fail during 'gen-image'.  To work around
	# this, explicitly create the /run/shm directory in the build chroot.
	mkdir -p "$CHROOT_DIR/run/shm"
	chmod 1777 "$CHROOT_DIR/run/shm"
    fi
    # copy in those users that be created when we install packages
    # needed for the build chroot
    copy_in_user _apt
    copy_in_user messagebus
    if [ -n "$CHROOT_USER" ]; then
	copy_in_user "$CHROOT_USER"
	run_in_chroot "adduser $CHROOT_USER sudo"
    fi
}

setup_mtab()
{
    log "Linking /etc/mtab to ../proc/self/mounts"
    schroot -c "$CHROOT_NAME" -u root -- ln -sf ../proc/self/mounts /etc/mtab
}

install_build_dependencies()
{
    local chroot

    log "Installing build dependencies: ${BUILD_DEPENDENCIES[*]}"
    if [ "${DO_OVERLAY}" = "yes" ]; then
	chroot="source:${CHROOT_NAME}"
    else
	chroot="${CHROOT_NAME}"
    fi
    schroot -c "$chroot" -u root -- <<EOF
test -z "${PROXY}" || export http_proxy=${PROXY}
apt-get update
apt-get upgrade
apt-get install -y ${BUILD_DEPENDENCIES[@]}
apt-get autoremove
apt-get clean
EOF
}

setup_ccache()
{
    mkdir -p "$CHROOT_DIR/usr/local/bin"
    for i in c++ cc clang g++ gcc ld ; do
	ln -s /bin/ccache "$CHROOT_DIR/usr/local/bin/$i"
    done
}

generate_tar()
{
    case "${CHROOT_FILE}" in
	*.gz)
	    if type -P pigz >/dev/null; then
		compress="pigz -9nm"
	    else
		compress="gzip -9n"
	    fi
	    ;;
	*.bz2)
	    compress="bzip2"
	    ;;
	*.xz)
	    compress="xz"
	    ;;
	*.zstd)
	    compress="zstd -T0 -14"
	    ;;
	*)
	    die "Unknown compression program for ${CHROOT_FILE}"
	    ;;
    esac

    mkdir -p -m0755 $(basename "$CHROOT_FILE")
    tar -C "${CHROOT_DIR}" -cf - . | $compress > "${CHROOT_FILE}"
    rm -rf "${CHROOT_DIR}"
    {
	echo
	echo "# entry added by $SCRIPTNAME"
	echo "[$CHROOT_NAME]"
	generate_schroot_entry --tar
    } > "$SCHROOT_CHROOT_D/$CHROOT_NAME"
}

# preparation
parse_options "$@"
check_prerequisites
select_debian_release
select_debian_arch
select_debian_mirror
select_debian_keyring
select_chroot_name
select_chroot_user
select_ccache
select_proxy
check_for_conflicting_schroot_entry
if ! is_native_chroot; then
    validate_binfmt_misc
fi

# the real work
select_packages
create_chroot
add_schroot_conf_entry
create_schroot_fstab
setup_mtab
install_build_dependencies
if [ "${DO_CCACHE}" = "yes" ]; then
    setup_ccache
fi
if [ "${DO_TAR}" = "yes" ]; then
    generate_tar
fi

log "Build chroot was successfully set up.  To use it to build a test" \
    "appliance, run './build-appliance --chroot=$CHROOT_NAME'; or to have" \
    "build-appliance use this chroot by default, add the following to the" \
    "config.custom file in the top-level directory:" \
    "" \
    "    BUILD_ENV=\"schroot -c $CHROOT_NAME --\"" \
    "    SUDO_ENV=\"schroot -c $CHROOT_NAME -u root --\"" \
    "" \
    "Alternatively, you may build an xfstests tarball on its own:" \
    "    BUILD_ENV=\"schroot -c $CHROOT_NAME --\"" \
    "    \$BUILD_ENV make clean" \
    "    \$BUILD_ENV make" \
    "    \$BUILD_ENV make tarball"