#!/bin/bash

# This script is based on drgn script for generating Arch Linux bootstrap
# images.
# https://github.com/osandov/drgn/blob/master/scripts/vmtest/mkrootfs.sh

set -euo pipefail

usage () {
	USAGE_STRING="usage: $0 [NAME]
       $0 -h

Build an Arch Linux root filesystem image for testing libbpf in a virtual
machine.

The image is generated as a zstd-compressed tarball.

This must be run as root, as most of the installation is done in a chroot.

Arguments:
  NAME   name of generated image file (default:
         libbpf-vmtest-rootfs-\$DATE.tar.zst)

Options:
  -h     display this help message and exit"

	case "$1" in
		out)
			echo "$USAGE_STRING"
			exit 0
			;;
		err)
			echo "$USAGE_STRING" >&2
			exit 1
			;;
	esac
}

while getopts "h" OPT; do
	case "$OPT" in
		h)
			usage out
			;;
		*)
			usage err
			;;
	esac
done
if [[ $OPTIND -eq $# ]]; then
	NAME="${!OPTIND}"
elif [[ $OPTIND -gt $# ]]; then
	NAME="libbpf-vmtest-rootfs-$(date +%Y.%m.%d).tar.zst"
else
	usage err
fi

pacman_conf=
root=
trap 'rm -rf "$pacman_conf" "$root"' EXIT
pacman_conf="$(mktemp -p "$PWD")"
cat > "$pacman_conf" << "EOF"
[options]
Architecture = x86_64
CheckSpace
SigLevel = Required DatabaseOptional
[core]
Include = /etc/pacman.d/mirrorlist
[extra]
Include = /etc/pacman.d/mirrorlist
[community]
Include = /etc/pacman.d/mirrorlist
EOF
root="$(mktemp -d -p "$PWD")"

packages=(
	busybox
	# libbpf dependencies.
	libelf
	zlib
	# selftests test_progs dependencies.
	binutils
	elfutils
	glibc
	iproute2
	# selftests test_verifier dependencies.
	libcap
)

pacstrap -C "$pacman_conf" -cGM "$root" "${packages[@]}"

# Remove unnecessary files from the chroot.

# We don't need the pacman databases anymore.
rm -rf "$root/var/lib/pacman/sync/"
# We don't need D, Fortran, or Go.
 rm -f "$root/usr/lib/libgdruntime."* \
	"$root/usr/lib/libgphobos."* \
	"$root/usr/lib/libgfortran."* \
	"$root/usr/lib/libgo."*
# We don't need any documentation.
rm -rf "$root/usr/share/{doc,help,man,texinfo}"

chroot "${root}" /bin/busybox --install

cat > "$root/etc/inittab" << "EOF"
::sysinit:/etc/init.d/rcS
::ctrlaltdel:/sbin/reboot
::shutdown:/sbin/swapoff -a
::shutdown:/bin/umount -a -r
::restart:/sbin/init
EOF
chmod 644 "$root/etc/inittab"

mkdir -m 755 "$root/etc/init.d" "$root/etc/rcS.d"
cat > "$root/etc/rcS.d/S10-mount" << "EOF"
#!/bin/sh

set -eux

/bin/mount proc /proc -t proc

# Mount devtmpfs if not mounted
if [[ -z $(/bin/mount -l -t devtmpfs) ]]; then
	/bin/mount devtmpfs /dev -t devtmpfs
fi

/bin/mount sysfs /sys -t sysfs
/bin/mount bpffs /sys/fs/bpf -t bpf
/bin/mount debugfs /sys/kernel/debug -t debugfs

echo 'Listing currently mounted file systems'
/bin/mount
EOF
chmod 755 "$root/etc/rcS.d/S10-mount"

cat > "$root/etc/rcS.d/S40-network" << "EOF"
#!/bin/sh

set -eux

ip link set lo up
EOF
chmod 755 "$root/etc/rcS.d/S40-network"

cat > "$root/etc/init.d/rcS" << "EOF"
#!/bin/sh

set -eux

for path in /etc/rcS.d/S*; do
	[ -x "$path" ] && "$path"
done
EOF
chmod 755 "$root/etc/init.d/rcS"

chmod 755 "$root"
tar -C "$root" -c . | zstd -T0 -19 -o "$NAME"
chmod 644 "$NAME"