setup_rootfs

#!/bin/sh -ex

dest_img="$1"

[ ! -d "$ROOTFS_BUILD_DIR" ] || rm -rf "$ROOTFS_BUILD_DIR"

mkdir "$ROOTFS_BUILD_DIR"

# being on a tmpfs inside the mount namespace is really nice.
# it can limit size of the file system, cleanup is free, and - of course - it's super fast.
# but mke2fs has problems with it, so no: mount -t tmpfs none "$ROOTFS_BUILD_DIR".
# however, not using a tmpfs leads other problems

mount -t tmpfs -o noatime none "$ROOTFS_BUILD_DIR"

bsdtar -xpf "$BASE_ROOTFS_TAR" -C "$ROOTFS_BUILD_DIR"

mkdir -p "$ROOTFS_BUILD_DIR/boot"

run_mounted() {
	# exporting in a loop is a hassle
	{
		[ ! -f .env.rootfs-customization ] || grep -v '^#' .env.rootfs-customization
		echo ./customize_rootfs
		echo "$ROOTFS_BUILD_DIR"
	} | xargs -od '\n' env
}

# this includes /proc/sys/fs/binfmt_misc, which allows running the binaries inside
mount --rbind /proc/ "$ROOTFS_BUILD_DIR/proc"
# /dev/shm, /dev/random, /dev/urandom and the likes are required for GPG and such
mount --rbind /dev "$ROOTFS_BUILD_DIR/dev"
mount --bind . "$ROOTFS_BUILD_DIR/mnt"
mount --bind "$PACMAN_CACHE_DIR/pkg" "$ROOTFS_BUILD_DIR/var/cache/pacman/pkg"
mount --bind "$PACMAN_CACHE_DIR/sync" "$ROOTFS_BUILD_DIR/var/lib/pacman/sync"
mount --bind /etc/resolv.conf "$ROOTFS_BUILD_DIR/etc/resolv.conf"

if [ -n "$EFI_MNT" ]; then
	mkdir -p "$ROOTFS_BUILD_DIR/efi"
	mount -t tmpfs -o noatime none "$ROOTFS_BUILD_DIR/efi"
fi

fork_pipe_wait() {
	local fd cmd="$1"
	local pipe wait_pipe
	pipe="$(mktemp -u rootfs-builder-$$-cleanup-pipe.XXXXXXXXXX)"

	mkfifo "$pipe"

	( ( cat <"$pipe" >/dev/null ; eval "$cmd" ; ) & ) &
	# TODO cat has to open the pipe first
	sleep 3

	exec {fd}<>"$pipe"

	if [ $# -gt 1 ]; then
		eval "$2=$fd"
	fi

	rm "$pipe"
}

subshell_ppid() {
	# even $( sh -c 'echo $PPID' ) or sh .. | read doesn't necessarily yield the correct result (depending on the shell)

	# this grep sees another file than the awk that follows:
	# grep PPid < /proc/self/status | awk '{ print $2 }'
	# awk '/^PPid:/ { print $2 }' < /proc/self/status

	awk '/^PPid:/ { "grep PPid /proc/"$2"/status" | getline ; print $2 }' < /proc/self/status
}

umount_secondaries() {
	umount "$ROOTFS_BUILD_DIR/etc/resolv.conf"
	umount "$ROOTFS_BUILD_DIR/var/cache/pacman/pkg"
	umount "$ROOTFS_BUILD_DIR/mnt"

	umount -l "$ROOTFS_BUILD_DIR/dev"
	umount -l "$ROOTFS_BUILD_DIR/proc"
}

cleanup_mnt() {
	# if any processes are still in the mount namespace, umount fails with 'target busy'
	# pacman forks a gpg-agent

	set +x

	# $$ returns the pid of the shell and doesn't change in subshells
	local own_pid="$(subshell_ppid)"

	# double-forked, so PPID is not sane ($$ would likely be)
	local pppid="$1"

	local pids="$(ls /proc/ | grep '[0-9]' | grep -v "^$pppid\$" | grep -v "^$own_pid\$")"
	local own_mnt_ns="$(stat -Lc '%i' /proc/self/ns/mnt)"

	for pid in $pids; do
		mnt_ns="/proc/$pid/ns/mnt"
		[ -r "$mnt_ns" ] || continue
		[ "$(stat -Lc '%i' "$mnt_ns")" == "$own_mnt_ns" ] || continue

		echo "killing stray process $pid - $(tr '\0' ' ' < "/proc/$pid/cmdline")"
		kill "$pid"
	done

	# umount to be able to do rmdir
	if mountpoint -q "$ROOTFS_BUILD_DIR/etc/resolv.conf"; then
		umount_secondaries
	fi

	if mountpoint -q "$ROOTFS_BUILD_DIR/efi"; then
		umount "$ROOTFS_BUILD_DIR/efi"
	fi

	umount "$ROOTFS_BUILD_DIR"
	rmdir "$ROOTFS_BUILD_DIR"
}

fork_pipe_wait "cleanup_mnt $$"

# TODO the whole point of mountns was to be able to utilise cleanup
# "fork" another mount namespace for ./run_mounted to run in.
# have the cleanup func run in there (no relying on parent pids or such).
# wait for cleanup using fds
run_mounted

umount_secondaries

if [ -n "$EFI_MNT" ]; then
	mkfs.vfat -i "${EFI_UUID//-/}" -F 32 "$EFI_IMG"
	# there should be no hidden files here
	mcopy -i "$EFI_IMG" -spQ "$ROOTFS_BUILD_DIR"/efi/* ::

	umount "$ROOTFS_BUILD_DIR/efi"
fi

apparent_size="$(du -xsm "$ROOTFS_BUILD_DIR" | awk '{ print $1 }')"
# this can fail because of the host FS
mke2fs -F -L "system" -U "$ROOTFS_UUID" -d "$ROOTFS_BUILD_DIR" \
	-O "^has_journal" \
	-m 2 \
	-t ext4 \
	"$dest_img" \
	$(( apparent_size * 105 / 100 + ROOTFS_WIGGLEROOM_MB ))M 2>&1