archbuild/makechrootpkg: Delete subvolumes in roots

The systemd package creates a subvolume at /var/lib/machines (through
tmpfiles), if it can. We need to delete this subvolume before we can
delete the parent subvolume.

Look through the root for inodes with the number 256. These identify
subvolume roots.

archbuild.in

@@ -52,9 +52,7 @@ if ${clean_first} || [[ ! -d "${chroots}/${repo}-${arch}" ]]; then
 
 		lock 9 "$copy.lock" "Locking chroot copy '$copy'"
 
-		if is_btrfs "${copy}"; then
-			{ type -P btrfs && btrfs subvolume delete "${copy}"; } &>/dev/null
-		fi
+		subvolume_delete_recursive "${copy}"
 		rm -rf --one-file-system "${copy}"
 	done
 	exec 9>&-

lib/archroot.sh

@@ -20,3 +20,23 @@ check_root() {
 is_btrfs() {
 	[[ -e "$1" && "$(stat -f -c %T "$1")" == btrfs ]]
 }
+
+##
+#  usage : subvolume_delete_recursive( $path )
+#
+#    Find all btrfs subvolumes under and including $path and delete them.
+##
+subvolume_delete_recursive() {
+	local subvol
+
+	is_btrfs "$1" || return 0
+
+	while IFS= read -d $'\0' -r subvol; do
+		if ! btrfs subvolume delete "$subvol" &>/dev/null; then
+			error "Unable to delete subvolume %s" "$subvol"
+			return 1
+		fi
+	done < <(find "$1" -xdev -depth -inum 256 -print0)
+
+	return 0
+}

makechrootpkg.in

@@ -97,10 +97,8 @@ create_chroot() {
 
 		stat_busy "Creating clean working copy [$copy]"
 		if is_btrfs "$chrootdir" && ! mountpoint -q "$copydir"; then
-			if [[ -d $copydir ]]; then
-				btrfs subvolume delete "$copydir" >/dev/null ||
-					die "Unable to delete subvolume %s" "$copydir"
-			fi
+			subvolume_delete_recursive "$copydir" ||
+				die "Unable to delete subvolume %s" "$copydir"
 			btrfs subvolume snapshot "$chrootdir/root" "$copydir" >/dev/null ||
 				die "Unable to create subvolume %s" "$copydir"
 		else