btrfs-progs: tests: make sure we don't create bitmaps for empty fs

Add test case is to make sure on a relative large empty fs, we won't
create bitmaps to unnecessarily increase the size of free space tree.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

tests/mkfs-tests/024-fst-bitmaps/test.sh

@@ -0,0 +1,34 @@
+#!/bin/bash
+# Basic check if mkfs supports the runtime feature free-space-tree
+
+source "$TEST_TOP/common"
+
+check_prereq mkfs.btrfs
+check_prereq btrfs
+
+setup_root_helper
+
+setup_loopdevs 4
+prepare_loopdevs
+dev1=${loopdevs[1]}
+tmp=$(_mktemp fst-bitmap)
+
+test_do_mkfs()
+{
+	run_check $SUDO_HELPER "$TOP/mkfs.btrfs" -f "$@"
+	if run_check_stdout "$TOP/btrfs" check "$dev1" | grep -iq warning; then
+		_fail "warnings found in check output"
+	fi
+}
+
+test_do_mkfs -m raid1 -d raid0 ${loopdevs[@]}
+
+run_check_stdout $SUDO_HELPER "$TOP/btrfs" inspect-internal dump-tree \
+	-t free_space "$dev1" > "$tmp.dump-tree"
+cleanup_loopdevs
+
+if grep -q FREE_SPACE_BITMAP "$tmp.dump-tree"; then
+	rm -f -- "$tmp*"
+	_fail "free space bitmap should not be created for empty fs"
+fi
+rm -f -- "$tmp*"