btrfs-progs: fsck-tests: Check if clear space cache works

Add test case to check the basic function of --clear-space-cache.

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

tests/fsck-tests/024-clear-space-cache/test.sh

@@ -0,0 +1,48 @@
+#!/bin/bash
+# confirm that clearing space cache works
+
+source $TOP/tests/common
+
+check_prereq btrfs
+check_prereq mkfs.btrfs
+
+setup_root_helper
+prepare_test_dev 1G
+
+run_check $SUDO_HELPER $TOP/mkfs.btrfs -f $TEST_DEV
+run_check_mount_test_dev
+
+# Create files that takes at least 3 data chunks, while
+# can still be removed to create free space inside one chunk.
+
+for i in $(seq 0 6); do
+	run_check $SUDO_HELPER dd if=/dev/zero of=$TEST_MNT/file_${i} bs=1M \
+		count=64 > /dev/null 2>&1
+done
+sync
+
+# Remove file 1 3 5 to create holes
+for i in 1 3 5; do
+	run_check $SUDO_HELPER rm $TEST_MNT/file_${i}
+done
+
+sync
+
+run_check_umount_test_dev
+
+# Clear space cache and re-check fs
+run_check $TOP/btrfs check --clear-space-cache v1 $TEST_DEV
+run_check $TOP/btrfs check $TEST_DEV
+
+# Manually recheck space cache and super space cache generation
+run_check_stdout $TOP/btrfs inspect-internal dump-tree -t root $TEST_DEV | \
+	grep -q FREE_SPACE
+if [ $? -eq 0 ]; then
+	_fail "clear space cache doesn't clear all space cache"
+fi
+
+run_check_stdout $TOP/btrfs inspect-internal dump-super $TEST_DEV |
+	grep -q 'cache_generation.*18446744073709551615'
+if [ $? -ne 0 ]; then
+	_fail "clear space cache doesn't set cache_generation correctly"
+fi