btrfs-progs: tests: Add new test case for file extent false alerts

Lowmem mode exposed several false alerts, all related to file extents
check.

1) Partly written prealloc extent
   Cause lowmem mode to report missing csum or prealloc extent should
   not have csum

2) Compressed inline extent
   Cause lowmem mode to find mismatch on inline len and item len.
   While no error message is output but exit silently.

Reported-by: Chris Murphy <chris@colorremedies.com>
Reported-by: Christoph Anton Mitterer <calestyo@scientia.net>
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>

tests/fsck-tests/025-file-extents/test.sh

@@ -0,0 +1,42 @@
+#!/bin/bash
+# Confirm btrfs check can check file extents without causing false alert
+
+source $TOP/tests/common
+
+check_prereq btrfs
+check_prereq mkfs.btrfs
+check_global_prereq xfs_io
+check_global_prereq fallocate
+
+setup_root_helper
+prepare_test_dev 128M
+
+# Do some write into a large prealloc range
+# Lowmem mode can report missing csum due to wrong csum range
+test_paritical_write_into_prealloc()
+{
+	run_check $SUDO_HELPER "$TOP/mkfs.btrfs" -f "$TEST_DEV"
+	run_check_mount_test_dev
+
+	run_check fallocate -l 128K "$TEST_MNT/file"
+	sync
+	run_check xfs_io -c "pwrite 0 64K" "$TEST_MNT/file"
+	run_check_umount_test_dev
+	run_check "$TOP/btrfs" check "$TEST_DEV"
+}
+
+# Inline compressed file extent
+# Lowmem mode can cause silent error without any error message
+# due to too restrict check on inline extent size
+test_compressed_inline_extent()
+{
+	run_check $SUDO_HELPER "$TOP/mkfs.btrfs" -f "$TEST_DEV"
+	run_check_mount_test_dev -o compress=lzo,max_inline=2048
+
+	run_check xfs_io -f -c "pwrite 0 1K" "$TEST_MNT/file"
+	run_check_umount_test_dev
+	run_check "$TOP/btrfs" check "$TEST_DEV"
+}
+
+test_paritical_write_into_prealloc
+test_compressed_inline_extent