[PATCH v2] fstests: btrfs: add a regression test case to make sure scrub can detect errors

[Qu Wenruo <wqu@suse.com>]

There is a regression in v6.1-rc kernel, which will prevent btrfs scrub
from detecting corruption (thus no repair either).

The regression is caused by commit 786672e9e1a3 ("btrfs: scrub: use
larger block size for data extent scrub").

The new test case will:

- Create a data extent with 2 sectors
- Corrupt the second sector of above data extent
- Scrub to make sure we detect the corruption

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
Changelog:
v2:
- Remove include for common/btrfs
  Which is included by default.

- Add comment for why including common/filter
  Needed by _btrfs_get_*() helpers.

- Migrated to btrfs/278
  Which is the latest result by "./new btrfs" on for-next branch.

- Add "-s 4k" for _scratch_mkfs
  To support systems with larger page sizes.

- Remove comments from the template
---
 tests/btrfs/281     | 62 +++++++++++++++++++++++++++++++++++++++++++++
 tests/btrfs/281.out |  2 ++
 2 files changed, 64 insertions(+)
 create mode 100755 tests/btrfs/281
 create mode 100644 tests/btrfs/281.out

diff --git a/tests/btrfs/281 b/tests/btrfs/281
new file mode 100755
index 00000000..69b5ac02
--- /dev/null
+++ b/tests/btrfs/281
@@ -0,0 +1,62 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2022 SUSE Linux Products GmbH. All Rights Reserved.
+#
+# A regression test for offending commit 786672e9e1a3 ("btrfs: scrub: use
+# larger block size for data extent scrub"), which makes btrfs scrub unable
+# to detect corruption if it's not the first sector of an data extent.
+#
+
+. ./common/preamble
+_begin_fstest auto quick scrub
+
+# For _btrfs_get_*() helpers which needs filtering.
+. ./common/filter
+
+_supported_fs btrfs
+_require_scratch
+
+# Need to use 4K as sector size
+_require_btrfs_support_sectorsize 4096
+_require_scratch
+
+_scratch_mkfs -s 4k >> $seqres.full
+_scratch_mount
+
+# Create a data extent with 2 sectors
+$XFS_IO_PROG -fc "pwrite -S 0xff 0 8k" $SCRATCH_MNT/foobar >> $seqres.full
+sync
+
+first_logical=$(_btrfs_get_first_logical $SCRATCH_MNT/foobar)
+echo "logical of the first sector: $first_logical" >> $seqres.full
+
+second_logical=$(( $first_logical + 4096 ))
+echo "logical of the second sector: $second_logical" >> $seqres.full
+
+second_physical=$(_btrfs_get_physical $second_logical 1)
+echo "physical of the second sector: $second_physical" >> $seqres.full
+
+second_dev=$(_btrfs_get_device_path $second_logical 1)
+echo "device of the second sector: $second_dev" >> $seqres.full
+
+_scratch_unmount
+
+# Corrupt the second sector of the data extent.
+$XFS_IO_PROG -c "pwrite -S 0x00 $second_physical 4k" $second_dev >> $seqres.full
+_scratch_mount
+
+# Redirect stderr and stdout, as if btrfs detected the unrepairable corruption,
+# it will output an error message.
+$BTRFS_UTIL_PROG scrub start -B $SCRATCH_MNT &> $tmp.output
+cat $tmp.output >> $seqres.full
+_scratch_unmount
+
+if ! grep -q "csum=1" $tmp.output; then
+	echo "Scrub failed to detect corruption"
+fi
+
+echo "Silence is golden"
+
+# success, all done
+status=0
+exit
diff --git a/tests/btrfs/281.out b/tests/btrfs/281.out
new file mode 100644
index 00000000..3678e27f
--- /dev/null
+++ b/tests/btrfs/281.out
@@ -0,0 +1,2 @@
+QA output created by 281
+Silence is golden
-- 
2.38.0