[PATCH v3] btrfs: add a test case to make sure scrub can repair parity corruption

[Qu Wenruo <wqu@suse.com>]

There is a kernel regression caused by commit 75b470332965 ("btrfs:
raid56: migrate recovery and scrub recovery path to use error_bitmap"),
which leads to scrub not repairing corrupted parity stripes.

So here we add a test case to verify the P/Q stripe scrub behavior by:

- Create a RAID5 or RAID6 btrfs with minimal amount of devices
  This means 2 devices for RAID5, and 3 devices for RAID6.
  This would result the parity stripe to be a mirror of the only data
  stripe.

  And since we have control of the content of data stripes, the content
  of the P stripe is also fixed.

- Create an 64K file
  The file would cover one data stripe.

- Corrupt the P stripe

- Scrub the fs
  If scrub is working, the P stripe would be repaired.

  Unfortunately scrub can not report any P/Q corruption, limited by its
  reporting structure.
  So we can not use the return value of scrub to determine if we
  repaired anything.

- Verify the content of the P stripe

- Use "btrfs check --check-data-csum" to double check

By above steps, we can verify if the P stripe is properly fixed.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
Changelog:
v3:
- Fix the "YOUR NAME HERE" boilerplate

v2:
- Rebase to the latest misc-next
- Use space_cache=v2 mount option instead of nospace_cache
  New features like block group tree and extent tree v2 requires v2
  cache
- Fix a white space error
---
 tests/btrfs/297     | 85 +++++++++++++++++++++++++++++++++++++++++++++
 tests/btrfs/297.out |  2 ++
 2 files changed, 87 insertions(+)
 create mode 100755 tests/btrfs/297
 create mode 100644 tests/btrfs/297.out

diff --git a/tests/btrfs/297 b/tests/btrfs/297
new file mode 100755
index 00000000..a0023861
--- /dev/null
+++ b/tests/btrfs/297
@@ -0,0 +1,85 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2023 SUSE Linux Products GmbH. All Rights Reserved.
+#
+# FS QA Test 297
+#
+# Make sure btrfs scrub can fix parity stripe corruption
+#
+. ./common/preamble
+_begin_fstest auto quick raid scrub
+
+. ./common/filter
+
+_supported_fs btrfs
+_require_odirect
+_require_non_zoned_device "${SCRATCH_DEV}"
+_require_scratch_dev_pool 3
+_fixed_by_kernel_commit 486c737f7fdc \
+	"btrfs: raid56: always verify the P/Q contents for scrub"
+
+workload()
+{
+	local profile=$1
+	local nr_devs=$2
+
+	echo "=== Testing $nr_devs devices $profile ===" >> $seqres.full
+	_scratch_dev_pool_get $nr_devs
+
+	_scratch_pool_mkfs -d $profile -m single >> $seqres.full 2>&1
+	# Use v2 space cache to prevent v1 space cache affecting
+	# the result.
+	_scratch_mount -o space_cache=v2
+
+	# Create one 64K extent which would cover one data stripe.
+	$XFS_IO_PROG -f -d -c "pwrite -S 0xaa -b 64K 0 64K" \
+		"$SCRATCH_MNT/foobar" > /dev/null
+	sync
+
+	# Corrupt the P/Q stripe
+	local logical=$(_btrfs_get_first_logical $SCRATCH_MNT/foobar)
+
+	# The 2nd copy is pointed to P stripe directly.
+	physical_p=$(_btrfs_get_physical ${logical} 2)
+	devpath_p=$(_btrfs_get_device_path ${logical} 2)
+
+	_scratch_unmount
+
+	echo "Corrupt stripe P at devpath $devpath_p physical $physical_p" \
+		>> $seqres.full
+	$XFS_IO_PROG -d -c "pwrite -S 0xff -b 64K $physical_p 64K" $devpath_p \
+		> /dev/null
+
+	# Do a scrub to try repair the P stripe.
+	_scratch_mount -o space_cache=v2
+	$BTRFS_UTIL_PROG scrub start -BdR $SCRATCH_MNT >> $seqres.full 2>&1
+	_scratch_unmount
+
+	# Verify the repaired content directly
+	local output=$($XFS_IO_PROG -c "pread -qv $physical_p 16" $devpath_p | _filter_xfs_io_offset)
+	local expect="XXXXXXXX:  aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa  ................"
+
+	echo "The first 16 bytes of parity stripe after scrub:" >> $seqres.full
+	echo $output >> $seqres.full
+	if [ "$output" != "$expect" ]; then
+		echo "Unexpected parity content"
+		echo "has:"
+		echo "$output"
+		echo "expect"
+		echo "$expect"
+	fi
+
+	# Last safenet, let btrfs check --check-data-csum to do an offline scrub.
+	$BTRFS_UTIL_PROG check --check-data-csum $SCRATCH_DEV >> $seqres.full 2>&1
+	if [ $? -ne 0 ]; then
+		echo "Error detected after the scrub"
+	fi
+	_scratch_dev_pool_put
+}
+
+workload raid5 2
+workload raid6 3
+
+echo "Silence is golden"
+status=0
+exit
diff --git a/tests/btrfs/297.out b/tests/btrfs/297.out
new file mode 100644
index 00000000..41c373c4
--- /dev/null
+++ b/tests/btrfs/297.out
@@ -0,0 +1,2 @@
+QA output created by 297
+Silence is golden
-- 
2.41.0