[PATCH v3] fstests: btrfs/049: add regression test for compress-force mount options

[Qu Wenruo <wqu@suse.com>]

Since kernel commit d4088803f511 ("btrfs: subpage: make lzo_compress_pages()
compatible"), lzo compression no longer respects the max compressed page
limit, and can cause kernel crash.

The upstream fix is 6f019c0e0193 ("btrfs: fix a out-of-bound access in
copy_compressed_data_to_page()").

This patch will add such regression test for all possible compress-force
mount options, including lzo, zstd and zlib.

And since we're here, also make sure the content of the file matches
after a mount cycle.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
Changelog:
v2:
- Also test zlib and zstd
- Add file content verification check
v3:
- Use $tmp.good as a known good file source
- Also make sure we didn't get short read for the good copy
---
 tests/btrfs/049     | 67 +++++++++++++++++++++++++++++++++++++++++++++
 tests/btrfs/049.out |  6 ++++
 2 files changed, 73 insertions(+)
 create mode 100755 tests/btrfs/049

diff --git a/tests/btrfs/049 b/tests/btrfs/049
new file mode 100755
index 00000000..c1f35dc9
--- /dev/null
+++ b/tests/btrfs/049
@@ -0,0 +1,67 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2021 SUSE Linux Products GmbH. All Rights Reserved.
+#
+# FS QA Test 049
+#
+# Test if btrfs will crash when using compress-force mount option against
+# incompressible data
+#
+. ./common/preamble
+_begin_fstest auto quick compress dangerous
+
+# Override the default cleanup function.
+_cleanup()
+{
+	cd /
+ 	rm -r -f $tmp.*
+}
+
+# Import common functions.
+. ./common/filter
+
+# real QA test starts here
+
+# Modify as appropriate.
+_supported_fs btrfs
+_require_scratch
+
+pagesize=$(get_page_size)
+
+# Read the content from urandom to a known safe location
+$XFS_IO_PROG -f -c "pwrite -i /dev/urandom 0 $pagesize" "$tmp.good" > /dev/null
+
+# Make sure we didn't get short read
+if [ $(_get_filesize "$tmp.good") != "$pagesize" ]; then
+	_fail "Got a short read from /dev/urandom"
+fi
+
+workload()
+{
+	local compression=$1
+
+	echo "=== Testing compress-force=$compression ==="
+	_scratch_mkfs -s "$pagesize">> $seqres.full
+	_scratch_mount -o compress-force="$compression"
+	cp "$tmp.good" "$SCRATCH_MNT/$compression"
+
+	# When unpatched, compress-force=lzo would crash at data writeback
+	_scratch_cycle_mount
+
+	# Make sure the content matches
+	if [ "$(_md5_checksum $tmp.good)" != \
+	     "$(_md5_checksum $SCRATCH_MNT/$compression)" ]; then
+		_fail "Content of '$SCRATCH_MNT/file' mismatch with known good copy"
+	else
+		echo "OK"
+	fi
+	_scratch_unmount
+}
+
+workload lzo
+workload zstd
+workload zlib
+
+# success, all done
+status=0
+exit
diff --git a/tests/btrfs/049.out b/tests/btrfs/049.out
index cb0061b3..41bffeaa 100644
--- a/tests/btrfs/049.out
+++ b/tests/btrfs/049.out
@@ -1 +1,7 @@
 QA output created by 049
+=== Testing compress-force=lzo ===
+OK
+=== Testing compress-force=zstd ===
+OK
+=== Testing compress-force=zlib ===
+OK
-- 
2.34.0