generic: test mounting filesystem after fsync of a tmpfile

Test that if we fsync a tmpfile, without adding a hard link to it, and
then power fail, we will be able to mount the filesystem without
triggering any crashes, warnings or corruptions.

This test is motivated by an issue in btrfs where this scenario triggered
a warning (without any side effects). The following linux kernel patch
fixes the issue in btrfs:

  "Btrfs: fix warning when replaying log after fsync of a tmpfile"

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/generic/509

@@ -0,0 +1,58 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2018 SUSE Linux Products GmbH. All Rights Reserved.
+#
+# FS QA Test No. 509
+#
+# Test that if we fsync a tmpfile, without adding a hard link to it, and then
+# power fail, we will be able to mount the filesystem without triggering any
+# crashes, warnings or corruptions.
+#
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+tmp=/tmp/$$
+status=1	# failure is the default!
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+_cleanup()
+{
+	_cleanup_flakey
+	cd /
+	rm -f $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+. ./common/dmflakey
+
+# real QA test starts here
+_supported_fs generic
+_supported_os Linux
+_require_scratch
+_require_xfs_io_command "-T"
+_require_dm_target flakey
+
+rm -f $seqres.full
+
+_scratch_mkfs >>$seqres.full 2>&1
+_require_metadata_journaling $SCRATCH_DEV
+_init_flakey
+_mount_flakey
+
+# Create our tmpfile, write some data to it and fsync it. We want a power
+# failure to happen after the fsync, so that we have an inode with a link
+# count of 0 in our log/journal.
+$XFS_IO_PROG -T \
+	-c "pwrite -S 0xab 0 64K" \
+	-c "fsync" \
+	$SCRATCH_MNT | _filter_xfs_io
+
+# Simulate a power failure and mount the filesystem to check that it succeeds.
+_flakey_drop_and_remount
+
+_unmount_flakey
+
+status=0
+exit

tests/generic/509.out

@@ -0,0 +1,3 @@
+QA output created by 509
+wrote 65536/65536 bytes at offset 0
+XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)

tests/generic/group

@@ -511,3 +511,4 @@
 506 shutdown auto quick metadata quota
 507 shutdown auto quick metadata
 508 shutdown auto quick metadata
+509 auto quick log