tests/generic/057

#! /bin/bash
# SPDX-License-Identifier: GPL-2.0
# Copyright (C) 2015 SUSE Linux Products GmbH. All Rights Reserved.
#
# FS QA Test No. 057
#
# This test is motivated by an fsync issue discovered in btrfs.
# The issue was that we could lose file data, that was previously fsync'ed
# successfully, if we end up adding a hard link to our inode and then persist
# the fsync log later via an fsync of other inode for example.
#
# The btrfs issue was fixed by the following linux kernel patch:
#
#  Btrfs: fix fsync data loss after adding hard link to inode
#
. ./common/preamble
_begin_fstest metadata auto quick log

# Override the default cleanup function.
_cleanup()
{
	_cleanup_flakey
	rm -f $tmp.*
}

# Import common functions.
. ./common/filter
. ./common/dmflakey

# real QA test starts here
_supported_fs generic
_require_scratch
_require_hardlinks
_require_dm_target flakey

_scratch_mkfs >> $seqres.full 2>&1
_require_metadata_journaling $SCRATCH_DEV
_init_flakey
_mount_flakey

# Create our test file with some data.
$XFS_IO_PROG -f -c "pwrite -S 0xaa -b 8K 0 8K" \
	$SCRATCH_MNT/foo | _filter_xfs_io

# Make sure the file is durably persisted.
sync

# Append some data to our file, to increase its size.
$XFS_IO_PROG -f -c "pwrite -S 0xcc -b 4K 8K 4K" \
	$SCRATCH_MNT/foo | _filter_xfs_io

# Fsync the file, so from this point on if a crash/power failure happens, our
# new data is guaranteed to be there next time the fs is mounted.
$XFS_IO_PROG -c "fsync" $SCRATCH_MNT/foo

# Add one hard link to our file. This made btrfs write into the in memory fsync
# log a special inode with generation 0 and an i_size of 0 too. Note that this
# didn't update the inode in the fsync log on disk.
ln $SCRATCH_MNT/foo $SCRATCH_MNT/foo_link

# Now make sure the in memory fsync log is durably persisted.
# Creating and fsync'ing another file will do it.
touch $SCRATCH_MNT/bar
$XFS_IO_PROG -c "fsync" $SCRATCH_MNT/bar

# As expected, before the crash/power failure, we should be able to read the
# 12Kb of file data.
echo "File content before:"
od -t x1 $SCRATCH_MNT/foo

_flakey_drop_and_remount

# After mounting the fs again, the fsync log was replayed.
# The btrfs fsync log replay code didn't update the i_size of the persisted
# inode because the inode item in the log had a special generation with a
# value of 0 (and it couldn't know the correct i_size, since that inode item
# had a 0 i_size too). This made the last 4Kb of file data inaccessible and
# effectively lost.
echo "File content after:"
od -t x1 $SCRATCH_MNT/foo

status=0
exit