linux-kernel - Re: Directory is not persisted after writing to the file within directory if system crashes

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Message-ID: <d039a3c8-c4f7-487c-a848-2a26ea26f77d@gmail.com>
Date: Sat, 25 Oct 2025 12:49:42 +0300
From: Vyacheslav Kovalevsky <slava.kovalevskiy.2014@...il.com>
To: Filipe Manana <fdmanana@...nel.org>
Cc: clm@...com, dsterba@...e.com, linux-btrfs@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: Directory is not persisted after writing to the file within
 directory if system crashes

On 24/10/2025 19:17, Filipe Manana wrote:
> I converted that to a test case for fstests and couldn't reproduce,
> "dir", "file1" and "dir/file2" exist after the power failure.
>
> The conversion for fstests:
>
> #! /bin/bash
> # SPDX-License-Identifier: GPL-2.0
> # Copyright (c) 2025 SUSE S.A.  All Rights Reserved.
> #
> # FS QA Test 780
> #
> # what am I here for?
> #
> . ./common/preamble
> _begin_fstest auto quick log
>
> _cleanup()
> {
> _cleanup_flakey
> cd /
> rm -r -f $tmp.*
> }
>
> . ./common/filter
> . ./common/dmflakey
>
> _require_scratch
> _require_dm_target flakey
>
> rm -f $seqres.full
> On 24/10/2025 19:17, Filipe Manana wrote:
> _scratch_mkfs >>$seqres.full 2>&1 || _fail "mkfs failed"
> _require_metadata_journaling $SCRATCH_DEV
> _init_flakey
> _mount_flakey
>
> touch $SCRATCH_MNT/file1
>
> _scratch_sync
>
> mkdir $SCRATCH_MNT/dir
> echo -n "hello world" > $SCRATCH_MNT/file1
> ln $SCRATCH_MNT/file1 $SCRATCH_MNT/dir/file2
>
> $XFS_IO_PROG -c "fsync" $SCRATCH_MNT/
>
> # Simulate a power failure and then mount again the filesystem to replay the
> # journal/log.
> _flakey_drop_and_remount
>
> ls -R $SCRATCH_MNT/ | _filter_scratch
>
> _unmount_flakey
>
> # success, all done
> _exit 0

I think the line with `echo` may not be the correct translation:
 > echo -n "hello world" > $SCRATCH_MNT/file1

In the original test, the file was opened with `O_SYNC` flag, if you 
remove it, the directory will be there when the system crashes. I also 
forgot to close the file after the `creat` call in the original test, 
may be important as well.

The test itself is quite weird (why would `dir` be gone after seemingly 
unrelated operation?), any detail can matter.

Please run the original test with a real system crash. I will also 
double check everything on my side.