Re: [PATCH] generic: test fsync of a file truncated to a length of zero

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Feb 17, 2026 at 06:33:30PM +0000, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> Test that if we truncate a file to 0, fsync it, add a hard link to the
> file and then fsync the parent directory, after a power failure the file
> has a size of 0 (and the hardlink exists too).
> 
> This exercises a bug fixed by the following kernel patch for btrfs:
> 
>   "btrfs: fix zero size inode with non-zero size after log replay"
> 
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

This looks ok to me
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  tests/generic/788     | 59 +++++++++++++++++++++++++++++++++++++++++++
>  tests/generic/788.out |  5 ++++
>  2 files changed, 64 insertions(+)
>  create mode 100755 tests/generic/788
>  create mode 100644 tests/generic/788.out
> 
> diff --git a/tests/generic/788 b/tests/generic/788
> new file mode 100755
> index 00000000..0234cc7f
> --- /dev/null
> +++ b/tests/generic/788
> @@ -0,0 +1,59 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2026 SUSE S.A.  All Rights Reserved.
> +#
> +# FS QA Test 788
> +#
> +# Test that if we truncate a file to 0, fsync it, add a hard link to the file
> +# and then fsync the parent directory, after a power failure the file has a
> +# size of 0 (and the hardlink exists too).
> +#
> +. ./common/preamble
> +_begin_fstest auto quick log
> +
> +_cleanup()
> +{
> +	_cleanup_flakey
> +	cd /
> +	rm -r -f $tmp.*
> +}
> +
> +. ./common/filter
> +. ./common/dmflakey
> +
> +_require_scratch
> +_require_dm_target flakey
> +
> +[ "$FSTYP" = "btrfs" ] && _fixed_by_kernel_commit xxxxxxxxxxxx \
> +	"btrfs: fix zero size inode with non-zero size after log replay"
> +
> +_scratch_mkfs >>$seqres.full 2>&1 || _fail "mkfs failed"
> +_require_metadata_journaling $SCRATCH_DEV
> +_init_flakey
> +_scratch_mount
> +
> +mkdir $SCRATCH_MNT/dir
> +$XFS_IO_PROG -f -c "pwrite -S 0xab 0 64K" $SCRATCH_MNT/dir/foo | _filter_xfs_io
> +
> +# Persist the file and directory.
> +_scratch_sync
> +
> +# Truncate the file to 0 and fsync it.
> +$XFS_IO_PROG -c "truncate 0" -c "fsync" $SCRATCH_MNT/dir/foo
> +
> +# Create a link to foo in the same dir.
> +ln $SCRATCH_MNT/dir/foo $SCRATCH_MNT/dir/bar
> +
> +# Fsync the directory.
> +$XFS_IO_PROG -c "fsync" $SCRATCH_MNT/dir
> +
> +# Simulate a power failure and then mount again the filesystem to replay the
> +# journal/log.
> +_flakey_drop_and_remount
> +
> +echo "file size after power failure: $(stat -c %s $SCRATCH_MNT/dir/foo)"
> +echo "file link count after power failure: $(stat -c %h $SCRATCH_MNT/dir/foo)"
> +[ -f $SCRATCH_MNT/dir/bar ] || echo "link dir/bar is missing"
> +
> +# success, all done
> +_exit 0
> diff --git a/tests/generic/788.out b/tests/generic/788.out
> new file mode 100644
> index 00000000..37f3f36a
> --- /dev/null
> +++ b/tests/generic/788.out
> @@ -0,0 +1,5 @@
> +QA output created by 788
> +wrote 65536/65536 bytes at offset 0
> +XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> +file size after power failure: 0
> +file link count after power failure: 2
> -- 
> 2.47.2
> 
>