Re: [PATCH v8 13/13] fstests: test UUID consistency for clones with metadata_uuid

[Zorro Lang <zlang@kernel.org>]

On Sat, Jul 25, 2026 at 03:39:10PM +0800, Anand Jain wrote:
> Btrfs and xfs uses the metadata_uuid superblock feature to change the
> on-disk UUID without rewriting every block header. This patch adds a
> sanity check to ensure UUID consistency when a filesystem with
> metadata_uuid enabled is cloned.
> 
> Signed-off-by: Anand Jain <asj@kernel.org>
> ---
>  tests/generic/806     | 74 +++++++++++++++++++++++++++++++++++++++++++
>  tests/generic/806.out |  6 ++++
>  2 files changed, 80 insertions(+)
>  create mode 100644 tests/generic/806
>  create mode 100644 tests/generic/806.out
> 
> diff --git a/tests/generic/806 b/tests/generic/806
> new file mode 100644
> index 000000000000..6d3166491006
> --- /dev/null
> +++ b/tests/generic/806
> @@ -0,0 +1,74 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2026 Anand Jain <asj@kernel.org>.  All Rights Reserved.
> +#
> +# FS QA Test 806
> +#
> +# Verify that the cloned filesystem UUID remains consistent, even when the
> +# `metadata_uuid` feature is enabled.
> +#
> +
> +. ./common/preamble
> +. ./common/filter
> +
> +_begin_fstest auto quick mount clone
> +
> +_require_test
> +_require_block_device $TEST_DEV
> +_require_loop
> +
> +_cleanup()
> +{
> +	cd /
> +	rm -r -f $tmp.*
> +	umount $mnt1 $mnt2 2>/dev/null
> +	_loop_image_destroy "${devs[@]}" 2> /dev/null
> +}
> +
> +filter_pool()
> +{
> +	sed -e "s|${devs[0]}|DEV1|g" -e "s|${mnt1}|MNT1|g" \
> +	    -e "s|${devs[1]}|DEV2|g" -e "s|${mnt2}|MNT2|g" | _filter_spaces
> +}
> +
> +# Create base loop device and its clone, applying the metadata_uuid tuning
> +# callback to the base filesystem before the copy occurs.
> +devs=()
> +_loop_image_create_clone devs _change_metadata_uuid

Should we have and run a _require_metadata_uuid before changing it?
As I know, btrfs can do `_require_btrfs_fs_feature metadata_uuid`.

> +mkdir -p $TEST_DIR/$seq
> +mnt1=$TEST_DIR/$seq/mnt1
> +mnt2=$TEST_DIR/$seq/mnt2
> +mkdir -p $mnt1
> +mkdir -p $mnt2
> +
> +# Get the uuid from the source device
> +fsuuid=$(blkid -s UUID -o value ${devs[0]})
> +
> +# Mount both clone and baseline
> +_mount $(_common_dev_mount_options) $(_clone_mount_option) ${devs[0]} $mnt1 || \
> +						_fail "Failed to mount dev1"
> +_mount $(_common_dev_mount_options) $(_clone_mount_option) ${devs[1]} $mnt2 || \
> +						_fail "Failed to mount dev2"
> +
> +findmnt -o SOURCE,TARGET,UUID "${devs[0]}" | tail -n +2 | \
> +				sed -e "s/${fsuuid}/FSUUID/g" | filter_pool
> +findmnt -o SOURCE,TARGET,UUID "${devs[1]}" | tail -n +2 | \
> +				sed -e "s/${fsuuid}/FSUUID/g" | filter_pool
> +
> +# Cycle mounts and reverse the initialization order to ensure UUID tracking
> +# doesn't mismatch or flip when metadata_uuid optimization is active.
> +echo "**** mount cycle ****"
> +_unmount $mnt1
> +_unmount $mnt2
> +_mount $(_common_dev_mount_options) $(_clone_mount_option) ${devs[1]} $mnt2 || \
> +						_fail "Failed to mount dev2"
> +_mount $(_common_dev_mount_options) $(_clone_mount_option) ${devs[0]} $mnt1 || \
> +						_fail "Failed to mount dev1"
> +
> +findmnt -o SOURCE,TARGET,UUID "${devs[0]}" | tail -n +2 | \
> +				sed -e "s/${fsuuid}/FSUUID/g" | filter_pool
> +findmnt -o SOURCE,TARGET,UUID "${devs[1]}" | tail -n +2 | \
> +				sed -e "s/${fsuuid}/FSUUID/g" | filter_pool
> +
> +status=0
> +exit
> diff --git a/tests/generic/806.out b/tests/generic/806.out
> new file mode 100644
> index 000000000000..918f422ecddf
> --- /dev/null
> +++ b/tests/generic/806.out
> @@ -0,0 +1,6 @@
> +QA output created by 806
> +DEV1 MNT1 FSUUID
> +DEV2 MNT2 FSUUID
> +**** mount cycle ****
> +DEV1 MNT1 FSUUID
> +DEV2 MNT2 FSUUID
> -- 
> 2.43.0
>