[PATCH v6 11/11] fstests: test UUID consistency for clones with metadata_uuid

[Anand Jain <asj@kernel.org>]

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     | 84 +++++++++++++++++++++++++++++++++++++++++++
 tests/generic/806.out | 19 ++++++++++
 2 files changed, 103 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..801671fb9ce9
--- /dev/null
+++ b/tests/generic/806
@@ -0,0 +1,84 @@
+#! /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
+}
+
+# Collect and print device resolution properties across user-space tools
+print_info()
+{
+	local mntpt=$1
+	local tgt=$(findmnt -no SOURCE $mntpt)
+	local fsuuid=$(blkid -s UUID -o value $tgt)
+
+	echo "mntpt=$mntpt tgt=$tgt fsuuid=$fsuuid" >> $seqres.full
+	echo
+	findmnt -o SOURCE,TARGET,UUID "$tgt" | tail -n +2 | \
+				sed -e "s/${fsuuid}/FSUUID/g" | filter_pool
+	awk -v dev="$tgt" '$1 == dev { print $1, $2 }' /proc/self/mounts | \
+								filter_pool
+	df --all --output=source,target "$tgt" | tail -n +2 | filter_pool
+}
+
+# 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
+mkdir -p $TEST_DIR/$seq
+mnt1=$TEST_DIR/$seq/mnt1
+mnt2=$TEST_DIR/$seq/mnt2
+mkdir -p $mnt1
+mkdir -p $mnt2
+
+# 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"
+
+print_info $mnt1
+print_info $mnt2
+
+# Cycle mounts and reverse the initialization order to ensure UUID tracking
+# doesn't mismatch or flip when metadata_uuid optimization is active.
+echo
+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"
+
+print_info $mnt1
+print_info $mnt2
+
+status=0
+exit
diff --git a/tests/generic/806.out b/tests/generic/806.out
new file mode 100644
index 000000000000..7315e791ba51
--- /dev/null
+++ b/tests/generic/806.out
@@ -0,0 +1,19 @@
+QA output created by 806
+
+DEV1 MNT1 FSUUID
+DEV1 MNT1
+DEV1 MNT1
+
+DEV2 MNT2 FSUUID
+DEV2 MNT2
+DEV2 MNT2
+
+**** mount cycle ****
+
+DEV1 MNT1 FSUUID
+DEV1 MNT1
+DEV1 MNT1
+
+DEV2 MNT2 FSUUID
+DEV2 MNT2
+DEV2 MNT2
-- 
2.43.0