[PATCH 6/9] fstests: verify f_fsid for cloned filesystems

Anand Jain
2026-02-26T14:42:10Z

Verify that the cloned filesystem provides an f_fsid that is persistent
across mount cycles, yet unique from the original filesystem's f_fsid.

Signed-off-by: Anand Jain <asj@kernel.org>
---
tests/generic/792 | 57 +++++++++++++++++++++++++++++++++++++++++++
tests/generic/792.out | 7 ++++++
2 files changed, 64 insertions(+)
create mode 100644 tests/generic/792
create mode 100644 tests/generic/792.out

diff --git a/tests/generic/792 b/tests/generic/792
new file mode 100644
index 000000000000..3a2f463dc76e
--- /dev/null
+++ b/tests/generic/792
@@ -0,0 +1,57 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2026 Anand Jain <asj@kernel.org>. All Rights Reserved.
+#
+# FS QA Test 792
+# Verify f_fsid and s_uuid of cloned filesystems across mount cycle.
+
+. ./common/preamble
+
+_begin_fstest auto quick mount clone
+
+_require_test
+_require_scratch_dev_pool 2
+
+[ "$FSTYP" = "btrfs" ] && _fixed_by_kernel_commit xxxxxxxxxxxx \
+ "btrfs: use on-disk uuid for s_uuid in temp_fsid mounts"
+[ "$FSTYP" = "btrfs" ] && _fixed_by_kernel_commit xxxxxxxxxxxx \
+ "btrfs: derive f_fsid from on-disk fsuuid and dev_t"
+
+_cleanup()
+{
+ cd /
+ rm -r -f $tmp.*
+ umount $mnt2 2>/dev/null
+ _scratch_dev_pool_put
+}
+
+_scratch_dev_pool_get 2
+_scratch_mkfs_sized_clone >$seqres.full 2>&1
+devs=($SCRATCH_DEV_POOL)
+mnt2=$TEST_DIR/mnt2
+mkdir -p $mnt2
+
+_scratch_mount $(_clone_mount_option)
+_mount $(_common_dev_mount_options) $(_clone_mount_option) ${devs[1]} $mnt2 || \
+ _fail "Failed to mount dev2"
+
+fsid_scratch=$(stat -f -c "%i" $SCRATCH_MNT)
+fsid_clone=$(stat -f -c "%i" $mnt2)
+
+echo "**** fsid initially ****"
+echo $fsid_scratch | sed -e "s/$fsid_scratch/FSID_SCRATCH/g"
+echo $fsid_clone | sed -e "s/$fsid_clone/FSID_CLONE/g"
+
+# Make sure fsid still match across a mount cycle, also reverse the order.
+echo "**** fsid after mount cycle ****"
+_scratch_unmount
+_unmount $mnt2
+_mount $(_common_dev_mount_options) $(_clone_mount_option) ${devs[1]} $mnt2 || \
+ _fail "Failed to mount dev2"
+_scratch_mount $(_clone_mount_option)
+
+stat -f -c "%i" $SCRATCH_MNT | sed -e "s/$fsid_scratch/FSID_SCRATCH/g"
+stat -f -c "%i" $mnt2 | sed -e "s/$fsid_clone/FSID_CLONE/g"
+
+status=0
+exit
diff --git a/tests/generic/792.out b/tests/generic/792.out
new file mode 100644
index 000000000000..27ecbce2225e
--- /dev/null
+++ b/tests/generic/792.out
@@ -0,0 +1,7 @@
+QA output created by 792
+**** fsid initially ****
+FSID_SCRATCH
+FSID_CLONE
+**** fsid after mount cycle ****
+FSID_SCRATCH
+FSID_CLONE
--
2.43.0