Re: [PATCH v8 08/13] fstests: verify f_fsid for cloned filesystems

[Zorro Lang <zlang@kernel.org>]

On Sat, Jul 25, 2026 at 03:39:05PM +0800, Anand Jain wrote:
> 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/802     | 64 +++++++++++++++++++++++++++++++++++++++++++
>  tests/generic/802.out |  4 +++
>  2 files changed, 68 insertions(+)
>  create mode 100644 tests/generic/802
>  create mode 100644 tests/generic/802.out
> 
> diff --git a/tests/generic/802 b/tests/generic/802
> new file mode 100644
> index 000000000000..910807c11584
> --- /dev/null
> +++ b/tests/generic/802
> @@ -0,0 +1,64 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2026 Anand Jain <asj@kernel.org>.  All Rights Reserved.
> +#
> +# FS QA Test 802
> +# Check that the cloned filesystem provides an f_fsid that is persistent
> +# across mount cycles if the block device maj:min remains unchanged.
> +
> +. ./common/preamble
> +
> +_begin_fstest auto quick mount clone
> +
> +_require_test
> +_require_block_device $TEST_DEV
> +_require_loop
> +
> +_fixed_by_fs_commit btrfs xxxxxxxxxxxx \
> +	"btrfs: use on-disk uuid for s_uuid in temp_fsid mounts"
> +_fixed_by_fs_commit btrfs xxxxxxxxxxxx \
> +	"btrfs: derive f_fsid from on-disk fsuuid and dev_t"
> +
> +_cleanup()
> +{
> +	cd /
> +	rm -r -f $tmp.*
> +	umount $mnt1 $mnt2 2>/dev/null
> +	_loop_image_destroy "${devs[@]}" 2> /dev/null
> +}
> +
> +# Setup base loop device and its clone
> +devs=()
> +_loop_image_create_clone devs
> +mkdir -p $TEST_DIR/$seq

Better to `rm -rf $TEST_DIR/$seq` before creating a new one.

> +mnt1=$TEST_DIR/$seq/mnt1
> +mnt2=$TEST_DIR/$seq/mnt2
> +mkdir -p $mnt1
> +mkdir -p $mnt2
> +
> +# Mount both filesystems simultaneously using mandatory clone mount options
> +_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]} $mnt2 || \
> +						_fail "Failed to mount dev2"
> +
> +# Capture baseline filesystem IDs for comparison
> +fsid_scratch=$(stat -f -c "%i" $mnt1)
> +fsid_clone=$(stat -f -c "%i" $mnt2)
> +
> +# Verify that the fsids remain stable after a mount cycle, even when the
> +# mount order is reversed.
> +echo "**** fsid after 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"
> +
> +# Compare post mount-cycle values against the baseline
> +stat -f -c "%i" $mnt1 | sed -e "s/$fsid_scratch/FSID_SCRATCH/g"
> +stat -f -c "%i" $mnt2 | sed -e "s/$fsid_clone/FSID_CLONE/g"

Hmm... what if "$fsid_scratch" is same with "$fsid_clone"?

> +
> +status=0
> +exit

_exit 0

> diff --git a/tests/generic/802.out b/tests/generic/802.out
> new file mode 100644
> index 000000000000..0202a9a2c108
> --- /dev/null
> +++ b/tests/generic/802.out
> @@ -0,0 +1,4 @@
> +QA output created by 802
> +**** fsid after mount cycle ****
> +FSID_SCRATCH
> +FSID_CLONE
> -- 
> 2.43.0
>