Re: [PATCH v8 07/13] fstests: verify fanotify isolation on cloned filesystems

[Anand Suveer Jain <asj@kernel.org>]

On 2/9/26 02:23, Zorro Lang wrote:
> On Sat, Jul 25, 2026 at 03:39:04PM +0800, Anand Jain wrote:
>> Verify that fanotify events are correctly routed to the appropriate
>> watcher when cloned filesystems are mounted.
>> Helps verify kernel's event notification distinguishes between devices
>> sharing the same FSID/UUID.
>>
>> Signed-off-by: Anand Jain <asj@kernel.org>
>> ---
>>  tests/generic/801     | 143 ++++++++++++++++++++++++++++++++++++++++++
> 
> `g/801` is already taken. To avoid merge conflicts, you can use a higher
> temporary number, and I'll assign the proper number when merging.
> 

Let me bump-it up to 90x.

>>  tests/generic/801.out |   7 +++
>>  2 files changed, 150 insertions(+)
>>  create mode 100644 tests/generic/801
>>  create mode 100644 tests/generic/801.out
>>
>> diff --git a/tests/generic/801 b/tests/generic/801
>> new file mode 100644
>> index 000000000000..904ba9440b3d
>> --- /dev/null
>> +++ b/tests/generic/801
>> @@ -0,0 +1,143 @@
>> +#! /bin/bash
>> +# SPDX-License-Identifier: GPL-2.0
>> +# Copyright (c) 2026 Anand Jain <asj@kernel.org>.  All Rights Reserved.
>> +#
>> +# FS QA Test 801
>> +# Verify fanotify FID functionality on cloned filesystems by setting up
>> +# watchers and making sure notifications are in the correct logs files.
>> +
>> +. ./common/preamble
>> +
>> +_begin_fstest auto quick mount clone
>> +
>> +_require_test
>> +_require_block_device $TEST_DEV
> 
> Which test condition requires `TEST_DEV` to be a block device?

You're right, I think this is a leftover from earlier prototyping
with scsi_device. The test only needs loop devices backed by
$TEST_DIR. I'll remove it in the following ver.

> 
>> +_require_loop
>> +_require_command "$SEMANAGE_PROG" semanage
>> +_require_command "$FSNOTIFYWAIT_PROG" fsnotifywait
>> +_require_fanotify_function
>> +_require_unique_f_fsid
>> +
>> +_cleanup()
>> +{
>> +	cd /
>> +	[[ -n $pid1 ]] && { kill -TERM "$pid1" 2> /dev/null; wait $pid1; }
>> +	[[ -n $pid2 ]] && { kill -TERM "$pid2" 2> /dev/null; wait $pid2; }
>> +
>> +	if [ "$semanage_added" = "yes" ]; then
>> +		semanage permissive -d unconfined_t >/dev/null 2>&1 || true
>> +	fi
>> +
>> +	umount $mnt1 $mnt2 >/dev/null 2>&1
>> +	_loop_image_destroy "${devs[@]}" 2> /dev/null
>> +	rm -r -f $tmp.*
>> +}
>> +
>> +# Run fsnotifywait in unbuffered mode to watch filesystem-wide create events
>> +monitor_fanotify()
>> +{
>> +	local mmnt=$1
>> +	exec stdbuf -oL $FSNOTIFYWAIT_PROG -m -F -S -e create "$mmnt" 2>&1
>> +}
>> +
>> +# Transform f_fsid into the hi.lo format used in fanotify FID logs
>> +fsid_to_fid_parts()
>> +{
>> +	local fsid=$1
>> +	# Pad to 16 hex chars (64-bit), then split into two 32-bit halves
>> +	local padded=$(printf '%016x' "0x${fsid}")
>> +	local hi=$(printf '%x' "0x${padded:0:8}")   # strips leading zeros
>> +	local lo=$(printf '%x' "0x${padded:8:8}")   # strips leading zeros
>> +	echo "${hi}.${lo}"
>> +}
>> +
>> +# Create base loop device and its clone
>> +devs=()
>> +_loop_image_create_clone devs
>> +mkdir -p $TEST_DIR/$seq
>> +mnt1=$TEST_DIR/$seq/mnt1
>> +mnt2=$TEST_DIR/$seq/mnt2
>> +mkdir -p $mnt1
>> +mkdir -p $mnt2
>> +
>> +# Mount both base and clone filesystems using required 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]} $mnt2 || \
>> +						_fail "Failed to mount dev2"
>> +
>> +# Fetch filesystem IDs to verify the kernel can differentiate between them
>> +fsid1=$(stat -f -c "%i" $mnt1)
>> +fsid2=$(stat -f -c "%i" $mnt2)
>> +
>> +log1=$tmp.fanotify1
>> +log2=$tmp.fanotify2
>> +
>> +pid1=""
>> +pid2=""
>> +echo "Setup FID fanotify watchers on both mnt1 and mnt2"
>> +
>> +# Permit unconfined_t domains when SELinux is enforcing to prevent fanotify
>> +# blockages
>> +semanage_added="no"
>> +if [ "$(getenforce 2>/dev/null)" = "Enforcing" ]; then
>> +    if ! semanage permissive -l | grep -q "unconfined_t"; then
>> +        semanage permissive -a unconfined_t >/dev/null 2>&1 && semanage_added="yes"
>> +    fi
>> +fi
> 
> Looks like semanage/SELinux isn't a necessary requirement of this test case,
> if so that `_require_command "$SEMANAGE_PROG" semanage` also can be:
> 
>   if [ "$(getenforce 2>/dev/null)" = "Enforcing" ]; then
>       _require_command "$SEMANAGE_PROG" semanage
>   fi
> 
> right? And please replace semanage with $SEMANAGE_PROG.
> 

Absolutely, that is the right way. I'll update it. Thanks!. More below.

>> +
>> +# Start asynchronous fanotify monitors
>> +( monitor_fanotify "$mnt1" > "$log1" ) &
>> +pid1=$!
>> +( monitor_fanotify "$mnt2" > "$log2" ) &
>> +pid2=$!
>> +sleep 2
> 
> Are you using `sleep 2` to ensure `fsnotifywait` is fully set up?
> I'm not sure if `sleep 2` is 100% reliable here. Since the subsequent tests
> strictly depend on `fsnotifywait` starting up properly, is there a more
> robust approach than `sleep 2`? For example, could we check the output
> in `$log1` and `$log2` to make sure that? Or any other better idea?
> 
>> +
>> +if ! kill -0 "$pid1" 2>/dev/null || ! kill -0 "$pid2" 2>/dev/null; then
> 
> `kill 0` only can make sure the process is running, can't make sure it's
> fully set up, right?
> 

I rely on checking whether the userspace process is still
running after a 2 second delay.

Matching specific stdout strings a common pattern in fstests
tends to be fragile across different versions of userspace
utilities. For instance, the "Watches established" string
in fsnotifywait isn't guaranteed across versions:

$ fsnotifywait -m -F -S -e create /btrfs
Setting up filesystem watches.
Watches established.
^C


>> +	cat "$log1"
>> +	cat "$log2"
>> +	_fail "$FSNOTIFYWAIT_PROG setup failed"
>> +fi
>> +
>> +echo "Trigger file creation on mnt1"
>> +touch $mnt1/file_on_mnt1
>> +sync
>> +sleep 1
>> +
>> +echo "Trigger file creation on mnt2"
>> +touch $mnt2/file_on_mnt2
>> +sync
>> +sleep 1
>> +
>> +echo "Verify fsid in the fanotify"
>> +kill $pid1 $pid2
>> +wait $pid1 $pid2 2>/dev/null
>> +pid1=""
> 
> unset pid1
> 
>> +pid2=""
> 
> unset pid2
> 

Added.

>> +
>> +e_fsid1=$(fsid_to_fid_parts "$fsid1")
>> +e_fsid2=$(fsid_to_fid_parts "$fsid2")
>> +
>> +# Dump debug details to the full log
>> +echo $fsid1 $e_fsid1 $fsid2 $e_fsid2 >> $seqres.full
>> +cat $log1 >> $seqres.full
>> +cat $log2 >> $seqres.full
>> +
>> +# Ensure monitor 1 only captured events belonging to mnt 1 and fsid 1
>> +if grep -qF "$e_fsid1" "$log1" && ! grep -qF "$e_fsid2" "$log1"; then
>> +	echo "SUCCESS: mnt1 events found"
>> +else
>> +	[ ! -s "$log1" ] && echo "  - mnt1 received no events."
>> +	grep -qF "$e_fsid2" "$log1" && echo "  - mnt1 received event from mnt2."
>> +fi
>> +
>> +# Ensure monitor 2 only captured events belonging to mnt 2 and fsid 2
>> +if grep -qF "$e_fsid2" "$log2" && ! grep -qF "$e_fsid1" "$log2"; then
>> +	echo "SUCCESS: mnt2 events found"
>> +else
>> +	[ ! -s "$log2" ] && echo "  - mnt2 received no events."
>> +	grep -qF "$e_fsid1" "$log2" && echo "  - mnt2 received event from mnt1."
>> +fi
>> +
>> +status=0
>> +exit
> 
> _exit 0
> 

Added.

Thanks.
Anand

> Thanks,
> Zorro
> 
>> diff --git a/tests/generic/801.out b/tests/generic/801.out
>> new file mode 100644
>> index 000000000000..d7b318d9f27c
>> --- /dev/null
>> +++ b/tests/generic/801.out
>> @@ -0,0 +1,7 @@
>> +QA output created by 801
>> +Setup FID fanotify watchers on both mnt1 and mnt2
>> +Trigger file creation on mnt1
>> +Trigger file creation on mnt2
>> +Verify fsid in the fanotify
>> +SUCCESS: mnt1 events found
>> +SUCCESS: mnt2 events found
>> -- 
>> 2.43.0
>>