[PATCH] fstests: btrfs: add a new test case to verify quick qgroup inherit

[Qu Wenruo <wqu@suse.com>]

[BUG]
There is a bug report that simple quota exposed a bug in the quick
qgroup inherit, that if there is a multi-level qgroup parent
relationship, only the direct parent got updated.

[TEST CASE]
The test case will create the following subvolume and qgroups first:

- A new subvolume at '/subv1'
- Qgroup 1/1
- Qgroup 2/1

And subvolume '/subv1' is assgiend to qgroup 1/1, so 1/1 is the direct
parent.
Then qgroup 1/1 is also assigned to 2/1, so 2/1 is an indirect parent of
subvolume '/subv1'.

Then the trigger part is to creating a snapshot of '/subv1' and also
assigned the new snapshot into qgroup 1/1 during the snapshot creation.

Since 1/1 is the parent of '/subv1' and the new snapshot, and qgroup 1/1
fully owns '/subv1', we can do a quick inherit.

After the triggering part, just finish the test case and the fsck after
the test case should detect any qgroup inconsistency.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 tests/btrfs/339     | 45 +++++++++++++++++++++++++++++++++++++++++++++
 tests/btrfs/339.out |  2 ++
 2 files changed, 47 insertions(+)
 create mode 100755 tests/btrfs/339
 create mode 100644 tests/btrfs/339.out

diff --git a/tests/btrfs/339 b/tests/btrfs/339
new file mode 100755
index 00000000..6581b61b
--- /dev/null
+++ b/tests/btrfs/339
@@ -0,0 +1,45 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2025 SUSE S.A.  All Rights Reserved.
+#
+# FS QA Test 339
+#
+# Make sure when doing a quick inherit for snapshot, all parent qgroups
+# including direct and indirect parents are properly updated.
+#
+. ./common/preamble
+_begin_fstest auto quick qgroup
+
+_fixed_by_kernel_commit xxxxxxxxxxxx \
+	"btrfs: qgroup: update all parent qgroups when doing quick inherit"
+
+# For the automatic fsck at unmount.
+_require_scratch
+_require_btrfs_qgroup_report
+
+# This will imply mkfs and enable regular qgroup.
+_require_scratch_qgroup
+_scratch_mount
+
+# Create a subvolume along with qgroups 1/1 and 2/1.
+# The subvolume qgroup is assgiend to 1/1, and 1/1 is assigned to 2/1.
+_btrfs subvolume create $SCRATCH_MNT/subv1
+subvolid=$(_btrfs_get_subvolid $SCRATCH_MNT subv1)
+_btrfs qgroup create 1/1 $SCRATCH_MNT
+_btrfs qgroup create 2/1 $SCRATCH_MNT
+_btrfs qgroup assign 1/1 2/1 $SCRATCH_MNT
+_btrfs qgroup assign 0/$subvolid 1/1 $SCRATCH_MNT
+
+# All above assign should result quick update, no need for a full rescan
+echo "Before quick inherit:" >> $seqres.full
+_btrfs qgroup show -p --sync $SCRATCH_MNT >> $seqres.full
+
+# The next snapshot creation will create a snapshot and assign it to 1/1,
+# which is the same parent of the source subvolume, and we can do a quick inherit
+# without marking qgroup inconsistent.
+_btrfs subv snap -i 1/1 $SCRATCH_MNT/subv1 $SCRATCH_MNT/snap1
+echo "After quick inherit:" >> $seqres.full
+_btrfs qgroup show -p --sync $SCRATCH_MNT >> $seqres.full
+
+echo "Silence is golden"
+_exit 0
diff --git a/tests/btrfs/339.out b/tests/btrfs/339.out
new file mode 100644
index 00000000..293ea808
--- /dev/null
+++ b/tests/btrfs/339.out
@@ -0,0 +1,2 @@
+QA output created by 339
+Silence is golden
-- 
2.51.2