btrfs: add test for subvolid reuse with squota

Squotas are likely to leave qgroups that outlive deleted subvolids.
Before the kernel patch
2b8aa78cf127 ("btrfs: qgroup: fix qgroup id collision across mounts")
this would lead to a repeated subvolid which would collide on an
existing qgroup id and error out with EEXIST. In snapshot creation, this
would lead to a read only fs.

Add a test which exercises the path that could create duplicate
subvolids but with squotas enabled, which should avoid the trap.

Signed-off-by: Boris Burkov <boris@bur.io>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>
[zlang: Remove _supported_fs line]

diff --git a/tests/btrfs/331 b/tests/btrfs/331
new file mode 100755 (executable)
index 0000000..c9d351f
--- /dev/null
+++ b/tests/btrfs/331
@@ -0,0 +1,43 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2024 Meta Platforms, Inc.  All Rights Reserved.
+#
+# FS QA Test 331
+#
+# Test that btrfs does not recycle subvolume ids across remounts in a way that
+# breaks squotas.
+#
+. ./common/preamble
+_begin_fstest auto quick qgroup snapshot
+
+_fixed_by_kernel_commit 2b8aa78cf127 \
+       "btrfs: qgroup: fix qgroup id collision across mounts"
+
+_require_scratch_enable_simple_quota
+
+_scratch_mkfs >> $seqres.full
+_scratch_mount
+$BTRFS_UTIL_PROG quota enable --simple $SCRATCH_MNT
+
+# Create a gap in the subvolume IDs
+sv=$SCRATCH_MNT/sv
+for i in $(seq 100); do
+       $BTRFS_UTIL_PROG subvolume create $sv.$i >> $seqres.full
+done
+for i in $(seq 50 100); do
+       $BTRFS_UTIL_PROG subvolume delete $sv.$i >> $seqres.full
+done
+
+# Cycle mount triggers reading the tree_root's free objectid.
+_scratch_cycle_mount
+
+# Create snapshots that could go into the used subvolid space.
+$BTRFS_UTIL_PROG subvolume create $sv.BOOM >> $seqres.full
+for i in $(seq 10); do
+       $BTRFS_UTIL_PROG subvolume snapshot $sv.BOOM $sv.BOOM.$i >> $seqres.full
+done
+
+# success, all done
+echo "Silence is golden"
+status=0
+exit

diff --git a/tests/btrfs/331.out b/tests/btrfs/331.out
new file mode 100644 (file)
index 0000000..0097e61
--- /dev/null
+++ b/tests/btrfs/331.out
@@ -0,0 +1,2 @@
+QA output created by 331
+Silence is golden