[PATCH v3 1/2] btrfs: test qgroup limit handling on fsverity rollback

[Daniel Linjama <daniel@dev.linjama.com>]

Test that the subvolume and the filesystem stay writable when an fsverity
enable and its rollback hit the qgroup limit, and that the subvolume is
still reachable after a remount with no verity or orphan items left behind.

This exercises a bug fixed by kernel commit 76bf149cd029 ("btrfs: handle
lack of space when cleaning up verity items").

Assisted-by: LLM
Signed-off-by: Daniel Linjama <daniel@dev.linjama.com>
---
Changes since v2:
- The fix is in mainline as 76bf149cd029, fill it in.

Changes since v1:
- Use _require_qgroup_rescan(); the _qgroup_rescan helper already waits
  with -w.
- Fill the qgroup with a single xfs_io write instead of a loop of dd
  calls, xfs_io instead of dd elsewhere too.
- Both suggested by Qu Wenruo.
- Look for leftover items of the target inode only, like btrfs/058 does.

v2: https://lore.kernel.org/fstests/20260916062356.690137-1-daniel@dev.linjama.com/
v1: https://lore.kernel.org/fstests/20260915053815.307674-1-daniel@dev.linjama.com/

 tests/btrfs/354     | 126 ++++++++++++++++++++++++++++++++++++++++++++
 tests/btrfs/354.out |   2 +
 2 files changed, 128 insertions(+)
 create mode 100755 tests/btrfs/354
 create mode 100644 tests/btrfs/354.out

diff --git a/tests/btrfs/354 b/tests/btrfs/354
new file mode 100755
index 0000000..170bd9b
--- /dev/null
+++ b/tests/btrfs/354
@@ -0,0 +1,126 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2026 Daniel Linjama.  All Rights Reserved.
+#
+# FS QA Test 354
+#
+# Test that a failed fsverity enable in a subvolume whose qgroup is at its
+# limit leaves the filesystem usable.
+#
+. ./common/preamble
+_begin_fstest auto quick qgroup limit verity
+
+# Override the default cleanup function.
+_cleanup()
+{
+	cd /
+	_restore_fsverity_signatures
+	rm -f $tmp.*
+}
+
+# Import common functions.
+. ./common/filter
+. ./common/verity
+
+# real QA test starts here
+
+_require_scratch_verity
+_require_btrfs_command inspect-internal dump-tree
+_require_qgroup_rescan
+_require_no_compress
+_require_scratch_size $((2 * 1024 * 1024))
+_disable_fsverity_signatures
+
+_fixed_by_kernel_commit 76bf149cd029 \
+	"btrfs: handle lack of space when cleaning up verity items"
+
+subv=$SCRATCH_MNT/sub
+target=$subv/target
+
+prepare()
+{
+	_scratch_mkfs_verity &>> $seqres.full
+	_scratch_mount
+	_btrfs quota enable $SCRATCH_MNT
+	_qgroup_rescan $SCRATCH_MNT >> $seqres.full 2>&1
+	_btrfs subvolume create $subv
+	subvolid=$(_btrfs_get_subvolid $SCRATCH_MNT sub)
+	_btrfs qgroup limit 200M 0/$subvolid $SCRATCH_MNT
+}
+
+create_target()
+{
+	$XFS_IO_PROG -f -c "pwrite -q -b 1m 0 128m" $target
+	ino=$(stat -c %i $target)
+	sync
+}
+
+fill_qgroup()
+{
+	# Writes until the qgroup limit is hit.
+	$XFS_IO_PROG -f -c "pwrite -q -b 64k 0 256m" $subv/filler &>/dev/null
+	sync
+	$BTRFS_UTIL_PROG qgroup show -re $SCRATCH_MNT >> $seqres.full 2>&1
+}
+
+enable_fsverity()
+{
+	if _fsv_enable $target >> $seqres.full 2>&1; then
+		_notrun "could not exhaust the qgroup limit, verity enable succeeded"
+	fi
+}
+
+check_rollback()
+{
+	touch $SCRATCH_MNT/canary 2>> $seqres.full || \
+		echo "filesystem was forced read-only by the failed verity enable"
+	if $FSVERITY_PROG measure $target >> $seqres.full 2>&1; then
+		echo "verity is enabled on the target after a failed enable"
+	fi
+}
+
+check_remount()
+{
+	_scratch_unmount
+	_try_scratch_mount >> $seqres.full 2>&1 || \
+		_fail "cannot mount the filesystem after the failed verity enable"
+	ls $subv >/dev/null 2>> $seqres.full || \
+		echo "cannot read the subvolume after the failed verity enable"
+	$XFS_IO_PROG -c "pread -q 0 1m" $target >> $seqres.full 2>&1 || \
+		echo "cannot read the target file after the failed verity enable"
+	_scratch_unmount
+}
+
+check_leftover_items()
+{
+	local dump=$($BTRFS_UTIL_PROG inspect-internal dump-tree -t $subvolid $SCRATCH_DEV)
+	local verity_items=$(echo "$dump" | grep -c "($ino VERITY_\(DESC\|MERKLE\)_ITEM")
+	local orphans=$(echo "$dump" | grep -c "(ORPHAN ORPHAN_ITEM $ino)")
+
+	echo "$dump" >> $seqres.full
+	[ "$verity_items" -eq 0 ] || \
+		echo "$verity_items verity items left behind by the failed enable"
+	[ "$orphans" -eq 0 ] || \
+		echo "$orphans orphan items left behind by the failed enable"
+}
+
+check_subvol_mount()
+{
+	_try_scratch_mount -o subvol=sub >> $seqres.full 2>&1 || \
+		_fail "cannot mount the quota limited subvolume on its own"
+}
+
+prepare
+create_target
+fill_qgroup
+enable_fsverity
+check_rollback
+check_remount
+check_leftover_items
+check_subvol_mount
+
+echo "Silence is golden"
+
+# success, all done
+status=0
+exit
diff --git a/tests/btrfs/354.out b/tests/btrfs/354.out
new file mode 100644
index 0000000..8bc7ecf
--- /dev/null
+++ b/tests/btrfs/354.out
@@ -0,0 +1,2 @@
+QA output created by 354
+Silence is golden
-- 
2.55.0