[PATCH] btrfs: add a test case to verify that per-fs features directory gets updated

[Qu Wenruo <wqu@suse.com>]

Although btrfs has a per-fs feature directory, it's not properly
refreshed after new features are enabled.

We had some attempts to do that properly, like commit 14e46e04958d
("btrfs: synchronize incompat feature bits with sysfs files").
But unfortunately that commit get later reverted as some call sites is
not safe to update sysfs files.

Now we have a new patch to properly refresh that per-fs features
directory, titled "btrfs: update fs features sysfs directory asynchronously".

So it's time to add a test case for it. The test case itself is pretty
straightforward:

- Make a very basic 3 disks btrfs
  Only using the very basic profiles (DUP/SINGLE) so that even older
  mkfs.btrfs can support.

- Make sure per-fs features directory doesn't contain "raid1c34" file

- Balance the metadata to RAID1C3 profile

- Verify the per-fs features directory contains "raid1c34" feature file

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 tests/btrfs/283     | 73 +++++++++++++++++++++++++++++++++++++++++++++
 tests/btrfs/283.out |  2 ++
 2 files changed, 75 insertions(+)
 create mode 100755 tests/btrfs/283
 create mode 100644 tests/btrfs/283.out

diff --git a/tests/btrfs/283 b/tests/btrfs/283
new file mode 100755
index 00000000..6c431273
--- /dev/null
+++ b/tests/btrfs/283
@@ -0,0 +1,73 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2023 SUSE Linux Products GmbH. All Rights Reserved.
+#
+# FS QA Test 283
+#
+# Make sure that per-fs features sysfs interface get properly updated
+# when a new feature is added.
+#
+. ./common/preamble
+_begin_fstest auto quick balance
+
+# Override the default cleanup function.
+# _cleanup()
+# {
+# 	cd /
+# 	rm -r -f $tmp.*
+# }
+
+# Import common functions.
+# . ./common/filter
+
+# real QA test starts here
+
+# Modify as appropriate.
+_supported_fs btrfs
+_require_scratch_dev_pool 3
+
+# We need the global features support
+_require_btrfs_fs_sysfs
+
+global_features="/sys/fs/btrfs/features"
+# Make sure we have support RAID1C34 first
+if [ ! -f "${global_features}/raid1c34" ]; then
+	_notrun "no RAID1C34 support"
+fi
+
+_scratch_dev_pool_get 3
+
+# Go the very basic profile first, so that even older progs can support it.
+_scratch_pool_mkfs -m dup -d single >>$seqres.full 2>&1
+
+_scratch_mount
+uuid="$(findmnt -n -o UUID "$SCRATCH_MNT")"
+per_fs_features="/sys/fs/btrfs/${uuid}/features"
+
+# First we need per-fs features directory
+if [ ! -d "${per_fs_features}" ]; then
+	_notrun "no per-fs features sysfs directory"
+fi
+
+# Make sure the per-fs features doesn't include raid1c34
+if [ -f "${per_fs_features}/raid1c34" ]; then
+	_fail "raid1c34 feature found unexpectedly"
+fi
+
+# Balance to RAID1C3
+$BTRFS_UTIL_PROG balance start -mconvert=raid1c3 "$SCRATCH_MNT" >> $seqres.full
+
+# Check if the per-fs features directory contains raid1c34 now
+# Make sure the per-fs features doesn't include raid1c34
+if [ ! -f "${per_fs_features}/raid1c34" ]; then
+	_fail "raid1c34 feature not found"
+fi
+
+echo "Silence is golden"
+
+_scratch_unmount
+_scratch_dev_pool_put
+
+# success, all done
+status=0
+exit
diff --git a/tests/btrfs/283.out b/tests/btrfs/283.out
new file mode 100644
index 00000000..efb2c583
--- /dev/null
+++ b/tests/btrfs/283.out
@@ -0,0 +1,2 @@
+QA output created by 283
+Silence is golden
-- 
2.39.0