[PATCH] btrfs test scan but not register the single device fs

[Anand Jain <anand.jain@oracle.com>]

Recently, in the kernel commit 0d9436739af2 ("btrfs: scan but don't
register device on single device filesystem"), we adopted an approach
where we scan the device to validate it. However, we do not register
it in the kernel memory since it is not required to be remembered.

However, the seed device should continue to be registered because
otherwise, the mount operation for the sprout device will fail.

This patch ensures that we honor the mount requirements and do not break
anything while making changes in this part of the code.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 tests/btrfs/298     | 53 +++++++++++++++++++++++++++++++++++++++++++++
 tests/btrfs/298.out |  2 ++
 2 files changed, 55 insertions(+)
 create mode 100755 tests/btrfs/298
 create mode 100644 tests/btrfs/298.out

diff --git a/tests/btrfs/298 b/tests/btrfs/298
new file mode 100755
index 000000000000..1d10d27c1354
--- /dev/null
+++ b/tests/btrfs/298
@@ -0,0 +1,53 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2023 Oracle.  All Rights Reserved.
+#
+# FS QA Test 298
+#
+#   Check if the device scan registers for a single-device seed and drops
+#  it from the kernel if it is eventually marked as non-seed.
+#
+. ./common/preamble
+_begin_fstest auto quick seed
+
+_supported_fs btrfs
+_require_command "$BTRFS_TUNE_PROG" btrfstune
+_require_scratch_dev_pool 2
+_scratch_dev_pool_get 1
+_spare_dev_get
+
+$WIPEFS_PROG -a $SCRATCH_DEV
+$WIPEFS_PROG -a $SPARE_DEV
+
+echo "#setup seed sprout device" >> $seqres.full
+_scratch_mkfs "-b 300M" >> $seqres.full 2>&1
+$BTRFS_TUNE_PROG -S 1 $SCRATCH_DEV
+_scratch_mount >> $seqres.full 2>&1
+$BTRFS_UTIL_PROG device add $SPARE_DEV $SCRATCH_MNT
+_scratch_unmount
+$BTRFS_UTIL_PROG device scan --forget
+
+echo "#Scan seed device and check using mount" >> $seqres.full
+$BTRFS_UTIL_PROG device scan $SCRATCH_DEV >> $seqres.full
+_mount $SPARE_DEV $SCRATCH_MNT
+umount $SCRATCH_MNT
+
+echo "#check again, ensures seed device still in kernel" >> $seqres.full
+_mount $SPARE_DEV $SCRATCH_MNT
+umount $SCRATCH_MNT
+
+echo "#Now scan of non-seed device makes kernel forget" >> $seqres.full
+$BTRFS_TUNE_PROG -f -S 0 $SCRATCH_DEV >> $seqres.full 2>&1
+$BTRFS_UTIL_PROG device scan $SCRATCH_DEV >> $seqres.full
+
+echo "#Sprout mount must fail for missing seed device" >> $seqres.full
+_mount $SPARE_DEV $SCRATCH_MNT > /dev/null 2>&1
+[[ $? == 32 ]] || _fail "mount failed to fail"
+
+_spare_dev_put
+_scratch_dev_pool_put
+
+# success, all done
+echo Silence is golden
+status=0
+exit
diff --git a/tests/btrfs/298.out b/tests/btrfs/298.out
new file mode 100644
index 000000000000..634342678f11
--- /dev/null
+++ b/tests/btrfs/298.out
@@ -0,0 +1,2 @@
+QA output created by 298
+Silence is golden
-- 
2.39.3