[PATCH] btrfs: Add test for the single-dev feature

["Guilherme G. Piccoli" <gpiccoli@igalia.com>]

The SINGLE_DEV btrfs feature allows to mount the same filesystem
multiple times, at the same time. This is the fstests counter-part,
which checks both mkfs/btrfstune (by mounting the FS twice), and
also unsupported scenarios, like device replace / remove.

Suggested-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
---

Hi folks, this test was a suggestion by Josef for the SINGLE_DEV feature
we're trying to introduce in the kernel [0].

Some design decisions:

(a) The number 300 was selected since seems we already skipped 298 in
the code base, given that the test btrfs/298 is being worked upstream.

(b) About mounting twice the same filesystem - how to accomplish that
in a proper fashion? I went with the naive / trivial approach, just created
temporary directories on top of $SCRATCH_MNT, but I'm not sure if that is
the way to go. Is it guaranteed that $SCRATCH_MNT is writable prior to
any mount command?

(c) The way to be sure we have two different devices holding the same
image was using SCRATCH_DEV_POOL and dd'ing the first device to the 2nd
one - is there any better alternative than this one?

Suggestions / reviews much appreciated!
Cheers,

Guilherme

[0] https://lore.kernel.org/linux-btrfs/20230803154453.1488248-1-gpiccoli@igalia.com/


 tests/btrfs/300     | 107 ++++++++++++++++++++++++++++++++++++++++++++
 tests/btrfs/300.out |   5 +++
 2 files changed, 112 insertions(+)
 create mode 100755 tests/btrfs/300
 create mode 100644 tests/btrfs/300.out

diff --git a/tests/btrfs/300 b/tests/btrfs/300
new file mode 100755
index 000000000000..120e790906ea
--- /dev/null
+++ b/tests/btrfs/300
@@ -0,0 +1,107 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2023 Guilherme G. Piccoli (Igalia S.L.).  All Rights Reserved.
+#
+# FS QA Test 300
+#
+# Test for the btrfs single-dev feature - both mkfs and btrfstune are
+# validated, as well as explicitly unsupported commands, like device
+# removal / replacement.
+#
+. ./common/preamble
+_begin_fstest auto mkfs quick
+. ./common/filter
+_supported_fs btrfs
+
+_require_btrfs_mkfs_feature single-dev
+_require_btrfs_fs_feature single_dev
+
+_require_scratch_dev_pool 2
+_scratch_dev_pool_get 2
+
+_require_command "$BTRFS_TUNE_PROG" btrfstune
+_require_command "$WIPEFS_PROG" wipefs
+
+# Used random hash to avoid name collision.
+DIR_a="563b01de1f_a"
+DIR_b="563b01de1f_b"
+
+# Override the default cleanup function.
+_cleanup()
+{
+	cd /
+	rm -r -f $tmp.*
+	rm -rf $SCRATCH_MNT/$DIR_a
+	rm -rf $SCRATCH_MNT/$DIR_b
+}
+
+# Helper to mount a btrfs fs
+# Arg 1: device
+# Arg 2: mount point
+mount_btrfs()
+{
+	$MOUNT_PROG -t btrfs $1 $2
+	[ $? -ne 0 ] && _fail "mounting $1 on $2 failed"
+}
+
+mkdir $SCRATCH_MNT/$DIR_a
+mkdir $SCRATCH_MNT/$DIR_b
+
+DEV1=$(echo $SCRATCH_DEV_POOL | $AWK_PROG '{ print $1 }')
+DEV2=$(echo $SCRATCH_DEV_POOL | $AWK_PROG '{ print $2 }')
+
+
+# Part 1
+# First test involves a mkfs with single-dev feature enabled.
+# If it succeeds and mounting that FS *twice* also succeeds,
+# we're good and continue.
+$WIPEFS_PROG -a $DEV1 >> $seqres.full 2>&1
+$WIPEFS_PROG -a $DEV2 >> $seqres.full 2>&1
+
+$MKFS_BTRFS_PROG -O single-dev $DEV1 >>$seqres.full 2>&1
+dd if=$DEV1 of=$DEV2 bs=64M conv=fsync >> $seqres.full 2>&1
+
+mount_btrfs $DEV1 $SCRATCH_MNT/$DIR_a
+mount_btrfs $DEV2 $SCRATCH_MNT/$DIR_b
+
+$UMOUNT_PROG $SCRATCH_MNT/$DIR_b
+$UMOUNT_PROG $SCRATCH_MNT/$DIR_a
+
+
+# Part 2
+# Second test is similar to the first with the difference we
+# run mkfs with no single-dev mention, and make use of btrfstune
+# to set such feature.
+$WIPEFS_PROG -a $DEV1 >> $seqres.full 2>&1
+$WIPEFS_PROG -a $DEV2 >> $seqres.full 2>&1
+
+$MKFS_BTRFS_PROG $DEV1 >>$seqres.full 2>&1
+$BTRFS_TUNE_PROG --convert-to-single-device $DEV1
+dd if=$DEV1 of=$DEV2 bs=64M conv=fsync >> $seqres.full 2>&1
+
+mount_btrfs $DEV1 $SCRATCH_MNT/$DIR_a
+mount_btrfs $DEV2 $SCRATCH_MNT/$DIR_b
+
+$UMOUNT_PROG $SCRATCH_MNT/$DIR_b
+$UMOUNT_PROG $SCRATCH_MNT/$DIR_a
+
+
+# Part 3
+# Final part attempts to run some single-dev unsupported commands,
+# like device replace/remove - it they fail, test succeeds!
+mount_btrfs $DEV1 $SCRATCH_MNT
+
+$BTRFS_UTIL_PROG device replace start $DEV1 $DEV1 $SCRATCH_MNT 2>&1 \
+	| _filter_scratch
+
+$BTRFS_UTIL_PROG device remove $DEV1 $SCRATCH_MNT 2>&1 \
+	| sed -e "s,\B$DEV1,DEV1,g"
+
+$UMOUNT_PROG $SCRATCH_MNT
+_scratch_dev_pool_put 2
+
+# success, all done
+status=0
+echo "Finished"
+
+exit
diff --git a/tests/btrfs/300.out b/tests/btrfs/300.out
new file mode 100644
index 000000000000..5f13cfb228fb
--- /dev/null
+++ b/tests/btrfs/300.out
@@ -0,0 +1,5 @@
+QA output created by 300
+ERROR: ioctl(DEV_REPLACE_STATUS) failed on "SCRATCH_MNT": Invalid argument
+
+ERROR: error removing device 'DEV1': Invalid argument
+Finished
-- 
2.41.0