btrfs: Add test to check if shrink works well with fstrim

There is a bug in trim code which leads to fstrim accessing beyond
device boundary.

The test case will check if fstrim, then shrink, then fstrim, all of
them works without problem.

The fix is titled "btrfs: trim: fix underflow in trim length to prevent
access beyond device boundary".

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/btrfs/217

@@ -0,0 +1,62 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2020 SUSE Linux Products GmbH. All Rights Reserved.
+#
+# FS QA Test 217
+#
+# Test if the following workload would cause problem:
+# - fstrim
+# - shrink device
+# - fstrim
+#
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+
+here=`pwd`
+tmp=/tmp/$$
+status=1	# failure is the default!
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+_cleanup()
+{
+	cd /
+	rm -f $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# remove previous $seqres.full before test
+rm -f $seqres.full
+
+# real QA test starts here
+
+# Modify as appropriate.
+_supported_fs btrfs
+_supported_os Linux
+_require_scratch_size $((5 * 1024 * 1024)) #kB
+_require_fstrim
+
+# Create a 5G fs
+_scratch_mkfs_sized $((5 * 1024 * 1024 * 1024)) >> $seqres.full
+_scratch_mount
+
+# Fstrim to populate the device->alloc_status CHUNK_TRIMMED bits
+$FSTRIM_PROG -v $SCRATCH_MNT >> $seqres.full 2>&1 || \
+	_notrun "FSTRIM not supported"
+
+
+# Shrink the fs to 4G, so the existing CHUNK_TRIMMED bits are beyond
+# device boundary
+$BTRFS_UTIL_PROG filesystem resize 1:-1G "$SCRATCH_MNT" >> $seqres.full
+
+# Do fstrim again to trigger the bug
+$FSTRIM_PROG -v $SCRATCH_MNT >> $seqres.full
+
+echo "Silence is golden"
+
+# success, all done
+status=0
+exit

tests/btrfs/217.out

@@ -0,0 +1,2 @@
+QA output created by 217
+Silence is golden

tests/btrfs/group

@@ -219,3 +219,4 @@
 214 auto quick send snapshot
 215 auto quick
 216 auto quick seed
+217 auto quick trim dangerous