[PATCH v2] fstest: btrfs: test single 4k extent after subpagesize buffered writes

[Liu Bo <bo.li.liu@oracle.com>]

This is to test if COW enabled btrfs can end up with single 4k extents
when doing subpagesize buffered writes.

The patch to fix the problem is
  https://patchwork.kernel.org/patch/8527991/

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
---
v2: - Teach awk to know system's pagesize.
    - Add "Silence is golden" to output.
    - Use local variables to lower case.
    - Add comments to make code clear.

 tests/btrfs/027     | 102 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 tests/btrfs/027.out |   2 ++
 tests/btrfs/group   |   1 +
 3 files changed, 105 insertions(+)
 create mode 100755 tests/btrfs/027
 create mode 100644 tests/btrfs/027.out

diff --git a/tests/btrfs/027 b/tests/btrfs/027
new file mode 100755
index 0000000..19d324b
--- /dev/null
+++ b/tests/btrfs/027
@@ -0,0 +1,102 @@
+#! /bin/bash
+# FS QA Test 027
+#
+# When btrfs is using cow mode, buffered writes of sub-pagesize can end up with
+# single 4k extents.
+# Ref:
+#     "Stray 4k extents with slow buffered writes"
+#     https://www.spinics.net/lists/linux-btrfs/msg52628.html
+#
+#-----------------------------------------------------------------------
+# Copyright (c) 2016 Liu Bo.  All Rights Reserved.
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it would be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write the Free Software Foundation,
+# Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+#-----------------------------------------------------------------------
+#
+
+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.*
+
+	# restore expire
+	echo $default_expire > /proc/sys/vm/dirty_expire_centisecs
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# remove previous $seqres.full before test
+rm -f $seqres.full
+echo "Silence is golden"
+
+# real QA test starts here
+
+# Modify as appropriate.
+_supported_fs btrfs
+_supported_os Linux
+_require_scratch
+_require_xfs_io_command "fiemap"
+
+_scratch_mkfs >> $seqres.full 2>&1
+_scratch_mount
+
+default_expire=`cat /proc/sys/vm/dirty_expire_centisecs`
+# Make it flush dirty pages more frequently to make sure we reproduce the bug.
+echo 50 > /proc/sys/vm/dirty_expire_centisecs
+
+tfile=$SCRATCH_MNT/testfile
+pagesize=$(get_page_size)
+sublen=$((RANDOM % pagesize))
+
+$XFS_IO_PROG -f -c "pwrite 0 $pagesize" $tfile > /dev/null 2>&1
+# write some subpagesize data first.
+$XFS_IO_PROG -c "pwrite $pagesize $sublen" $tfile > /dev/null 2>&1
+
+# Mix up "abnormal" subpagesize writes with normal pagesize based writes
+toff=$((pagesize + sublen))
+for ((i = 0; i < 10000; i++))
+do
+	tlen=$pagesize
+	if [ $((i % 2)) = 0 ]; then
+		tlen=$((pagesize * 3))
+	fi
+	if [ $((i % 1000)) = 0 ]; then
+		tlen=$((RANDOM % pagesize))
+	fi
+
+	$XFS_IO_PROG -c "pwrite $toff $tlen" $tfile > /dev/null 2>&1
+	toff=$((toff + tlen))
+done
+
+sync
+
+# check for single PAGESIZE extent
+$XFS_IO_PROG -c "fiemap -v" $tfile >> $seqres.full 2>&1
+$XFS_IO_PROG -c "fiemap -v" $tfile | \
+awk -v pgsize=$pagesize '{n = pgsize/512; if ($4 == n) print $4}'
+
+# success, all done
+status=0
+exit
diff --git a/tests/btrfs/027.out b/tests/btrfs/027.out
new file mode 100644
index 0000000..ef78cda
--- /dev/null
+++ b/tests/btrfs/027.out
@@ -0,0 +1,2 @@
+QA output created by 027
+Silence is golden
diff --git a/tests/btrfs/group b/tests/btrfs/group
index a2fa412..f06d5fe 100644
--- a/tests/btrfs/group
+++ b/tests/btrfs/group
@@ -29,6 +29,7 @@
 024 auto quick compress
 025 auto quick send clone
 026 auto quick compress prealloc
+027 auto
 029 auto quick clone
 030 auto quick send
 031 auto quick subvol clone
-- 
2.5.0