@@ -91,6 +91,8 @@ Preparing system for tests:
              - set TEST_XFS_SCRUB=1 to have _check_xfs_filesystem run
                xfs_scrub -vd to scrub the filesystem metadata online before
                unmounting to run the offline check.
+             - setenv LOGWRITES_DEV to a block device to use for power fail
+               testing.
 
         - or add a case to the switch in common/config assigning
           these variables based on the hostname of your test

@@ -0,0 +1,84 @@
+##/bin/bash
+#
+# Copyright (c) 2015 Facebook, Inc.  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
+#
+#
+# common functions for setting up and tearing down a dm log-writes device
+
+_require_log_writes()
+{
+	_require_dm_target log-writes
+	_require_test_program "log-writes/replay-log"
+}
+
+_init_log_writes()
+{
+	local BLK_DEV_SIZE=`blockdev --getsz $SCRATCH_DEV`
+	LOGWRITES_NAME=logwrites-test
+	LOGWRITES_DMDEV=/dev/mapper/$LOGWRITES_NAME
+	LOGWRITES_TABLE="0 $BLK_DEV_SIZE log-writes $SCRATCH_DEV $LOGWRITES_DEV"
+	$DMSETUP_PROG create $LOGWRITES_NAME --table "$LOGWRITES_TABLE" || \
+		_fatal "failed to create log-writes device"
+	$DMSETUP_PROG mknodes > /dev/null 2>&1
+}
+
+_log_writes_mark()
+{
+	[ $# -ne 1 ] && _fatal "_log_writes_mark takes one argument"
+	$DMSETUP_PROG message $LOGWRITES_NAME 0 mark $1
+}
+
+_log_writes_mkfs()
+{
+	_scratch_options mkfs
+	_mkfs_dev $SCRATCH_OPTIONS $LOGWRITES_DMDEV
+	_log_writes_mark mkfs
+}
+
+_mount_log_writes()
+{
+	mount -t $FSTYP $MOUNT_OPTIONS $* $LOGWRITES_DMDEV $SCRATCH_MNT
+}
+
+_unmount_log_writes()
+{
+	$UMOUNT_PROG $SCRATCH_MNT
+}
+
+# _replay_log <mark>
+#
+# This replays the log contained on $INTEGRITY_DEV onto $SCRATCH_DEV upto the
+# mark passed in.
+_replay_log()
+{
+	_mark=$1
+
+	$here/src/log-writes/replay-log --log $LOGWRITES_DEV --replay $SCRATCH_DEV \
+		--end-mark $_mark > /dev/null 2>&1
+	[ $? -ne 0 ] && _fatal "replay failed"
+}
+
+_log_writes_remove()
+{
+	$DMSETUP_PROG remove $LOGWRITES_NAME > /dev/null 2>&1
+	$DMSETUP_PROG mknodes > /dev/null 2>&1
+}
+
+_cleanup_log_writes()
+{
+	$UMOUNT_PROG $SCRATCH_MNT > /dev/null 2>&1
+	_log_writes_remove
+}

@@ -21,6 +21,10 @@ they have.  This is done with _require_<xxx> macros, which may take parameters.
 
 	_require_statx
 
+ (4) Device mapper requirement.
+
+	_require_dm_target
+	_require_log_writes
 
 ====================
 GENERAL REQUIREMENTS

@@ -102,3 +106,19 @@ _require_statx
 
      The test requires the use of the statx() system call and will be skipped
      if it isn't available in the kernel.
+
+
+==========================
+DEVICE MAPPER REQUIREMENTS
+==========================
+
+_require_dm_target <name>
+
+     The test requires the use of the device mapper target and will be skipped
+     if it isn't available in the kernel.
+
+_require_log_writes
+
+     The test requires the use of the device mapper target log-writes.
+     The test also requires the test program log-writes/replay-log is built
+     and will be skipped if either isn't available.