The throtl test group uses null_blk devices as test target in its test
cases. To prepare for supporting scsi_debug device as the additional
test target, introduce three helper functions below to abstract null_blk
specific operations:

 _configure_throtl_blkdev() : Sets up the null_blk device
 _delete_throtl_blkdev()    : Removes the null_blk device for testing
 _exit_throtl_blkdev()      : Cleans up the null_blk device

Support two options of _configure_throtl_blkdev(), --sector_size and
--memory_backed so that each test case can tailor the setup according to
specific requirements.

Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
---
 tests/throtl/002 |  5 ++---
 tests/throtl/003 |  5 ++---
 tests/throtl/004 |  2 +-
 tests/throtl/006 |  2 +-
 tests/throtl/007 |  5 ++---
 tests/throtl/rc  | 45 ++++++++++++++++++++++++++++++++++++++++++---
 6 files changed, 50 insertions(+), 14 deletions(-)

diff --git a/tests/throtl/002 b/tests/throtl/002
index 02b0969..bed876d 100755
--- a/tests/throtl/002
+++ b/tests/throtl/002
@@ -13,14 +13,13 @@ QUICK=1
 test() {
 	echo "Running ${TEST_NAME}"
 
-	local page_size max_secs
+	local page_size
 	local io_size_kb block_size
 	local iops=256
 
 	page_size=$(getconf PAGE_SIZE)
-	max_secs=$((page_size / 512))
 
-	if ! _set_up_throtl max_sectors="${max_secs}"; then
+	if ! _set_up_throtl --sector_size "${page_size}"; then
 		return 1;
 	fi
 
diff --git a/tests/throtl/003 b/tests/throtl/003
index 8276d87..d76a0d5 100755
--- a/tests/throtl/003
+++ b/tests/throtl/003
@@ -13,11 +13,10 @@ QUICK=1
 test() {
 	echo "Running ${TEST_NAME}"
 
-	local page_size max_secs
+	local page_size
 	page_size=$(getconf PAGE_SIZE)
-	max_secs=$((page_size / 512))
 
-	if ! _set_up_throtl max_sectors="${max_secs}"; then
+	if ! _set_up_throtl --sector_size "${page_size}"; then
 		return 1;
 	fi
 
diff --git a/tests/throtl/004 b/tests/throtl/004
index d1461b9..d623097 100755
--- a/tests/throtl/004
+++ b/tests/throtl/004
@@ -26,7 +26,7 @@ test() {
 	} &
 
 	sleep 0.6
-	echo 0 > "/sys/kernel/config/nullb/$THROTL_DEV/power"
+	_delete_throtl_blkdev
 	wait $!
 
 	_clean_up_throtl
diff --git a/tests/throtl/006 b/tests/throtl/006
index b6f47d1..263415f 100755
--- a/tests/throtl/006
+++ b/tests/throtl/006
@@ -34,7 +34,7 @@ test_meta_io() {
 test() {
 	echo "Running ${TEST_NAME}"
 
-	if ! _set_up_throtl memory_backed=1; then
+	if ! _set_up_throtl --memory_backed; then
 		return 1;
 	fi
 
diff --git a/tests/throtl/007 b/tests/throtl/007
index ae59c6f..83d8dc7 100755
--- a/tests/throtl/007
+++ b/tests/throtl/007
@@ -14,11 +14,10 @@ QUICK=1
 test() {
 	echo "Running ${TEST_NAME}"
 
-	local page_size max_secs
+	local page_size
 	page_size=$(getconf PAGE_SIZE)
-	max_secs=$((page_size / 512))
 
-	if ! _set_up_throtl max_sectors="${max_secs}"; then
+	if ! _set_up_throtl --sector_size "${page_size}"; then
 		return 1;
 	fi
 
diff --git a/tests/throtl/rc b/tests/throtl/rc
index 327084b..d20dc94 100644
--- a/tests/throtl/rc
+++ b/tests/throtl/rc
@@ -21,15 +21,54 @@ group_requires() {
 	_have_program bc
 }
 
+_configure_throtl_blkdev() {
+	local sector_size=0 memory_backed=0
+	local -a args
+
+	while [[ $# -gt 0 ]]; do
+		case $1 in
+			--sector_size)
+				sector_size="$2"
+				shift 2
+				;;
+			--memory_backed)
+				memory_backed=1
+				shift
+				;;
+			*)
+				echo "WARNING: unknown argument: $1"
+				shift
+				;;
+		esac
+	done
+
+	args=("$THROTL_DEV")
+	((sector_size)) && args+=(max_sectors="$((sector_size / 512))")
+	((memory_backed)) && args+=(memory_backed=1)
+	if _configure_null_blk "${args[@]}" power=1; then
+		return
+	fi
+	return 1
+}
+
+_delete_throtl_blkdev() {
+	echo 0 > "/sys/kernel/config/nullb/$THROTL_DEV/power"
+}
+
+_exit_throtl_blkdev() {
+	_exit_null_blk
+	unset THROTL_DEV
+}
+
 # Create a new null_blk device, and create a new blk-cgroup for test.
 _set_up_throtl() {
 
-	if ! _configure_null_blk $THROTL_DEV "$@" power=1; then
+	if ! _configure_throtl_blkdev "$@"; then
 		return 1
 	fi
 
 	if ! _init_cgroup2; then
-		_exit_null_blk
+		_exit_throtl_blkdev
 		return 1
 	fi
 
@@ -58,7 +97,7 @@ _clean_up_throtl() {
 	fi
 
 	_exit_cgroup2
-	_exit_null_blk
+	_exit_throtl_blkdev
 }
 
 _throtl_set_limits() {
-- 
2.51.0