[PATCH blktests v2 10/16] common: Introduce _dd() helper function

@@ -246,3 +246,34 @@ set_scheduler() {
 		return 1
 	fi
 }
+
+# Issue dd command with five arguments and record command line in FULL file.
+# args: target device, r/w, start sector, sector len, block size in bytes
+_dd() {
+	local target_dev=${1}
+	local rw=${2}
+	local -i start_sector=${3}
+	local -i start_byte=$(( start_sector * 512 ))
+	local -i sector_count=${4}
+	local -i bs=${5}
+	local -i block_count=$(( sector_count * 512 / bs ))
+
+	local _cmd="dd bs=${bs} count=${block_count}"
+
+	if [[ ${rw} = "read" ]]; then
+		_cmd="${_cmd} if=${target_dev} of=/dev/null"
+		_cmd="${_cmd} iflag=skip_bytes skip=${start_byte}"
+	elif [[ ${rw} = "write" ]]; then
+		_cmd="${_cmd} if=/dev/zero of=${target_dev}"
+		_cmd="${_cmd} oflag=seek_bytes,direct seek=${start_byte}"
+	fi
+
+	echo "${_cmd}" >> "$FULL" 2>&1
+
+	if ! eval "${_cmd}" >> "$FULL" 2>&1 ; then
+		echo "dd command failed"
+		return 1
+	fi
+
+	sync
+}