[PATCH blktests v3 06/13] common: Introduce _dd() helper function

[Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>]

To analyze dd command failures found by blktests, need to confirm dd
command options. Introduce the helper function which executes dd and
records dd command options in FULL file for quick analysis.

Reviewed-by: Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
---
 common/rc | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/common/rc b/common/rc
index 153a323..fe0e5d8 100644
--- a/common/rc
+++ b/common/rc
@@ -214,3 +214,34 @@ _test_dev_in_hotplug_slot() {
 _filter_xfs_io_error() {
 	sed -e 's/^\(.*\)64\(: .*$\)/\1\2/'
 }
+
+# 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
+}
-- 
2.20.1