[script] Improve flash_all

images are not necessary in the current dir
Add a -s option to specify serial to use

scripts/flash_all

@@ -1,17 +1,55 @@
 #!/bin/bash
+haveSerial=false
+serial=""
+function usage {
+	echo -e "Usage: $(basename $0) [-s serialNumber] [IMGLIST]"
+	echo -e "	IMGLIST is a list of file in .img separated by space"
+	echo -e "	If no IMGLIST provied all the .img in the current directory will be flashed"
+	echo -e "	e.g. $(basename $0) -s 132456789 out/target/device/boot.img out/target/device/system.img"
+}
+
+while getopts ":s:" opt; do
+	case $opt in
+		s) echo "Using Serial $OPTARG"
+		serial=$OPTARG
+		haveSerial=true
+		;;
+		\?)
+		echo "Invalid option: -$OPTARG" >&2
+		usage
+		exit 1
+		;;
+	esac
+done
+shift $(( OPTIND - 1 ))
+
 if [ $# -eq 0 ];
 then
 	imgList=$(ls *.img)
-	echo "Flashing all images $imgList"
+	echo "Flashing all images in current path $imgList"
 else
 	imgList=$@
 	echo "Flashing $imgList"
 fi
-
 if [ -z "$imgList" ];
 then
 	echo "No img to Flash"
 	exit 1
 else
-	adb reboot bootloader; for img in $imgList; do fastboot flash ${img%.img} $img; done && fastboot reboot
+	echo "Reboot device in fastboot"
+	if $haveSerial ; then
+		adb -s $serial reboot bootloader;
+	else
+		adb reboot bootloader;
+	fi
+	echo "Flashing images"
+	for img in $imgList; do
+		imageName=$(basename $img)
+		imageName=${imageName%.img}
+		if $haveSerial ; then
+			fastboot -s $serial -S 256M flash ${imageName} $img;
+		else
+			fastboot -S 256M flash ${imageName} $img;
+		fi
+	done && fastboot reboot
 fi