USB storage on Android Magnus Jahnen

USB mass storage on Android

Implementation of an Android Framework for USB storage access without root rights

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Bachelor thesis 23.04.2014

USB storage on Android Magnus Jahnen

USB storage on Android

1. Introduction

2. Basics of USB

3. USB mass storage class

4. FAT32 file system

5. Implementation

6. Results

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USB storage on Android Magnus Jahnen

Introduction

• USB features in Android since 3.1 Honeycomb

• Mass storage access: Currently two proprietary applications available

• USB-Stick Plugin-TC (Plugin for Total Commander)

• Nexus Media Importer

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USB storage on Android Magnus Jahnen

Basics of USB

• Stands for: Universal Serial Bus

• Standard by the USB Implementers forum

• Host (master) and multiple clients (slaves)

• Host powers the client and manages communication process

• USB On the go as part of USB 2.0

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USB storage on Android Magnus Jahnen

Client Device Hierarchy

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USB storage on Android Magnus Jahnen

Endpoints

• Unidirectional communication pipes

• Different types

• Control

• Interrupt

• Bulk

• Isochronous

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USB storage on Android Magnus Jahnen

USB mass storage class

• Determined by class and subclass in interface descriptor

• Two different types

• Control/Bulk/Interrupt (CBI) [obsolete]

• Bulk-only transfer (BBB)

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USB storage on Android Magnus Jahnen

Bulk-only transfer

• USB interface must have IN and OUT bulk endpoint

• Different protocols (specified by interface subclass)

• Reduced Block Commands (RBC)

• SCSI transparent command set (most commonly used)

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USB storage on Android Magnus Jahnen

SCSI transparent command set

• Command Block Wrapper (CBW)

• Includes SCSI command

• Command Status Wrapper (CSW)

• Actual supported standard resp. SCSI commands determined by issuing an INQUIRY

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USB storage on Android Magnus Jahnen

SCSI commands

• INQUIRY

• READ CAPACITY(10)

• READ(10)

• REQUEST SENSE

• TEST UNIT READY

• WRITE(10)

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USB storage on Android Magnus Jahnen

FAT32 file system

• Belongs to FAT family

• Developed by Microsoft

• Released in 1996 with Windows 95B

• Most commonly used on mass storage devices for maximum compatibility

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USB storage on Android Magnus Jahnen

General layout

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USB storage on Android Magnus Jahnen

FAT

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USB storage on Android Magnus Jahnen

Data Area

• Structured in clusters

• Directories and files

• Directories have a defined structure

• Files save raw data from user

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USB storage on Android Magnus Jahnen

Implementation

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partition

handling of partitionsand partition tables

fs

file system abstraction

driver

low level block device communication

USB storage on Android Magnus Jahnen

Driver package

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uses

creates

ScsiInquiry+ScsiInquiry(): ctor+serialize(ByteBuffer buffer): void

CommandBlockWrapper#CommandBlockWrapper(...): ctor+serialize(ByteBuffer buffer): void

ScsiBlockDevice

BlockDeviceDriverFactory

«interface»BlockDeviceDriver

+init(): void+read(long deviceOffset, ByteBuffer buffer): void+write(long deviceOffset, ByteBuffer buffer): void+getBlockSize(): int

USB storage on Android Magnus Jahnen

Results

• Supported features:

• Bulk-only transfer

• FAT32 (MBR)

• Usual directory/file operations

• Features tested on various devices

• Requirements:

• Android 3.1 or later

• Hardware and software enabled USB host support

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USB storage on Android Magnus Jahnen

Demonstration

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USB storage on Android Magnus Jahnen

Thank you for your attention! Questions?

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USB storage on Android Magnus Jahnen

Image resources (In the order they appear)

• http://diepresse.com/layout/diepresse/files/mobilesleben/android-logo.png

• http://developer.android.com/guide/topics/connectivity/usb/index.html

• https://play.google.com/store/apps/details?id=de.hechler.tcplugins.full.usb

• https://play.google.com/store/apps/details?id=com.homeysoft.nexususb.importer

• http://en.wikipedia.org/wiki/File:USB.png

• http://www.sprut.de/electronic/interfaces/usb/deskriptor.htm

• http://www.iconarchive.com/show/icons8-metro-style-icons-by-visualpharm/Computer-Hardware-Mouse-icon.html (http://www.visualpharm.com/)

• http://www.softicons.com/system-icons/web0.2ama-icons-by-chrfb/usb-stick-icon

• http://www.iconarchive.com/show/icons8-metro-style-icons-by-visualpharm/Phones-Headset-icon.html (http://www.visualpharm.com/)

• http://www.clker.com/cliparts/d/5/f/b/1195437711991895099Machovka_harddisk.svg.hi.png

• http://www.center.hu/images/cikkek/win95/win95logo.jpg

• http://ferienwohnungen-koehnke.de/kurbeitrag/

• http://www.tecnigen.com/wp-content/uploads/2013/07/usbandroid.png

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