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Case study 2

Case study 2. Android – Mobile OS. Sources and extra reading. Silberschatz , Galvin, Gagne. Operating System Concepts Essentials. 8th Edition. ISBN: 978-0-470-88920-6 A. Tanenbaum . Modern Operating Systems. 3rd Edition. ISBN: 0136006639

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Case study 2

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  1. Case study 2 Android – Mobile OS

  2. Sources and extra reading Silberschatz, Galvin, Gagne. Operating System Concepts Essentials. 8th Edition. ISBN: 978-0-470-88920-6 A. Tanenbaum. Modern Operating Systems. 3rd Edition. ISBN: 0136006639 H. Al-Rayes. Studying Main Differences between Android & Linux Operating Systems. Diyala University. Android Developer Website. http://developer.android.com

  3. Topics covered in this session • History of Android • Android design principles • Android Architecture • Memory Management • Threads and Scheduling • Android File System • Security • Programming Interface

  4. History of Android • What is android? Linux 2.6 based operating system for mobile devices. • Open source and released under Apache Licence (Carriers can modify it before distributing). • Google acquired android in 2005. • Android 1.0 released 2008. • In 2012 Android 4.2 released • Improvements include support for new devices: • Cameras • Multi core CPU • Barometer • etc

  5. Design principles – What is required of a mobile OS? • Long battery life. • Fast boot up. • Fast response. • Applications (Programming environment?) • Security • How do these differ from the needs of a desktop system? • Consider how the above are met by the system design.

  6. Mobile hardware differences • Battery • Touch screen • Portable (Mobile CPU) • More limited memory • Fewer devices

  7. Android Architecture Source: http://developer.android.com/about/versions/index.html

  8. Android Architecture Source: http://developer.android.com/about/versions/index.html

  9. Android Architecture Source: http://developer.android.com/about/versions/index.html

  10. Android Architecture Source: http://developer.android.com/about/versions/index.html

  11. Android Architecture Source: http://developer.android.com/about/versions/index.html

  12. Application life cycle

  13. Memory management • Android uses it’s own virtual machine to manage application memory. • Dalvik VM allows multiple instances of VM to be running efficiently in parallel.

  14. Process Management • Differences between mobile app cycle and desktop app cycle? • Key principles: • Android does not usually kill an app, they keep running even after you switch, but saves state • Task killers? • Android kills apps when memory usage too high. • But saves it’s state for quick restart. • Uses Linux’s time sliced scheduling policy based on priority

  15. Process Priorities • Split into background and foreground. • What happens if UI thread is starved?

  16. Disk I/O

  17. Why not use swapping? • What needs storing? Consider a map application (Lat/long). • Swapping to flash affecting life.

  18. Android File System • Supports multiple different file systems (based on Linux Kernel). • Usually yaffs2/vfat/ext4, depending on device manufacturer. • Partitions: • /boot (Included android kernel) • /system (Android GUI and pre-installed applications). – Read only • /recovery (Backup) • /data (User data) • /cache (Frequently accessed data) • /misc (Contains misc system settings in form of on/off switches) • /sdcard (SD card)

  19. Security • Android seeks to be the most secure and usable operating system for mobile platforms by re-purposing traditional operating system security controls to: • Protect user data • Protect system resources (including the network) • Provide application isolation • To achieve these objectives, Android provides these key security features: • Robust security at the OS level through the Linux kernel • Mandatory application sandbox for all applications • Secure interprocess communication • Application signing • Application-defined and user-granted permissions

  20. Security Continued • Assigns .unique user ID (UID) to each android application. • Uses UNIX style file permissions due to different UIDs • Ensures app A doesn’t read app B’s files. • Ensures app A doesn’t exhaust B’s memory • Ensures app A doesn’t exhaust B’s CPU usage • Ensures app A doesn’t exhaust user Bs devices (GPS, BT) • Linux kernel enforces security between applications • Stops memory corruption errors causing vulnerabilities. • Read only system partition

  21. Security Continued • Use of restricted APIs require application permissions. • Application Signing. Application packages are signed to identify author and prevent tampering. Some windows 7 system files are signed in a similar way.

  22. Programming for Android • Each program runs in it’s own VM. • Need to understand an activities lifecycle. • Make use of Android SDK • Applications programmed in Java, with layouts coded in XML. • Packaged as .apk files for delivery through Android store. • Importance of file size + data usage.

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