This talk explores the options when trying to bing up a device using an Android Board Support Package (BSP) or AOSP. In particular the options when you don't want to ship a traditional Android device or you have an existing Embedded Linux code base, but all you have available is Android. Headless can mean both be an Android without Java and a device without a display, both are discussed.

2. Making a
Headless-Android
Device
Lessons Learned
Oslo Embedded S/W Meetup, 2018
Patricia Aas & Johan Herland
Pictures from pixabay.com (CC0)

3. Patricia Aas
Vivaldi Technologies
Cisco Systems
Opera Software
Twitter: @pati_gallardo
Johan Herland
Cisco Systems
Opera Software
Git Dev Community
Twitter: @jherland

4. Outline
- Why?
- Architecture
- Devices
- Composition
- Gpu Access
- Lessons Learned

5. So… What do we know?

7. And why should you care?

8. The Problem
Full Android
Using Google’s AOSP, or a more
customized Android Board Support
Package (BSP) from a chip vendor.
Embedded Linux
No Android parts.
Typically based on
glibc, busybox, etc.

9. Unchartered Territory

10. Important questions
Do you have:
- Existing codebase?
- Upstream BSP?
- 3rd party dependencies?
What kind of device:
- Display?
- Single or multiple apps?
- Custom H/W?

11. Architecture : Deep Dive

12. Full Stack Android
- Java App ecosystem
- Graphics infrastructure
- Supported by modern SoCs
- Linux kernel w/Android features
- Libc : Bionic
Embedded Linux
- Stable/well-known components
- “Mix-and-match”
- C/C++ or web apps
- “Vanilla” kernel (or not...)
- Libc : GNU glibc

13. Bionic
- Developed specifically for Android
- Focus: small size and speed
- Compatibility:
- Almost all of C11 and POSIX
- Some GNU/BSD extensions
- C++ : “It’s complicated”
GNU glibc
- Used “everywhere”
- Focus:
- Application support
- Standards compliance
- Completeness
- Compatibility: Yes ☺

14. Platform Architecture - Embedded Linux
Linux kernel
Device drivers GNU glibc
Libraries (SSL, SQLite, etc.) System utils (systemd, busybox)H/W abstraction (OpenGL, alsalib, etc.)
Compositor (XServer, Wayland)
Application framework (Qt, GTK)
Apps
Services/daemons (sshd, httpd)
Your application

15. Platform Architecture - Full Stack Android
Linux kernel (w/Android features: binder, wakelocks, etc.)
Device drivers Bionic libc
H/W Abstraction Layer (HWC, etc.) Libraries (SSL, SQLite, etc.)
Services (SurfaceFlinger, AudioFlinger, etc.)
Android runtime (ART;
previously Dalvik JVM)
Android Application Framework
Android Apps
System utils (init, ADB, toolbox)
Your application

16. Platform Architecture - Headless Android based on Bionic
Linux kernel (w/Android features: binder, wakelocks, etc.)
Device drivers Bionic libc
H/W Abstraction Layer (HWC, etc.) Libraries (SSL, SQLite, etc.)
Services? (SurfaceFlinger, etc.)
System utils (init, ADB, toolbox)
Your application

17. Platform Architecture - Headless Android based on glibc
Linux kernel (w/Android features: binder, wakelocks, etc.)
Device drivers Bionic libc
H/W Abstraction Layer (HWC, etc.) Libraries (SSL, SQLite, etc.)
Services? (SurfaceFlinger, etc.)
System utils (systemd, busybox)
GNU glibc
Hybris?
Your application

18. Embedded LinuxFull stack Android Headless GlibcHeadless Bionic

19. Devices

20. Display Composition
- No display
- Single full-screen app
- Multiple apps

21. No display
Multi app
Single app
Embedded LinuxFull stack Android Headless GlibcHeadless Bionic

22. No Display
Traditional Embedded
- Appliance / IOT
No Graphics Integration
No Composition

23. No display
Multi app
Single app
Embedded LinuxFull stack Android Headless GlibcHeadless Bionic
Java app/service C/C++ app/service C/C++ app/daemon C/C++ app/daemon
No bionic dependencies

24. No display
Multi app
Single app
Embedded LinuxFull stack Android Headless GlibcHeadless Bionic
Java app/service C/C++ app/service C/C++ app/daemon C/C++ app/daemon
OpenWRT et al

25. Single full-screen app
Single-purpose device :
- Digital signage
- Kiosk-style device
- Videoconferencing endpoint
Needs Graphics Integration
No Complex Composition

26. No display
Multi app
Single app
Embedded LinuxFull stack Android Headless GlibcHeadless Bionic
Java app/service
One “home screen” app EGL Window/Framebuffer
C/C++ app/service C/C++ app/daemon C/C++ app/daemon
SurfaceFlinger/HWC SurfaceFlinger/HWC via
e.g. Hybris
Needs glibc/bionic bridge
for graphics integration

27. No display
Multi app
Single app
Embedded LinuxFull stack Android Headless GlibcHeadless Bionic
Java app/service
One “home screen” app EGL Window/Framebuffer
C/C++ app/service C/C++ app/daemon C/C++ app/daemon
SurfaceFlinger/HWC SurfaceFlinger/HWC via
e.g. Hybris
Cisco Webex Board Cisco Webex Room Series
Cisco TelePresence MX/SX
Tesla Car OS?
OpenWRT et al

28. Multiple Apps
Consumer Device :
- Phone
- Tablet
- Smart TV
Needs App Store (e.g. Google Play)
Needs Complex Composition

29. No display
Multi app
Single app
Embedded LinuxFull stack Android Headless GlibcHeadless Bionic
Java app/service
One “home screen” app
App Store (Google’s Play
Store if CDD-compliant)
Multiple apps composited
by XServer/Wayland
EGL Window/Framebuffer
C/C++ app/service C/C++ app/daemon C/C++ app/daemon
Multiple apps composited
by SurfaceFlinger/HWC
via e.g. Hybris
Multiple apps composited
by SurfaceFlinger/HWC
SurfaceFlinger/HWC SurfaceFlinger/HWC via
e.g. Hybris
Needs glibc/bionic bridge
Needs complex composition

30. No display
Multi app
Single app
Embedded LinuxFull stack Android Headless GlibcHeadless Bionic
Java app/service
One “home screen” app
App Store (Google’s Play
Store if CDD-compliant)
Multiple apps composited
by XServer/Wayland
EGL Window/Framebuffer
C/C++ app/service C/C++ app/daemon C/C++ app/daemon
Multiple apps composited
by SurfaceFlinger/HWC
via e.g. Hybris
Multiple apps composited
by SurfaceFlinger/HWC
SurfaceFlinger/HWC SurfaceFlinger/HWC via
e.g. Hybris
Kindle Fire Boot2Qt (1st version) Sailfish (Jolla), Ubuntu Touch
Cisco Webex Board Cisco Webex Room Series
Samsung Tizen, LG webOS
Cisco TelePresence MX/SX
Tesla Car OS?
OpenWRT et al

31. Composition

32. Composition
Need to get pixels on screen
- Compose just one window
with OpenGL
- Compose multiple windows
using external composer /
Hardware Composer

33. The Hardware Composer
Standardized Android porting
API for rendering to the screen.
Takes a set of surfaces and
composes them to the full frame
for the screen.

34. LibHybris : Runtime Linker Magic

35. What is LibHybris?
Dynamically loads and links
bionic libc and bionic linked libs
into a glibc process
Gives access to the bionic libs in
a glibc process
Creator : Carsten Munk

36. Linux kernel (w/Android features: binder, wakelocks, etc.)
Headless Glibc Android using LibHybris
Your Compositor / GUI App
LibHybris
Bionic
SurfaceFlinger / HWC
OpenGL shared lib
GUI lib
GNU glibc
Other libs

37. A bionic GPU process?
Pipe GPU commands over a
local pipe to a bionic process
that does the composition.

38. Linux kernel (w/Android features: binder, wakelocks, etc.)
Headless Glibc Android using a Bionic GPU Process + IPC
GUI AppCompositor
GUI lib
GNU glibc
IPC-GL client
SurfaceFlinger / HWC
OpenGL shared lib
Bionic
IPC
Other libs
IPC-GL server

39. Chromium GPU Process Architecture

40. Communication Architecture
Renderer
Gpu Process
Browser Renderer
IPC Channels
Shared Memory
Gpu Memory BuffersCommand Buffers

41. Client
Renderer / Browser
- Write commands to
shared memory
- Update ‘put’ pointer
- Signal GPU process
@pati_gallardo

42. Server
GPU Process
- Read commands from
shared memory
- Validate command and
arguments
- Make actual call@pati_gallardo

43. Gpu
Process
Command
Buffer
IPC Channel
Command
Stream
Ordering
Barrier
Unverified Sync Token
Wait Sync Token
Wait Sync TokenCommandCommand
Command
Command
Command Command
CommandVerified Sync TokenBrowser
Renderer
Renderer
Command
Command
CommandCommand
CommandCommand

44. Not Exactly Cut A nd Paste
@pati_gallardo

45. Lessons Learned
CC image courtesy of penjelly on Flickr

46. Existing Codebase
Porting to Java?
Porting from glibc to Bionic?
Rewrite to Android APIs?
What about other APIs you use?
- Do they exist in Android?

47. 3rd-party dependencies?
Port to Bionic? Really !?
Will upstream accept the port?
Remove deps if possible!
What about alternative deps?
Push towards glibc platform!

48. Bringup & Maintenance
Minimize custom hardware!
Decouple customizations from
upstream BSP/platform
Keep changes out of the BSP
- Above the Android APIs
- Or below user space
(kernel drivers, device tree)

49. Maintaining Patches

50. Avoid patches when you can!
Minimize changes to the BSP itself
Decouple your changes from the guts of
Android

51. Structure your patches!
Patches across many different repos:
- Common scheme for maintenance
- Enumerate your current patchset
- Integrating new upstream release:
- Remove and Refresh

52. Big Ball of Mud

53. Plan for updates!
AOSP / BSP : Every year
3rd-party dependencies : Varies
Strict security policies (e.g. OpenSSL)
Chromium : Every month
Chip vendor : Hopefully never!

54. Too many patches!
- Can’t update Android version
- Can’t update 3rd-party libs
- Security pipeline clogged
- Project stalled!

55. Wrap it up!

56. No display
Multi app
Single app
Embedded LinuxFull stack Android Headless GlibcHeadless Bionic
Java app/service
One “home screen” app
App Store (Google’s Play
Store if CDD-compliant)
Multiple apps composited
by XServer/Wayland
EGL Window/Framebuffer
C/C++ app/service C/C++ app/daemon C/C++ app/daemon
Multiple apps composited
by SurfaceFlinger/HWC
via e.g. Hybris
Multiple apps composited
by SurfaceFlinger/HWC
SurfaceFlinger/HWC SurfaceFlinger/HWC via
e.g. Hybris
Your code + 3rd-party
dependencies built
against Bionic
Your code +
3rd-party
dependencies
built against
glibc
Bionic / Glibc
bridge
needed for
graphics &
composition

57. No display
Multi app
Single app
Embedded LinuxFull stack Android Headless GlibcHeadless Bionic
Java app/service
One “home screen” app
App Store (Google’s Play
Store if CDD-compliant)
Multiple apps composited
by XServer/Wayland
EGL Window/Framebuffer
C/C++ app/service C/C++ app/daemon C/C++ app/daemon
Multiple apps composited
by SurfaceFlinger/HWC
via e.g. Hybris
Multiple apps composited
by SurfaceFlinger/HWC
SurfaceFlinger/HWC SurfaceFlinger/HWC via
e.g. Hybris

58. Plan for maintenance

59. Questions?

60. Feedback, please
Swag!