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DevnsDemo
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README

Copyright (c) 2011-2013 Cellrox Ltd.


**** What is this demo? *****

This is an uber-simplified demo use case of device namespaces. The demo uses
a secondary device namespace on an Android phone to place the phone "on hold"
while the screen alternates among a delightful palette of colors. Visually it
looks like a mere screensaver, but unlike a screensaver, the primary container
is switched to a non-active namespace and does not have access to any physical
device.

We provide this use case with the hope that it will serve as sample code for
other uses of device namespaces. We will be glad to hear about other exciting
use cases and refer to them from this site.


***** How does it work? *****

The demo employs two device namespaces: the primary (root namespace) runs
Android, and a secondary runs a program that displays the palette. Upon
request, it switches to the secondary namespace, and then listens to input
events to perform a switch back to the primary namespace.

This demo has 4 components:
- devns: service that accepts and executes requests for namespace switch.
- devns_init: init process of the secondary namespace, displays the palette.
- devns_switch: a CLI utility to request a switch to secondary namespace.
- DevnsDemo: an Android application to request a namespace switch via GUI.

The service 'devns' starts at boot time. It first forks the secondary device
namespace and executes 'devns_init' there. The two programs communicate over
a pipe. Then it creates a FIFO and listens to request to switch.

When started, 'devns_init' waits for a switching notification from 'devns'.
When notified, it starts drawing the palette, while waiting for an input event
(e.g. touch-screen or a button), and then requests to switch back via the FIFO.

Note: 'devns_init' could also draw continuously to the screen, and the device
namespace would ensure that the output would be seen only when the secondary
namespace is active. We use an explicit notification purposely to avoid loading
the CPU unnecessarily.

The application DevnsDemo provides a GUI to request a namespace switch, and
the utility 'devns_switch' provides CLI (usable via ADB) for the same purpose.


***** How to use this demo? *****

This demo was made for AOSP 4.2.2 emulator (goldfish-x86). For instructions
how to download AOSP, see: http://source.android.com/source/downloading.html.
After you download the AOSP, follow the instructions below:

1. Apply the device namespace patches to the AOSP kernel sources, and compile
the kernel. For instructions, see:
https://www.github.comm/Cellrox/devns-patches/wiki/DeviceNamespace:Patches

 -> This will generate a kernel with device namespaces enabled for AOSP.

2. Apply the devns-demo patch by running devns-patch.sh at the root of the
AOSP source tree.

 -> This will patch:
    build/target/product/core.mk
    system/core/rootdir/init.rc

3. Clone the devns-demo git repository at the root of an Android source tree:
   $ git clone https://github.com/Cellrox/devns-demo.git

 -> This will create the folder "devns-demo":
    devns-demo/devns - native components
    devns-demo/DevnsDemo - demo switch application

4. Compile the Android sources to create a ROM. For instructions on how to
compile AOSP, see: http://source.android.com/source/building-running.html.

5. Boot the ROM, with the emulator:
  $ emulator -show-kernel -kernel PATH_TO_COMPILED_KENREL

6. Android will boot with two device namespaces: the primary runs Android,
and a secondary runs 'devns_init' program that paints the display in changing
colors. You can switch between them:

 -> Switch to secondary via GUI:   Start the application "Devns Switch Demo",
    and click "switch to secondary namespace", -or-

 -> Switch to secondary via CLI: "adb shell devns_switch 1"

 These will switch to secondary devns, which will show colors changing.

 -> Switch back to primary:  click on the screen, or use vol-down button

 This will restore the Android in the primary namespace.

7. Enjoy exploring device namespaces


***** How to get in touch? *****

Contact us at mailto:oss@cellrox.com
Developer contacts: {orenl,amir} =at= cellrox.com

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