Abstract
Chromium OS consists of three major components:
- The Chromium-based browser and the window manager
- System-level software and user-land services: the kernel, drivers, connection manager, and so on
- Firmware
High-level design
We'll look at each component, starting with the firmware.
Firmware
The firmware plays a key part to make booting the OS faster and
more secure. To achieve this goal we are removing unnecessary components
and adding support for verifying each step in the boot process. We are
also adding support for system recovery into the firmware itself. We can
avoid the complexity that's in most PC firmware because we don't have
to be backwards compatible with a large amount of legacy hardware. For
example, we don't have to probe for floppy drives.
Our firmware will implement the following functionality:
- : The recovery firmware can re-install Chromium OS in the event that the system has become corrupt or compromised.
- : Each
time the system boots, Chromium OS verifies that the firmware, kernel,
and system image have not been tampered with or become corrupt. This
process starts in the firmware.
- : We have improved boot performance by removing a lot of complexity that is normally found in PC firmware.
System-level and user-land software
From here we bring in the
Linux kernel, drivers, and user-land daemons. Our kernel is mostly
stock except for a handful of patches that we pull in to improve boot
performance. On the user-land side of things we have streamlined the
init process so that we're only running services that are critical. All
of the user-land services are managed by Upstart. By using Upstart we
are able to start services in parallel, re-spawn jobs that crash, and
defer services to make boot faster.
Here's a quick list of things that we depend on:
- D-Bus: The browser uses D-Bus to interact with the rest of the system. Examples of this include the battery meter and network picker.
- Connection Manager: Provides a common API for interacting
with the network devices, provides a DNS proxy, and manages network
services for 3G, wireless, and ethernet.
- WPA Supplicant: Used to connect to wireless networks.
- Autoupdate: Our autoupdate daemon silently installs new system images.
- Power Management: (ACPI on Intel) Handles power management events like closing the lid or pushing the power button.
- xscreensaver: Handles screen locking when the machine is idle.
- Standard Linux services: NTP, syslog, and cron.
Chromium and the window manager
The window manager is
responsible for handling the user's interaction with multiple client
windows. It does this in a manner similar to that of other X window
managers, by controlling window placement, assigning the input focus,
and exposing hotkeys that exist outside the scope of a single browser
window. Parts of the ICCCM (Inter-Client Communication Conventions
Manual) and EWHM (Extended Window Manager Hints) specifications are used
for communication between clients and the window manager where
possible.
The window manager also uses the XComposite extension to redirect client
windows to offscreen pixmaps so that it can draw a final, composited
image incorporating their contents itself. This lets windows be
transformed and blended together. The Clutter library is currently used
to animate these windows and to render them via OpenGL or OpenGL|ES.
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