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Genode components overview
Norman Feske
Genode comes with a growing number of components apparently scattered across
various repositories. This document provides an overview of these components
and outlines the systematics behind them.
Categorization of components
Genode components usually fall into one of four categories, namely device
drivers, resource multiplexers, protocol stacks, and applications. Each
of them is briefly characterized as follows:
:Device drivers: translate hardware resources into device-independent
session interfaces. Naturally, a device driver is specific to a
particular hardware platform. The hardware resources are accessed
via core's IO_MEM, IO_PORT, and IRQ services. The functionality of
the driver is made available to other system components by announcing
one of Genode's device-independent session interfaces, which are
'platform_session', 'framebuffer_session', 'input_session', 'block_session',
'audio_out_session', 'log_session', 'nic_session', and 'timer_session'
(see 'os/include/' for the interface definitions). Those interfaces are
uniform across hardware platforms and kernel base platforms. Usually,
each device driver can accommodate only one client at a time.
:Resource multiplexers: provide mechanisms to multiplex device resources
to multiple clients. A typical resource multiplexer requests one
of Genode's device-independent session interface (usually connected
to a device driver) and, in turn, announces a service of the same kind.
However, in contrast to a device driver, a resource multiplexer is able
to serve more than one client at the same time.
:Protocol stacks: translate low-level interfaces to higher-level
interfaces (or sometimes vice versa). Typically, a protocol stack comes
in the form of a library, which uses a device-independent session
interface as back end and provides a high-level library interface as
front end. However, protocol stacks also exist in the form of
distinct components that implement translations between different
session interfaces.
:Applications: implement functionality using APIs as provided by
protocol stacks.
:Runtime environments: enable existing 3rd-party software to be executed
as a Genode sub systems.
Device drivers
Device drivers usually reside in the 'src/drivers' subdirectory of source-code
repositories. The most predominant repositories hosting device drivers are
'os', 'dde_ipxe', 'dde_linux'.
Platform devices
:'os/src/drivers/platform/': Platform drivers for various platforms.
On x86, the platform driver uses the PCI controller as found on x86 PC
hardware. A client can probe for a particular device and request information
about physical device resources (using the 'platform_device' interface). I/O
resources for MMIO regions, I/O ports, and interrupts can be requested by the
provided device abstraction.
On x86 platforms that use the APIC (namely Fiasco.OC, NOVA, and hw_x86_64)
this simple ACPI parser traverses the ACPI tables and reports device-resource
information (e.g., interrupt lines of PCI devices).
In addition to our ACPI base driver, the acpica component uses the
ACPICA library to provide access to dynamic functions like battery
states, events (e.g., notebook lid close and power buttons), as well
as reset and power off. The componenten reports ACPI events and
states as reports and itself responds to system state changes of
certain configuration ROMs.
UART devices
The UART device drivers implement the UART-session interface.
Driver for the PL011 UART as found on many ARM-based platforms.
Driver for the i8250 UART as found on PC hardware.
Driver for the UART as found on OMAP4-based hardware.
Driver for the UART as found on Exynos-5-based hardware.
Framebuffer and input drivers
Framebuffer and input drivers implement the framebuffer-session interface and
input-session interfaces respectively.
Pseudo input driver without accessing any hardware. This component is useful
to resolve a dependency from an input session for scenarios where no user
input is required.
Driver for the 'i8042' PS/2 controller as found in x86 PCs. It supports both
mouse (including ImPS/2, ExPS/2) and keyboard.
Driver for the PL050 PS/2 controller as found on ARM platforms such as
VersatilePB. The physical base address used by the driver is obtained at
compile time from a header file called 'pl050_defs.h'. The version of the
VersatilePB platform can be found at 'os/include/platform/vpb926/' and
is made available to the driver via the SPECS machinery of the Genode build
Input driver for Egalaxy touchscreen and Freescale's MPR121
capacitative touch buttons on i.MX53.
Driver using VESA mode setting on x86 PCs. For more information, please refer
to the README file in the driver directory.
Driver for boot-time initialized framebuffers (e.g., UEFI GOP)
discovered from the 'platform_info' ROM
Driver for the PL110/PL111 LCD display.
Driver for HDMI output on OMAP4 SoCs.
Driver for HDMI output on Exynos-5 SoCs.
Driver for LCD output on i.MX53 SoCs.
Driver for the HDMI output of the Raspberry Pi.
Serves as both framebuffer and input driver on Linux using libSDL. This
driver is only usable on the Linux base platform.
Intel Graphics GPU multiplexer for Broadwell and newer.
Framebuffer driver for Intel i915 compatible graphic cards based on
the Linux Intel KMS driver.
USB driver that makes USB HID and USB storage devices available as input
sessions and block session respectively. For examples of using this driver,
refer to the run scripts at 'dde_linux/run/usb_hid' and
Timer drivers
The timer driver located at 'os/src/drivers/timer' implements the timer-session
interface. Technically, it is both a device driver (accessing a timer
device) and a resource multiplexer (supporting multiple timer-session clients
at the same time). Depending on the base platform, the implementation uses
different time sources. Time sources are either hardware timers, a time source
provided by the kernel, or a pseudo time source (busy):
:'nova': NOVA kernel semaphores
:'okl4_x86': Programmable Interval Timer (PIT) device
:'foc': IPC timeout
:'fiasco': IPC timeout
:'pistachio': Programmable Interval Timer (PIT) device
:'linux': nanosleep()
:'hw': kernel timer
:'sel4': PIT on x86, EPIT on Wandboard
Audio drivers
Audio drivers implement the Audio_out session interface defined at
'os/include/audio_out_session/' for playback and optionally the audio_in
interface for recording.
Uses ALSA as back-end on the Linux base platform and supports only playback.
Sound drivers ported from OpenBSD. Currently, the repository
includes support for Intel HD Audio as well as for Ensoniq AudioPCI
(ES1370) compatible sound cards.
Block drivers
All block drivers implement the block-session interface defined at
Driver for SD-cards connected via the PL180 device as found on the PBX-A9
Driver for SD-cards connected to the SD-card controller of the OMAP4 SoC.
Driver for SD-cards and eMMC connected to Exynos-5-based platforms.
Driver for SD-cards connected to the Freescale i.MX53 platform like the
Quick Start Board or the USB armory device.
Driver for SD-cards connected to the Raspberry Pi.
USB driver that makes USB storage devices available as block sessions.
For an example of using this driver, refer to the run script at
Driver for SATA disks and CD-ROMs on x86 PCs.
USB Mass Storage Bulk-Only driver using the USB session interface.
Network interface drivers
All network interface drivers implement the NIC session interface
defined at 'os/include/nic_session'.
Driver that uses a Linux tap device as back end. It is only useful on the
Linux base platform.
Native device driver for the LAN9118 network adaptor as featured on the
PBX-A9 platform.
Device driver for Cadence EMAC PS network adaptor as featured on the
Xilinx Zynq.
Device drivers ported from the iPXE project. Supported devices are Intel
E1000 and pcnet32.
The wifi_drv component is a port of the Linux mac802.11 stack, including the
iwlwifi driver. It enables the use of Intel Wireless 6xxx and 7xxx cards.
For the OMAP4 platform, the USB driver contains the networking driver.
Driver for ethernet NICs of the i.MX SoC family.
General-purpose I/O drivers
Driver for accessing the GPIO pins of OMAP4 platforms.
Driver for accessing the GPIO pins of i.MX53 platforms.
Driver for accessing the GPIO pins of Raspberry Pi platforms.
Driver for accessing the GPIO pins of Exynos4 platforms, e.g.,
Resource multiplexers
By convention, resource multiplexers are located at the 'src/server'
subdirectory of a source repository.
:Framebuffer and input: The framebuffer and input session interfaces can be
multiplexed using the Nitpicker GUI server, which allows multiple clients to
create and manage rectangular areas on screen. Nitpicker uses one input
session and one framebuffer session as back end and, in turn, provides
so-called nitpicker sessions to one or multiple clients. Each nitpicker
session contains a virtual framebuffer and a virtual input session. Nitpicker
(including a README file) is located at 'os/src/server/nitpicker'.
:Audio output: The audio mixer located at 'os/src/server/mixer' enables
multiple clients to use the audio-out interface. The mixing is done by simply
adding and clamping the signals of all present clients.
:Networking: The NIC bridge located at 'os/src/server/nic_bridge' multiplexes
one NIC session to multiple virtual NIC sessions using a proxy-ARP
implementation. Each client has to obtain a dedicated IP address visible to
the physical network. DHCP requests originating from the virtual NIC sessions
are delegated to the physical network.
:Block: The block-device partition server at 'os/src/server/part_block' reads
the partition table of a block session and exports each partition found as
separate block session. For using this server, please refer to the run
script at 'os/run/part_block'.
:File system: The FAT file-system service allows multiple clients to
concurrently access the same FAT-formatted block device. It is located
at 'libports/src/server/fatfs_fs' and supports FAT, FAT32, and exFAT.
:Terminal: The terminal_mux service located at gems/src/server/terminal_mux
is able to provide multiple terminal sessions over one terminal-client
session. The user can switch between the different sessions using a keyboard
shortcut, which brings up an ncurses-based menu.
Protocol stacks
Protocol stacks come either in the form of separate components that translate
one session interface to another, or in the form of libraries.
Separate components:
Translates a nitpicker session to a pair of framebuffer and input sessions.
Each 'nit_fb' instance is visible as a rectangular area on screen presenting
a virtual frame buffer. The area is statically positioned. For more
information, please refer to 'os/src/server/nit_fb/README'.
Window manager that implements the nitpicker session interface but manages
each client view as a separate window. The window decorations are provided
by a so-called decorator (e.g., 'gems/src/app/decorator'). The behaviour
is defined by a so-called window layouter such as the floating window
layouter located at 'gems/src/app/floating_window_layouter/'.
Implements the same translation as 'nit_fb' but by presenting an interactive
window rather than a statically positioned screen area.
Provides each file contained in a tar file obtained via Genode's ROM session
as separate ROM session.
Provides each file of an ISO9660 file system accessed via a block session as
separate ROM session.
A file-system implementation that keeps all data in memory.
A file-system server that contains various file-systems ported from the
NetBSD kernel.
A file system server that makes the file system of a Linux base platform
available to Genode.
A pseudo file system that can be used as a front end to core's TRACE
Provides the content of a ROM file as a block session, similar to the
loop-mount mechanism on Linux
Provides the content of a RAM dataspace as a block session. In contrast
to 'rom_block', this server provides a writeable block device.
Adapter for forwarding LOG messages to a terminal session.
Adapter for forwarding terminal output to a LOG session.
Adapter that writes LOG messages to files on a file system.
Provides a LOG session, printing log output on screen via a nitpicker
The rom_logger component requests a ROM session and writes the
content of the ROM dataspace to the LOG.
The ROM filter provides a ROM module that depends on the content of
other ROM modules steered by the filter configuration, e.g., dynamic
switching between configuration variants dependent on the state of
the system.
A file-system server using the VFS library and plugins as backend.
Forwards terminal output to a LOG session.
Provides terminal sessions that target files on a file system.
Provides a terminal session via a graphical terminal using a framebuffer
session and an input session.
Provides one or multiple terminal sessions over TCP connections.
For further information, refer to 'gems/src/server/tcp_terminal/README'.
The terminal crosslink service allows to terminal clients to talk to each
A block service that fetches a virtual block device over the network from
a HTTP server.
A ROM service that translates the 'File_system' session interface to the
'ROM' session' interface. Each request for a ROM file is handled by looking
up an equally named file on the file system.
Please refer to 'os/src/server/fs_rom' for more information.
A simple ROM service that provides ROM modules that change in time according
to a configured timeline.
A service that implements both the report session interface and the ROM
session interface. It reflects incoming reports as ROM modules.
Report server that writes reports to file-systems
This component is both a report service and a ROM service. The
clients of the report service can issue new clipboard content, which
is then propagated to the clients of the ROM service according to a
configurable information-flow policy.
OpenVPN enables access to remote network resources through a secure tunnel
by providing an encrypted connection to a remote host. It is plugged between
NIC server (such as a network driver) and NIC client.
A component that merges input events from multiple sources into a single
A component that transforms ACPI events into Genode input events.
A wrapper for nitpicker's session interface that applies alpha-blending to
the of views a nitpicker client.
C runtime ported from FreeBSD.
Accesses files on a block device that contains a FAT32 file system.
Accesses files on a block device that contains an exFAT file system.
Accesses files on a block device that contains an ext2 file system.
Standard C++ library
Mesa OpenGL API with backends for software rasterization (egl_swrast)
and Intel Graphics (egl_i965)
Subset of the POSIX thread and semaphore API.
Runtime of the Python scripting language.
PDF rendering engine.
Translates the libSDL API to framebuffer and input sessions.
Library for implementing pseudo-graphical applications (i.e., VIM) that
run on a text terminal.
A library for video decoding, conversion, and streaming.
Runtime for the Lua scripting language.
Qt5 framework, using nitpicker session and NIC session as back end.
A VFS plugin that makes a jitter-based random-number generator available
as a file within the process-local VFS.
Library providing a common interface to a variety of archive
Library for processing LZ4 lossless compression archives.
Library for processing LZMA archives.
GnuPG library for OpenPGP processing, e.g., signature verification.
Applications are Genode components that use other component's services but
usually do not provide services. They are typically located in the 'src/app/'
subdirectory of a repository. Most applications come with README files
located in their respective directory.
Nitpicker client application that sets a composition of PNG images as
desktop background.
Graphical application for interactively starting and killing subsystems.
:'gems/app/launcher': Graphical launcher of Genode subsystems.
:'os/app/cli_monitor': Command-line-based launcher of Genode subsystems.
Graphical hypertext browser used for Genode's default demonstration scenario.
Example programs for using the Mesa OpenGL graphics stack.
Arora is a Qt-based web browser using the Webkit engine.
Application that allows the debugging of a process via GDB over a remote
Graphical application starter implemented using Qt.
Several example applications that come with Qt.
Simple utility to serialize the execution of multiple components
Ports of popular commandline-based Unix software such as VIM, bash,
coreutils, binutils, gcc, findutils, and netcat. The programs are supposed
to be executed within the Noux runtime environment.
Lighttpd is a fast and feature-rich web server. The port of lighttpd uses
a file-system session to access the website content and the web-server
Convenient, runtime-configurable frontend to the tracing facility.
The ROM-reporter component requests a ROM session and reports the
content of the ROM dataspace to a report session with the same label
as the ROM session.
Component transforming core and kernel output to Genode LOG output.
Package-management components
Tool for querying subsystem information from a depot.
Tool for managing the download of depot content.
Subsystem init configuration generator based on blueprints.
A runtime-configurable frontend to the libcURL library for
downloading content.
Tool for extracting archives using libarchive.
This component verifies detached OpenPGP signatures using libgcrypt.
Runtime environments
:'ports/src/noux': Noux is an experimental implementation of a UNIX-like API
that enables the use of unmodified command-line based GNU software. For using
noux, refer to the run script 'ports/run/'.
:'ports/src/app/seoul': Seoul is a virtual-machine monitor developed for
the use with the NOVA platform. It virtualizes 32bit x86 PC hardware
including various peripherals.
:'os/src/server/loader': A service that allows the creation and destruction
of Genode subsystems via a session interface. For further information,
refer to 'os/src/server/loader/README'.
:'ports/src/app/dosbox': A port of DosBox for executing DOS software.
:'ports/src/virtualbox': VirtualBox running on top of the NOVA hypervisor.