

                      ==========================
                      Genode components overview
                      ==========================

                             Norman Feske


Abstract
########

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.

The scope of this document is limited to the Genode main repository maintained
by Genode Labs. Many additional components and device drivers can be found in
the community-maintained
[https://github.com/genodelabs/genode-world/ - Genode-World] repository.


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 via
  one of Genode's device-independent session interfaces, which are
  'platform_session', 'capture_session', 'event_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', 'pc'. The main source tree is accompanied
by a variety of optional source-code repositories, each hosting the support of
a different SoC family such as NXP's i.MX, Allwinner, Xilinx Zynq, or RISC-V.

:Repositories maintained by Genode Labs:

  [https://github.com/orgs/genodelabs/repositories]


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.

:_os/src/drivers/acpi/_:
  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).

:_os/src/app/pci_decode/_:
  A component that reports the physical information about PCI devices after
  parsing and initializing the PCI bus. The reported information is usually
  consumed by the platform driver.

:_os/src/app/smbios_decoder/_:
  A component that parses SMBIOS information on x86 platforms and makes the
  result available as a report.

:_libports/src/app/acpica/_:
  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.

:_os/src/drivers/uart/spec/pbxa9/_:
  Driver for the PL011 UART as found on many ARM-based platforms.

:_os/src/drivers/uart/spec/x86/_:
  Driver for the i8250 UART as found on PC hardware.


Framebuffer and input drivers
=============================

Framebuffer and input drivers are implemented as clients of the
capture-session and event-session interfaces respectively.

:_os/src/drivers/ps2/x86/_:
  Driver for the 'i8042' PS/2 controller as found in x86 PCs. It supports both
  mouse (including ImPS/2, ExPS/2) and keyboard.

:_os/src/drivers/ps2/pl050/_:
  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
  system.

:_libports/src/drivers/framebuffer/vesa/_:
  Driver using VESA mode setting on x86 PCs. For more information, please refer
  to the README file in the driver directory.

:_libports/src/drivers/framebuffer/boot/_:
  Driver for boot-time initialized framebuffers (e.g., UEFI GOP)
  discovered from the 'platform_info' ROM

:_os/src/drivers/framebuffer/pl11x/_:
  Driver for the PL110/PL111 LCD display.

:_os/src/drivers/framebuffer/sdl/_:
  Serves as both framebuffer and input driver on Linux using libSDL. This
  driver is only usable on the Linux base platform.

:_os/src/drivers/framebuffer/virtio/_:
  Driver for the Virtio virtual graphics device as supported by Qemu.

:_os/src/drivers/gpu/intel/_:
  An Intel Graphics GPU multiplexer for Broadwell and newer.

:_pc/src/drivers/framebuffer/intel/_:
  Framebuffer driver for Intel i915 compatible graphic cards based on
  the Linux Intel KMS driver.

:_pc/src/drivers/usb_host/_:
  USB host-controller driver that provides an USB session interface to
  USB drivers.

:_dde_linux/src/drivers/usb_hid/_:
  USB Human Interface Device driver using the USB session interface.


Timer drivers
=============

The timer driver located at _base/src/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.

:_os/src/drivers/audio/spec/linux/_:
  Uses ALSA as back-end on the Linux base platform and supports only playback.

:_dde_bsd/src/drivers/audio/_:
  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
_os/include/block_session/_.

:_os/src/drivers/sd_card/pl180/_:
  Driver for SD-cards connected via the PL180 device as found on the PBX-A9
  platform.

:_os/src/drivers/sd_card/imx53/_:
  Driver for SD-cards connected to the Freescale i.MX53 platform like the
  Quick Start Board or the USB armory device.

:_os/src/drivers/ahci/_:
  Driver for SATA disks and CD-ROMs on x86 PCs.

:_os/src/drivers/nvme/_:
  Driver for NVMe block devices on x86 PCs.

:_os/src/drivers/usb_block/_:
  USB Mass Storage Bulk-Only driver using the USB session interface and provides
  a block-session interface.


Network interface drivers
=========================

All network interface drivers implement the NIC session interface
defined at _os/include/nic_session/_.

:_os/src/drivers/nic/spec/linux/_:
  Driver that uses a Linux tap device as back end. It is only useful on the
  Linux base platform.

:_os/src/drivers/nic/lan9118/_:
  Native device driver for the LAN9118 network adaptor as featured on the
  PBX-A9 platform.

:_dde_ipxe/src/drivers/nic/_:
  Device drivers ported from the iPXE project. Supported devices are Intel
  E1000 and pcnet32.

:_pc/src/drivers/nic/pc/_:
  The PC NIC-driver component uses network driver code of the Linux kernel
  to drive common network cards as found in commodity PC hardware.

:_pc/src/drivers/wifi/_:
  The wifi driver 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.

:_dde_linux/src/drivers/usb_net/_:
  USB network driver using the USB session interface.


Resource multiplexers
#####################

By convention, resource multiplexers are located at the _src/server/_
subdirectory of a source repository.

:Framebuffer and input: Framebuffer and input devices can be multiplexed using
  the Nitpicker GUI server, which allows multiple clients to create and manage
  rectangular areas on screen. Nitpicker serves as broker between input
  devices, output devices, and graphical applications. It provides an event
  service for input drivers, a capture service for output drivers, and a GUI
  service for the applications. Each GUI session contains a virtual
  framebuffer and a virtual input interface. 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.

  The NIC router located at _os/src/server/nic_router/_ multiplexes one NIC
  session to multiple virtual NIC sessions by applying network address
  translation (NAT).

  The NIC-uplink component located at _os/src/server/nic_uplink/_ connects
  a NIC client directly to a network driver (as uplink client) without routing.

: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.run_.

:File system: The VFS file-system server allows multiple clients to
  concurrently access the same virtual file system. It is located at
  _os/src/server/vfs/_. The VFS can be assembled out of several builtin
  file-system types (like a RAM file system, or pseudo file systems for
  various Genode session interfaces) as well as external plugins such as rump
  (mounting file systems supported by the NetBSD kernel).

: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
===================

:_os/src/server/gui_fb/_:
  Translates a GUI session to a pair of framebuffer and input sessions.
  Each 'gui_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/gui_fb/README_.

:_gems/src/server/wm/_:
  Window manager that implements the GUI 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/_.

:_demo/src/server/liquid_framebuffer/_:
  Implements the same translation as 'gui_fb' but by presenting an interactive
  window rather than a statically positioned screen area.

:_os/src/server/tar_rom/_:
  Provides each file contained in a tar file obtained via Genode's ROM session
  as separate ROM session.

:_os/src/server/lx_fs/_:
  A file system server that makes the file system of a Linux base platform
  available to Genode.

:_os/src/server/vfs_block/_:
  Provides the content of a file obtained from a VFS as a block session,
  similar to the loop-mount mechanism on Linux

:_os/src/server/terminal_log/_:
  Adapter for forwarding LOG messages to a terminal session.

:_os/src/server/log_terminal/_:
  Adapter for forwarding terminal output to a LOG session.

:_demo/src/server/nitlog/_:
  Provides a LOG session, printing log output on screen via a GUI session.

:_os/src/app/rom_logger/_:
  The rom_logger component requests a ROM session and writes the
  content of the ROM dataspace to the LOG.

:_os/src/server/rom_filter/_:
  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.

:_gems/src/server/file_terminal/_:
  Provides terminal sessions that target files on a file system.

:_gems/src/server/terminal/_:
  Provides a terminal session via a graphical terminal using a framebuffer
  session and an input session.

:_gems/src/server/tcp_terminal/_:
  Provides one or multiple terminal sessions over TCP connections.
  For further information, refer to _gems/src/server/tcp_terminal/README_.

:_os/src/server/terminal_crosslink/_:
  The terminal crosslink service allows to terminal clients to talk to each
  other.

:_os/src/server/fs_rom/_:
  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.

  For use cases where ROMs are known to be static, the
  _os/src/server/cached_fs_rom/_ can be considered as a faster alternative to
  the regular 'fs_rom' server. Note that 'cached_fs_rom' is not supported
  in base-linux though.

:_os/src/server/chroot/_:
  An intermediate file-system server that makes a sub directory of a file
  system available as the root of a file system handed out to its client.

:_os/src/server/dynamic_rom/_:
  A simple ROM service that provides ROM modules that change in time according
  to a configured timeline.

:_os/src/server/report_rom/_:
  A service that implements both the report session interface and the ROM
  session interface. It reflects incoming reports as ROM modules.

:_os/src/server/fs_report/_:
  Report server that writes reports to file-systems

:_os/src/server/clipboard/_:
  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.

:_os/src/server/event_filter/_:
  A component that transforms and merges input events from multiple sources
  into a single event stream.

:_libports/src/app/acpi_event/_:
  A component that transforms ACPI events into Genode input events.

:_gems/src/server/gui_fader/_:
  A wrapper for nitpicker's GUI session interface that applies alpha-blending
  to the of views a GUI client.

:_os/src/server/black_hole/_:
  Mockup implementation of Genode session interfaces.

:_dde_linux/src/app/wireguard/_:
  Port of the Linux implementation of the WireGuard VPN as Genode component.


VFS plugins
===========

VFS plugins are file-system drivers in the form of shared libraries that
implement the VFS-plugin interface. They can be combined with any application
based on Genode's C runtime, with the VFS server, and with non-POSIX
components that use the Genode's VFS library directly.

:_os/src/lib/vfs/tap/_:
  A VFS plugin that allows for packet-level access of a NIC or uplink session.

:_gems/src/lib/vfs/trace/_:
  A VFS plugin that makes core's TRACE service accessible as a pseudo
  file system.

:_gems/src/lib/vfs/import/_:
  A VFS plugin that pre-populates a VFS with initial content.

:_gems/src/lib/vfs/pipe/_:
  A VFS plugin that provides bi-directional pipes for exchanging streamed
  data between components.

:_gems/src/lib/vfs/ttf/_:
  A VFS plugin that makes rendered pixel data of the glyphs of Truetype fonts
  available as a pseudo file system.

:_libports/src/lib/vfs/jitterentropy/_:
  A VFS plugin that provides random numbers based on the jitter of executing
  CPU instructions.

:_libports/src/lib/vfs/lwip/_:
  A VFS plugin that uses the light-weight IP (lwIP) stack to provide a
  network socket interface as a pseudo file system.

:_dde_linux/src/lib/vfs/lxip/_:
  A VFS plugin that uses the TCP/IP stack ported from the Linux kernel to
  provide a network socket interface as a pseudo file system.

:_libports/src/lib/vfs/fatfs/_:
  A VFS plugin that allows for the mounting of FAT-formatted block devices.

:_os/src/lib/vfs/tap/_:
  A VFS plugin for the interaction with raw network packets.

:_dde_rump/src/lib/vfs/rump/_:
  A VFS plugin that enables the use of NetBSD's file-system drivers such
  as ext2 or msdos.


Libraries
=========

:_libports/lib/mk/libc/_:
  C runtime ported from FreeBSD.

:_libports/lib/mk/stdcxx/_:
  Standard C++ library

:_libports/lib/mk/mesa_api/_:
  Mesa OpenGL API with backends for software rasterization (egl_swrast)
  and Intel Graphics (egl_i965)

:_libports/lib/mk/mupdf/_:
  PDF rendering engine.

:_libports/lib/mk/ncurses/_:
  Library for implementing pseudo-graphical applications (i.e., VIM) that
  run on a text terminal.

:_libports/lib/mk/qt5_*/_:
  Qt5 framework, using GUI session and NIC session as back end.

:_libports/lib/mk/vfs_jitterentropy.mk_:
  A VFS plugin that makes a jitter-based random-number generator available
  as a file within the process-local VFS.

:_libports/lib/mk/libarchive.mk_:
  Library providing a common interface to a variety of archive
  formats.

:_libports/lib/mk/lz4.mk_:
  Library for processing LZ4 lossless compression archives.

:_libports/lib/mk/liblzma.mk_:
  Library for processing LZMA archives.

:_libports/lib/mk/libgcrypt.mk_:
  GnuPG library for OpenPGP processing, e.g., signature verification.


Applications
############

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.

:_gems/src/app/backdrop/_:
  GUI client application that sets a composition of PNG images as desktop
  background.

:_demo/src/app/launchpad/_:
  Graphical application for interactively starting and killing subsystems.

:_demo/src/app/scout/_:
  Graphical hypertext browser used for Genode's default demonstration scenario.

:_ports/src/app/gdb_monitor/_:
  Application that allows the debugging of a process via GDB over a remote
  connection.

:_libports/src/app/qt5/qt_launchpad/_:
  Graphical application starter implemented using Qt.

:_libports/src/app/qt5/examples/_:
  Several example applications that come with Qt.

:_os/src/app/sequence/_:
  Simple utility to serialize the execution of multiple components

:_ports/src/noux-pkg/_:
  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.

:_ports/src/app/lighttpd/_:
  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
  configuration.

:_os/src/app/trace_logger/_:
  Convenient, runtime-configurable frontend to the tracing facility.

:_os/src/app/rom_reporter/_:
  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.

:_os/src/app/log_core/_:
  Component transforming core and kernel output to Genode LOG output.


Package-management components
=============================

:_gems/src/app/depot_query/_:
  Tool for querying subsystem information from a depot.

:_gems/src/app/depot_download_manager/_:
  Tool for managing the download of depot content.

:_gems/src/app/depot_deploy/_:
  Subsystem init configuration generator based on blueprints.

:_gems/src/app/depot_remove/_:
  Tool for the orderly removal of depot content.

:_libports/src/app/fetchurl/_:
  A runtime-configurable frontend to the libcURL library for
  downloading content.

:_libports/src/app/extract/_:
  Tool for extracting archives using libarchive.

:_ports/src/app/verify/_:
  This component verifies detached OpenPGP signatures using libgcrypt.


Runtime environments
####################

:_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/virtualbox6/_: VirtualBox running on top of the NOVA hypervisor.

:_os/src/server/vmm/_: A virtual machine monitor that is based on
  hardware-assisted virtualization of ARM platforms. It is supported on
  the base-hw kernel only.

:_os/src/server/cpu_balancer/_: The CPU balancer intercepts the interaction
  of components with core's low-level services to migrate threads dynamically
  between CPU cores.

