

              ===============================================
              Release notes for the Genode OS Framework 20.02
              ===============================================

                               Genode Labs



This year's [https://genode.org/about/road-map - road map] is all about making
Genode and Sculpt OS more approachable. It turns out that the first release of
the year already pays tribute to that goal. First, it equips Sculpt OS with a
much more logical and welcoming graphical user interface
(Section [Redesign of the administrative user interface of Sculpt OS]).
Second, it greatly reduces the friction when hosting existing applications on
Genode by smoothening several rough edges with respect to POSIX compatibility,
and by generally improving performance.

Most topics of the release are closely related to Sculpt. The biggest
break-though is certainly the ability of running Sculpt OS on 64-bit ARM
hardware (Section [Sculpt OS on 64-bit ARM i.MX8 hardware]) along with our
custom virtual machine monitor (VMM). On PC hardware, Sculpt users can enjoy
an updated audio driver and optimizations of the Seoul VMM. Furthermore,
Sculpt's window manager received the much anticipated ability to use virtual
desktops.

At the framework-API level, the most significant changes are the introduction
of dedicated types for inter-thread synchronization patterns
(Section [Base-framework refinements]) and a new library for
bringing the benefits of the Genode architecture to the application level
(Section [New sandbox library based on the init component]).


Redesign of the administrative user interface of Sculpt OS
##########################################################

On our [https://genode.org/about/road-map - road map] for 2020, we stated
the reducing of the barrier of entry as our main concern of the year.
We highlighted the ease of use of Sculpt OS as one particular work area.


Removing Unix from the picture
------------------------------

Until now, Sculpt's administrative user interface - lyrically called
Leitzentrale - employed a small Unix runtime and the Vim editor as utility for
basic file operations and for the tweaking of configurations. Even though this
was a practical intermediate solution, we have to face the fact that not
everyone loves the Unix command-line interface as much as we do. Quite the
opposite, actually. When presenting Sculpt, we can clearly sense that people
with a non-Unix background are put off by it. The audience generally loves the
runtime graph, visual cues, and discoverability. Furthermore, command-line
interfaces are (albeit wrongly) perceived as archaic and impenetrable relics
by many computer users who are otherwise perfectly happy with the notion of
files and directories. We identified that file-manipulation tasks performed in
the Leitzentrale are rare and simple. Relying on Unix for those basic tasks is
like taking a sledgehammer to crack a nut. On average, the Leitzentrale is
used in just a few moments a day for basic things like browsing a file-system
hierarchy, glimpsing at the reports stored on the report file system, deleting
or copying a file or two, or tweaking a configuration file. With a Unix shell
presenting one barrier, Vim is certainly an even higher one. Familiarity with
Vim should definitely not be a prerequisite for using an operating system.
Following this reasoning, we decided to swap out the command-line interface
and Vim by a simple GUI-based file browser and a notepad-like editor, which do
not require any learning curve.

Note that even once the Unix command-line interface is removed from Sculpt's
Leitzentrale, advanced users will still be able to manipulate Sculpt's config
file system via a Unix runtime deployed as a regular component, similar to the
use of the noux-system package we have today.


New user-interface layout
-------------------------

The move away from the command-line interface goes hand in hand with the
redesign of the overall user-interface layout. A new panel at the top of the
screen contains two centered tabs for switching between the runtime graph and
the file-system browser.

[image sculpt_20.02_panel]

The storage-management functionality has been moved from the former storage
dialog into the respective nodes of the runtime graph. E.g., to format a block
device, the user can now select a USB or storage node of the graph to get a
menu of block-device-level operations.

[image sculpt_20.02_storage]

The network-management is now located at a drop-down menu that can be toggled
via a button at the right side of the panel.

[image sculpt_20.02_network]

A new button on the left side of the panel allows the user to toggle a
drop-down menu for GUI settings. At the current time, there is only the option
to adjust the font size. In the future, the dialog will give easy access to
the screen-resolution options and the keyboard layout.

The log-message view is now hidden in another drop-down menu that can be
toggled via a panel button. So when starting the system, the user is greeted
with only the runtime graph, which is a much nicer and cleaner looking
experience.

Informative or diagnostic messages are displayed in the left-bottom corner of
the screen.

[image sculpt_20.02_message]

The "Files" tab of the panel switches the main screen area to a simple file
browser that lists all file systems available. By toggling one of the
file-system buttons, the directory hierarchy can be browsed. When hovering
a file, an "Edit" or "View" button appears, which can be used to open
the file in a text area that appears on the right side of the file browser.
The editor supports the usual notepad-like motions, operations, and
shortcuts (control-c for copy, control-v for paste, control-s for save).

[image sculpt_20.02_editor]


Half-way there
--------------

With the current release, one can already accomplish a lot without having to
resort to a command-line interface: connecting to the network, managing
storage devices, installing and deploying software, inspecting the system
state, and tweaking configurations.

There are still a few gaps though. In particular the file browser does
not yet support file operations like the copying, renaming, or removal of
files. For these tasks, the current version of Sculpt still features the
Unix-based inspect window, which can be accessed by toggling the "Inspect"
button inside the USB or storage dialog. Once selected, the panel presents an
"Inspect" tab that features the familiar Unix shell and Vim. Note, however,
that we keep the inspect window only as an interim solution. It will
eventually be removed. As with every new feature, there are still rough edges
to be expected in the editor and file browser, e.g., the editing of files with
long lines or the browsing of directories with many entries is not
appropriately covered yet.

To see the current new version of Sculpt OS in action, you may find the
following presentation entertaining.

:Live demonstration of Sculpt OS at FOSDEM 2020:

  [https://fosdem.org/2020/schedule/event/uk_sculpt/]

The new version 20.02 of Sculpt OS is part of this release and can be built
from source and used right now. Several Genode developers already provide
ready-to-use packages for the new version. The software depots by alex-ab,
cnuke, skalk are worth exploring. A downloadable system image along with an
updated manual will be released shortly.


Sculpt OS on 64-bit ARM i.MX8 hardware
######################################

Within the past two releases, big steps were taken to support ARMv8 hardware in
the Genode OS framework. After implementing basic support for Raspberry Pi 3,
and the i.MX 8M Evaluation Kit, the network card was enabled for the latter.
Moreover, we updated the Linux TCP/IP, and C library ports, as well as
the Noux environment to support the architecture. Finally, with the latest
releases, a new ARMv8-compliant virtual-machine monitor for the base-hw kernel
entered the framework.

The rapid achievements motivated us to strive for a more ambitious scenario to
run on top of the currently focused ARMv8 hardware platform. So why not using
Sculpt OS on the i.MX 8M System-on-Chip?


Persistent storage
==================

There were several challenges to cope with initially. First, persistent
storage was needed. Luckily, the Genode OS framework contained already an
SD-card driver implementation for the i.MX series. The driver was written for
Genode from scratch and initially supported the i.MX53 SoC only. From then, it
got extended repeatedly to drive the SD-card controller of several i.MX6 and
i.MX7 platforms. Therefore, it was not a big issue to support the new hardware
too. However, when we later used it in Sculpt, it turned out that the driver
has some low-latency requirements. If those were not met, it got stuck. This
was the time where the CPU-quota mechanism came in handy in a real-world
scenario. It helped to let the interrupt handler of the driver be scheduled in
time, and thereby let the driver run stable.

Having a working block device is one part, but it is of little use without a
file system. In Sculpt OS, the NetBSD rump kernel's ext2 file-system is
typically used to host the depot package system and for keeping configuration
files persistent. Unfortunately, the version of NetBSD as used in Genode's
rump kernel port does not contain the ARMv8 architecture. Of course, we could
have upgraded the rump kernel as a whole. But this software stack is quite
complex with a lot of threads reproducing a sophisticated state machine. It
took some time in the past to meet its required semantics. Therefore,
backporting some header definitions and a few architecture-dependent functions
seemed more attractive. Luckily, it turned out to be the right decision, and
after a day of backporting work, the file system could run on ARMv8.

Display engine
==============

One of the more challenging tasks was certainly the enabling of the Display
Controller Subsystem (DCSS) of the i.MX 8M SoC. Originally, we hoped to profit
from our experiences with the Image Processing Unit (IPU), the display engine
of former i.MX SoCs. But as it turned out, the DCSS is a completely new
design, and has not much in common with the IPU. When first writing a driver
for the IPU of the i.MX53, we were surprised by the complexity and flexibility
of this piece of hardware. Back then, it took months to get something
meaningful working. To not lose too much time by re-implementing a driver from
scratch, we decided to take the DDE Linux approach, which worked out pretty
fast. The resulting driver should provide the same flexibility like the Linux
original one. However, as the i.MX 8M EVK board provides a HDMI connector
only, we did not test more than that. The configuration of the driver is
analogous to the Intel framebuffer driver, and looks like the following:

! <config>
!   <connector name="HDMI-A-1" width="1920" height="1080" hz="60" enabled="true"/>
! </config>

Later, when using the driver in practice within the Sculpt OS, we could
experience a slightly sluggish behaviour, which was due to a missing
architectural back end of the blitting library of Genode. After tweaking this
too, the graphical user interface experience was good.


USB and Input
=============

The last missing I/O device to run Sculpt OS on the ARMv8 was something for
user generated input. Therefore, the existent USB host controller driver for
the i.MX series got updated. The only roadblock here was the powering of the
device. As there is no platform driver for the target hardware yet, which
would manage power and clocks, the hardware either has to be pre-configured
correctly, or the driver has to enable it on its own. Ethernet card, SD-card,
and the display engine were all already powered by the bootloader, but not
USB. In contrast to the first devices, the u-boot bootloader turns off USB
explicitly as soon as it starts the OS. As an interim solution, we patched
u-boot to not turn off the USB host controller, and enforced u-boot to
initialize the powering in our boot scripts. Therefore, if one wants to use
USB on the i.MX 8M EVK, make sure to take our modified version. As a
convenient solution, you can use the 'uboot' port within the base repository.
Just issue the following command in the Genode directory:

! tool/ports/prepare_port uboot

Finally, you have to copy u-boot to the SD-card as root user:

! dd if=`tool/ports/current uboot`/imx8q_evk/imx-mkimage/iMX8M/flash.bin \
!    of=/dev/sd<?> bs=1k seek=33 conv=fsync

Of course, you have to replace 'sd<?>' with the correct device node of your
attached SD-card.

After enabling the USB host controller driver, we could successfully re-use the
USB HID client driver to drive keyboard and mouse connected to the board. As a
nice side-effect, the list of possible storage devices got extended with USB
mass storage too by adding the USB block client driver.


Missing libraries
=================

Finally, when building the necessary and optional packages for Sculpt OS, we
stumbled across several libraries that needed to be adapted to compile and
link for ARMv8 too. Mostly, the inclusion of some other compilation units and
headers was sufficient. The related libraries are: libssl, libcrypto, libpng,
and Mesa. With the latter two, it is now even possible to execute Qt5
components on the target hardware.

Apart from all the new driver components and extended libraries, the Sculpt
manager had to be slightly modified to execute on the i.MX 8M hardware. In its
original form it is inherently dependent on x86 drivers, as it for example
generates configurations for some of those drivers. For the time being, the
changes to the Sculpt manager are not yet part of the official release.
Nevertheless, you can produce a Sculpt OS image to be run on an i.MX 8M EVK
board by using the following
[https://github.com/skalk/genode/commits/sculpt_20.02_imx8q_evk - topic branch].

Alternatively, you can also have a look at Sculpt OS on ARMv8 hardware by
following the video recordings of the following talk at FOSDEM 2020.

:Live demonstration of Sculpt OS on i.MX 8M EVK at FOSDEM 2020:

  [https://fosdem.org/2020/schedule/event/uk_genode_armv8/]


Base framework and OS-level infrastructure
##########################################

New sandbox library based on the init component
===============================================

The init component is Genode's canonical mechanism for the composition of
components. This role was further amplified when init became
[https://genode.org/documentation/release-notes/17.02#Dynamically_reconfigurable_init_component - dynamically reconfigurable].
The latter change cleared the ground for system scenarios like Sculpt OS, the
on-target deployment of packages, and dynamic device discovery. One typical
pattern found in such scenarios is one dynamically configured instance of init
accompanied by a controlling component that is usually called "manager". The
manager would consume reports of the subsystem hosted within the dynamic init,
and adjust the init configuration according to a domain-specific policy. Such
a configuration change, in turn, may trigger new reports, which effectively
turns this setting into a feedback control loop.

Whereas this established pattern is suitable for many scenarios, it is not
always natural. In particular if the manager does not only need to
manage a subsystem but also wants to intercept a service used by the
subsystem, the roles are no longer clear-cut. A practical example is a
GUI application that employs the menu-view component for the GUI rendering
while processing keyboard events locally. This application would need to
intercept the menu-view's GUI session to obtain the stream of user input
events. For such an application, the most natural approach would be the
co-location of the init functionality with the application logic into a
single all-encompassing component.

To accommodate such scenarios where a domain-specific management component is
tightly coupled with a dynamic subsystem, we extracted the child-management
functionality from the init component into a new library called "sandbox". The
library API is located at
[https://github.com/genodelabs/genode/blob/master/repos/os/include/os/sandbox.h - os/include/os/sandbox.h].

In addition to the hosting of components, the sandbox API also allows for the
interaction with the sandboxed children by providing locally implemented
services. The latter mechanism is illustrated by a new test available at
_os/src/test/sandbox_.


POSIX compatibility improvements
================================

During the release cycle of Genode 20.02, we continued our mission to host
POSIX software effortlessly as Genode components. In particular, we followed
up the line of work pursued with the two previous releases
[https://genode.org/documentation/release-notes/19.08#Consolidation_of_the_C_runtime_and_Noux - 19.08] and
[https://genode.org/documentation/release-notes/19.11#C_runtime_with_improved_POSIX_compatibility - 19.11]
with respect to the traditional Unix mechanisms fork, execve, and pipes.
After covering several edge cases - cloexec, file-descriptor lifetimes,
line-buffer handling, vfork, just to name a few - as needed by programs like
make, bash, and tclsh, we eventually reached a state where the website
generator of [https://genodians.org] works without the need for the now
deprecated Noux runtime.

For years we have been running complex software stacks like the Qt-based web
browser on top of our C runtime but not without carefully placed tweaks and
occasional patches. With the current release, we address the area of
concurrency and introduce a thorough reimplementation of the synchronization
primitives namely POSIX mutexes and condition variables as well as semaphores.
We also reaped the fruit of our labor by replacing our custom Qt thread back
end by the standard POSIX-thread based implementation. Further, we reduced the
number of threads in Qt applications by moving the QPA event handling to the
component entrypoint and removing the timed-semaphore utility from LibC.

Beyond Qt, we also address synchronization issues revealed by running a
third-party port of [https://grpc.io/ - gRPC] in our network back ends and
amended thread-local errno in the C runtime. Finally, our POSIX thread
implementation supports cleanup handlers now.


Base-framework refinements
==========================

Replacing the 'Lock' type by new 'Mutex' and 'Blockade' types
-------------------------------------------------------------

Up to now, Genode's lock implementation supports mainly two flavours of usage.
On the one hand, it is used to protect critical sections where the lock is
initialized as unlocked. In the contention case, the lock holder is supposed
to release the critical section. On the other hand, the lock is used as
blockade to synchronize startup between various executions of threads. Here
the lock is initialized as locked during instantiation whereby the thread that
releases the lock is not necessarily the same thread as the creator of the
lock.

We decided to make the two usage patterns more obvious by introducing two
separate classes, called 'Mutex' and 'Blockade'. The reasons are twofold.
First, during code review, the usage pattern at hand becomes more obvious.
Second, by codifying the programmer's intent behind the use of a
synchronization primitive, Genode becomes able to perform additional checks,
and diagnose certain dead-lock situations and other usage errors on the spot.

The separation got introduced shortly before this release. Up to now, it is
only used in 'Genode::Thread', 'Genode::Heap', and 'Genode::Registry'. The
plan is to cultivate the usage across all Genode sources over the next
releases and to ultimately remove the 'Genode::Lock' from the public API.

The 'Mutex' class is more restrictive compared to the 'Lock' class.

* At initialization time, it is always unlocked.
* To enter and leave a critical section the methods 'acquire()' and
  'release()' are used.
* A 'Mutex::Guard' is provided, which will 'acquire()' a mutex at
  construction time and release it automatically at destruction time of
  the guard.
* No thread is permitted to lock twice. The code will generate a warning if
  a dead-lock is detected.
* Only the lock holder is permitted to release the mutex. The code will
  generate a warning and will not release the mutex if this rule is violated.

! Genode::Mutex mutex;
! mutex.acquire();
! mutex.release();
!
! {
!   Genode::Mutex::Guard guard(mutex) /* acquire() during construction */
! }                                   /* release() on guard object destruction */
!
! Genode::Mutex::Guard guard(mutex);
! mutex.acquire();                    /* <-- Will cause a warning about the dead-lock */

The 'Blockade' class is always initialized as locked and provides the methods
'block()' and 'wakeup()'. Beside the initialization aspect, the 'Blockade'
behaves up to now like the 'Genode::Lock' implementation.

! Genode::Blockade blockade;
!
! /* step */    /* thread A */        /* thread B */
! 0:            -start thread B-
! 1:            ...                     -startup-
! 2:            blockade.block();       ...
! 3:            -sleep-                 ...
! 4:            -sleep-                 blockade.wakeup();
! 5:            ...                     ...


Performance optimization of the XML parser
------------------------------------------

Genode's XML parser used to rely on C++ exceptions while parsing, which is an
almost historic artifact inherited from the initial implementation. The
performance penalties of exceptions in the rare use of XML was acceptable
back when we started. But modern Genode systems like Sculpt OS rely on the
dynamic processing of XML like a back bone. The overhead became particularly
apparent when executing [Sculpt OS on 64-bit ARM i.MX8 hardware]. Prompted by
this observation, we reworked the code such that exceptions are no longer
thrown in any hot code path. The public interface of 'Xml_node' remains
unchanged.


New polling variant for register framework
------------------------------------------

Genode's register framework has offered a 'wait_for' method for a long time.
This function sleeps for a certain amount of microseconds and checks if one or
more given conditions become true. The number of attempts to sleep and check
the conditions must also be specified. In case the conditions are not met
after these attempts, a polling timeout exception is thrown. The function
simply returns in case of success. With the current Genode release, we have
added a 'wait_for_any' method with almost the same semantics but instead of
waiting for all conditions to become true, it returns if any condition is
met, and thus, implements a logical OR.


Migration to modern block-device API
====================================

With release 19.02, Genode introduced two new APIs for block-session handling.
The client side of a block session now uses the job API in order to send block
requests to the server, which in turn receives those jobs as requests through
the Request API. These two APIs replace Genode's 'Block::Driver' and
'Block::Session_component' implementations that used the packet stream API
directly, which turned out to be error prone for block session implementations.
Instead, these new APIs wrap the packet stream handling in a controlled
manner while handling all corner cases and even the overcommit of packets.
With the current release, we have adapted Genode's AHCI driver and partition
manager to these new interfaces, with the plan to adjust all block session
clients/servers to the new APIs with Genode release 20.05.

During this line of work, the AHCI driver received a major cleanup. For
example, dynamic memory allocations were removed, the whole initialization
state machine has been removed, ATAPI support for Qemu has been re-enabled,
and Exynos5 AHCI support is gone - since the platform is outdated and not
supported by Genode any more.


Updated audio driver based on OpenBSD 6.6
=========================================

In this release, we updated the 3rd-party sources of the audio driver component
to OpenBSD 6.6 and adapted the emulation glue code. While doing so, we fixed
a bug regarding the 'delay()' implementation where the function expects
microseconds but was given milliseconds. This led to a increased start-up
time of the component. We also fixed the logging back end that accidentally
was rendered silent and brought in the 'printf' back end from DDE Linux to
be able to produce better formatted LOG messages in the future.

Until now the component only supported HDA and EAP (ES1370 PCI) devices. The
first is primarily intended to be used with real hardware whereas the latter
was used during the initial porting effort in Qemu. That being said, the EAP
driver apparently also works on hardware according to community feedback.

Since the HDA driver does not work when used in VirtualBox and users expressed
the desire to also use audio when running in a VM, we enabled another driver,
for which a device-model in VirtualBox exists: the AC97 ICH. As it turned out,
using this driver, we can produce audio, albeit the quality is far from
usable. Nevertheless, with the driver enabled, interested parties are free to
investigate the cause for the current issues.

All in all, this update is solely a catch up effort to stay more
up-to-date with the upstream changes and to pull in HDA quirks for more
recent systems. More interesting changes to the driver component, like
reworking the OpenBSD kernel emulation layer and bringing support for USB
audio devices, are scheduled for future releases.


Support for unlabeled LOG output
================================

In situations where a Genode system is remotely controlled and monitored,
it is useful to allow a special component to produce log output with no
Genode label applied. This way, such a component can produce log data in
a format that is immediately suitable for a controller. This feature can be
enabled for a component by rewriting the label of the component's LOG session
to "unlabeled".

! <route>
!   <service name="LOG"> <parent label="unlabeled"/> </service>
!   ...
! </route>


Libraries and applications
##########################

Custom virtual machine monitor on ARM
=====================================

The ARMv8-compliant virtual-machine monitor introduced in the previous release
19.11 now contains new device models to enable the interaction with a
virtual-machine via network and terminal services. The new virtual ethernet
card and console implementations are compliant to the virtualization standard
VIRTIO 1.1.

Currently, the VMM cannot be configured to contain specific devices. It is
hard-wired to provide exactly:

* One virtual ethernet card that connects to Genode's "Nic" service,
* A VIRTIO console that opens up a session to the "Terminal" service using the
  label "console", and
* The traditional PL011 serial device model, which connects to a
  "Terminal" service too but uses the label "earlycon"


Seoul VMM
=========

During the usage of Seoul on Sculpt, it became apparent that the Seoul VMM
caused a constant CPU load even when the guest VM was idling. After some
investigation it became clear that having a fixed rate to synchronize the
guest graphic memory with the Genode GUI service was the main reason for the
constant load. With this release, we added the feature to dynamically adjust
the GUI refresh rate depending on the rate of user interactivity.
Additionally, if all virtual CPUs go to idle state, the GUI refresh is stopped
completely. With these measures, the overall CPU load could be reduced
noticeably.


TCP terminal
============

The TCP terminal is a long-living component in the Genode OS framework since
release 11.11. It can be used, e.g., to connect to a headless Genode system
via telnet. Until now, it always listened to incoming network connections at
configured ports. The port had to be configured for each terminal session
client.

The TCP terminal got extended to either listen to incoming network
connections, or to directly connect to another network server, dependent on
the policy defined for the corresponding terminal client. The following
example configuration illustrates the differences:

! <config>
!   <policy label="client" ip="10.0.0.5" port="1234"/>
!   <policy label="another_client"       port="4567"/>
! </config>

If only a port is described in the policy, the TCP terminal will listen on
that port for incoming connections. If an IP address is provided additionally,
it connects to the IP address using the given port.


Virtual desktops
================

Genode's GUI stack enables a high degree of flexibility. Beside the fundamental
nitpicker component, responsible for basically multiplexing input events and
framebuffer content, there is the window-manager component, and example
implementations of a window-layouter, and decorator. The interplay of the
latter three allows a window management that scales from simple to rich and
sophisticated without lowering its security properties. For a brief description
of its architecture, please refer to the release notes of
[https://genode.org/documentation/release-notes/14.08 - 14.08].

In this architecture, the window layouter is responsible for the arrangement
of the different windows. It exports a data model of the window layout.
Although, the example implementation of the window layouter introduced in
14.08 was simple, it already contained a notion of having different virtual
screens and screen sections, beside the actual window placements. However,
until now there was no use-case of switching dynamically between different
virtual screens respectively window sets related to them.

While using more and more different graphical components within Sculpt, the
window layouter in its initial form hit a limit. Although it already allowed to
switch in-between different windows via configured key-combinations, it became
inconvenient when having more than a handful windows hiding each other.

Therefore, the window layouter now got extended to allow switching dynamically
in between several pre-defined virtual screens. For the time being, one has to
assign a new window to a screen in the rule-set of the window layouter
initially by hand. Defining the currently visible screen can either be done by
editing the rule-set, or by using pre-configured key-combinations.

The new default configuration of the window layouter as exported by its
corresponding depot package looks like the following:

! <config rules="rom">
!   <rules>
!     <screen name="screen_1"/>
!     <screen name="screen_2"/>
!     <screen name="screen_3"/>
!     <screen name="screen_4"/>
!     <screen name="screen_5"/>
!     <screen name="screen_6"/>
!     <screen name="screen_7"/>
!     <screen name="screen_8"/>
!     <screen name="screen_9"/>
!     <screen name="screen_0"/>
!     <assign label_prefix="" target="screen_1" xpos="any" ypos="any"/>
!   </rules>
!
!   <press key="KEY_SCREEN">
!     <press key="KEY_ENTER" action="toggle_fullscreen"/>
!     <press key="KEY_1"     action="screen" target="screen_1"/>
!     <press key="KEY_2"     action="screen" target="screen_2"/>
!     <press key="KEY_3"     action="screen" target="screen_3"/>
!     <press key="KEY_4"     action="screen" target="screen_4"/>
!     <press key="KEY_5"     action="screen" target="screen_5"/>
!     <press key="KEY_6"     action="screen" target="screen_6"/>
!     <press key="KEY_7"     action="screen" target="screen_7"/>
!     <press key="KEY_8"     action="screen" target="screen_8"/>
!     <press key="KEY_9"     action="screen" target="screen_9"/>
!     <press key="KEY_0"     action="screen" target="screen_0"/>
! ...

As can be seen, individual keys are assigned to switch to a specific virtual
screen. By default ten screens are defined that are accessible via the number
keys. The first screen definition in the rules configuration marks the
currently visible screen.


Menu-view widget renderer
=========================

The line of work described in Section
[Redesign of the administrative user interface of Sculpt OS] called for
the enhancement of Genode's GUI-rendering component. This component - named
menu view - was
[https://genode.org/documentation/release-notes/14.11#New_menu_view_application - originally introduced in Genode 14.11]
for the rendering of the relatively simple menus of an application launcher.
Its software design largely deviates from the beaten track of established
widget toolkits, which come in the form of client-side libraries. The
menu view is not a complete toolkit but solely a dialog renderer sandboxed
in a dedicated component. This design reinforces the strict separation of the
view from the application logic, fosters screen-resolution independence, and -
most importantly - keeps the complexity of pixel processing out of the
application program. Because of the latter, it lends itself to the
implementation of security-sensitive interactive applications.

It would certainly be misguiding to tout our menu-view as feature competitive
with existing toolkits. We certainly won't recommend using it over Qt in
general. But Sculpt's custom administrative user interface "Leitzentrale"
presented us with the perfect playground to explore and grow the potential of
our novel approach.

In contrast to the previous iteration of the Leitzentrale GUI, which relied on
a small Unix runtime and Vim for editing text files, the new version ought to
feature a simple text editor integrated in the GUI. A text editor requires
a much tighter interplay between the view and the actual program logic
compared to an application with just a bunch of buttons. Think about cursor
handling, scrolling text, displaying textual selections, or placing a text
cursor with the mouse. On the course of the work towards the text-area
component featured in the new Leitzentrale, the menu view received the
following improvements:

:Text-cursor support:

  The label widget gained the ability to display one or multiple text cursors,
  as illustrated by the following example:

  ! <label text="...">
  !   <cursor at="10"/>
  ! </label>

  For the display of multiple cursors, each cursor must feature a distinctive
  'name' attribute.

:Character position featured in the hover report:

  The hovering information provided by the menu view used to be at the
  granularity of widgets, which is insufficient for placing a text cursor with
  the mouse. Hence, the information of a hovered label additionally provides
  the character position within the label now.

:Unquoting label text attribute values:

  The text displayed in label widgets is provided by a 'text' attribute value,
  which raises the question of how to present '"' characters on the GUI. With
  the new version, the attribute value can contain XML-quoted characters,
  specifically "&quot;".

:Support for displaying text selections:

  Similarly to the way of how a <cursor> can be defined for a <label>
  widget, a selection can now be expressed as follows:

  ! <label ...>
  !   <selection at="2" length="12"/>
  ! </label>

:Support of multiple '<float>' widgets within a '<frame>':

  We refined the hover reporting of <float> widgets such that a float widget
  never responds to hovering unless a child is hovered. This way, it becomes
  possible to stack multiple float widgets within one frame and still reach
  all child widgets. This is useful for aligning multiple widgets within one
  screen area independently from each other. For example, for left-aligning,
  centering, and right-aligning the elements of a panel.

:Enforcing the minimum size of a label:

  The new '<label min_ex="..">' attribute can be used to enforce a minimum
  width in the unit of the size of the character 'x'. In the absence of a
  'text' attribute, the minimum height of a label is implicitly set to 0. The
  combination of both changes makes the label usable as a horizontal spacer.

:Basic support for styling labels:

  The new version allows for the customization of the text color and alpha
  value of the label widget by the means of a style-definition file. The
  mechanism is exemplified with the new "invisible" label style that sets the
  alpha value to zero.

With these few incremental changes in place, the menu-view widget renderer
becomes usable as the basis of the simple text editor used in Sculpt's new user
interface.


Self-hosting the tool chain on 64-bit ARM
=========================================

With our ongoing ARM 64-bit effort, we have successfully updated Genode's tool
chain with release
[https://genode.org/documentation/release-notes/19.05#Broadened_CPU_architecture_support_and_updated_tool_chain - 19.05].
With the current release, we have additionally managed to make Genode's tool
chain self hosting on ARM 64-bit, which means the tool chain can compile
source code on ARM 64-bit directly.


Platforms
#########

Execution on bare hardware (base-hw)
====================================

The generic code base of the base-hw kernel underwent several cosmetic changes
to reduce or eliminate the application of certain problematic constructs like
too much inheritance, pointers, and dynamic casts. Those changes were
motivated to ease the translation of several kernel parts to the Ada/SPARK
language in the context of the Spunky project. For more information regarding
this experiment to write a Genode kernel in Ada/SPARK, please have a look at
the recent [https://genodians.org/m-stein/index - genodians.org article series]
of Martin Stein or listen to his recent
[https://video.fosdem.org/2020/AW1.125/ada_spunky.mp4 - FOSDEM talk].

Moreover, the IPC path implementation got simplified to lower the overhead
costs introduced by the transfer of capabilities. Together with the mentioned
Spunky cleanup efforts, this change measurably improved IPC performance.

The base-hw kernel now exports time consumption of individual threads via
the trace service analogously to the implementation for NOVA. Thereby, it
becomes possible to use for instance the top component within the Sculpt OS
also on this kernel.

Until now, support for the Raspberry Pi 3 was limited to Qemu emulation only.
Thanks to a contribution of Tomasz Gajewski, it is now possible to execute
Genode on all four CPUs of the actual hardware concurrently.


Execution on Linux
==================

Traditionally, the Linux version of Genode serves us as very handy development
vehicle but it was never intended as an actual target platform. On Linux,
Genode is usually executed as a multi-process application on top of a regular
GNU/Linux desktop distribution by specifying 'KERNEL=linux' and 'BOARD=linux'
to the run tool.

However, thanks to the work of Johannes Kliemann, Genode has become able to
run on a bare-bone Linux kernel without any other user land.
We blatantly used to refer to this idea as the
[https://genode.org/about/challenges#Platforms - microkernelization of Linux].
Johannes picked up the idea, supplemented Genode's core with the services
needed for user-level device drivers (IRQ, IOMEM, IOPORT) and supplemented
the tooling for the integration of Genode scenarios into a bootable initrd
image. This target of execution can be addressed by specifying 'KERNEL=linux'
and 'BOARD=pc' to the run tool now. If specified, the run tool will produce a
bootable Linux system image for the given run script and run it in Qemu.

That said, as this line of work is still considered as an experimental
playground - not for productive use - the work flow is not entirely automated.
In particular, one needs to prepare a suitable
[https://github.com/jklmnn/linux/commits/genode - Linux kernel] manually.
If you are interested in the topic, please refer to the background information
given in the [https://github.com/genodelabs/genode/pull/2829 - issue tracker].

