

              ===============================================
              Release notes for the Genode OS Framework 15.08
              ===============================================

                               Genode Labs



The version 15.08 marks the beginning of Genode as day-to-day OS as one of the
project's core developers switched to using Genode/NOVA on his machine,
stressing the OS infrastructure we created over the course of the last seven
years. Thanks to components like VirtualBox, the Noux runtime for GNU software,
the Linux wireless stack and Rump-kernel-based file systems, the transition
went actually much smoother than expected. So other members of the team plan
to follow soon. Section [Genode as day-to-day operating system] gives an
overview of the taken approach. Genode's use as general-purpose OS provided
the incentive for most of the improvements featured by the current release,
starting with the addressing of the long-standing kernel-memory management
deficiencies of the NOVA kernel (Section [NOVA kernel-resource management]),
over enhancements of Genode's tracing and file-system facilities, to vast
improvements of the guest-host integration of VirtualBox when running on
Genode.

The release is accompanied with a second line of work led by our friends
at Codelabs: Enabling Genode to run on top of their Muen separation
kernel as described in Section [Genode on top of the Muen Separation Kernel].
Muen is a low-complexity kernel for the 64-bit x86 architecture that
statically partitions the machine into multiple domains. In contrast to
microkernels like the ones already supported by Genode, the assignment
of physical resources (such as memory, CPU time, and devices) happens at
system-integration time. Since an isolation kernel does not have to deal
with dynamic resource management at runtime, it is less complex than
a general-purpose microkernel. This makes it relatively easy to reason about
its strong isolation properties, which, in turn, makes it attractive for
high-assurance computing. With Genode being able to run within a Muen
domain, the rich component infrastructure of Genode can be combined with
the strong isolation guarantees of Muen.


Genode on top of the Muen Separation Kernel
###########################################

_This section was written by Adrian-Ken Rueegsegger and Reto Buerki who_
_conducted the described line of work independent from Genode Labs._

After completing our x86_64 port of the Genode base-hw kernel, which was
featured in the
[https://genode.org/documentation/release-notes/15.05#Principal_support_for_the_64-bit_x86_architecture - previous release (15.05)],
we immediately started working on our main goal: running a Genode system as
guest on the Muen Separation Kernel (SK). This would enable the Muen platform
to benefit from the rich ecosystem of Genode.

For those who have not read the 15.05 Genode release notes, [https://muen.sk - Muen]
is an Open-Source microkernel, which uses the [https://spark-2014.org/ - SPARK]
programming language to enable light-weight formal methods for high assurance.
The 64-bit x86 kernel, currently consisting of a little over 5'000 LOC, makes
extensive use of the latest Intel virtualization features and has been formally
proven to contain no runtime errors at the source-code level.

The new 'hw_x86_64_muen' platform, as the name implies, extends the 'hw_x86_64'
base-hw kernel by replacing the PIC and timer drivers with paravirtualized
variants.

In contrast to other kernels supported by Genode, the architecture with Muen is
different in the sense that the entire 'hw_x86_64_muen' Genode system runs as
guest VM in VMX non-root mode on the SK. From the perspective of Muen, Genode
is executed on top of the kernel like any other guest OS without special
privileges.

[image muen_system_overview]
  Genode running on top of the Muen Separation Kernel alongside other subjects

This loose coupling of Muen and Genode base-hw enables the robust combination
of a static, low-complexity SK with a feature-rich and extensive OS framework.
The result is a flexible platform for the construction of component-based
high-assurance systems.

People interested in giving the 'hw_x86_64_muen' platform a spin can find a
small tutorial at _repos/base-hw/doc/x86_64_muen.txt_.


NOVA kernel-resource management
###############################

For several years, the NOVA kernel has served as Genode's primary base
platform on x86. The main reasons for this choice are: the kernel provides -
among the supported x86 kernels - the richest feature set like the support of
IOMMUs, virtualization, and SMP. It also offers a clean design and a stable
kernel interface. The available kernel-interface specification and the
readable and modern source base are a pleasure to work with. Hence, Genode
Labs is able to fully commit to the maintenance and further evolution of this
kernel.

Nevertheless, since the beginning, the vanilla kernel lacks one essential
feature to reliably host Genode as user-land, namely the proper management of
the memory used by the kernel itself (in short kernel-memory management). In
the past, we already extended the kernel to free up kernel resources when
destroying kernel objects, e.g., protection domains and page-tables, threads,
semaphores, and portals. Still, on Genode/NOVA, a component may trigger
arbitrary kernel-memory consumption during RPC by delegating memory,
capabilities, or by creating other components via Genode's core component. If
the kernel memory gets depleted, the kernel panics with an "Out of memory"
message and the entire Genode scenario stops.

In principal, the consumption of kernel memory can be deliberately provoked by
a misbehaving (greedy) component. But also during the regular day-to-day usage
of Genode, can such a situation occur when the system is used in a highly
dynamic fashion. For example, compiling and linking source code within the
noux environment constantly creates and destroys protection domains, threads,
and memory mappings. Our nightly test of compiling Genode within noux triggers
this condition every once in a while.

The main issue here is that the consumption of kernel memory is not accounted
by Genode. The kernel interface does not support such a feature. Kernels like
seL4 as well as Genode's custom base-hw kernel show how this problem can be
solved.

To improve the current situation - where the overall kernel memory is a fixed
amount - we extended NOVA in the following ways: First, the NOVA kernel
accounts any kernel memory consumption per protection domain. Second, each
process has a limited amount of kernel-memory quota it can use. Last, the
kernel detects when the quota limit of a protection domain is reached.

If the third condition occurs, the kernel stops the offending thread and
(optionally) notifies a handler thread. This so called out-of-memory (OOM)
handler thread receives information about the current situation and may
respond to it in the following ways:

* Stop the thread of the depleted protection domain, or
* Transfer kernel-memory quota between protection domains (upgrading the limit
  if desired), or
* Free up kernel memory if possible, e.g., revoke memory delegations, which
  can be re-created.

We implemented the steps above inside the NOVA kernel and extended Genode's
core component to handle such OOM situations. All system calls beside the IPC
call/reply may now return an error code upon depletion of the quota. Most of
these system calls can solely be performed by core and are handled inside
core's NOVA-specific platform code.

In the case of IPC call/reply operations, we desired to handle OOM cases
transparently to Genode user-level components. Therefore, each thread in
Genode/NOVA now gets constructed with an OOM IPC portal attached. This portal
is served by the pager thread in core and is traversed on OOM occurrences
during IPC operations. If a pager thread receives such an OOM IPC, it decodes
the involved IPC sender and IPC receiver and locates the appropriate
core-internal paging objects. The currently implemented out-of-memory policy
tries to upgrade the quota. If this is not possible, an attempt to revoke
memory mappings from the OOM-causing protection domain is made. This
implicitly frees-up some kernel memory (e.g., mapping nodes). If none of the
responses suffices, the handler stops the OOM-causing thread and writes a
message to the system log.

The current policy implementation constitutes a rather rough heuristic, which
may not suffice under all circumstances. In the future, we would like to
specify a distinct policy per component, e.g. depending on prior known memory
usage patterns. For example, some components follow well-known usage patterns
and therefore a fixed upper quota limit can be specified. Other components are
highly dynamic and desire quota upgrades on demand. There are many more
combinations imaginable.

Our current plan is to collect more experience over the next months with this
new kernel mechanism. Based on our observations, we may externalize such
policy decisions and possibly make them configurable per component.

The current implementation however, already avoids the situation that the
kernel goes out of service if a single component misbehaves
kernel-memory-wise.


Genode as day-to-day operating system
#####################################

At the beginning of June, Genode reached the probably most symbolic milestone
in the project's history: Norman - one of the core developers - replaced his
Linux-based working environment with a Genode-based system. This system is
composed of the following ingredients:

[image turmvilla_scenario]

The machine used is a Lenovo Thinkpad X201. We settled on this five-year-old
machine for several reasons. First, it is a very solid platform with a nice
form factor. Second, it features Intel's AMT (Active Management Technology),
which is handy to obtain low-level system logs in the case something goes
wrong. Third, refurbished machines of this type can be obtained for as little
as 200 EUR. Finally, an older machine reinforces the need for good performance
of the operating system. So it creates a natural incentive for Norman to find
and address performance bottlenecks.

Our modified version of the NOVA microhypervisor is the used kernel.

The user interface is based on our custom GUI stack including the nitpicker
GUI server as well as the window manager and its companion components
(decorator, layouter, pointer) we introduced in
[https://genode.org/documentation/release-notes/14.08#New_GUI_architecture - version 14.08].
The display is driven by the VESA driver. User input is handled by the PS/2
driver for handling the laptop keyboard and trackpoint, and the USB driver for
handling an externally connected keyboard and mouse.

Network connectivity is provided by our port of the Intel Wireless stack that
we introduced with the version
[https://genode.org/documentation/release-notes/14.11#Intel_wireless_stack - 14.11].

Our custom AHCI driver provides access to the physical hard disk. File-system
access is provided by our
[https://genode.org/documentation/release-notes/14.02#NetBSD_file_systems_using_rump_kernels - Rump-kernel-based file-system server].

A simple Genode shell called CLI monitor allows the user to start and kill
subsystems dynamically. Initially, the two most important subsystems are
VirtualBox and Noux.

VirtualBox executes a GNU/Linux-based guest OS that we refer to as "rich OS".
The rich OS serves as a migration path from GNU/Linux to Genode. It is used
for all tasks that cannot be accomplished directly on Genode yet. At the
beginning of the transition, the daily routine still very much depends on the
rich OS. By moving more and more functionality over to the Genode world, we
will eventually be able to make the rich OS obsolete step by step. Thanks to
VirtualBox' excellent host-guest-integration features, the VirtualBox window
can be dynamically resized and the guest mouse cursor integrates seamlessly
with Genode's pointer. VirtualBox is directly connected to the wireless
network driver. So common applications like Firefox can be used.

The noux runtime allows us to use command-line-based GNU software directly on
Genode. Coreutils and Bash are used for managing files. Vim is used for
editing files. Unlike the rich OS, the noux environment has access to the
Genode partition of the hard disk. In particular, it can be used to update the
Genode system. It has access to a number of pseudo files that contain status
information of the underlying components, e.g., the list of wireless access
points. Furthermore, it has limited access to the configuration interfaces of
the base components. For example, it can point the wireless driver to the
access point to use, or change the configuration of the nitpicker GUI server
at runtime.

As a bridge between the rich OS and the Genode world, we combine VirtualBox'
shared-folder mechanism with Genode's VFS infrastructure. The shared folder is
represented by a dedicated instance of a RAM file system, which is mounted in
both the VFS of VirtualBox and the VFS of noux.

As evidenced by Norman's use since June, the described system setup is
sufficient to be productive. So other members of the Genode team plan to
follow in his footsteps soon. At the same time, the continued use of the
system from day to day revealed a number of shortcomings, performance
limitations, and rough edges, which we eventually eliminated. It goes without
saying that this is an ongoing effort. Eating our own dog food forces us to
address the right issues to make the daily life more comfortable.

Feature-wise the switch to Genode motivated three developments, namely the
enhancement of Genode's CLI monitor, the improvement of the window manager,
and the creation of a CPU-load monitoring tool.


Interactive management of subsystem configurations
==================================================

The original version of CLI monitor obtained the configuration data of its
subsystems at start time via the Genode::config mechanism. But for managing
complex scenarios, the config node becomes very complex. Hence, it is
preferable to have a distinct file for each subsystem configuration.

The new version of CLI monitor scans the directory '/subsystems' for files
ending with ".subsystem". Each file has the same syntax as the formerly used
subsystem nodes. This change has the welcome implication that subsystem
configurations can be changed during the runtime of the CLI monitor, e.g., by
using a concurrently running instance of noux with access to the _subsystems/_
directory. This procedure has become an essential part of the daily work flow
as it enables the interactive evolution of the Genode system.


Window-management improvements
==============================

To make the window manager more flexible while reducing its complexity at the
same time, we removed the formerly built-in policy hosting the decorator and
layout components as children of the window manager. Those components are no
longer child components but siblings. The relationship of the components is
now solely expressed by the configuration of their common parent, i.e., init.
This change clears the way to dynamically replace those components during
runtime (e.g., switching between different decorators).

To improve the usability of the windowed GUI, we enabled the layouter to
raise windows on click and to let the keyboard focus follow the pointer.
Furthermore, the window manager, the decorator, and the floating window
layouter became able to propagate the usage of an alpha channel from the
client application to the decorator. This way, the decorator can paint the
decoration elements behind the affected windows, which would otherwise be
skipped. Consequently, partially transparent windows can be properly displayed.


CPU-load monitoring
===================

During daily system use, we started to wish to know in detail where the CPU
cycles are spent. For example, the access of a file by the rich OS involves
several components, including the guest OS itself, VirtualBox, rump_fs (file
system), part_blk (partition access), ahci_drv (SATA device access), core, and
NOVA. Investigating performance issues requires a holistic view of all those
components. For this reason, we enhanced our existing tracing infrastructure
(Section [Enhanced tracing facilities]) to allow the creation of CPU-load
monitoring tools. The first tool in this category is the graphical CPU-load
monitor located at _gems/app/cpu_load_display/_, which displays a timeline of
the CPU load where each thread is depicted with a different color. Thanks to
this tool, we have become able to explore performance issues in an interactive
way. In particular, it helped us to identify and resolve a long-standing
inaccuracy problem in our low-level timer service.


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

Improved audio support
======================

In the previous release, we replaced our old audio driver with a new one that
provided the same audio-out session interface. Complementing the audio-out
session, we are now introducing a new audio-in session interface that can be
used to record audio frames. It is modeled after the audio-out interface in
the way how it handles the communication between the client and the server. It
uses shared memory in the form of the Audio_in::Stream to transport the frames
between the components. A server component captures frames and puts them into
a packet queue, which is embedded in the Audio_in::Stream. The server
allocates packets from this queue to store the recorded audio frames. If the
queue is already full, the server will override already allocated packets and
will notify the client by submitting an 'overrun' signal. The client has to
cope with this situation, e.g., by consuming packets more frequently. A client
can install a signal handler to respond to a progress signal, which is sent by
the server when a new Audio_in::Packet has been submitted to the packet queue.
For now, all audio-in server components only support one channel (left)
although the audio-in session interface principally supports multiple
channels.

The _dde_bsd_ audio_drv is the first and currently only audio driver component
that was extended to provide the audio-in session. To express this fact, the
driver was renamed from _audio_out_drv_ to _audio_drv_. In contrast to its
playback functionality, which is enabled by default, recording has to be
enabled explicitly by setting the configuration attribute 'recording' to
'yes'. If the need arises, playback may be disabled by setting 'playback' to
'no'. In addition, it is now possible to configure the driver by adjusting the
mixer in the driver's configuration node. For the time being, the interface as
employed by the original OpenBSD mixer utility is used.

The following snippet shows how to enable and configure recording on a
Thinkpad X220 where the headset instead of the internal microphone is used as
source:

! <start name="audio_drv">
!   <resource name="RAM" quantum="8M"/>
!   <provides>
!     <service name="Audio_out"/>
!     <service name="Audio_in"/>
!   </provides>
!   <config recording="yes">
!     <mixer field="outputs.master" value="255"/>
!     <mixer field="record.adc-0:1_source" value="sel2"/>
!     <mixer field="record.adc-0:1" value="255"/>
!   </config>
! </start>

In addition to selecting the recording source, the playback as well as the
recording volume are raised to the maximum. Information about all available
mixers and settings in general may be obtained by specifying the 'verbose'
attribute in the config node.

The enriched driver is accompanied by a simple monitor application, which
directly plays back all recorded audio frames and shows how to use the
audio-in session. It can be tested by executing the
_repos/dde_bsd/run/audio_in.run_ run script.

There are also changes to the audio-out session itself. The length of a period
was reduced from 2048 to 512 samples to accommodate for a lower latency when
mixing audio-out packets. A method for invalidating all packets in the queue
was also added.


File-system infrastructure
==========================

Unlike traditional operating systems that rely on a global name space for
files, each Genode component has a distinct view on files. Many low-level
components do not even have the notion of files. Whereas traditional operating
systems rely on a virtual file system (VFS) implemented in the OS kernel,
Genode's VFS has the form of a library that can optionally be linked to a
component. The implementation of this library originated from the noux runtime
introduced in version
[https://genode.org/documentation/release-notes/11.02#Noux_-_an_execution_environment_for_the_GNU_userland - 11.02],
and was later integrated into our C runtime in version
[https://genode.org/documentation/release-notes/14.05#Per-process_virtual_file_systems - 14.05].
With the current release, we take the VFS a step further by making it
available to components without a C runtime. Thereby, low-complexity
security-sensitive components such as CLI monitor become able to benefit from
the powerful VFS infrastructure.

The VFS itself received a welcome improvement in the form of private RAM file
systems. A need for process-local storage motivated a conversion of the
existing ram_fs server component to an embeddable VFS file system. This
addition to the set of VFS plugins enables components to use temporary file
systems without relying on the resources of an external component.


Unified networking components
=============================

Having had a good experience with our Block::Driver implementation, which
wraps the block-session interface and takes care of the packet-stream
handling, thus easing the implementation of driver and other block components,
we observed that this approach did not provide enough flexibility for
NIC-session servers. For example, NIC servers are bi-directional and when a
network packet arrives the server has to make sure that there are enough
resources available to dispatch the network packet to the client. This has to
be done because the server must never block, e.g., by waiting for allocations
to succeed or for an empty spot in the packet queue of a client. Therefore,
such a non-blocking NIC server needs to validate all preconditions for
dispatching the packet in advance and, if they cannot be met, drop the network
packet.

In order to implement this kind of behavior, NIC-session servers must have
direct access to the actual NIC session. For this reason, we removed the
Nic::Driver interface from Genode and added a Nic::Session_component that
offers common basic packet-stream-signal dispatch functionality. Servers may
now inherit from this component and implement their own policy.

We adjusted all servers that implement NIC sessions to the new interface
(dde_ipxe, wifi, usb, nic_bridge, OpenVPN, ...), and thereby unified all
networking components within Genode.


Enhanced tracing facilities
===========================

Recent Genode-based system scenarios like the one described in Section
[Genode as day-to-day operating system] consist of dozens of components that
interact with each other. For reasoning about the behaviour of such scenarios
and identifying effective optimization vectors, tools for gathering a holistic
view of the system are highly desired.

With the introduction of our light-weight
[https://genode.org/documentation/release-notes/13.08#Light-weight_event_tracing - event-tracing facility]
in version 13.08, we laid the foundation for such tools. The current release
extends core's TRACE service with the ability to obtain statistics about CPU
utilization. More specifically, it enables clients of core's TRACE service to
obtain the execution times of trace subjects (i.e., threads). The execution
time is delivered as part of the 'Subject_info' structure. In addition to the
execution time, the structure delivers the information about the affinity of
the subject with a physical CPU.

At the current stage, the feature is available solely on NOVA since this is
our kernel of choice for using Genode as our day-to-day OS. On all other base
platforms, the returned execution times are 0. To give a complete picture of
the system's threads, the kernel's idle threads (one per CPU) are featured as
trace subjects as well. Of course, idle threads cannot be traced but their
corresponding trace subjects allow TRACE clients to obtain the idle time of
each CPU.

By obtaining the trace-subject information in periodic intervals, a TRACE
client is able to gather statistics about the CPU utilization attributed to
the individual threads present (or no longer present) in the system. One
instance of such a tool is the new trace-subject reporter located at
_os/src/app/trace_subject_reporter_. It acts as a TRACE client, which delivers
the gathered trace-subject information in the form of XML-formatted data to a
report session. This information, in turn, can be consumed by a separate
component that analyses the data. In contrast to the low-complexity
trace-subject reporter, which requires access to the privileged TRACE services
of core, the (potentially complex) analysing component does not require access
to core's TRACE service. So it isn't as critical as the trace-subject monitor.
The first representative of a consumer of trace-subject reports is the
CPU-load display mentioned in Section [CPU-load monitoring] and depicted in
Figure [nano3d].

In addition to the CPU-monitoring additions, the tracing facilities received
minor refinements. Up to now, it was not possible to trace threads that use a
CPU session other than the component's initial one. A specific example is
VirtualBox, which employs several CPU sessions, one for each priority. This
problem has been solved by associating the event logger of each thread with
its actual CPU session. Consequently, the tracing mechanism has become able to
trace VirtualBox, which is pivotal for our further optimizations.


Low-complexity software rendering functions
===========================================

Our ambition to use Genode as our day-to-day OS raises the need for custom
graphical applications. Granted, it is principally possible to base such
applications on Qt5, which is readily available to native Genode components.
However, for certain applications like status displays, we prefer to avoid the
dependency on an overly complex GUI tool kit. To accommodate such
applications, Genode hosts a small collection of low-complexity graphics
functions called painters. All of Genode's low-complexity graphical components
such as nitpicker, launchpad, window decorator, or the terminal are based on
this infrastructure.

With the current release, we extend the collection with two new painters
located at _gems/include/polygon_gfx_. Both draw convex polygons with an
arbitrary number of points. The shaded-polygon painter interpolates the color
and alpha values whereas the textured-polygon painter applies a texture to the
polygon. The painters are accompanied by simplistic 3D routines located at
_gems/include/nano3d/_ and a corresponding example (_gems/run/nano3d.run_).

[image nano3d]

With the nano3d demo and our new CPU load display, the screenshot above shows
two applications that make use of the new graphics operations.


Device drivers
##############

Completing the transition to the new platform driver
====================================================

Until now, the platform driver on x86-based machines was formed by the ACPI
and PCI drivers. The ACPI driver originally executed the PCI driver as a slave
(child) service. The ACPI driver parsed the ACPI tables and provided the
relevant information as configuration during the PCI-driver startup. We
changed this close coupling to the more modern and commonly used
[https://genode.org/documentation/release-notes/14.02#New_session_interface_for_status_reporting - report_rom mechanism].

When the new ACPI driver finishes the ACPI table parsing, it provides the
information via a report to any interested and registered components. The
report contains among other the IRQ re-routing information. The PCI driver is
a component, which - according to its session routing configuration - plays
the role of a consumer of the ACPI report.

With this change of interaction of ACPI and PCI driver, the policy for devices
must be configured solely at the PCI driver and not at the ACPI driver. The
syntax, however, stayed the same as introduced with release 15.05.

Finally, the PCI driver 'pci_drv' got renamed to 'platform_drv' as already
used on most ARM platforms. All files and session interfaces containing
PCI/pci in the names were renamed to Platform/platform. The x86 platform
interfaces moved to _repos/os/include/platform/x86/_ and the implementation of
the platform driver to _repos/os/src/drivers/platform/x86/_.

An example x86 platform configuration snippet looks like this:

!<start name="acpi_drv" >
! <resource .../>
! <route>
!  ...
!  <service name="Report"> <child name="acpi_report_rom"/> </service>
! </route>
!</start>
!
!<start name="acpi_report_rom" >
! <binary name="report_rom"/>
! <resource .../>
! <provides> <service name="ROM" /> <service name="Report" /> </provides>
! <config>
!  <rom> <policy label="platform_drv -> acpi" report="acpi_drv -> acpi"/> </rom>
! </config>
! <route> ... </route>
!</start>
!
!<start name="platform_drv" >
! <resource name="RAM" quantum="3M" constrain_phys="yes"/>
! <provides> <service name="Platform"/> </provides>
! <route>
!  <service name="ROM">
!   <if-arg key="label" value="acpi"/> <child name="acpi_report_rom"/>
!  </service>
!  ...
! </route>
! <config>
!  <policy label="ps2_drv"> <device name="PS2"/> </policy>
!  <policy label="nic_drv"> <pci class="ETHERNET"/> </policy>
!  <policy label="fb_drv"> <pci class="VGA"/> </policy>
!  <policy label="wifi_drv"> <pci class="WIFI"/> </policy>
!  <policy label="usb_drv"> <pci class="USB"/> </policy>
!  <policy label="ahci_drv"> <pci class="AHCI"/> </policy>
!  <policy label="audio_drv"> <pci class="AUDIO"/> <pci class="HDAUDIO"/> </policy>
! </config>
!</start>

In order to unify and simplify the writing of run scripts, we added the
commonly used platform configuration to the file
_repos/base/run/platform_drv.inc_. This file may be included by any test run
script in order to setup a default platform driver configuration.

In addition, the snippet provides the following functions:
'append_platform_drv_build_components', 'append_platform_drv_config' and
'append_platform_drv_boot_modules'. The functions add necessary information to
the 'build_components', 'config' and 'boot_modules' run variables. The
_platform_drv.inc_ also contains the distinction between various ARM/x86
platforms and includes the necessary pieces. Hence, run scripts are largely
relieved from platform-specific peculiarities.

The body of an example run script looks like this:

! set build_components { ... }
!
! source ${genode_dir}/repos/base/run/platform_drv.inc
! append_platform_drv_build_components
!
! build $build_components
!
! create_boot_directory
!
! set config { ... }
!
! append_platform_drv_config
!
! append config { ... }
!
! install_config $config
!
! append_platform_drv_boot_modules
!
! build_boot_image $boot_modules
!
! run_genode_until ...


BCM57cxx network cards
======================

During Hack'n Hike 2015, we had access to a server that featured a Broadcom
network card. Therefore Guido Witmond performed the first steps to enable
Broadcom's BCM 57cxx cards. With this preliminary work in place, we were
quickly able to perform the additional steps required to add BCM 57cxx support
to Genode.


VESA driver refinements
=======================

The VESA driver now reports the frame buffer's line width instead of the
visible width to the client. This fixes a possible distortion if these widths
differ, at the cost that content in the right-most area might be invisible in
such cases.


VirtualBox
##########

Policy-based mouse pointer
==========================

In the previous release, we implemented support for the transparent
integration of the guest mouse pointer with nitpicker via the VirtualBox guest
additions and the vbox_pointer component, which is capable of rendering
guest-provided mouse-pointer shapes. Now, we extended vbox_pointer by a
policy-based configuration that allows the selection of ROMs containing the
actual mouse shape based on the nitpicker session label or domain. With this
feature in place, it is possible to integrate several VirtualBox instances as
well as dedicated pointer shapes for specific components. To see the improved
vbox_pointer in action give _run/vbox_pointer_ a shot.


Dynamic adaptation to screen size changes
=========================================

VirtualBox now notifies the guest operating system about screen-size changes
(for example if the user resizes a window, which shows the guest frame
buffer). The VirtualBox guest additions can use this information to adapt the
guest frame buffer to the new size.


SMP support
===========

Guest operating systems can now use multiple virtual CPUs, which are mapped to
multiple host CPUs. The number of virtual CPUs can be configured in the
'.vbox' file.


Preliminary audio support
=========================

At some point, the use of VirtualBox as a stop-gap solution for using Genode
as everyday OS raises the need to handle audio. With this release, we address
this matter by enabling preliminary audio support in our VirtualBox port. A
back end that uses the audio-out and audio-in sessions to playback and record
sound samples has been added. It disguises itself as the OSS back end that is
already used by vanilla VirtualBox. Since Genode pretends to be FreeBSD in the
eyes of VirtualBox (because Genode's libc is based on FreeBSD's libc), the
provisioning of an implementation of the OSS back end as used on FreeBSD host
systems is the most natural approach. The audio support is complemented by
adding the necessary device models for the virtual HDA as well as the AC97
devices to our VirtualBox port.

For now, it is vital to have the guest OS configure the virtual device in a
way that considers the current implementation. For example, we cannot
guarantee distortion-free playback or recording if the guest OS uses a period
that is too short, typically 10ms or less. There are also remaining issues
with the mixing/filtering code in VirtualBox. Therefore, we bypass it to
achieve better audio quality. As a consequence, the device model of the VM has
to use the same sample rate as is used by the audio-out and audio-in sessions
(44.1kHz).

Enabling audio support is done be adding
! <AudioAdapter controller="HDA" driver="OSS" enabled="true"/>
to the .vbox file manually or configuring the VM accordingly by using the GUI.


Platforms
#########

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

Bender chain loader on base-hw x86_64
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

On Intel platforms, we use the Bender chain loader from the
[https://github.com/alex-ab/morbo - Morbo multiboot suite] to detect available
COM ports of PCI plug-in cards, the AMT SOL device, or as fall back the
default comport 1. The loader stores the I/O port information of the detected
cards into the BIOS data area (BDA), from where it is retrieved by core on
boot and subsequently used for logging. With this release, we added the BDA
parsing to base-hw on x86-64 and enabled the feature in the run tool. As a
prerequisite, we had to fix an issue in bender triggered by the loading of
only one (large) multi-boot kernel. Consequently, its binary in
_tool/boot/bender_ was updated.


Revised page-table handling
~~~~~~~~~~~~~~~~~~~~~~~~~~~

One of the main advantages of the base-hw platform is that the memory trading
concept of Genode is universally applied even with regard to kernel objects.
For instance, whenever a component wants to create a thread, it pays for the
thread's stack, UTCB, and for the corresponding kernel object. The same
applies to objects needed to manage the virtual address space of a component
with the single exception of page tables.

Normally, when the quota, which was donated by a component to a specific
service, runs out, the component receives an exception the next time it tries
to invoke the service. The component can respond by upgrading the respective
session quota. However, in the context of page-fault resolution, this is
particularly difficult to do. The allocation and thereby the shortage of
memory becomes evident only when the client produces a page fault. Therefore,
there is no way to inform the component to upgrade its session quota before
resolving the fault.

Instead of designing a sophisticated protocol between core and the other
components to solve this problem, we decided to simplify the current
page-fault resolution by using a static set of page-tables per component.
Formerly, page tables were dynamically allocated from core's memory allocator.
Now, an array of page tables gets allocated during construction of a
protection domain. When a component runs out of page tables, all of its
mappings get flushed, and the page tables are populated from scratch. This
change greatly simplifies the page-table handling inside of base-hw.


Dynamic interrupt mode setting on x86_64
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

On x86-based hardware, user-level device drivers have become able to specify
the trigger mode and polarity of the interrupts when requesting an IRQ
session. On ARM, those session parameters are ignored. This change enables the
x86_64 platform to support devices, which use arbitrary trigger modes and
polarity settings, e.g., AHCI on QEMU and real hardware.


Fiasco.OC
=========

Genode's device-driver support when using the Fiasco.OC kernel as base
platform received an upgrade.

First, principle support for the Raspberry Pi was added. To make this platform
useful in practice, a working USB driver is important. I.e., the network
interface is connected via USB. Hence the USB driver got enabled for
Fiasco.OC, too. As a result, Genode's software stack can now be used on the
Raspberry Pi by using either our custom base-hw kernel or Fiasco.OC.

Second, support for the Odroid-X2 platform using the Exynos4412 SoC was added,
which includes the drivers for clock management (CMU), power management
(PMU) as well as USB.

Thanks to Reinier Millo Sánchez and Alexy Gallardo Segura for having
contributed this line of work.


Removal of deprecated features
##############################

We dropped the support for the *ARM Versatile Express* board from the Genode
source tree to relieve our automated testing infrastructure from supporting a
platform that remained unused for more than two years.

The device driver environment kit (DDE Kit) was originally intended as a
common API among the execution environments of ported user-level device
drivers. However, over the course of the past years, we found that this
approach could not fulfill its promise while introducing a number of new
problems. We reported our experiences in the release notes of versions
[https://genode.org/documentation/release-notes/12.05#Re-approaching_the_Linux_device-driver_environment - 12.05] and
[https://genode.org/documentation/release-notes/14.11#Roundup - 14.11].
To be able to remove the DDE-Kit API, we reworked the USB driver, our port of
the Linux TCP/IP stack, and the wireless driver accordingly.

