

              ===============================================
              Release notes for the Genode OS Framework 14.11
              ===============================================

                               Genode Labs



With version 14.11 of the Genode OS framework, we are happy to close one of
the last functional gaps that prevented us from using Genode for our
day-to-day computing needs, namely wireless networking. With the availability
of the Intel wireless stack, Genode becomes suddenly useful on most modern
laptops. With the wireless stack being one of the most complex driver stacks
ported to the framework ever, the undertaking was extremely challenging.
Section [Intel wireless stack] tells the story of how we managed to transplant
the driver stack from Linux to Genode.

The second highlight of the release is the new implementation of a trading
scheme for CPU resources. When Genode was originally designed in 2006, we
envisioned to trade CPU resources between components similarly to how memory
is managed throughout Genode. However, the schedulers of the existing base
platforms did not allow us to realize this idea - until now. With the new
scheduler of our custom base-hw kernel that is described in Section
[Trading CPU time between components using the HW kernel], Genode becomes
finally able to not just assign priorities to subsystems, as already supported
on most kernels of the L4 family, but also to guarantee the provisioning of
processing time to subsystems. This way, we can achieve low interrupt
latencies for untrusted driver code like huge 3rd-party driver stacks, which
would normally require us to assign a high priority (with the risk of starving
other subsystems) to the component. It also allows Genode users to partition
the CPU time between different subsystems in a straight-forward way.

Further highlights of version 14.11 are a new dynamic linker with a code
complexity of less than 20% of the old one, VirtualBox version 4.3.16 with
support for regular vbox configuration files, networking for the Raspberry Pi,
and new GUI components.


Intel wireless stack
####################

Since the very beginning, it was our primary goal to develop the Genode OS
Framework as the basis for a usable general-purpose OS. To achieve this goal,
we have to overcome various obstacles, device-driver support for common
hardware being one of the most tricky jobs. Over the years, we accumulated
driver support for essential devices (PS/2, LAN adapters, USB, ATA/SATA). We
even dared to port the madwifi driver to provide proof-of-concept wireless
network support for Atheros chipsets. Alas, recent Intel-based notebooks come
with wireless chipsets from Intel like the IWL6xxx almost exclusively. Up to
now, Genode lacked support for these devices but since we had great success
with porting existing drivers from Linux in the past, we approached this issue
in classical fashion. We decided to port the _iwlwifi_ driver as well as its
wireless stack from Linux to Genode using the DDE-Linux approach. In addition,
we also ported the _WPA supplicant_ application to enable Wi-Fi Protected
Access (WPA).

In the following, we tell our war story of about six months of struggle,
setbacks, and adventures. We start with presenting our initially vague idea of
a Genode component that would enable us to access protected wireless networks.
The overview is followed by the description of the many steps that were needed
to turn our vague idea into a working component. Finally, we give a glimpse on
the future of the driver and provide quick instructions for using it.


Component overview
==================

[image wifi]

The first figure depicts the _wifi_drv_ component, which consists of four
parts. The first part is the iwlwifi driver, which manages the hardware by
communicating with the firmware that runs on the wireless card. Second, there
is the wireless stack _mac80211_, which performs all IEEE 802.11 related
networking operations including the translation of IEEE 802.11 radio frames to
ordinary 802.3 ethernet frames. Furthermore, there is the WPA supplicant,
which handles the authentication of a client at the access point. Last but not
least, the component has to interface with Genode clients. Therefore, the
wifi_drv implements the NIC session interface, which is used by the TCP/IP
stack to send and receive ethernet frames.

Since wireless networking itself is a comprehensive field, we decided early on
to reuse as much functionality as possible. The following sections will
describe the steps taken in more detail.


Driver
======

In the classical DDE-Linux manner, we started by porting the iwlwifi driver.
Porting a Linux driver is a laborious but essentially a straightforward task.
All needed source files must be added to the _dde_linux_ repository. These
files are normally selected by examining Linux's build configuration for the
driver in Makefile and Kconfig file types. The next step is to create a Linux
emulation environment for the driver. The central piece of this environment is
the _lx_emul.h_ header file. It combines all declarations and data structures,
which are scattered over many header files in the original Linux sources, into
a single file.

Several times during the creation of the emulation environment, a decision has
to be taken whether the original Linux header is used or the declaration is
added to the emulation header. Since we have ported Linux code to Genode
before, e.g., the USB stack and TCP/IP stack, we developed a sense for which
parts of Linux should be taken from the original header files and which parts
are better provided by the emulation header. We also learned by experience
that it is best to keep the number of used original header files as low as
possible. Otherwise future updates become complex and tiresome. The emulation
environment is completed iteratively by extending the header file after each
compile pass. In the end the linker sends his greetings with a long list of
undefined symbols. At this point, we just use a dummy implementation for each
undefined symbol like the following:

!typedef long DUMMY;
!#define DUMMY(retval, name) \
!        DUMMY name(void) { \
!        if (SHOW_DUMMY) \
!                PDBG( #name " called (from %p) not implemented",\
!                     __builtin_return_address(0)); \
!        return retval; \
!}
!
!DUMMY(0, kmalloc)

Most of the symbols the compiler complains about are not needed by our port
anyway. These are merely functions the vanilla Linux kernel uses for
accounting or rather internal book keeping of resources as well as checking
permissions, which are not needed inside our driver component. However, we can
use these dummies to trace the function calls when we execute the component.
Hence, the decision whether to implement or to ignore the function can be
postponed.

The fundamental functionality required by the iwlwifi driver boils down to the
usual PCIe resource allocation, IRQ handling, and DMA mapping as well as
regular memory allocation. On that account, it is worth mentioning that we use
the vanilla 'skbuff' implementation for network-packet buffer management from
Linux. Though we have previously implemented this functionality specifically
for our USB network driver, we saved us the trouble this time. An sk_buff is
allocated by the driver if it receives a packet and is passed to the wireless
stack. The stack, in return, submits sk_buffs to the driver to transmit
packets.

Nowadays, most work in the Linux kernel is done in workqueues in an
asynchronous way by using multiple kernel threads. By contrast, we try to
minimize the usage of threads in our driver ports to minimize the emulation
effort of the manifold synchronization primitives provided by the Linux kernel
API. In fact, we employ cooperative tasks to implement the concurrent
execution of code. Although this approach is more complex because preemption
points must be defined manually, it is worthwhile since debugging becomes much
easier with the absence of actual thread concurrency. In addition, we get away
with implementing certain synchronization primitives like mutexes or the whole
RCU handling in a much simpler way. As a prominent example of simplification,
atomic operations may be implemented as straight assignment statements.

In the original Linux implementation, loading the firmware of the wireless
card is an asynchronous operation to mitigate the effect of delays due to
file-system operations. On Genode, we access the firmware directly via a ROM
connection in the driver server with minimal side effects on other system
servers. Therefore, we execute the assigned callback function directly
accepting the possible delay at the ROM server.

The iwlwifi driver implements the network-device operations needed by the
wireless stack. After the driver loaded the firmware, it initializes the
device and registers itself at the wireless stack.

When using cooperative tasks, it is still important to provide the expected
behavior and semantics of the original execution environment. The iwlwifi
driver handles an IRQ by using the _threaded_irq_ mechanism. Meant as a
replacement for the 'tasklet' mechanism, the top-half is executed in the
interrupt context whereas the bottom-half is executed in a dedicated kernel
thread. For this purpose, our port adds an IRQ task that mimics these
semantics. Up to now, we did not add priorities to our cooperative tasks. In
the usb_drv component, all tasks have the same priority. Unfortunately, we did
not get away that easily in the wifi_drv component and had to employ a
scheduler with priorities.


Mac80211 stack
==============

With the iwlwifi driver experiencing its first successful compilation, it was
time to port the wireless stack of Linux to Genode. The stack consists of the
_mac80211_ layer that abstracts the device handling and takes charge of
converting the 802.11 frames to 802.3 frames. It also handles various
management tasks like beacon frames and rate control. The design of the stack
is highly asynchronous and event driven. In a nutshell, the stack adds
received requests to a workqueue for delayed processing and, hence, remains
recipient for further requests at all times. On request completion, the
originating component will get notified. Received packets in form of sk_buffs
are monitored by the wireless stack and passed to other subsystems by calling
'netif_receive_skb()'.

Most requests are issued by the _cfg80211_ layer, which manages requests from
userspace via a netlink-bus based interface called _nl80211_. For this reason,
we added support for AF_NETLINK by adding the corresponding source files to
the wifi_drv component. While doing so it became clear that we would need to
provide an interface for using netlink from the WPA supplicant. On that
account, we created the 'Socket_call' interface.


Configuration
=============

As mentioned before, the configuration of network devices on Linux is done by
using the Netlink API nowadays. In the context of wireless networking, it
replaces the old 'ioctl()' based _Wireless Extension_ interface with nl80211.
Nl80211 enables the user to configure all wireless related properties
including association with an access point (AP) and scanning for available
networks.

Support for using protected wireless networks on Linux is split between the
kernel and the user space. The so-called supplicant that handles
authentication against a given access point runs in user space whereas the
cryptographic operations on bulk traffic are executed in the kernel. On Linux,
the WPA supplicant is used for the user-space work.

The supplicant scans for available networks and tries to authenticate at a
known network retrieved from the configuration file. After a suitable network
was discovered, the supplicant tries to associate and authenticate at the
access point of the network. If this undertaking is successful, the actual
IEEE 802.1X authentication takes place. Up to this point, the whole
communication with the AP is done unencrypted. While performing the
authentication, the WPA supplicant needs access to the raw EAPoL ethernet
frames, which is provided by Linux via the AF_PACKET protocol. This protocol
is used by the WPA supplicant in its 'l2_packet' back end and, therefore, must
be provided by our driver, too. Since we already implemented the Socket_call
interface, enabling AF_PACKET was a straight-forward procedure. The driver
initializes the af_packet protocol family and switches incoming traffic to its
protocol hook in case of EAPoL frames. All other packets are passed to our NIC
session front end.

Since the WPA supplicant is normally executed in userspace using the _libnl_
library, it depends on a working libc. The Genode libc is a port of the
FreeBSD libc whereas the nl80211 back end of the WPA supplicant expects a
Linux-based user land, i.e., glibc. Therefore, we decided to split up the
supplicant into separate modules, one for the back end and one for the front
end. We created a port of libnl, which uses a specially tailored Linux user
emulation environment similar to the emulation of the kernel environment in
DDE Linux. The libnl emulation implements various socket related functions
like 'socket', 'bind', 'sendto', and 'recvfrom'. These socket functions are
mapped to the internal Socket_call interface, which talks to the kernel parts.
The nl80211 back end driver is linked against this static libnl library. The
WPA supplicant on the other hand is linked against Genode's regular libc. To
make sure that each part can only access the symbols that it is supposed to
see on linking, we use symbol maps like the following for
_wpa_driver_nl80211.lib.so_.

!{
!  global:
!    /* array containing all drivers, from drivers.c */
!    wpa_drivers;
!    /* ethernet frame handling, from l2_packet_linux.c */
!    l2_packet_*;
!    poll;
!  local:
!    *;
!};

The _wpa_drivers_ array is used by the WPA supplicant to access its internal
driver back end and functions. The 'l2_packet_*' functions are used by the
EAPoL authentication-handling code. The 'poll' function is required by the
supplicant's event handling and therefore mandatory. All file descriptors as
well as sockets opened by the back end are processed by the WPA supplicant.
All other symbols are kept local to prevent the runtime linker from running
into symbol clashes.


NIC session front end
=====================

The front end connects the wifi_drv component to Genode clients. When the
TCP/IP stack of an application wants to send an ethernet frame, it calls the
'Nic::Driver::tx()' method. The component takes the frame and puts it into a
freshly allocated sk_buff. After that, it calls the 'ndo_start_xmit()'
function. This function is part of the 'struct netdev_ops' and is implemented
by the wireless stack. On packet reception, the wireless stack will pass on
the 'sk_buff' by calling 'netif_receive_skb()'. The front end extracts all
data it needs from this 'sk_buff' and copies it into the packet stream.

During development of this complex interplay between the NIC session front end
and the driver, we also had to cope with Linux-internal semantics of the
interface. One prominent example is the handling of head room in the protocol
header data in the sk_buff. Shrinking or expanding the head room at the right
places is crucial. Otherwise, the driver will produce corrupt packets.


The final picture
=================

In summary, it can be stated that the 'wifi_drv' turned out to be more complex
than we anticipated after our first investigations. The final structure of our
port looks like follows.

[image wifi_complete]

The figure depicts our new component that uses three threads: The first thread
executes the WPA supplicant's code, another thread executes the whole Linux
kernel code, and the last thread acts as IRQ handler. The Linux thread
implements a cooperative task model for concurrent kernel tasks, namely the
'irq' task that runs on the highest priority, the 'timer' task, the 'work'
task, the 'socket_call' task, and the 'linux' task.


Roundup
=======

In its current state, the wifi_drv is tested with Intel wireless 6205 and 6300
cards and performs reasonable well for an unoptimized component. Other cards
might also work and could be enabled by editing
_src/lib/wifi/drivers/net/wireless/iwlwifi/pcie/drv.c_ in the
_dde_linux/contrib_ directory manually. The driver does not support changing
the network at the moment. This is merely a limitation of the current
NIC-session interface, though. The link state is not forwarded to the TCP/IP
stack, which therefore will not send a new DHCP request. But, transparent
changes among access points within the same LAN without network
reconfiguration are possible.

The current version of the wifi_drv is one of the most voluminous drivers
ported to date. All in all, it contains about 215,000 lines of 3rd-party code.
The code written to connect this code to Genode amounts to about 8,500 lines
of code while the 'lx_emul.h' header alone takes 3,245 lines. Porting the
whole stack raises the opportunity to enable other wireless drivers in the
future with minimal effort. Furthermore, it should be possible to enable more
userland tools that use the nl80211 interface, for example, a dedicated
wireless-network scanner or even hostapd.

Prior to the wifi_drv component, all ported drivers more or less used the
DDE-Kit library to perform low-level tasks, e.g., PCI, IRQ, and memory
handling. The original idea behind DDE Kit was to provide a C-based API to
ease the porting of drivers, which are mostly written in C whereas Genode is
written in C++. During porting the wireless stack, however, we disregarded DDE
Kit at all and implemented the needed functionality by using Genode primitives
directly. We realized that using a more generic interface like DDE Kit has no
advantages because we had to circumvent it more than once in the past. It
became more of a burden than a blessing. Also, we recognized that the idea of
creating a synergy among various projects utilizing DDE-Linux drivers by
providing a common DDE Kit interface did not came to fruition. So we see no
benefit in using DDE Kit in future driver ports in the future.

In the future, we plan to address the necessary optimization of the driver
component and also want to add a simpler front end to configure the WPA
supplicant. For now, we utilize the regular POSIX front end. Furthermore, the
user has to specify the network prior to starting the driver. A mechanism,
which uses a report session to notify the user about all available networks
and that is able to change the configuration of the WPA supplicant on the fly
is currently under progress.


Usage
=====

The following instructions may help you to get started because using the
driver is somewhat laborious at the moment. For building the driver, you have
to add _drivers/wifi_ and  _drivers/rtc_ to the build_components list in your
run script in addition to the normally required components.

For starting the driver, you may use the following configuration snippet as a
starting point:

!<start name="wifi_drv">
!  <resource name="RAM" quantum="32M"/>
!  <provides><service name="Nic"/></provides>
!  <config>
!    <libc stdout="/dev/log" stderr="/dev/log" rtc="/dev/rtc">
!      <vfs>
!        <inline name="wpa_supplicant.conf">
!network={
!  ssid="foobar"
!  key_mgmt=WPA-PSK
!  psk="foobarfoobar"
!}
!        </inline>
!        <dir name="dev"> <log/> <rtc/>
!           <jitterentropy name="random"/>
!           <jitterentropy name="urandom"/>
!        </dir>
!      </vfs>
!    </libc>
!  </config>
!  <route>
!    <service name="Rtc"> <any-child /> </service>
!    <any-service> <parent/> <any-child /> </any-service>
!  </route>
!</start

Since we are using 'wpa_supplicant' to handle all network management, we have
to configure it. As mentioned before, we use the common POSIX configuration
file format for this purpose, and therefore use the same configuration syntax
as on any other OS. By convention, our port of the WPA supplicant is looking
for the configuration in '/wpa_supplicant.conf'. It is provided by creating an
inline file in the VFS configuration section. We provide a _/dev_ directory
populated with all required virtual devices. These devices are needed by
various parts of the WPA supplicant.

To run the driver, we need to add the following binaries to the list of boot
modules:

!rtc_drv vfs_jitterentropy.lib.so
!libc.lib.so libcrypto.lib.so libssl.lib.so
!wifi.lib.so wpa_supplicant.lib.so wpa_driver_nl80211.lib.so
!wifi_drv

Furthermore all Intel wireless cards supported by the 'iwlwifi' driver need a
specific firmware to work. You can download the archives containing the
firmware from [https://wireless.kernel.org/en/users/Drivers/iwlwifi]. The
firmware image also has to be added to the boot module list. If the firmware
is missing, the driver will complain and print an error message:

!Could not open file "iwlwifi-6000-6.ucode"

A exemplary run script can be found in _repos/dde_linux/run/wifi.run_.


Trading CPU time between components using the HW kernel
#######################################################

Up to the last Genode release, CPU scheduling in the HW-kernel was a matter of
absolute priority bands, each doing a round-robin schedule over all tasks with
the respective priority. While being pretty fast and manageable, this scheme
also had its disadvantages: First, there was no way to prevent
high-prioritized tasks from starving less important ones. Second, CPU time
could not be granted to tasks and passed between them by the means of quota.
To cope with these problems without much loss of performance, we decided to
come up with a new scheduler whose design was developed with the new feature
set in mind right from the start.

The new scheduler introduces the distinction between high-throughput-oriented
scheduling contexts - which we shortly call "fills" - and low-latency-oriented
scheduling contexts - called "claims". Examples for a typical fill would be
the processing of a GCC job or the rendering computations of a sophisticated
graphics program. They shall obtain as much CPU time as the system can spare
but there is no demand for a high responsiveness. In contrast, a good example
for the claim category would be a typical GUI-software stack covering the
control flow from user-input drivers through a chain of GUI components to the
drivers of the graphical output. Another example is a user-level device driver
that has to quickly respond to sporadic interrupts but is otherwise untrusted.
The low latency of such components is a key factor for usability and quality
of service. Besides introducing the distinction between "claim" and "fill"
scheduling contexts, we introduced the notion of a so-called "super period",
i.e., in the current version it is one second. The entire super period
corresponds to 100% of the CPU time of one CPU. Portions of it can be assigned
to scheduling contexts. A CPU quota thereby corresponds to a percentage of the
super period.

At the beginning of a super period, each claim has its full amount of assigned
CPU quota. The priority defines the absolute scheduling order within the super
period among those claims that are active and have quota left. As long as
there exist such claims, the scheduler stays in the claim mode and the quota
of the scheduled claims decreases. At the end of a super period, the quota of
all claims gets refreshed to the initial value. Every time the scheduler can't
find an active claim with CPU-quota left, it switches to the fill mode. Fills
are scheduled in a simple round-robin fashion with identical time slices. The
proceeding of the super period doesn't affect the scheduling order and
time-slices of this mode. The concept of quota and priority that is
implemented through the claim mode aligns nicely with Genode's way of
hierarchical resource management: Through CPU-sessions, each process becomes
able to assign portions of its CPU time and subranges of its priority band to
its children without knowing the global means of CPU time or priority.

Whereas the management of priorities was already existent at the thread and
CPU-session API, the management of CPU quota is new to these components. While
extending Genode's resource trading to CPU time, we closely followed the
existing patterns of how RAM quota is managed among RAM sessions. In the init
configuration, one can configure the assignment of CPU time via "resource"
tags that have the attribute "name" set to "CPU" and the attribute "quantum"
set to the percentage of CPU quota that init shall assign. The pattern is the
same as when donating RAM quota.

! <start name="test">
!   <resource name="CPU" quantum="75"/>
! </start>

This example configuration would cause init to try donating 75% of its CPU
quota to the child "test". Be aware that init and core do not preserve CPU
quota for their own requirements by default as it is done with RAM quota.
Hence, the configuration should consider such preservations if required. If no
preservation is configured, init and core depend on someone not using its
quota to the full extend or someone donating its quota temporarily on, e.g.,
IPC to a core service.

! <start name="init2">
!   <resource name="CPU" quantum="50"/>
!   ...
!   <config>
!     ...
!     <start name="test">
!       <resource name="CPU" quantum="50"/>
!     </start>
!   </config>
! <start>

This example configuration would result in process "init2" receiving 50% of
the CPU quota and process "test" receiving 50% of the CPU quota of "init2". So
both processes have 25% of the overall CPU time at disposal.

Once a process owns CPU quota, the process can apply it at the construction of
local threads. For this purpose, the thread constructor has been enhanced by
an argument that indicates the percentage of the program's CPU quota that
shall be assigned. So 'Thread(33, "test")' would cause the backing CPU session
to try granting 33% of the component's CPU quota to the new thread "test".
Note that the CPU quota of a thread can't be altered after construction for
now. A new thread participates in CPU scheduling with a context for only the
fill mode if the CPU quota is specified with 0 or not at all to the thread
constructor. That doesn't mean that such threads are never scheduled. But they
have no guarantee to receive CPU time during a super period and their priority
is ignored at all. If a thread gets constructed with a quota greater than 0,
it participates in CPU scheduling with a context for both claim and fill mode.
The claim context then uses the specified quota and priority as mentioned
earlier.


Base framework
##############

New dynamic linker
==================

In 2010, we added dynamic linking support to Genode. This enabled Genode to
load and share libraries among programs at runtime. Since, at the time, we did
not have a whole lot of experience with dynamic linking and dynamic ELF
loading, we decided to port FreeBSD's linker (rtld) to Genode. Up to this
point, the old linker has served its purpose well on all supported kernels and
hardware architectures.

Nevertheless, we were a little worried because it was hard to understand the
linker's internals and we did not want to trust a vital piece of code that we
could not comprehend in full. Also, the old linker heavily depended on libc
and C-style POSIX semantics, which we had to emulate in order to get the
program working.

As one of Genode's midterm goals is making most Genode applications binary
compatible for microkernels that support the same hardware architecture and
for the reasons above, we decided to implement a Genode specific linker. Our
future goal is to keep all kernel-dependent code within the linker (making it
kernel dependent) and to link Genode applications against this new version of
the linker (thus, making them kernel independent).

Genode's new dynamic linker can be found in _repos/base/src/lib/ldso_. It is a
drop-in replacement for the old linker, which has been removed from Genode's
source tree. The linker provides all the functionality the FreeBSD version
did: Loading and construction of shared libraries, a shared-object interface
(_repos/base/include/base/shared_object.h_) that is comparable to the DL
interface (dlopen, dlsym and friends), link map, and GDB debugging support.
The linker is entirely written in C++ and with a code size of about 1800 lines
significantly smaller then the old version with about 8000 code lines
including the emulation layer.


Low-level OS infrastructure
###########################

Graphics helpers for operating on alpha channels
================================================

For realizing graphical applications that are security critical, we wish to
avoid the complexity of sophisticated tool kits like Qt5. To ease the
development of such Genode-specific graphical applications, we introduced a
few common low-level interfaces and utilities for graphics in
[https://genode.org/documentation/release-notes/14.02#Unified_interfaces_for_graphics - version 14.02].

The current version refines those utilities with added support for layering
graphics using alpha channels. There is a new ALPHA8 pixel format that can be
used to apply graphics operations on alpha-channels. Furthermore, the new
'Texture_rgb565' and 'Texture_rgb888' types provide pixel conversion functions
for those common texture formats. This way, ordered dithering is automatically
applied when importing pixel data to a RGB565 texture.


Nitpicker GUI server
====================

The fundamental premise of the Nitpicker GUI server is to isolate GUI clients
from each other. However, there are situations where the user wants to issue
operations spanning multiple clients, for example hiding all views of a
subsystem regardless of how many clients are running within the subsystem.

Such operations should be applied to the global view stack to maintain the
global view stacking order when hiding and subsequently un-hiding subsystems.
To realize this functionality, nitpicker's session interface has been enhanced
by a new 'session_control' function. The function takes a session label and an
operation as arguments, and performs a control operation on one or multiple
sessions. The label is used to select the sessions, on which the operation is
applied. Internally, nitpicker creates a selector string by concatenating
the caller's session label with the supplied label argument. A session is
selected for the operation if its label starts with the selector string.
Thereby, the operation is limited to the caller session or any child session
of the caller. The supported control operations are the hiding of sessions,
the un-hiding of sessions, and the move of session views to the front of the
view stack while maintaining their partial order.

To enable the user to unambiguously identify the applications on screen,
nitpicker provides an X-ray mode that can be activated by the user at any
time. To enable a trusted application such as a panel to respond to the
activation of the X-ray mode, nitpicker has gained an option to report the
currently active mode to a report session. Furthermore, the user-input
handling was slightly refined to accommodate such trusted applications. While
X-ray mode is active, nitpicker filters motion events that are not referring
to the currently focused domain. However, domains configured as xray="no"
(such as a panel) need to obtain motion events regardless of the xray mode. So
we relaxed the motion-event filtering to accommodate such clients.


Nitpicker fader
===============

Some graphical applications should not be visible at all times but only when
needed, for example an on-screen display that is visible only when the user
changes the volume. To realize such applications on top of nitpicker,
nitpicker could provide support for toggling the visibility of views. But
adding view fading to nitpicker would increase nitpicker's complexity just for
the sake of visual presentation. Also, the fading/unfading would be limited to
whatever support nitpicker would provide. Alternatively, the fading could be
implemented in the respective nitpicker client. But this way, each client that
could potentially be used in an on-demand way had to be enhanced with a fading
feature. For example, an on-demand visible terminal could be useful in some
scenarios. So the terminal had to be enhanced.

Being component-based, Genode provides another alternative: The introduction
of a separate component that wraps the nitpicker session interface. The new
nit_fader sits in-between nitpicker and a client, and applies alpha-blending
to the client's virtual framebuffer. It is entirely optional and requires no
changes in nitpicker or any client. Because it can be instantiated per client,
it does not compromise the security of nitpicker. Even though it can access
the pixel data and the user input designated for a particular client, it
cannot leak this information to other clients. Therefore, the implementation
complexity of this component is not critical for confidentiality.

[image nit_fader_screenshot]

The current version of nit_fader obtains the alpha-blending value from its
configuration. It is able to dynamically respond to configuration changes. If
the configured alpha value changes, it performs a smooth transition between
the old and the new alpha value.


Growing tool kit for low-complexity GUI applications
====================================================

With the current release, we continue our line of GUI-related work started in
[https://genode.org/documentation/release-notes/14.08#New_GUI_architecture - version 14.08].
As a side product of implementing low-complexity GUI components directly on
Genode instead of using existing GUI tool kits, a library of common utilities
is evolving. The utilities are not strictly GUI-related but also cover the
construction of multi-process applications.


:'gems/animator.h':

  A utility for the smooth interpolation between two integer values. As the
  interpolation is not linear, it is suitable for fading effects. It is used
  by the scout widgets, the window decorator, the new nit_fader, and the
  new menu view.

:'gems/chunky_texture.h':

  A texture with its backing store allocated from a RAM session.

:'gems/file.h':

  A simple utility for obtaining the content of a file as a buffer.

:'gems/local_reporter.h':

  A utility for creating reports to a local report session. It is useful for
  components that host a local report service, for example the window manager
  or the new launcher application.

:'gems/png_image.h':

  A utility that provides the pixel data of a PNG image as a texture. Its
  main purpose is hiding the peculiarities of libpng and the life-time
  management of the involved memory allocations behind a simple interface.

:'gems/report_rom_slave.h':

  A utility for instantiating a local report-rom service as a child process.
  It is used by the window manager and the new launcher application.

:'gems/single_session_service.h':

  A utility for providing a locally implemented session as a service to a
  child process. It is useful for virtualizing services when hosting other
  components as child processes.

:'gems/texture_utils.h':

  Utilities for scaling a texture and for converting textures between
  different pixel formats.

:'gems/wrapped_nitpicker_session.h':

  A default implementation of a wrapped nitpicker session that can be used to
  selectively override a few functions of nitpicker's session interface while
  delegating all other functions to the wrapped nitpicker session.

:'gems/xml_anchor.h':

  A utility for converting an "anchor" XML attribute to a convenient object.

:'cli_monitor/ram.h':

  A utility for managing RAM among a number of child processes.

:'cli_monitor/child.h':

  A utility for creating child processes while dynamically managing their
  RAM resources.

As a note of caution, the API of those utilities should not be expected to be
stable. It is likely to change during the further evolution of Genode's GUI
architecture.


New menu view application
=========================

The new menu view application generates a simple dialog of widgets and reports
the hovered element. It is meant to be embedded into applications that require
simple GUIs but don't want to deal with the complexities of a full-blown
widget set.

The menu view takes a description of the dialog in the form of a ROM session
with XML data, for example:

! <dialog>
!   <frame>
!     <vbox>
!       <button name="virtualbox">
!         <label text="VirtualBox"/>
!       </button>
!       <button name="toolchain" hovered="yes">
!         <label text="Tool chain"/>
!       </button>
!       <button name="log" hovered="yes" selected="yes">
!         <label text="Log window"/>
!       </button>
!       <button name="config" selected="yes">
!         <label text="Configuration"/>
!       </button>
!     </vbox>
!   </frame>
! </dialog>

Given such a description, it renders a pixel representation of the dialog and
provides the result to a nitpicker session. The application dynamically
responds to changes of the XML model and thereby applies state transitions of
dialog elements. It does not perform any application logic. Even the hovering
of dialog elements is out of the scope of the menu view. However, the menu
view receives user input for its nitpicker session. It evaluates the user
input to determine the currently hovered widget and reports this information
to a report session. This way, the parent process of a menu view can implement
arbitrary application logic of a GUI application without dealing with any
graphical operations.

In the current form, the menu view is limited to fulfill the requirements of
the new launcher application. Hence, it solely provides a frame, button, and
label widget as well as a vertical box-layout widget. For experimenting with
the new menu view, there exists a run script at _gems/run/menu_view.run_.


New launcher application
========================

The new launcher application located at _gems/src/app/launcher/_ is a poster
child of a multi-process GUI application on Genode. Similar to the existing
launchpad, it can be used to dynamically start and kill subsystems. But in
contrast to the launchpad, which contained a widget library, the new launcher
delegates the (potentially complex and bug-prone) graphics processing to a
sandboxed child process (the menu view). The launcher is able to toggle
visibility of the dialog using the new nit_fader component, which is
instantiated as a child process as well. Thanks to this multi-process
technique, the complexity of the actual launcher, which needs to be ultimately
trusted by all launched subsystems, remains low and thereby trustworthy.

In addition to being able to start and kill subsystems, the launcher uses
nitpicker's new session-control interface (see Section [Nitpicker GUI server])
for toggling the visibility of subsystems. The new launcher can be explored
with the run script _gems/run/launcher.run_.


New input merger
================

The new input merger component allows the aggregation of user-input events
from an arbitrary number of sources. The aggregated stream of events is
provided as a single input session. Thereby, it allows the merging of user
input of multiple device drivers such as USB HID and PS/2 into one stream to
be consumed by a single component such as the nitpicker GUI server.

The input merger is located at _os/src/server/input_merger/_. Please refer to
the accompanied README file for configuring the component.


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

Improved Qt5 integration
========================

Genode's Qt5 support received optimizations as well as the ability for Qt5
application to participate in the window-resizing protocol of the window
manager. So, Qt5 windows can be resized by dragging their respective window
borders.


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

VirtualBox
==========

Since the last release, we intensively tested and stabilized VirtualBox on
Genode. We found several issues regarding the FPU handling and virtual TLB
flush handling, which caused VMs to just stop after a while. Additionally, we
enabled the missing VM-reboot feature and improved the handling of those VM
exits that caused the recompiler of VirtualBox to be used unnecessarily. As
the result of our stability improvements, we have become able to run VMs on
VirtualBox 4.2 for days without any trouble.

The second part of our work on VirtualBox deals with upgrading from version
4.2.24 to a recent 4.3 version. Our motivation was twofold: On the one hand,
VirtualBox 4.3 supports Windows 8 and multi-touch input pretty well, and on
the other hand, the (user) front end we used in our 4.2 port has limited
support to configure all the variations of virtual hardware setups that we
desire.

With the port to version 4.3.16 of VirtualBox, we now support the
configuration of VMs using VirtualBox .vbox files. These files are generated
as a result of creating and configuring a VM in the VirtualBox GUI. Such .vbox
files contain all features the virtual hardware should provide to a Guest VM.
In principal, a user of VirtualBox on Windows/Linux/MacOS is now able to
transfer the very same VM configuration over to Genode. An example
configuration for a setup with a shared folder between Guest VM and the Genode
world as well as networking looks as follows.

! ...
! <start name="ram_fs">
! ...
! </start>
! <start name="nic_drv">
! ...
! </start>
! ...
! <start name="virtualbox">
!   <resource name="RAM" quantum="2G"/
!   <config vbox_file="my.vbox" vm_name="MyVM">
!     <libc stdout="/dev/log" stderr="/dev/log">
!     <vfs>
!       <dir name="dev"> <log/> </dir>
!       <rom name="my.vbox" />
!       <dir name="vbox"> <fs label="share_with_vbox"/> </dir>
!   </config>
!   <route>
!     <service name="File_system">
!       <if-arg key="label" value="share_with_vbox" /> <child name="ram_fs"/>
!     </service>
!   </route>
! </start>
! ...

The corresponding my.vbox looks like this:

! ...
! <VirtualBox ...>
!   <Machine ...>
!     <Hardware ...>
!        ...
!        <SharedFolders>
!          <SharedFolder name="genode" hostPath="/vbox" writable="true" autoMount="true"/>
!        <SharedFolders>
!        <Network>
!           <Adapter slot="0" enabled="false" MACAddress="0800271D7901" cable="true" speed="0" type="82540EM">
!              <HostInterface/>
!           </Adapter>
!           ...
!        </Network>
!        ...
!     </Hardware ...>
!   </Machine ...>
! ...
! </VirtualBox>

In Genode, the ram_fs server is used to provide a directory called "/vbox" to
the VirtualBox VMM instance. In the Guest VM, this directory will appear as
"genode" and is mounted writable. As network adapter, we support E1000 and
PCNet. As network back end (provided by the host, which is Genode) we
currently support solely the "HostInterface" XML tag, which uses a
Genode-specific implementation using Genode's NIC-session interface. The MAC
address configured in the .vbox file remains unused. Instead, the MAC address
provided by the NIC server will be used. MAC addresses can be configured e.g.
in the Genode bridge directly for each NIC client.


Updated Seoul virtual machine monitor
=====================================

During Genode's Hack-and-Hike event, we met our long-term friend and former
university colleague Bernhard Kauer. Besides the nice time during the event,
it was also beneficial for the Seoul VMM on Genode. Bernhard reported about
his work on extending the virtual BIOS emulation in his Vancouver VMM. With
his recent changes, the VGA model becomes able to detect and emulate VESA
switching attempts as performed by code inside the VM. Xorg servers as well as
Genode use the x86emu library to emulate 16bit code of the Video BIOS provided
by the graphics card and system BIOS. Normally, this code contains
vendor-specific real mode instructions to perform the VESA mode switching.
Because the original version of Seoul did not provide any real-mode code as
Video BIOS, X.org's VESA driver could not work.

To benefit from Bernhard's work, we ported his changes over to the Seoul VMM,
which turned out to be easily doable since Seoul originated from Vancouver.
With the changes in place, we are now able to easily reuse existing Linux VMs
and we are also able to boot graphical Genode setups in Seoul. The run script
_repos/ports/run/seoul-genode.run_ showcases how to start Genode x86 setups
created by any other Genode run script directly as Guest VM inside Seoul.


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

DDE Linux
=========

With the addition of the WIFI driver to the DDE Linux repository, we decided
to do some cleanup within DDE Linux. First of all, we did not want to share
any Linux files between the drivers. So we moved the USB stack, LXIP, and the
WIFI drivers to different _src/lib/_ directories within _contrib/dde_linux/_.
So, we are now able to individually update the used kernel version for a
single DDE Linux driver with no side effects to other ported drivers. We
mostly update drivers to gain support for recent hardware like the WIFI
driver. After the split, we reverted LXIP to Linux version 3.9. because it
generally runs more stable and is better tested with this kernel version.


Raspberry Pi
============

Genode added principle support for the Raspberry Pi one year ago in
[https://genode.org/documentation/release-notes/13.11#Raspberry_Pi - version 13.11].
Back then, the driver support covered the interrupt controller, timer, UART,
display, and USB. The latter was particularly challenging because the DWC-OTG
USB host controller lacked public documentation. Hence, we ported the driver
from the official Raspberry-Pi Linux kernel, which principally allowed Genode
to support HID devices and thereby enabled interactive applications. However,
the USB driver dramatically impeded the performance of the system because the
host controller triggered an interrupt for each USB microframe, which results
in a rate of 8000 interrupts per second. This is already pretty bad for an OS
based on a monolithic kernel but it is overkill for a microkernel-based system
where each interrupt is delivered as an IPC message with the associated
context-switch costs.

:In-kernel USB SOF interrupt filtering:

For Linux, the Raspberry Pi developers relieved the problem by adding a fast
path for the highly frequent USB start-of-frame (SOF) interrupts. Each USB
interrupt is served by a low-footprint routine executed as a so-called "fast
interrupt" (FIQ) handler. Only if the frame number reaches a value that is
scheduled by the USB driver, the handler will trigger an artificial interrupt
to activate the actual USB driver. Those "interesting" interrupts occur at a
rate that is more than an order of magnitude lower than the SOF interrupt
rate.

Unfortunately, this optimization cannot be used as is on Genode where the USB
driver lives in user land and lacks the privileges to install a FIQ handler.
But the approach to hide SOF interrupts from the USB driver was worth
investigating. We decided to split the USB driver into two parts. One part is
the actual driver ported from Linux but without the FIQ optimization. With
more than 30,000 lines of code, this part is highly complex but it lives as an
unprivileged user process. The second part is a small USB SOF filter routine
that is integrated into the interrupt-controller driver in the base-hw
microkernel. The filter adds merely 100 lines of code to the kernel. Both the
USB driver and the in-kernel SOF filter access the physical DWC-OTG
controller. Each time when the USB driver schedules a micro frame, it writes
the frame number to an unused scratch register of the host controller. When an
USB interrupt comes in, the in-kernel SOF filter compares the current frame
number with the number reported by the USB driver. Only if the current frame
corresponds to the next scheduled frame, the filter propagates the interrupt
to the user-level USB driver. This way, the USB driver is activated only for
handling interesting events. Even though this optimization is not as
sophisticated as the FIQ optimization found in the Linux kernel, it is highly
effective compared to the original version while staying true to the
microkernel architecture.

With the USB SOF filter in place, the interactive performance of Genode on the
Raspberry Pi has reached a decent level. Furthermore, we could enable
networking. Using lwIP running separated from the USB network driver, netperf
reports a throughput of 50 MBit/second, which we find acceptable for this
platform.

:Framebuffer driver:

To accommodate the use of translucent nitpicker views as well as SDL
applications such as Supertux, we enhanced the framebuffer driver with an
configurable buffered mode. If enabled, the driver keeps the client pixels in
a separate pixel buffer that is copied to the physical frame buffer not before
the client explicitly issues a refresh operation. This way, intermediate
drawing states remain hidden from the user.


Default mode selection of VESA driver
=====================================

Unless explicitly configured to a specific resolution, the VESA driver used to
set a mode of 1024x768. When using a Genode system image across machines with
different displays, we had to provide different configurations to accommodate
the variety of displays. Because we longed for a way to let Genode
automatically adapt to the native display resolution, we changed the VESA
driver to pick the video mode with the highest resolution from the list of
available modes.

This works well if Genode is used on laptops because the native display
resolution is typically reported as the highest available mode. Unfortunately,
when using VGA, the highest available mode usually exceeds the native
resolution of the connected output device such as a data projector. In this
case, the default mode can be overridden by explicitly specifying a mode in
the configuration.


Build system and tools
######################

Updated tool chain
==================

The tool-chain has been updated to version 4.7.4, which fixes problems with
executing the tool-chain build script on the current version of Ubuntu Linux.


Improved tooling for using Intel AMT
====================================

We use Intel Active Management Technology (AMT) on diverse native test
hardware to forward serial output over network (SOL) to developer machines and
to power-on, reset, and power-off test machines. Until now, we used the tool
amttool, which uses a SOAP EOI protocol for communication. Newer hardware with
AMT version 9 or higher dropped the support for SOAP EOI - read
[https://software.intel.com/en-us/blogs/2012/12/01/intel-amt-wsman-interface-is-replacing-the-soapeoi-interface - a blog entry by Intel]
for more details - switched to the
[https://www.dmtf.org/standards/wsman - WSMAN interface]. The tool wsman on
Linux speaks the protocol and can be used as a replacement. We integrated the
support of wsman into our run tool infrastructure and use it by default if
installed - otherwise amttool will be used. Of course, you can enforce your
preferred tool by setting the RUN_OPT variable in your build.conf file or as
an  environment variable accordingly, e.g.

! RUN_OPT="--target amt --amt-tool wsman"   make run/printf
or
! RUN_OPT="--target amt --amt-tool amttool" make run/printf
