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The kernel provides a "recall" feature issued on threads to force a thread into an exception. In the exception the current state of the thread can be obtained and its execution can be halted/paused. However, the recall exception is only delivered when the next time the thread would leave the kernel. That means the delivery is asynchronous and Genode has to wait until the exception triggered. Waiting for the exception can either be done in the cpu_session service or outside the service in the protection domain of the caller. It turned out that waiting inside the cpu_service is prone to deadlock the system. The cpu_session interface is one of many session interfaces handled by the same thread inside Core. Deadlock situation: * The caller (thread_c) to pause some thread_p manages to establish the call to the cpu_session thread_s of Core but get be interrupted before issuing the actual pause (recall) command. * Now the - to be recalled thread_p - is scheduled and tries to invoke another service of Core, like making log output. * Since the Core thread_s is handling the session request of thread_c, the kernel uses the timeslice of thread_p to help to finish the request handled by thread_s. * Thread_s issues the actual pause/recall on thread_p and blocks inside Core to wait for the recall exception to be issued. * thread_p will leave not the kernel before finishing it actual IPC with thread_s which is blocked waiting for thread_p. That is the reason why the waiting/blocking for the recall exception taking place must be done on NOVA in the context of the caller (thread_1). Introduce a pause_sync call to the cpu_session which returns a semaphore capability to the caller. The caller blocks on the semaphore and is woken up when the pager of thread_p receives the recall exception with the state of thread_p.
=================================
Genode Operating System Framework
=================================
This is the source tree of the reference implementation of the Genode OS
architecture. For a general overview about the architecture, please refer to
the project's official website:
:Official project website for the Genode OS Framework:
[http://genode.org/documentation/general-overview]
The current implementation can be compiled for 8 different kernels: Linux,
L4ka::Pistachio, L4/Fiasco, OKL4, NOVA, Fiasco.OC, Codezero, and a custom
kernel for the MicroBlaze architecture. Whereas the Linux version serves us as
development vehicle and enables us to rapidly develop the generic parts of the
system, the actual target platforms of the framework are microkernels. There
is no "perfect" microkernel - and neither should there be one. If a microkernel
pretended to be fit for all use cases, it wouldn't be "micro". Hence, all
microkernels differ in terms of their respective features, complexity, and
supported hardware architectures.
Genode allows the use of each of the kernels listed above with a rich set of
device drivers, protocol stacks, libraries, and applications in a uniform way.
For developers, the framework provides an easy way to target multiple different
kernels instead of tying the development to a particular kernel technology. For
kernel developers, Genode contributes advanced workloads, stress-testing their
kernel, and enabling a variety of application use cases that would not be
possible otherwise. For users and system integrators, it enables the choice of
the kernel that fits best with the requirements at hand for the particular
usage scenario.
Directory overview
##################
The Genode source tree is composed of the following subdirectories:
:'doc':
This directory contains general documentation. Please consider the following
document for a quick guide to get started with the framework:
! doc/getting_started.txt
If you are curious about the ready-to-use components that come with the
framework, please review the components overview:
! doc/components.txt
:'base':
This directory contains the source-code repository of the fundamental
frameworks and interfaces of Genode. Furthermore, it contains the generic
parts of core.
:'os':
This directory contains the non-base OS components such as the init process,
device drivers, and basic system services.
:'demo':
This directory contains the source-code repository of various services and
applications that we use for demonstration purposes. For example, a graphical
application launcher called Launchpad and the Scout tutorial browser.
:'base-<platform>':
These directories contain platform-specific source-code repositories
complementing the 'base' repository. The following platforms are supported:
:'linux':
Linux kernel (both x86_32 and x86_64)
:'nova':
NOVA hypervisor developed at University of Technology Dresden
See [http://genode.org/documentation/platforms/nova]
:'foc':
Fiasco.OC is a modernized version of the Fiasco microkernel with a
completely revised kernel interface fostering capability-based
security. It is not compatible with L4/Fiasco.
See [http://genode.org/documentation/platforms/foc]
:'hw':
The hw platform allows the execution of Genode on bare ARM hardware
without the need for a separate kernel. The kernel functionality is
included in core.
See [http://genode.org/documentation/platforms/hw]
:'okl4':
OKL4 kernel (x86_32 and ARM) developed at Open-Kernel-Labs.
See [http://genode.org/documentation/platforms/okl4]
:'pistachio':
L4ka::Pistachio kernel developed at University of Karlsruhe.
See [http://genode.org/documentation/platforms/pistachio]
:'fiasco':
L4/Fiasco kernel developed at University of Technology Dresden.
See [http://genode.org/documentation/platforms/fiasco]
:'codezero':
Codezero microkernel developed by B-Labs
See [http://genode.org/documentation/platforms/codezero]
:'mb':
Support for running Genode natively on the MicroBlaze softcore CPU.
See [http://genode.org/documentation/platforms/microblaze]
:'host':
Pseudo platform documenting the interface between the generic and
platform-specific parts of the base framework. This is not a functional
base platform.
:'tool':
Source-code management tools and scripts. Please refer to the README file
contained in the directory.
:'hello_tutorial':
Tutorial for creating a simple client-server scenario with Genode. This
repository includes documentation and the complete source code.
:'libports':
This source-code repository contains ports of popular open-source libraries
to Genode, most importantly the C library. The repository contains no
upstream source code but means to download the code and adapt it to Genode.
For instructions about how to use this mechanism, please consult the README
file at the top level of the repository.
:'dde_linux':
This source-code repository contains the device driver environment for
executing Linux device drivers natively on Genode. Currently, this
repository hosts the USB stack.
:'linux_drivers':
Deprecated version of the Linux device driver environment featuring audio
drivers and the Intel GEM driver. This repository is in a transitionary
phase. Its functionality will be incorporated into 'dde_linux'.
:'dde_ipxe':
This source-code repository contains the device driver environment for
executing drivers of the iPXE project.
:'qt4':
This source-code repository contains the Genode version of Qt4 framework.
Please find more information about using Qt4 with Genode in the repository's
'README' file.
:'ports':
This source-code repository hosts ports of 3rd-party applications to
Genode. The repository does not contain upstream source code but provides
a mechanism for downloading the official source distributions and adapt
them to the Genode environment. The used mechanism is roughly the same
as used for the 'libports' repository. Please consult 'libports/README'
for further information.
:'ports-<platform>':
These platform-specific source-code repositories contain software that
capitalizes special features of the respective kernel platform. I.e.,
for the OKL4 base platform, a port of OKLinux is provided in 'ports-okl4'.
For the Fiasco.OC platform, 'ports-foc' hosts a port of the L4Linux
kernel. For further information, please refer to the README file at the
top level of the respective repository.
:'gems':
This source-code repository contains Genode applications that use
both native Genode interfaces as well as features of other high-level
repositories, in particular shared libraries provided by 'libports'.
Contact
#######
The best way to get in touch with Genode developers and users is the project's
mailing list. Please feel welcome to join in!
:Genode Mailing Lists:
[http://genode.org/community/mailing-lists]