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Spelling fixes reported by m-stein and ssumpf

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Norman Feske 2012-05-30 13:00:56 +02:00
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@ -62,9 +62,8 @@ former one naturally builds upon the just recently added file-system interface.
Furthermore, we decided to defer the live CD until July as we realized that we Furthermore, we decided to defer the live CD until July as we realized that we
first need to overhaul low-level components such as USB before the new live first need to overhaul low-level components such as USB before the new live
system can be expected to work as intended. Also, some of the scenarios we want system can be expected to work as intended. Also, some of the scenarios we want
to present depend on framework features that are just introduced with the to present depend on framework features just introduced with the current release,
current release, in particular the file-system infrastructure and the media in particular the file-system infrastructure and the media capabilities.
capabilities.
Re-approaching the Linux device-driver environment Re-approaching the Linux device-driver environment
@ -148,34 +147,34 @@ is that finding the right mix of reimplementation, slight modification, and
reuse is a matter of sure instinct of the DDE developer. reuse is a matter of sure instinct of the DDE developer.
Another way to put it is defining the problem as the search in an optimization Another way to put it is defining the problem as the search in an optimization
space for the economically most sensible solution. The optimization criterion space for the economically most sensible solution. The optimization criterion we
we set out to maximize is the ratio of feature code (the actual driver, no DDE set out to maximize is the ratio of feature code (the actual driver, no DDE nor
nor glue) to the number of lines of code that must be manually maintained. To glue) to the number of lines of code that must be manually maintained. To give
give the order of magnitude of the code we speak of, the traditional Linux DDE the order of magnitude of the code we speak of, the traditional Linux DDE
including the support for NIC, USB, and sound is comprised of more than 350.000 including the support for NIC, USB, and sound is comprised of more than 350.000
lines of code. The portion of modified or custom written code (code that must lines of code. The portion of modified or custom written code (code that must be
be manually maintained) is more than 40.000 lines of code. Given this manually maintained) is more than 40.000 lines of code. Given this complexity,
complexity, we found us hesitant to update the code to newer kernel versions. we found us hesitant to update the code to newer kernel versions. The
The engineering labour of such an update is significant yet not much rewarding engineering labour of such an update is significant yet not much of a rewarding
work. Apart from the burden of managing a piece of software that complex, our work. Apart from the burden of managing a piece of software that complex, our
confidence in the classical Linux DDE approach slipped further with each confidence in the classical Linux DDE approach slipped further with each
debugging session that involved Linux DDE. In our experience, Linux DDE still debugging session that involved Linux DDE. In our experience, Linux DDE still
significantly deviates from the semantics of the Linux kernel but in subtle significantly deviates from the semantics of the Linux kernel but in subtle
ways. Often problems go unnoticed until a driver uses a kernel API in a ways. Often problems go unnoticed until a driver uses a kernel API in a
slightly unusual way. For example, a driver calling 'udelay()' from the interrupt slightly unusual way. For example, a driver calling 'udelay()' from the interrupt
handler. The sheer complexity of the code base can make localizing such issues handler. The sheer complexity of the code base can make tracking down such issues
a painful experience. This is further amplified by the existence of certain a painful experience. This is further amplified by the existence of certain
invariants provided by the Linux kernel but absent in the Linux DDE. One invariants provided by the Linux kernel but absent in the Linux DDE. One
particular source of trouble is the control flow in the event of an interrupt. particular source of trouble is the control flow in the event of an interrupt.
In the Linux kernel, the interrupt handler can make the assumption that no code Within the Linux kernel, the interrupt handler can make the assumption that no
of the interrupted CPU can be executed until the interrupt handler returns. In code of the interrupted CPU can be executed until the interrupt handler returns.
contrast, Linux DDE models interrupts as independent threads and assumes that In contrast, Linux DDE models interrupts as independent threads and assumes that
all code is multi-processor safe. Consequently the control flows of the driver all code is multi-processor safe. Consequently the control flows of the driver
executed in the Linux kernel and the same driver executed in Linux DDE differs executed in the Linux kernel and the same driver executed in Linux DDE differs
in subtle ways, leading to the worst of all bugs namely race conditions. in subtle ways, leading to the worst of all bugs namely race conditions.
While our focus shifted away from the classical Linux DDE, we discovered the While our focus shifted away from the classical Linux DDE, we discovered the
beauty of creating extremely tight device driver environments. In contrast to beauty of creating extremely tight device-driver environments. In contrast to
the Linux DDE, which tried to be useful for a large range of driver classes on the Linux DDE, which tried to be useful for a large range of driver classes on
the cost of becoming complex, we created new slim DDEs for single drivers or a the cost of becoming complex, we created new slim DDEs for single drivers or a
strictly outlined class of drivers. One example is the DDE for iPXE networking strictly outlined class of drivers. One example is the DDE for iPXE networking
@ -200,13 +199,13 @@ multiple pseudo-thread contexts using cooperative scheduling.
The result is more than convincing for us. With a DDE of less than 4.000 lines The result is more than convincing for us. With a DDE of less than 4.000 lines
of code, we have become able to use the unmodified Linux-3.2 USB stack, which of code, we have become able to use the unmodified Linux-3.2 USB stack, which
comprises more than 60.000 lines of code. Only 3 lines had to be modified. In comprises more than 60.000 lines of code. Only 3 lines had to be modified. In
contrast to Linux DDE, the 4.000 lines of custom-written DDE code are contrast to Linux DDE, the 4.000 lines of custom-written DDE code are relatively
relatively easy to comprehend. For the most of the functions provided by the easy to comprehend. For most of the functions provided by the DDE, the
DDE, the implemented semantics is a rigid subset of the original functionality implemented semantics are a rigid subset of the original functionality as found
as found in the Linux kernel. Apparently the knowledge about the usage patterns in the Linux kernel. Apparently the knowledge of function usage patterns in a
of the functions in the particular driver allows for vast simplifications. particular driver allows for vast simplifications. Given our self-imposed rule
Given our self-imposed rule to not modify 3rd-party code, we expect that future to not modify 3rd-party code, we expect that future updates to new Linux kernel
updates to new Linux kernel versions will pose much less of a burden. versions will pose much less of a burden.
With our current approach of creating rigidly tailored DDEs, we are convinced With our current approach of creating rigidly tailored DDEs, we are convinced
to have found a healthy balance between the manual effort needed to create and to have found a healthy balance between the manual effort needed to create and
@ -324,9 +323,9 @@ libraries, executable binaries, and configuration data are passed to child
subsystems as ROM modules. But in contrast to core's ROM modules, this subsystems as ROM modules. But in contrast to core's ROM modules, this
information may be dynamic in nature. For example, the configuration of the information may be dynamic in nature. For example, the configuration of the
audio mixer may change at any time during the lifetime of the mixer. Also audio mixer may change at any time during the lifetime of the mixer. Also
executable binaries may change in the event of system updates. Providing the executable binaries may change in the event of system updates. Enabling the
system with the ability to respond to such changes is crucial to the use of system to respond to such changes is crucial the use of Genode as
Genode as general-purpose OS. general-purpose OS.
For existing users of the ROM session interface, there is nothing to consider. For existing users of the ROM session interface, there is nothing to consider.
API compatibility is maintained. However, by installing a signal handler using API compatibility is maintained. However, by installing a signal handler using
@ -382,7 +381,7 @@ supplying the new sub system as a single binary blob only. The server used to
implement heuristics and functionality for dealing with different kinds of implement heuristics and functionality for dealing with different kinds of
blobs such as ELF images or TAR archives. This has been replaced by a blobs such as ELF images or TAR archives. This has been replaced by a
session-local ROM service, which can be equipped with an arbitrary number of session-local ROM service, which can be equipped with an arbitrary number of
ROM modules supplied by the loader client prior starting the new sub system. ROM modules supplied by the loader's client prior starting a new subsystem.
Even though the TAR support has been removed, a separate instance of the Even though the TAR support has been removed, a separate instance of the
'tar_rom' service can be used within the subsystem to provide the formerly 'tar_rom' service can be used within the subsystem to provide the formerly
built-in functionality. built-in functionality.
@ -393,7 +392,7 @@ nitpicker session of the loaded subsystem. The corresponding source code
can be found at 'os/src/test/loader/'. The second example at can be found at 'os/src/test/loader/'. The second example at
'os/run/dynamic_config_loader.run' shows how the concept of dynamic ROM 'os/run/dynamic_config_loader.run' shows how the concept of dynamic ROM
sessions can be combined with the loader. As demonstrated by this example, sessions can be combined with the loader. As demonstrated by this example,
ROM images used by the loaded sub system can be updated at runtime by the ROM images used by the loaded subsystem can be updated at runtime by the
client of the loader session. client of the loader session.
@ -422,10 +421,10 @@ rather than individual file objects.
In-memory file system In-memory file system
~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~
As reference implementation of the new interface, there is the new 'ram_fs' As reference implementation of the new interface, a new 'ram_fs' service can be
service at 'os/src/server/ram_fs'. It stores sparse files in memory. At the found at 'os/src/server/ram_fs'. It stores sparse files in memory. At startup
startup, 'ram_fs' is able to populate the file-system content with directories, time, 'ram_fs' is able to populate the file-system with directories, ROM
ROM modules, and inline data as specified in its configuration. modules, and inline data as specified in its configuration.
Access to the file system can be tailored for each session depending on the Access to the file system can be tailored for each session depending on the
session's label. By default, no permissions are granted to any session. session's label. By default, no permissions are granted to any session.
@ -457,7 +456,7 @@ The following configuration illustrates the way of how to express policy.
The '<content>' sub node of the '<config>' node provides a way to pre-populate The '<content>' sub node of the '<config>' node provides a way to pre-populate
the file system with directories and files. Note that '<dir>' nodes can be the file system with directories and files. Note that '<dir>' nodes can be
arbitrarily nested. Files can be loaded from the ROM service. By adding the arbitrarily nested. Files can be loaded from the ROM service. By adding the
optional 'at' attribute to a '<rom>' node, the file name can be defined optional 'as' attribute to a '<rom>' node, the file name can be defined
independently from the ROM module name. In addition to creating files from independently from the ROM module name. In addition to creating files from
ROM modules, files can be created from data specified directly as part of the ROM modules, files can be created from data specified directly as part of the
configuration using '<inline>' nodes. The content of such nodes is used as configuration using '<inline>' nodes. The content of such nodes is used as
@ -498,7 +497,7 @@ File-system plugin for the C runtime
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
To enable libc-using programs to access the new file-system interface, there is To enable libc-using programs to access the new file-system interface, there is
the new libc plugin at 'libports/src/lib/libc_fs'. Using this plugin, files a new libc plugin at 'libports/src/lib/libc_fs'. Using this plugin, files
stored on a native Genode file system can be accessed using the traditional stored on a native Genode file system can be accessed using the traditional
POSIX file API. POSIX file API.
@ -548,7 +547,7 @@ work is required anyway.
On the other hand, there are 3rd-party applications that would be nice to On the other hand, there are 3rd-party applications that would be nice to
reuse as is without any manual patching work, for example the libSDL-based reuse as is without any manual patching work, for example the libSDL-based
'avplay' or the muPDF example application. To ease the integration of such 'avplay' or the muPDF application. To ease the integration of such
programs into Genode setups, we added the new 'config_args' library. At the programs into Genode setups, we added the new 'config_args' library. At the
startup of the program, this library inspects the config node for arguments and startup of the program, this library inspects the config node for arguments and
fills the argv structure to be passed to the 'main()' function. fills the argv structure to be passed to the 'main()' function.
@ -668,7 +667,7 @@ supported. We will complement the coverage of support as needed.
:SDL audio support: :SDL audio support:
The new libSDL audio backend enables the use of Genode's audio-session The new libSDL audio back end enables the use of Genode's audio-session
interface from SDL applications. This way, SDL programs can be combined interface from SDL applications. This way, SDL programs can be combined
with audio drivers as well as with the mixer component. with audio drivers as well as with the mixer component.
@ -679,7 +678,7 @@ SDL application:
! <sdl_audio_volume value="100"/> ! <sdl_audio_volume value="100"/>
! </config> ! </config>
Note that the SDL audio backend does respond to configuration changes at Note that the SDL audio back end does respond to configuration changes at
run time. By supplying the config dynamically rather than via a static run time. By supplying the config dynamically rather than via a static
file, the audio volume may get updated while the SDL application is running. file, the audio volume may get updated while the SDL application is running.
@ -738,7 +737,7 @@ player. It consists of the following pieces.
interfaces, in particular the audio mixer, framebuffer and input drivers, but interfaces, in particular the audio mixer, framebuffer and input drivers, but
also the nitpicker GUI server. also the nitpicker GUI server.
:qt_avplay: is a Qt4 frontend to 'avplay'. It spawns an instance of 'avplay' :qt_avplay: is a Qt4 front end to 'avplay'. It spawns an instance of 'avplay'
as a slave process. as a slave process.
[image media_player] [image media_player]
@ -766,7 +765,7 @@ GUI submits artificial keyboard events with key codes interpreted by the
Besides the separation of the codec from the GUI, the 'qt_avplay' example is Besides the separation of the codec from the GUI, the 'qt_avplay' example is
interesting because it makes use of Genode's new dynamic configuration interesting because it makes use of Genode's new dynamic configuration
facility. The SDL audio backend used by the codec repeatedly evaluates its facility. The SDL audio back end used by the codec repeatedly evaluates its
configuration during runtime. This configuration includes a volume prescale configuration during runtime. This configuration includes a volume prescale
factor. Via the dynamic configuration mechanism, the parent (the GUI) is able factor. Via the dynamic configuration mechanism, the parent (the GUI) is able
to update the value of the volume prescale factor at any time and thereby to update the value of the volume prescale factor at any time and thereby
@ -851,13 +850,13 @@ Noux
#### ####
Running GCC, binutils, coreutils natively on Genode Running GCC, binutils, coreutils natively on Genode
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ===================================================
We introduced support for stacked file systems alongside new glue for accessing We introduced support for stacked file systems alongside new glue code for
file-system implementations provided via Genode's new file-system-session accessing File-system implementations provided via Genode's new
interface. Using stacked file systems, an arbitrary number of file systems file-system-session Interface. Using stacked file systems, an arbitrary number
(such as TAR archives or file systems implemented as separate Genode of file systems (such as TAR archives or file systems implemented as separate
components) can be composed to form one merged virtual file system. Genode Components) can be composed to form one merged virtual file system.
An example is given via the 'ports/run/noux_bash.run' script. This run script An example is given via the 'ports/run/noux_bash.run' script. This run script
creates a virtual file system out of multiple TAR archives each containing the creates a virtual file system out of multiple TAR archives each containing the
@ -878,10 +877,10 @@ supported.
Networking support Networking support
~~~~~~~~~~~~~~~~~~ ==================
We desire to use a wide range of Unix networking tools such as wget, lynx, ssh, We desire to use a wide range of Unix networking tools such as wget, lynx, ssh,
netcat on Genode. For this reason, the second focus of our Noux-related and netcat on Genode. For this reason, the second focus of our Noux-related
developments is the added support for networking. The Noux syscall interface developments is the added support for networking. The Noux syscall interface
has been extended with system calls for 'socket', 'getsockopt', 'setsockopt', has been extended with system calls for 'socket', 'getsockopt', 'setsockopt',
'accept', 'bind', 'getpeername', 'listen', 'send', 'sendto', 'recv', 'accept', 'bind', 'getpeername', 'listen', 'send', 'sendto', 'recv',