This feature is not compatible with the forthcoming nonblocking parent
interface. The patch removes the use of feature in all places except for
the components of the demo repository, which will under go a redesign
anyway.
Issue #2120
Issue #2165
- use the correct memory free functions on errors
- report packet submit errors
- rename 'Usb::Packet_descriptor::transfer.timeout' as
'Usb::Packet_descriptor::transfer.polling_interval'
Fixes#2135
base generic code:
* Remove unused verbosity code from mmio framework
* Remove escape sequence end heuristic from LOG
* replace Core_console with Core_log (no format specifiers)
* move test/printf to test/log
* remove `printf()` tests from the log test
* check for exact match of the log test output
base-fiasco:
* remove unused Fiasco::print_l4_threadid function
base-nova:
* remove unused hexdump utility from core
base-hw:
* remove unused Kernel::Thread::_print_* debug utilities
* always print resource summary of core during startup
* remove Kernel::Ipc_node::pd_label (not used anymore)
base*:
* Turn `printf`,`PWRN`, etc. calls into their log equivalents
Ref #1987Fix#2119
* Supply Env to Input::Session_component
* Attach input event dataspace at Input::Client
* Process input events by lambda rather than pointer
* Supply Env and a label to Input::Connection
* Wm serves valid input_session to decorator
* Per-source signal handling at input_merger
* Base API update for dummy_input_drv, test_input
* Input API update for launcher, menu_view, terminal,
mupdf, sdl, seoul, virtualbox
Ref #1987
When run with the '--autopilot' run option, the 'usb_hid.run' script tests
the input events generated by a 'Pro Micro' microcontroller board. Setup
instructions for the Pro Micro can be found in the run script.
Fixes#2087
The nic_router component can be used to individually route IPv4 packets
between multiple NIC sessions. Thereby, it can translate between
different IP subnets. The component supports port forwarding, as well as
the partitioning of the TCP and UDP port spaces.
Fixes#114
In other contexts (IPv4) 'calc_checksum' merely returns a new checksum that is
then installed via 'checksum'. Thus, the UDP 'calc_checksum' that calculates AND
installs a new checksum is misleading.
Ref #114
Although the driver makes no use of interrupts it references Irq_handler
for unknown reasons. Moreover, this commit eliminates the lock that is
not necessary anymore, because the driver now runs single-threaded.
Ref #2072
* Unify uart drivers of different hardware drivers
* Remove deprecated IRQ activations
* Remove additional timer thread in Fiasco* KDB driver
* Move more generic UART definitions to specific supported
platforms (e.g.: pl011 -> pbxa9)
* Move internal definitions from global to local headers
Ref #1987Fix#2071
Use a seperate handle at each session.
Use SEEK_TAIL to append messages to files.
Increase packet buffer.
Refactor to component framework.
Fixes#1777
Issue #2060
Besides adapting the components to the use of base/log.h, the patch
cleans up a few base headers, i.e., it removes unused includes from
root/component.h, specifically base/heap.h and
ram_session/ram_session.h. Hence, components that relied on the implicit
inclusion of those headers have to manually include those headers now.
While adjusting the log messages, I repeatedly stumbled over the problem
that printing char * arguments is ambiguous. It is unclear whether to
print the argument as pointer or null-terminated string. To overcome
this problem, the patch introduces a new type 'Cstring' that allows the
caller to express that the argument should be handled as null-terminated
string. As a nice side effect, with this type in place, the optional len
argument of the 'String' class could be removed. Instead of supplying a
pair of (char const *, size_t), the constructor accepts a 'Cstring'.
This, in turn, clears the way let the 'String' constructor use the new
output mechanism to assemble a string from multiple arguments (and
thereby getting rid of snprintf within Genode in the near future).
To enforce the explicit resolution of the char * ambiguity, the 'char *'
overload of the 'print' function is marked as deleted.
Issue #1987
Core on seL4 is configured to run on native hardware, so some static
allocators are bit over dimensioned. Some run scripts fail on qemu because
solely 64M are available in the system - adjust the affected scripts.
Issue #2044
This patch adds the methods 'sigh_ack_avail()' and
'sigh_ready_to_submit()', which are needed to build asynchronously
operating file-system clients.
Fixes#2023
Conveying the ROM filename as the final label element simplifies
routing policy and session construction.
Annotations by nfeske:
This commit also changes the ROM session to use base/log.h instead of
base/printf.h, which produced build error of VirtualBox because the
vbox headers have a '#define Log', which collides with the content of
base/log.h. Hence, this commit has to take precautions to resolve this
conflict.
The commit alse refines the previous session-label change by adding a
new 'Session_label::prefix' method and removing the use of 'char const *'
from this part of the API.
Fixes#1787
Session_label constructor now takes a bare string rather than a
serialized argument buffer.
Replace all instances of previous constructor with 'label_from_args'
function.
Issue #1787
This patch establishes the sole use of generic headers across all
kernels. The common 'native_capability.h' is based on the version of
base-sel4. All traditional L4 kernels and Linux use the same
implementation of the capability-lifetime management. On base-hw, NOVA,
Fiasco.OC, and seL4, custom implementations (based on their original
mechanisms) are used, with the potential to unify them further in the
future.
This change achieves binary compatibility of dynamically linked programs
across all kernels.
Furthermore, the patch introduces a Native_capability::print method,
which allows the easy output of the kernel-specific capability
representation using the base/log.h API.
Issue #1993
In addition to modernizing the component now also supports using
empty RAM dataspace as backing store.
For example to use an ISO file the component has to be configured
as follows:
! <config file="image.iso" block_size="2048"/>
To use a empty RAM dataspace that is 256MiB large and has a block
size of 4KiB the configuration looks like this:
! <config size="256M" block_size="4096"/>
Either 'size' or 'file' has to specified. If both are declared the
'file' attribute is soley evaluated.
Issue #1987.
Fixes#2031.
* remove all 'Genode::env()' calls
* use attached roms to read configuration
* use compoenent framework
* remove all PDBG, PINF, PWRN macros
Issue #1987Fixes#2019
* use Component::* instead of Server::*
* do not use old printf format anymore
* do not use old Genode::env()->heap() anymore
* avoid pointers where possible, and use references instead
* throw away the thread-safe variants of list and AVL tree,
nic_bridge became single-threaded in the past
* introduce Ram_session_guard instead of Allocator_guard
Issue #1987
- platform_drv announces a separate "Acpi" session
- platform_drv waits for ROM "system" to change state to "acpi_ready"
- acpica waits for "Acpi" announcement
- acpica uses the platform driver via "Acpi" to reconfigure PCI devices
- acpica changes "system" state to "acpi_ready" after it ready with initialization
- platform_drv reacts on "system" state change to "acpi_ready" by announcing "Platform" session
- drivers start to operate as usual
Issue #2009
Replace 'attribute(...).has_value("yes")`
with 'attribute_value(..., false)'.
This allows for boolean configuration to be set with values such as
"true", "false", "yes", "no", or "1", "0".
Fixes#2002
A configuration policy must match against a policy node label,
label_prefix, or label_suffix atttribute. A fallback to
<default-policy/> is provided as a label wildcard.
Fixes#1901
The whole XML comment has to be parsed as one XML tag to support strange
but valid combinations like
<!---->
<!--invisible-tag></invisible-tag-->
Fixes#1424
Allocating a packet in the packet stream without a payload is not
allowed. Therefore we have to allocate CTRL message packets, that do
not have a payload, with a bogus length instead.
Directory_service::leaf_path returns a pointer offset from its argument
so pass member data rather than a constructor argument to leaf_path.
Issue #1775
This is an interim fix for solving the quota leakage problem of
the platform driver on x86 platforms. To properly fix that problem
one has to track which dataspaces where created by the platform driver,
so that freeing the dataspace and reversing the quota transfer is done
on correct dataspaces only.
Refer #1980
This patch removes the outdates doc/architecture.txt since the
topics are covered by the book. We keep repos/os/doc/init.txt
because it contains a few details not present in the book (yet).
The patch streamlines the terminology a bit. Furthermore, it
slightly adjusts a few source-code comments to improve the book's
functional specification chapter.
* Adds public timeout syscalls to kernel API
* Kernel::timeout installs a timeout and binds a signal context to it that
shall trigger once the timeout expired
* With Kernel::timeout_max_us, one can get the maximum installable timeout
* Kernel::timeout_age_us returns the time that has passed since the
calling threads last timeout installation
* Removes all device specific back-ends for the base-hw timer driver and
implements a generic back-end taht uses the kernel timeout API
* Adds assertions about the kernel timer frequency that originate from the
requirements of the the kernel timeout API and adjusts all timers
accordingly by using the their internal dividers
* Introduces the Kernel::Clock class. As member of each Kernel::Cpu object
it combines the management of the timer of the CPU with a timeout scheduler.
Not only the timeout API uses the timeout scheduler but also the CPUs job
scheduler for installing scheduling timeouts.
* Introduces the Kernel::time_t type for timer tic values and values inherited
from timer tics (like microseconds).
Fixes#1972
Evaluate fadt xml node in report from acpi_drv. If the io ports in the range
of 0xcf8+4 are necessary for the reset than the platform driver will
react on the 'system' state 'reset' and reboot.
Issue #1962
Will be/can be used by the platform driver to reset the machine, iif the
platform driver owns the resources, e.g. the I/O ports of PCI config access.
Issue #1962
This patch moves the thread operations from the 'Cpu_session'
to the 'Cpu_thread' interface.
A noteworthy semantic change is the meaning of the former
'exception_handler' function, which used to define both, the default
exception handler or a thread-specific signal handler. Now, the
'Cpu_session::exception_sigh' function defines the CPU-session-wide
default handler whereas the 'Cpu_thread::exception_sigh' function
defines the thread-specific one.
To retain the ability to create 'Child' objects without invoking a
capability, the child's initial thread must be created outside the
'Child::Process'. It is now represented by the 'Child::Initial_thread',
which is passed as argument to the 'Child' constructor.
Fixes#1939
These warnings are triggered by requests either using byte offsets or
reading a number of bytes that is not a multiple of the block size as
well as by components using the plugin with a different block size than
the backend block session provides.
Fixes#1964.
This patch supplements each existing connection type with an new
constructor that is meant to replace the original one. The new
one takes a reference to the component's environment as argument and
thereby does not rely on the presence of the globally accessible
'env()' interface.
The original constructors are marked as deprecated. Once we have
completely abolished the use of the global 'env()', we will remove them.
Fixes#1960
Replace size_t by uint8_t in accessors for the IPv4 header fields
'version' and 'header_length' - uint8_t is the smallest integral type
for 4 bit of information. Note, as the _internet header length_ field is
defined to reflect the number of 32-bit words the header occupies, we
also stick to the specification with our accessor.
Issue #1915
It turns out that the name function does not have much use in practice
except for naming the thread of the component's initial entrypoint. For
dynamically linked components, this thread is created by the dynamic
linker. It is named "ep" in these cases. Considering that we will
eventually turn all regular components into dynamically linked
executables, the additional information provided by the
Component::name() function remains unused. So it is better to not bother
the component developers with adding boilerplate code.
This patch cleans up the thread API and comes with the following
noteworthy changes:
- Introduced Cpu_session::Weight type that replaces a formerly used
plain integer value to prevent the accidental mix-up of
arguments.
- The enum definition of Cpu_session::DEFAULT_WEIGHT moved to
Cpu_session::Weight::DEFAULT_WEIGHT
- New Thread constructor that takes a 'Env &' as first argument.
The original constructors are now marked as deprecated. For the
common use case where the default 'Weight' and 'Affinity' are
used, a shortcut is provided. In the long term, those two
constructors should be the only ones to remain.
- The former 'Thread<>' class template has been renamed to
'Thread_deprecated'.
- The former 'Thread_base' class is now called 'Thread'.
- The new 'name()' accessor returns the thread's name as 'Name'
object as centrally defined via 'Cpu_session::Name'. It is meant to
replace the old-fashioned 'name' method that takes a buffer and size
as arguments.
- Adaptation of the thread test to the new API
Issue #1954
This patch moves the base library from src/base to src/lib/base,
flattens the library-internal directory structure, and moves the common
parts of the library-description files to base/lib/mk/base.inc and
base/lib/mk/base-common.inc.
Furthermore, the patch fixes a few cosmetic issues (whitespace and
comments only) that I encountered while browsing the result.
Fixes#1952
We report UNLINK_ERR_NO_PERM only for files in TAR archive, otherwise
UNLINK_ERR_NO_ENTRY is returned. This permits the arbitrary layering of
file systems with support for proper ENOENT reporting, for example,
when using 'rm -f non_existent_file' that aborts if EPERM is wrongly
reported.
The original 'Env' interface as returned by 'Genode::env()' has been
renamed to 'Env_deprecated' and moved to deprecated/env.h. The new version
of base/env.h contains the interface passed to modern components that
use the component API via base/component.h.
Issue #1832
This patch makes the former 'Process' class private to the 'Child'
class and changes the constructor of the 'Child' in a way that
principally enables the implementation of single-threaded runtime
environments that virtualize the CPU, PD, and RAM services. The
new interfaces has become free from side effects. I.e., instead
of implicitly using Genode::env()->rm_session(), it takes the reference
to the local region map as argument. Also, the handling of the dynamic
linker via global variables is gone. Now, the linker binary must be
provided as constructor argument.
Fixes#1949
This patch replaces the former 'Pd_session::bind_thread' function by a
PD-capability argument of the 'Cpu_session::create_thread' function, and
removes the ancient thread-start protocol via 'Rm_session::add_client' and
'Cpu_session::set_pager'. Threads are now bound to PDs at their creation
time and implicitly paged according to the address space of the PD.
Note the API change:
This patch changes the signature of the 'Child' and 'Process' constructors.
There is a new 'address_space' argument, which represents the region map
representing the child's address space. It is supplied separately to the
PD session capability (which principally can be invoked to obtain the
PD's address space) to allow the population of the address space
without relying on an 'Pd_session::address_space' RPC call.
Furthermore, a new (optional) env_pd argument allows the explicit
overriding of the PD capability handed out to the child as part of its
environment. It can be used to intercept the interaction of the child
with its PD session at core. This is used by Noux.
Issue #1938
Since the dynamic linker depends on the XML utils and we plan to replace
the ancient 'Arg_string' with XML, it is time to move the 'Xml_node' and
'Xml_generator' to base/include.
We will eventually remove the delivery of the number of occurred signals
to the recipient. There haven't been any convincing use cases for this
feature. In the contrary, it actually led to wrong design choices in the
past where the rate of signals carried information (such as the progress
of time) that should better be obtained via an explicit RPC call.
The old 'Signal_rpc_member' template retains the old interface for now.
But the new 'Signal_handler' omits the 'unsigned' argument from the
handler function.
This patch integrates three region maps into each PD session to
reduce the session overhead and to simplify the PD creation procedure.
Please refer to the issue cited below for an elaborative discussion.
Note the API change:
With this patch, the semantics of core's RM service have changed. Now,
the service is merely a tool for creating and destroying managed
dataspaces, which are rarely needed. Regular components no longer need a
RM session. For this reason, the corresponding argument for the
'Process' and 'Child' constructors has been removed.
The former interface of the 'Rm_session' is not named 'Region_map'. As a
minor refinement, the 'Fault_type' enum values are now part of the
'Region_map::State' struct.
Issue #1938
Currently the report name is used implicitly as first xml node name for the
report. This is inconvenient if one component wants to generate various xml
reports under various names (e.g. to steer consumers/clients slightly
differently) but with the same xml node tree structure.
Fixes#1940
Replace the Out_of_node_handles exception with Out_of_metadata.
Clients need to know when the server is out of internal resources,
but not why.
Cleanup and sort the errors at file_system_session.h.
Remove 'Size_limit_reached exception' from File_system, which was
internal to ram_fs.
Issue #1751Fixes#1909
Opening a VFS handle previously involved allocating from the global heap
at each VFS file system. By amending open with an allocator argument,
dynamic allocation can be partitioned.
A new close method is used to deallocate open handles.
Issue #1751
Issue #1891
The returned capacity had different semantics dependent on the card
type. For HIGH_CAPACITY cards, the memory capacity is specified in 512kB
blocks. So we should also return 512kB blocks for STANDARD_CAPACITY
cards.
Issue #1925
When init destroys a child server with an open session, the client must
be updated as it will otherwise store a pointer to a no-more existing
service object which will be dereferenced when the child client is
destroyed.
Fixes#1912
This commit introduces the new `Component` interface in the form of the
headers base/component.h and base/entrypoint.h. The os/server.h API
has become merely a compatibilty wrapper and will eventually be removed.
The same holds true for os/signal_rpc_dispatcher.h. The mechanism has
moved to base/signal.h and is now called 'Signal_handler'.
Since the patch shuffles headers around, please do a 'make clean' in the
build directory.
Issue #1832
Prevents the annoying warning about
WARNING: Image format was not specified for 'bin/test.img' and probing guessed raw.
Automatically detecting the format is dangerous for raw images, write operations on block 0 will be restricted.
Specify the 'raw' format explicitly to remove the restrictions.
If attached ROM dataspaces are not valid after update(), code that uses
these ROMs produces
void Genode::Volatile_object< <template-parameter-1-1> >::_check_constructed() const [with MT = Genode::Attached_dataspace]: Deref_unconstructed_object
In scenarios where the config ROM is loaded from a report ROM or any
other non-static ROM, config might try to access an invalid dataspace
capability. This patch prevents the component from aborting in this
case.
Fixes#1914
This patch removes the support for executing subsystems of CLI monitor
within the GDB monitor. There are multiple reasons: First, the feature
remained unused for multiple years. Second, it relied on the base/elf.h
header to determine whether the started binary is dynamically or
statically linked. This header, however, is going to be removed from the
Genode API. Third, the feature will eventually break with the upcoming
changes of how components are bootstrapped. Finally, there is the plan
to turn CLI monitor into a sole front end of a dynamically configurable
init component. Once we pursue this plan, we'd need to reconsider the
GDB support anyway.
Issue #1832
In addition to now using the framework the playback is triggered by a
timer. For now it is a periodic timer that triggers every 11 ms which
is roughly the current Audio:out period (*).
The driver now also behaves like the other BSD Audio_out driver, i.e,
it always advances the play pointer. That is vital for the Audio_out
stack above the driver to work properly (e.g. the mixer).
(*) It stands to reason if it would be better to use the async ALSA
timer interface instead of using the Timer session.
Fixes#1892.
This driver uses the Usb session interface and provides a Block session
to its client. See _repos/os/src/drivers/usb_block/README' for more
information.
Fixes#1885.
Instead of only hardcoding "hw" read 'alsa_device' attribute from the
config node to determine the proper playback device. The default value
is still "hw" in case the attribute is not present.
Fixes#1884.
The driver might end up in an endless loop on systems that do not
contain an i8042 controller when probing the AUX interface. This
leads to busy looping and in the end to not annoucing the Input
service. Components that wait for the announcement of the service
will therefore hang as well.
Normally a service gets announced only if it is usable but in this
case this is inconvient because it renders all scenarios that use
the input_merger non working on x86 systems that only provide USB
input and do not have PS/2 at all.
Ideally, the PS/2 driver should only be started if the system needs it.
That is currently not feasible and for the time being we post-pone the
inevitable and back down after several unsucessful attempts to read
from the AUX interface while initializing the driver.
Fixes#1871.
The 'usb_report_filter' component takes the devices report from the
USB driver and generates a new devices report after checking each
entry against its device white-list. Before emitting the new report
it changes the configuration of the USB driver to contain the
required policy entries.
See 'repos/os/src/app/usb_report_filter/README' for more details.
Issue #1863.
- Use 'label' attribute to identify device instead of
bus/dev and vendor_id/product_id
- Implement release_interface RPC
- Report 'label' as well as 'bus' and 'dev'
- Add policy handling to raw driver (includes reconfiguration
at runtime)
- Use own memory backing store for large DMA allocations
Issue #1863.
Now, the right PCI bus:device:function (BDF) is reported to the kernel
during assign_pci syscall - beforehand it was ever 0:0.0. The BDF is
needed to lookup the correct DMAR unit the kernel has to configure. This
was revealed as the DMAR unit for Intel graphics on x201 is not the same
as for all other PCI devices we have drivers for on this platform.
Fixes#1848
Because a check for the TEST_WRITE configuration was missing as condition for a
packet submit, the test caused unwanted write access to the device.
Ref #1824
This patch adds diagnostic messages during the label-policy application,
if no policy for the session label was found or if the domain configured
in the policy node does not exist.
From our observations we can tell that the error should not exceed 4%.
However, there is no reasonable explanation by now why the test results
are less stable on these platforms. We have tried several things that
did not lead to an explanation or improvement:
* changing the timing parameters of the scheduler
* switching off SMP
* double-checking the speed of userland and kernel timers
Ref #1805
The test threads previously used a stack size independent from the machine
word width. Qemu was previously configured to provide 64Mb of RAM which isn't
sufficient for x86_64.
Ref #1805
Print result error and error tolerance per test result. Use TCL commands
'format' and 'abs'to simplify calculations in the conclusion part of the run
script.
Ref #1805
This reverts commit d8b95c263b.
Some clients might want to fiddle with the clients play position
(e.g. the mixer) within 'Audio_out::start()' and we might reset
it to an old value if we do it afterwards.
Fixes#1796.
Since all Audio_out server components loop over the packet stream
queue it is save to reset the tail position to one after the play
position. We have to do this because we do not know exactly when
the play position changes (i.e. the driver has processed the packet)
and we might end up with a tail position before the current play
position.
Issue #1796.
Instead of bailing out if the channel list is incorrect check config
node attributes and default settings first.
Being there also fix flawed LOG messages.
Fixes#1794.
This patch unifies the mechanism of selecting server-side policies and
taking session-routing decisions based on session labels. In both cases,
XML nodes are scored against session labels. The score depends on the
XML attributes 'label' (exact match), 'label_prefix', and
'label_suffix'.
Issue #1766
* Provide paravirtualized block API for accessing the second partition
of the block device that is provided by the ESDHC driver.
* Provide paravirtualized serial API for sending log-output over Genodes
serial port.
* Use the latest Linux suggested in the USB Armory Wiki [1] when on USB Armory
while still using the older vendor Linux when on i.MX53 QSB. I.e.,
provide a device tree through RAM and a rootfs through the paravirtualized
block device when on USB Armory while providing ATAGs and Initrd when on
i.MX53 QSB.
* Switch on the LED on the USB Armory when the VMM catches a VM-exception
and switch it off again when as soon as the exception is handled. This
merely show-cases the ability to instrument the LED for such purposes. In an
ideal world, the LED is switched on as long as we're on the "Secure Side"
and switched off as long as we're not.
* For further information see repos/os/run/tz_vmm.run
[1] https://github.com/inversepath/usbarmory/wiki/Preparing-a-bootable-microSD-imageFixes#1497
Move ADMA2 stuff to extra header and unit. Move ESDHCv2 implementations to
extra unit. Use exceptions instead of error codes. Clean-up documentation.
Ref #1497
The manual termination of multi-block writes via "Stop Transmission" commands
seems to leave the card in a busy state sometimes. This causes errors on
subsequent commands. Thus, we have to synchronize manually with the
card-internal state via "Send State" commands. Additionally, the method
for issuing the manual "Stop Transmission" commands was refined.
Ref #1497
We have to issue a data synchronization barrier after writing a ADMA2
table to ensure that the corresponding write commands were actually
executed before issuing the SD command.
Ref #1497
On i.MX53 QSB, a "Send Op Cond" command during the driver initialization
returns another response value than on the USB Armory. As the check for
this response seems to have no relevance for the driver functionality (Linux
reads the value from MMIO but I can't find a place in the source code where
it is used), we simply remove it.
Ref #1497
Previously, it was not necessary to acknowledge an IRQ initially before using
it. However, since the IRQ framework changed lately it is. Adapt to this.
Ref #1497
Notify client initially to enforce a client-side ROM update. Otherwise,
a server-side ROM update between session creation and signal-handler
registration would go unnoticed.
Issue #1788
This patch changes the decorator to always apply stacking-order changes
immediately instead of deferring the re-stacking of the nitpicker views
to the next call of 'update_nitpicker_views'. The deferred application
did not always work when more then one windows changed their stacking
position at once because the cached '_neighbor' values interfered with
each other.
The eager re-stacking should not have negative effects on the user
experience because, in contrast to re-positioning, re-stacking a rare
operation.
This change makes it possible to reuse the generic window decorator
classes in include/decorator/ for decorators of a different structure.
E.g., instead of painting decorations on a single nitpicker session,
each window may paint its decorations into additional window-specific
nitpicker sessions.
In the event where a nitpicker session's quota was depleted by the
allocation of view handles, nitpicker would abort. The patch prevents
the abort by reflecting this condition as an Out_of_metadata exception
to the client. This way, the client can upgrade its session as needed.
The problem was triggered by running the decorator_stress test (changed
to generate 40 windows) with the themed_decorator.
This patch addresses the corner case that the specified neighbor view
is the first view of the view stack. If this is the case when inserting
the view in front of the neighbor (behind == false), the target position
within the view stack must be a null pointer, not the first view.
Because the conditions have become rather complicated, both cases
of 'behind' are handled separately now.
