This patch improves the config handling by falling back to a static
string (empty "<config />") if no valid config ROM module could be
found. This can happen initially, but also at runtime when the ROM
module dissapears, e.g., a ROM module accessed via fs_rom where the
corresponding file gets unlinked.
This patch reflects eventual allocation errors in a more specific way to
the caller of 'alloc_aligned', in particular out-of-metadata and
out-of-memory are considered as different conditions.
Related to issue #526.
The enable the use of 'Attached_ram_dataspace' objects as DMA buffers,
we need to pass the 'cached' flag to the constructor. By default, the
dataspace is cached, which corresponds to the original behaviour.
The 'Session_policy' helper could not cope well with configurations that
contain nodes of a type other than '<policy>'. This patch improves the
policy matching by skipping non-policy nodes.
This patch introduces support for ROM sessions that update their
provided data during the lifetime of the session. The 'Rom_session'
interface had been extended with the new 'release()' and 'sigh()'
functions, which are needed to support the new protocol. All ROM
services have been updated to the new interface.
Furthermore, the patch changes the child policy of init
with regard to the handling of configuration files. The 'Init::Child'
used to always provide the ROM dataspace with the child's config file
via a locally implemented ROM service. However, for dynamic ROM
sessions, we need to establish a session to the real supplier of the ROM
data. This is achieved by using a new 'Child_policy_redirect_rom_file'
policy to handle the 'configfile' rather than handling the 'configfile'
case entirely within 'Child_config'.
To see the new facility in action, the new 'os/run/dynamic_config.run'
script provides a simple scenario. The config file of the test program
is provided by a service, which generates and updates the config data
at regular intervals.
In addition, new support has been added to let slaves use dynamic
reconfiguration. By using the new 'Child_policy_dynamic_rom_file', the
configuration of a slave can be changed dynamically at runtime via the
new 'configure()' function.
The config is provided as plain null-terminated string (instead of a
dataspace capability) because we need to buffer the config data anyway.
So there is no benefit of using a dataspace. For buffering configuration
data, a 'Ram_session' must be supplied. If no 'Ram_session' is specified
at construction time of a 'Slave_policy', no config is supplied to the
slave (which is still a common case).
An example for dynamically reconfiguring a slave is provided by
'os/run/dynamic_config_slave.run'.
The new 'swap' and 'realloc' functions are needed in scenarios where
'Attached_ram_dataspace' is used to implement double buffering. The
particular use case is the implementation of dynamic ROM sessions.
The new 'Slave_policy' and 'Slave' classes are built upon the existing
child framework. They support the implementation of scenarios where a
service is started as a child of the client. This is usefull for
employing an existing service implementation as a local utility or
plugin.
