To implement fork semantics, we need to customize the bootstrapping of
the newly created process, in particular the startup of the main thread.
The CPU session interface provides a suitable hook. By virtualizing the
CPU connection of the process to core, we can defer (and parametrize)
the startup of the main thread. Furthermore, this enables us to detect
illegal attempts by the Noux process to create threads in addition to
the main thread.
By letting Noux processes talk to service implementations local to the
Noux server, we can track RAM allocations and RM operations. This is
needed as a prerequisite to implement fork.
It does not suffice to constrain the amount of returned data with chunk
size of the transport buffer because the client may have specified an
even smaller value. For example, libreadline reads single characters
from the terminal and expects a single character in return. A different
amount is interpreted as EOF.
When reading the values of environment variables supplied via Genode
config mechanism, the XML attribute values were taken as is. On the libc
side, however, the values are processed using Genode's 'Arg_string'
functions. When unquoted, 'Arg_string' expects values to be either
identifiers or numbers. In the general case, however, env values cannot
be expected to satisfy these requirements. Hence, it is better to always
quote these values when reading the XML config. An alternative (maybe
better) solution would be to not use the 'Arg_string' classes in the
libc side.
Norman Feske
Genode Labs