Hello Daniel,
I'd like to be able to use the native Fiasco.OC L4re APIs (actually to set thread affinity) from within my Genode application. Its not clear to me how to set up the target.mk to do such things.
Genode is not built upon L4re. It is using only the Fiasco.OC kernel bindings (called l4sys) and two other small components of L4re, namely sigma0 and bootstrap. Logically, both sigma0 and bootstrap actually belong to the kernel but they are contained in the L4re source tree for historical reasons.
It is not possible to intermix L4re and Genode code but of course, you can issue Fiasco.OC system calls by including the corresponding kernel bindings. See 'base-foc/src/base/ipc/ipc.cc' as an example. As you can see in this library code, we use to include Fiasco.OC header files into the dedicated C++ namespace 'Fiasco'. I would recommend you to do the same.
Setting the thread affinity is not yet supported though Genode's API because until recently, we used Genode with SMP only on Codezero and Linux, both handling the thread affinity transparently. However, there are two natural ways to support Fiasco.OC's explicit assignment of thread affinities, as session-construction argument for CPU sessions or by adding a 'set_affinity' function to Genode's 'Cpu_session' interface. Both variants were successfully prototyped for Pistachio but have not been merged with the official Genode API.
Personally, I have a preference to specifying the affinity as CPU session argument such that all threads of this session are implicitly bound to the specified CPU. This enables the assignment of complete Genode subsystems to a specific CPU. Also it would preserve the notion of having a "CPU session". Furthermore, the affinity would be subjected to session policies imposed by the process hierarchy (similar to how RT priorities are handled now) - affinities could be "virtualized". In contrast, by adding a 'set_affinity' call to the 'Cpu_session' interface, different threads of one CPU session could be bound to different CPUs.
In both cases, the propagation of the thread affinity to the Fiasco.OC kernel must happen within Genode's core by submitting the affinity as argument when creating a new thread (at 'base-foc/src/core/platform_thread.cc').
Which variant of setting the affinity would make more sense from your perspective?
Best regards Norman