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Hi Sid,

On 2023-06-27 22:39, Sid Agrawal wrote:
> I am trying to setup a scenario where the parent starts a child PD in
> the C code, i.e., there is no <start> node for the child in the config
> file. It is similar to the rm_nested test example [1].
>
> But in my scenario, I would like to start a server in the child and have
> the parent make RPC calls to it, and I need some help setting that up. I
> think the answer should be in some configuration of the ChildPolicy used
> to start the child, but I am missing something.

we explored this idea in the past [1] but ultimately disregarded it [2].

[1]
https://genode.org/documentation/release-notes/12.02#API_support_for_enslaving_services
[2] https://github.com/genodelabs/genode/issues/3754

You can still find a trace of it left as part of the qt_avplay component
in the genode-world repository [3]. There you can find the slave.h
header that implements the mechanism for hosting a service as a child.

[3] https://github.com/genodelabs/genode-world/tree/master/src/app/qt_avplay

For hosting and managing child components, I warmly recommend the use of
the sandbox library [4], which is far more flexible while easier to use
than the raw child.h interfaces. We plan to replace all manual uses of
child.h by the use of the sandbox library eventually.

[4]
https://genode.org/documentation/release-notes/20.02#New_sandbox_library_based_on_the_init_component

> Any help pointing me in the right direction would be very helpful.
> Thanks as always!

As a general advice, please try to avoid making a parent depend on a
child. It is better to either use an session interface that can be
provided by the parent and invoked by the child, or to use a second
child to interact with a child service. The latter approach is
extensively used by the depot_download_manager, which orchestrates the
downloading, verification, extraction, and installation of software in
Sculpt OS.

Cheers
Norman

--
Dr.-Ing. Norman Feske
Genode Labs

https://www.genode-labs.com · https://genode.org

Genode Labs GmbH · Amtsgericht Dresden · HRB 28424 · Sitz Dresden
Geschäftsführer: Dr.-Ing. Norman Feske, Christian Helmuth


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