Hello World config

[Norman Feske]

Hello Rudolf,

> I forged the hello tutorial, but my version didn't run, nor the hello_tutorial itself.
> There was two errors:
> 1) the Service "CAP" was not found , first the service "LOG" was  not found.
>   
> 2) The server was not found.
>      In the default route must be 
>          <any-service> <parent/> <any-child/> </any-service>
>      or an specific route

Thank you for the notice and sorry for the inconvenience. I have added
the missing pieces to the document:

 commit:
https://github.com/genodelabs/genode/commit/91de81a10a248a81ee067af9f10b574babe6b34b
 update:
http://genode.org/documentation/developer-resources/client_server_tutorial

> Does the <parent-provides>-Section need to be compelete ?

It needs to list all services that should made principally usable by the
children of the init process. These are not necessarily the entirety of
services provided by core. For example, if no child uses core's IO_PORT
service, there is no point in declaring it.

In addition to enabling init to deny access to parent services by not
listing them, the explicit declaration of the parent services is needed
to route session requests in an unambiguous way.

To learn more about the configuration of the init process, I recommend
the following document:

  http://genode.org/documentation/developer-resources/init

> Does a Child can read out all services provided by its parent and all
> brothers wfrom which it is allowed to access services ?

There is no way for a child to discover the environment outside its own
subsystem. This is on purpose. Strictly speaking, such a feature would
contradict with the principle of least privilege. In most situations, we
would reveal more information to the child than needed for its operation.

In Genode, the runtime behavior of each process should solely depend on
the information explicitly provided by the parent of the process. If the
behavior of a child process somehow depends on the environment outside
the process, it is the parent's responsibility to propagate such
information to the child, for example by providing a configuration that
expresses the desired policy but that entails no more information than that.

Best regards
Norman

-- 
Dr.-Ing. Norman Feske
Genode Labs

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