Explicit routing

[Norman Feske]

Hi Guido,

> However, when I take out the <default-route> entry and add explicit
> routes to hello.run for the hello-client serivce:
> 
>   <route>
>     <service name="PD"> <parent/> </service>
>     <service name="CPU"> <parent/> </service>
>     <service name="LOG"> <parent/> </service>
>     <service name="Hello"> <child name="hello_server"/> </service>
>     <service name="ROM" label="hello_client"> <parent/> </service>
>     <service name="ROM" label="ld.lib.so"> <parent/> </service>
>     <service name="ROM" label="hello_client -> config"> <parent/>
>         </service>
>     <service name="ROM" label="hello_client -> session_requests">
>         <parent/> </service>
>   </route>
> 
> I get these errors: (skipping things that go well)
> 
> [init] child "hello_client" resolves "ROM" label [hello_client]
> [init] Warning: hello_client: no route to service "ROM"
> [init] Error: hello_client: ROM environment session denied
> ...
> [init] child "hello_client" resolves "ROM" label [ld.lib.so]
> [init] Warning: hello_client: no route to service "ROM"
> [init] Error: hello_client: ROM environment session denied
> ...
> Makefile:312: recipe for target 'run/hello' failed
> 
> What's happening here?
> Why are my explicit routes to the labels I find in the first log not
> working?
> How can I make explicit routes work for these services?

The strings specified as values of a 'label' attribute are automatically
prefixed with the name of the start node because those session requests
normally originate from the component. So instead of specifying

  <service name="ROM" label="hello_client -> session_requests">
           <parent/> </service>

You just have to use

  <service name="ROM" label="session_requests"> <parent/> </service>

The "hello_client" part would be redundant because the routes are
defined in the context of "hello_client" already.

However, in contrast to regular routes like this, which are initiated by
the child, the ROM sessions for the binary and the dynamic linker are
initiated by the parent (on behalf of the child). Here, the automatic
scoping of the label attributes cannot be used. To explicitly route
those sessions, use the 'unscoped_label' or 'label_last' attributes.

For a description of the various label attributes in session routes,
please refer to Section "6.2.1. Session routing" of the Genode
Foundations book [1], in particular the part starting at page 176.

[1] https://genode.org/documentation/genode-foundations-18-05.pdf

Cheers
Norman

-- 
Dr.-Ing. Norman Feske
Genode Labs

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