Non-existing service tolerance

[Stefan Kalkowski]

Hi Markus,

in fact the desired behaviour you've described is actually implemented,
and for instance used by Genode's L4Linux clone to discover device
services. For instance, L4Linux probes for a NIC session to init, but if
there is no route to NIC defined init will answer with an exception
code. The ipc framework then throws the corresponding exception on the
client side which is caught by L4Linux. When catching the exception
Linux knows there is no device available and will return from it's
device driver's probing code.

For an example, have a look at: ports-foc/src/lib/l4lx/genode_net.cc:86

The point that matters is of course, that init's configuration doesn't
promise that such a service is available (no 'provides' or
'parent-provides' statement with the appropriate service name should be
available) this would clearly be a configuration bug.

I don't know if this satisfies your question, otherwise would you please
post an example (including the configuration)?

Regards Stefan

On 11.10.2012 13:00, Markus Partheymueller wrote:
> Hi Folks,
> 
> I recently stumbled across an issue when connecting to a service that
> is non-essential for the child. Currently, the connection attempt,
> although surrounded by a try-catch block, leads to an abort call by
> init. While this seems logical for essential services, it is not
> intended for service connections that are optional. I'd rather that
> one could try to connect to the service and react to a failure of this
> attempt in a way the client has to define. If the client can live
> without the service, it should be allowed to carry on. In my opinion,
> this decision should be up to the client, not to the service framework
> of genode.
> 
> Is there any chance to find out if a service exists without getting
> aborted? Any hint would be appreciated.
> 
> Cheers
> 
> Markus
> 
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-- 
Stefan Kalkowski
Genode Labs

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