Tracing with Genode

Torsten Frenzel frenzel at ...28...
Wed May 27 10:53:59 CEST 2015


currently, I explore Genode's tracing-feature and have a few questions regarding policy modules and trace buffers:

I'm working with the 15.02 release and found two examples of policy modules, called null and rpc_name. Are there other examples in branches of the repo on how to implement a custom policy module. In general what are the restrictions, when implementing a policy module?

Is it possible to extract more specific information for a certain event, for example, the name of the destination, that was called. Furthermore, the policy modules for Rpc_call and Rpc_returned events have access to a data structure of type Msgbuf_base. As far as I understood the message buffer contains the arch-depended marshalled data. Is there a generic mechanism to interpret these data in a meaningful way inside policy module or the trace monitor?

It would be helpful to accurately timestamp every recorded event with a value of a real time clock. But that would require access to service that provides such an information. Again, I cannot see how to get access to such a service from inside the policy module, because it hasn't access to the Genode runtime environment. Maybe the correct approach would be to use a fast timestamp function inside the policy module and later calculate the real time value in the trace monitor?

Is it possible to disable/enable specific types of events (, may be using the Trace::Control data structure)?

Is there a mechanism that the trace monitor is notified, when a trace-buffer is full or has reached a threshold?

When I played around with the test_trace program, I noticed that loading more than policy module into core fails. After some investigations I found that the slab_size for the constructed allocator used in the Policy_registry class for Trace::Policy objects is only 4 bytes, but Trace::Policy objects have a larger size of 26 bytes. When I changed the constructor in the session component as shown below everything works fine. So for some reason the compiler selects the Avl_node_base::Policy class in the template.

diff -r ./base/src/core/include/trace/session_component.h . 
< 		Tslab<Trace::Policy, 4096>  _policies_slab;
> 		Tslab<Policy, 4096>  _policies_slab;


More information about the users mailing list