[PATCH 3/6] Modify internalvar mechanism

[Tom Tromey]

Pedro> I noticed that patch 4 does some changes to 
Pedro> start_tracing to tweak the probes' semaphores, if any.
Pedro> What are these semaphores?  How do other stap tools
Pedro> handle them?  I ask because that bends a bit the definition
Pedro> of "trace" being a regular tracepoint at a given
Pedro> location, so I'd like to understand it.

While developing this, Sergio and I talked extensively to Roland and the
other SystemTap guys about the sdt.h implementation.  Today I finally
got around to writing up our notes:

http://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation

There is already some documentation about adding probes:

http://sourceware.org/systemtap/wiki/AddingUserSpaceProbingToApps

.. though it seems to focus a bit too much (IMO) on the dtrace
compatibility aspect.  You can see a simpler approach in the test suite
part of patch #4 -- you don't actually need anything more than the
#include.

Tom