How do you get the data from a signal handler?

[rsteinke w-link net]

	I'm looking up a signal handler, based on the object instance
and the callback function, and would like to get a pointer to
the callback data for that handler. I can get the handler id, but
can't figure out how to get any more information. The missing
step appears to be a way to get a pointer to the closure from
the handler id, which would then provide the desired pointer.
Is this a missing feature, or is this lack intentional?

Ron Steinke