I notice that backend/openmcl.lisp uses many symbols that are internal to the ccl package. In some cases, even exported symbols (such as ccl:%null-ptr) are referenced using the ccl:: notation.
This is bad practice, of course. It also causes usocket to be semi-broken on the development version of CCL: socket-connect uses the unexported symbols ccl::host-as-inet-host, ccl::port-as-inet-port, and ccl::inet-connect. These are no longer present.
I could probably add them back for the sake of compatibility, but I would prefer not to have to do this.
If there is functionality that usocket requires that is not available from a supported interface, I'd like to hear about it. The best way to do that would be to write tickets at http://trac.clozure.com/ccl.