One of InfiniBand’s upper-layer protocols is DAPL (for Direct Access Programming Library), available both in user mode (as uDAPL) and in kernel mode (as kDAPL). DAPL is the result of an attempt early on to provide a common API for both InfiniBand and iWARP (Ethernet) devices. For whatever reason, DAPL never really seems to have caught on. Intel MPI uses (used?) it, as does OpenMPI (though OpenMPI also uses verbs natively through the openib BTL).
Having written and (successfully, albeit certainly not easily) deployed an application written against the uDAPL API, I feel confident in saying that it is to be avoided at all costs. It may appear, initially, to be easier to use than verbs, but it isn’t. The documentation isn’t always internally consistent, and I’ve had to work around several painfully-debugged issues with the uDAPL library. Given that verbs works with both InfiniBand and iWARP adapters, I can’t see a compelling reason to use DAPL.
To paraphrase someone much better-informed on the matter than I, “who the **** still uses DAPL?”